HK40018414B - Turn-on procedure for a load control device - Google Patents

Description

Switching-on process for a load control device

Cross Reference to Related Applications

Priority of U.S. provisional patent application No.62/463,159 filed 24.2.2017, U.S. provisional patent application No.62/562,008 filed 22.9.2017, and U.S. provisional patent application No.62/580,671 filed 2.11.2017, the entire disclosures of which are incorporated herein by reference.

Background

Light Emitting Diode (LED) light sources, such as LED light engines, are replacing traditional incandescent, fluorescent, and halogen lamps as the primary forms of lighting devices. The LED light source may comprise a plurality of light emitting diodes mounted on a single structure and disposed in a suitable housing. LED light sources may be more efficient and provide longer operating lifetimes than incandescent, fluorescent, and halogen lamps. An LED driver control device (e.g., an LED driver) may be coupled between a power source, such as an Alternating Current (AC) power source or a Direct Current (DC) power source, and an LED light source for regulating power supplied to the LED light source. For example, the LED driver may regulate a voltage provided to the LED light source, a current supplied to the LED light source, or both the current and the voltage.

Different control techniques may be employed to drive the LED light sources, including, for example, current load control techniques and voltage load control techniques. LED light sources driven by current load control techniques are characterized by a nominal current (e.g., about 350 milliamps), and the magnitude (e.g., peak or average magnitude) of the current through the LED light source may be adjusted to ensure that the LED light source is illuminated to the proper intensity and/or color. LED light sources driven by voltage load control techniques are characterized by a nominal voltage (e.g., about 15 volts) to which the voltage across the LED light source can be adjusted to ensure proper operation of the LED light source. If an LED light source rated for voltage load control techniques includes multiple parallel LED strings, current balancing adjustment elements may be used to ensure that the parallel strings have the same impedance, and thus draw the same current in each parallel string.

The light output of the LED light source may be dimmed. Methods for dimming LED light sources may include, for example, Pulse Width Modulation (PWM) techniques and Constant Current Reduction (CCR) techniques. In pulse width modulation dimming, a pulse signal with a varying duty cycle may be supplied to the LED light source. For example, if a current load control technique is used to control the LED light source, the peak current supplied to the LED light source may remain constant during the on-time of the duty cycle of the pulse signal. However, the duty cycle of the pulse signal may be varied to vary the average current supplied to the LED light source, thereby varying the intensity of the light output of the LED light source. As another example, if a voltage load control technique is used to control the LED light source, the voltage supplied to the LED light source may remain constant during the on-time of the duty cycle of the pulse signal. However, the duty cycle of the load voltage may be varied to adjust the intensity of the light output. Constant current reduction dimming may be used if the LED light source is controlled using current load control techniques. In constant current reduction dimming, current may be continuously supplied to the LED light source. However, the DC amplitude of the current supplied to the LED light source may be varied to adjust the intensity of the light output.

U.S. patent No.8,492,987 entitled "LOAD CONTROL DEVICE FOR LIGHT EMITTING DIODE LIGHT SOURCE-EMITTING DIODE LIGHT SOURCE" entitled in 2013, 7/23/7; us patent No.9,655,177 entitled "FORWARD CONVERTER with primary SIDE CURRENT sensing CIRCUIT (FORWARD CONVERTER HAVING A PRIMARY-SIDE CURRENT SENSE CIRCUIT") entitled 5/16/2017; and united states patent No.9,247,608 entitled "LOAD CONTROL DEVICE FOR LIGHT EMITTING DIODE LIGHT SOURCE-EMITTING DIODE LIGHT SOURCE" entitled "at 26.1.2016, describes an example of an LED driver; the entire disclosures of the above U.S. patents are incorporated herein by reference.

Disclosure of Invention

As described herein, a load control device for controlling the intensity of a lighting load may be configured to turn on the lighting load for a fast turn-on time that may be substantially consistent between different lighting loads having different load voltages. The load control device may include: a power converter circuit that may be configured to receive a first voltage and produce a second voltage across a capacitor; and a control circuit operably coupled to the power converter circuit for controlling the power converter circuit to generate the second voltage across the capacitor. The control circuit may be configured to determine a learned voltage (e.g., a learned capacitor voltage and/or a learned load voltage) based on a magnitude of the second voltage of the capacitor. For example, the control circuit may measure the magnitude of the second voltage of the capacitor and/or store the measured voltage as a learned voltage. The control circuit may determine an operating parameter of the power converter circuit from the learned voltage. The control circuit may be configured to control the power converter circuit as the capacitor charges in dependence on the operating parameter until the magnitude of the second voltage reaches the threshold value.

In an example, the load control device may further include a load regulation circuit configured to receive the second voltage (e.g., a bus voltage) and control a magnitude of a load current conducted through the lighting load. The control circuit may be operatively coupled to the load regulation circuit for controlling the magnitude of the load current to control the intensity of the lighting load. The control circuit may determine an on-time for controlling a semiconductor switch of the power converter circuit from the learned voltage and use the preload on-time to control the semiconductor switch to conduct to charge the capacitor until the magnitude of the second voltage reaches a threshold.

In another example, the power converter circuit may operate as a load regulation circuit to control the magnitude of a load current conducted through the lighting load. The control circuit may be operatively coupled to the power converter circuit for controlling the magnitude of the load current to control the intensity of the lighting load. The control circuit may set an amplitude of a target current control signal for controlling the power converter circuit based on the learned voltage to charge the capacitor until the amplitude of the second voltage reaches a threshold.

Drawings

FIG. 1 is a simplified block diagram of an example Light Emitting Diode (LED) driver for controlling the intensity of an LED light source.

Fig. 2 is a simplified flow diagram of an example turn-on process for controlling a power converter circuit of an LED driver.

Fig. 3 is a simplified schematic diagram of an example LED driver showing a power converter circuit and an LED driver circuit.

Fig. 4 is a plot showing an example relationship between learned load voltage and on-time for controlling the field effect transistor of the power converter circuit of fig. 3.

Fig. 5A and 5B show example waveforms of bus voltage for the LED driver of fig. 3 with two different LED light sources turned on.

Fig. 6 is a simplified flow diagram of another example turn-on process for controlling a power converter circuit of an LED driver.

Fig. 7 is a simplified block diagram of another example LED driver.

Fig. 8 is a simplified schematic diagram of another example LED driver.

Fig. 9A is an example plot of a relationship between operating frequency and target current for the LED driver of fig. 8.

Fig. 9B is an example plot of the relationship between the magnitude of the target current control signal and the target current for the LED driver of fig. 8.

Fig. 10A and 10B show example waveforms illustrating the operation of the LED driver of fig. 8.

Fig. 11A shows an example waveform illustrating the operation of the LED driver of fig. 8 when the LED driver learns the load voltage.

Fig. 11B shows example waveforms illustrating operation of the LED driver of fig. 8 when the LED driver turns on the LED light source using the learned load voltage.

Fig. 12 is a simplified flowchart of another example turn-on process for controlling a power converter circuit of an LED driver.

Detailed Description

Fig. 1 is a simplified block diagram of a Light Emitting Diode (LED) driver 100 for controlling the intensity of an LED light source 102, e.g., an LED light engine. The LED light source 102 is shown as a plurality of LEDs connected in series, but may comprise a single LED or a plurality of LEDs connected in parallel, or a suitable combination thereof, depending on the particular lighting system. Additionally, the LED light source 102 may alternatively include one or more Organic Light Emitting Diodes (OLEDs). LED driver 100 may be adapted to work with a plurality of different LED light sources that may be rated to operate using different load control techniques, different dimming techniques, and different magnitudes of load current and voltage.

LED driver 100 may include a hot terminal H and a neutral terminal N for receiving an Alternating Current (AC) voltage V from an AC power source (not shown)_AC. LED driver 100 may include a Radio Frequency (RFI) filter and rectifier circuit 110, which may receive AC voltage V_AC. The RFI filter and rectifier circuit 110 may operate to minimize noise provided on the AC power source and generate a rectified voltage V_RECT. The LED driver 100 may include a power converter circuit 120, such as a buck-boost flyback (flyback) converter, which may receive a rectified voltage V_RECTAnd across a capacitor (e.g. a storage capacitor, e.g. a bus capacitor C)_BUS) Generating a variable Direct Current (DC) bus voltage V_BUS. Power converter circuit 120 may alternatively include any suitable power converter circuit for generating an appropriate bus voltage, such as a boost converter, a buck converter, a single-ended primary inductor converter (SEPIC), a Cuk converter, or other suitable power converter circuit. The power converter circuit 120 may also provide electrical isolation between the AC power source and the LED light source 102 and/or operate as a Power Factor Correction (PFC) circuit to adjust the power factor of the LED driver 100 towards the power factor unity.

LED driver 100 may include a load regulation circuit, such as LED drive circuit 130, which may receive bus voltage V_BUSAnd controls the amount of power delivered to the LED light source 102 in order to control the intensity of the LED light source. The LED driver circuit 130 may include a controllable impedance circuit, such as a linear regulator, as will be described in more detail below. To control the amount of power delivered to the LED light source 102, the LED drive circuit 130 may be configured to control the load current I through the LED light source 102_LOADAnd/or a load voltage V across the LED light source_LOADThe amplitude of (c).

LED driver 100 may include a control circuit 140 for controlling the operation of power converter circuit 120 and/or LED driver circuit 130.The control circuitry 140 may include, for example, a controller or any other suitable processing device, such as a microcontroller, Programmable Logic Device (PLD), microprocessor, Application Specific Integrated Circuit (ASIC), or Field Programmable Gate Array (FPGA). The control circuit 140 may be configured to control the LED drive circuit 130 to switch the LED light source 102 on and off, and to adjust the present intensity L of the LED light source 102_PRESTowards the target intensity L_TRGTAdjusting (e.g., dimming), the range of target intensities may span the dimming range of the LED light source, e.g., at the low end intensity L_LE(e.g., about 0.1% to 10%) and high end intensity L_HE(e.g., about 100%). The control circuit 140 may be configured to control the LED drive circuit 130 to control the load voltage V across the LED light source 102_LOADAnd/or the load current I through the LED light source_LOADThereby controlling the amount of power delivered to the LED light source (e.g., depending on the operating mode of the LED driver, as will be described in more detail below). In an example, when power is first supplied to the LED driver 100, the control circuit 140 may be configured to execute a start-up routine to illuminate the LED light source 102 prior to executing a turn-on routine (e.g., a turn-on process).

The control circuit 140 may be configured to control the load current I through the LED light source 102 using two different operating modes_LOADAmplitude of or load voltage V across the LED light source_LOADAmplitude of (d): a current load control mode (e.g., for using a current load control technique) and a voltage load control mode (e.g., for using a voltage load control technique). The control circuit 140 may be configured to adjust the LED driving circuit 130 to control the load current I through the LED light source 102 in the current load control mode_LOADOr adjust the LED driving circuit 130 to control the load voltage V across the LED light source in the voltage load control mode_LOADThe amplitude of (c). When operating in the current load control mode, the control circuit 140 may be configured to control the intensity of the LED light source 102 using two different dimming modes: a PWM dimming mode (e.g., for using PWM dimming techniques) and a CCR dimming mode (e.g., for using CCR dimming techniques). When operating in the voltage load control mode, the LED driver 100 mayIs configured to adjust the amount of power delivered to the LED light source 102 using PWM dimming techniques.

The control circuit 140 may be coupled to a memory 150 for storing an operating characteristic (e.g., target intensity L) of the LED driver 100_TRGTLow end intensity L_LEHigh end strength L_HEEtc.). The memory 150 may be implemented as an external Integrated Circuit (IC) or as internal circuitry of the control circuit 140. The LED driver 100 may also include a communication circuit 160, which may be coupled to, for example, a wired communication link, or a wireless communication link, such as a Radio Frequency (RF) communication link or an Infrared (IR) communication link. The control circuit 140 may be configured to determine the target intensity L of the LED light source 102 in response to digital messages received via the communication circuit 160_TRGTOr operating characteristics stored in the memory 150. The control circuit 140 may be configured to execute a turn-on routine, for example, in response to receiving a command to turn on the LED light source 102.

The LED driver 100 may further include a power supply 170, which may receive the rectified voltage V_RECTAnd generates a plurality of Direct Current (DC) supply voltages for powering the circuitry of the LED driver. Specifically, power supply 170 may generate a first non-isolated supply voltage V for powering control circuitry of power converter circuit 120_CC1(e.g., about 14 volts), a second isolated supply voltage V for powering control circuitry of the LED driver circuit 130_CC2(e.g., about 9 volts) and a third non-isolated supply voltage V for powering control circuit 140_CC3(e.g., about 5 volts).

As previously described, the control circuit 140 may manage the operation of the power converter circuit 120 and/or the LED driver circuit 130 to control the intensity of the LED light source 102. Control circuit 140 may receive bus voltage feedback signal V from power converter circuit 120_BUS-FBWhich may represent the bus voltage V_BUSThe amplitude of (c). The control circuit 140 may control the bus voltage control signal V_BUS-CNTLIs provided to the power converter circuit 120 to provide the bus voltage V_BUSTowards the target bus voltage V_BUS-TRGT(e.g., from about 8 volts to 60 volts). When operating in the current load control mode, the LED drive circuit 130 may be responsive to a peak current control signal V provided by control circuit 140_IPKControlled at a minimum load current I_LOAD-MINAnd the maximum load current I_LOAD-MAXTo conduct a load current I through the LED light source 102_LOADPeak amplitude of (I)_PK。

The control circuit 140 may receive a load current feedback signal V_ILOADWhich may represent the load current I flowing through the LED light source 102_LOADAverage amplitude of (I)_AVE. The control circuit 140 may also receive a regulator voltage feedback signal V_REG-FBThe signal may represent a regulator voltage V across a linear regulator of the LED driver circuit 130_REG(e.g., a controllable impedance voltage) as will be described in more detail below. Bus voltage V_BUSAnd regulator feedback voltage V_REG-FBMay represent the load voltage V across the LED light source 102_LOADThe amplitude of (c).

The control circuit 140 may be configured to control the LED drive circuit 130 to control the amount of power delivered to the LED light source 102 using two different modes of operation (e.g., a current load control mode and a voltage load control mode). During the current load control mode, the LED drive circuit 130 may be responsive to the load current feedback signal V_ILOAD(e.g., using closed loop control) to regulate the load current I through the LED light source 102_LOADPeak amplitude of (I)_PK. Target load current I_TRGTMay be stored in the memory 150 and may be programmed to any particular magnitude depending on the LED light source 102.

To control the intensity of the LED light source 102 during the current load control mode, the control circuit 140 may control the LED drive circuit 130 to adjust the amount of power delivered to the LED light source 102 using a PWM dimming technique and/or a CCR dimming technique. Using PWM dimming techniques, the control circuit 140 may pass the load current I through the LED light source 102_LOADPeak amplitude of (I)_PKControlling to a target load current I_TRGTAnd pulse width modulating the load current I_LOADTo dim the LED light source 102 and achieve a target load current I_TRGT. In particular, the LED driver circuit 130 may be responsive to controlled byDimming control signal V provided by control circuit 140_DIMDuty cycle of DC_DIMTo control the load current I_LOADDuty cycle of DC_ILOAD. The intensity of the LED light source 102 may depend on the pulse width modulated load current I_LOADDuty cycle of DC_ILOAD. Using CCR dimming technique, the control circuit 140 may not vary the load current I_LOADPulse width modulation is performed, but the target load current I can be adjusted_TRGTIn order to adjust the load current I through the LED light source 102_LOADAverage amplitude of (I)_AVE(which may be equal to the load current I in CCR dimming mode_LOADPeak amplitude of (I)_PK)。

During the voltage load control mode, the LED drive circuit 130 may couple the load voltage V across the LED light source 102_LOADTo a target load voltage V (e.g., a DC voltage)_TRGT. Target load voltage V_TRGTMay be stored in the memory 150 and may be programmed to any particular magnitude depending on the LED light source 102. The control circuit 140 may be configured to dim the LED light source 102 during the voltage load control mode using only the PWM dimming technique. In particular, the control circuit 140 may adjust the load voltage V_LOADDuty cycle of DC_VLOADTo dim the LED light source 102. An example of the configuration process of the LED driver 100 is described in more detail in U.S. patent No.8,492,988 entitled CONFIGURABLE LOAD CONTROL DEVICE FOR LIGHT EMITTING DIODE LIGHT source (CONFIGURABLE LOAD CONTROL DEVICE LIGHT EMITTING DIODE LIGHT SOURCES), entitled, 7/23/2013, the entire disclosure of which is incorporated herein by reference.

The control circuit 140 may be configured to determine or learn one or more operating characteristics of the LED light source 102 (e.g., measure or receive an indication of one or more operating characteristics of the LED light source 102) (e.g., learned load characteristics). For example, when the control circuit 140 operates in the current control mode, the control circuit may be configured to determine the representative load voltage V_LOADThe magnitude of the voltage. During the current control mode, the load voltage V generated across the LED light source 102_LOADCan be taken asDependent on the load current I_LOADIs detected (e.g., control circuit 140 will load current I_LOADRegulated target load current I_TRGT) And internal circuitry for the LED light source. The control circuit 140 may be configured to determine (e.g., measure) a representative load voltage V_LOADOf the magnitude of (e.g., when the target intensity L is_TRGTAt high end intensity L_HETime) and/or store the measurement in memory 150 as a learned load voltage V_LEARNED。

Since the control circuit 140 may operate to minimize the regulator voltage V across the linear regulator of the LED driver circuit 130_REG(e.g., about 0.4 to 0.6V), so the bus voltage V_BUSMay be approximately equal to the load voltage V_LOADAnd thus represents the load voltage V_LOADThe amplitude of (c). Control circuit 140 may be configured to use bus voltage feedback signal V from power converter circuit 120_BUS-FBTo determine (e.g., measure) the capacitance C stored in the bus bar_BUSBus voltage V in_BUSAnd/or storing the measurement in the memory 150 as the learned load voltage V_LEARNED(e.g., learned capacitor voltage). The control circuit 140 may be configured to control the output voltage by deriving the bus voltage V from the bus voltage_BUSMinus the regulator voltage V_REGE.g., as a feedback signal V from the regulator voltage_REG-FBDetermined) to calculate the load voltage V_LOADAnd using the calculated value as the learned load voltage V_LEARNED. The control circuit 140 may include a load voltage measurement circuit (not shown) coupled across the LED light source 102 for directly measuring the load voltage V_LOADMay be stored as a learned load voltage V_LEARNED. Additionally or alternatively, the control circuit 140 may be configured to determine (e.g., measure) the intensity L indicated at the low end_LEAt a load voltage V_LOADAnd/or storing the measurement in memory 150 as a learned load voltage V_LEARNED。

The control circuit 140 may be configured to use the learned load voltage V_LEARNEDTo control the power converter circuit 120 and/or the LED driver circuit 130. For example, the control circuit 140 may be configured to respond to the learned load voltage V when the LED light source 102 is turned on_LEARNEDTo control the power converter circuit 120. The control circuit 140 may be configured to control the bus capacitor C_BUSResponsive to learned load voltage V_LEARNEDAnd the rate of charging to ensure the bus voltage V_BUSQuickly increasing to an appropriate level and the LED light sources 102 are lit as quickly as possible. For example, the control circuit 140 may be responsive to the learned load voltage V in response to receiving a command to turn on the LED light source 102 and/or in response to supplying power to the LED driver 100 to turn on the LED light source_LEARNEDTo control the power converter circuit 120 using open loop control until the bus voltage V_BUSReaches or exceeds the charging threshold V_TH-CH. Threshold value V of charging_TH-CHMay for example depend on the learned load voltage V_LEARNED. For example, the control circuit 140 may be configured to learn the load voltage V according to the learned load voltage_LEARNEDAn operating parameter (e.g., a preload parameter) is determined and used to control the power converter circuit 120 with open loop control (e.g., as will be described in more detail below). In addition, the charging threshold V_TH-CHMay be a fixed threshold (e.g., a predetermined threshold). At bus voltage V_BUSReaches or exceeds the bus voltage threshold V_TH-BUSThereafter, the control circuit 140 may then respond to the bus voltage feedback signal V_BUS-FBUsing closed loop control to begin controlling power converter circuit 120 to convert bus voltage V to_BUSTowards the target bus voltage V_BUS-TRGTAnd (6) adjusting.

Fig. 2 is a simplified flow diagram of an example turn-on process 200 for controlling a power converter circuit of an LED driver (e.g., power converter circuit 120 of LED driver 100). For example, the turn-on process 200 may be performed by a control circuit (e.g., the control circuit 140) at step 210 in response to receiving a command to turn on the LED light source 102 and/or in response to supplying power to an LED driver to turn on the LED light source. The control circuit may retrieve the learned load characteristic (e.g., learned negative) from the memory 150 at step 212Voltage V on load_LEARNED) And may be based on the learned load voltage V at step 214_LEARNEDDetermining a charging threshold V_TH-CHThe value of (c). The control circuit may learn the load voltage V based on the learned load voltage in step 216_LEARNEDAn operating parameter (e.g., the preload on-time) of the power converter circuit is determined and the operating parameter is used to control the power converter circuit at step 218. When the magnitude of the capacitor voltage (e.g., bus voltage V) is at step 220_BUS) Less than charging threshold V_TH-CHThe control circuit may continue to control the power converter circuit using the operating parameter at step 218. When the magnitude of the capacitor voltage is greater than or equal to the charging threshold V at step 220_TH-CHAt this point, the control circuit may begin controlling the power converter circuit to move the magnitude of the capacitor voltage toward the target capacitor voltage (e.g., the target bus voltage V) using closed loop control at step 222_BUS-TRGT) Adjust and then exit the turn-on process 200.

Fig. 3 is a simplified schematic diagram of a load control device, such as an LED driver 300 (e.g., LED driver 100 of fig. 1), for controlling the intensity of an LED light source 302. LED driver 300 may include a flyback converter circuit 320 (e.g., power converter circuit 120), an LED drive circuit 330 (e.g., LED drive circuit 130), and a control circuit 340 (e.g., control circuit 140). The flyback converter circuit 320 may include a flyback transformer 310 having a primary winding coupled in series with a flyback switching transistor (e.g., a Field Effect Transistor (FET) Q312) or other suitable semiconductor switch. The secondary winding of flyback transformer 310 may be coupled to bus capacitor C via diode D314_BUS. The power converter circuit 320 may include a voltage divider including a capacitor C across the bus_BUSTwo resistors R316, R318 coupled for generating a bus voltage feedback signal V_BUS-FB。

The control circuit 340 may generate a bus voltage control signal V_BUS-CNTLA flyback controller 322 for controlling the flyback converter circuit 320. The flyback controller 322 may receive from the control circuit 140 via a filter circuit 324 (e.g., a resistor-capacitor filter) and an optocoupler circuit 326Bus voltage control signal V_BUS-CNTLThe filter circuit and optocoupler circuit can provide electrical isolation between the power converter circuit 320 and the control circuit 340. The flyback controller 322 may also receive a control signal representative of the current through the FET Q312 from a feedback resistor R328, which may be coupled in series with the FET. The flyback controller 322 may render the FET Q312 conductive and non-conductive to selectively conduct current through the flyback transformer 310 to generate the bus voltage V_BUS. For example, the flyback controller 322 may be configured to respond to a bus voltage control signal V_BUS-CNTLAdjusting the on-time t of the FET Q312_ON(e.g., the time that the FET Q312 conducts during each operating cycle of the power converter circuit 320) to control the bus voltage V_BUSThe amplitude of (c).

The LED driver circuit 330 may include a linear regulator (e.g., a controllable impedance circuit) including a power semiconductor switch, e.g., a regulating Field Effect Transistor (FET) Q332 coupled in series with the LED light source 302, for conducting a load current I_LOADBy means of an LED light source. The control circuit 340 may generate a peak current control signal V_IPKWhich may be coupled to the gate of the regulating FET Q332 through a filter circuit 334, an amplifier circuit 336, and a gate resistor R338. The control circuit 340 may be configured to control the peak current control signal V_IPKDuty cycle of DC_IPKTo conduct a load current I through the LED light source 302_LOADPeak amplitude of (I)_PKControlled to a target load current I_TRGT。

The LED driver circuit 330 may include a load current feedback circuit 342 coupled in series with the regulating FET Q332 and a regulator voltage feedback circuit 344 coupled in parallel with the regulating FET Q332. The load current feedback circuit 342 may generate a load current feedback signal V_ILOADWhich may be provided to the control circuit 340 and may represent the load current I_LOADAverage amplitude of (I)_AVE. The regulator voltage feedback circuit 344 may generate a regulator voltage feedback signal V_REG-FBThe signal may also be provided to the control circuit 340 and may represent the voltage across the regulating FET Q332 and the load current feedback circuit 342Regulator voltage V generated by series combination_REG. Other examples of feedback CIRCUITs for the LED driver CIRCUIT 330 are described in more detail in U.S. patent No.8,466,628 entitled "CLOSED-LOOP LOAD CONTROL CIRCUIT with wide OUTPUT RANGE HAVING A WIDE OUTPUT RANGE" granted on 2013, month 6, 18, the entire disclosure of which is incorporated herein by reference.

When operating in the current load control mode, the control circuit 340 may control the regulating FET Q332 to operate in the linear region such that the load current I_LOADPeak amplitude of (I)_PKMay depend on the DC magnitude of the gate voltage at the gate of the regulating transistor Q332. In other words, the regulating FET Q332 may provide a controllable impedance in series with the LED light source 302. If the regulator voltage V_REGMay be driven into the saturation region such that the regulating FET Q332 may become fully conductive and the control circuit 340 may no longer be able to control the load current I_LOADPeak amplitude of (I)_PK. Thus, the control circuit 340 can adjust the bus voltage V_BUSTo prevent the regulator voltage V from being exceeded_REGIs reduced to the minimum regulator voltage threshold V_REG-MIN(e.g., about 0.4 volts) or less. Further, the control circuit 340 may also be configured to adjust the bus voltage V_BUSTo regulate the regulator voltage V_REGIs controlled to be less than a maximum regulator voltage threshold V_REG-MAX(e.g., about 0.6 volts) to prevent the power dissipated in the regulating FET Q332 from becoming too large, thereby improving the overall efficiency of the LED driver 300.

When operating in the voltage load control mode, the control circuit 340 may be configured to drive the regulating FET Q332 into the saturation region such that the load voltage V_LOADMay be approximately equal to the bus voltage V_BUSMagnitude of (minus the on-state drain-source resistance R of Q332 due to FET regulation_DS-ONAnd a small voltage drop caused by the resistance of the feedback resistor R344).

The LED driver circuit 330 may further include a dimming FET Q350, which may be coupled to the gate of the dimming FET Q332Between the road public ends. Dimming control signal V from control circuit 340_DIMMay be provided to the gate of the dimming FET Q350. The regulating FET Q332 may become non-conductive when the dimming FET Q350 becomes conductive, and the regulating FET Q332 may become conductive when the dimming FET Q250 becomes non-conductive. When using PWM dimming techniques during the current load control mode, the control circuit 340 may adjust the dimming control signal V_DIMDuty cycle of DC_DIMThereby controlling when the regulating FET conducts the load current I_LOADAnd thus the intensity of the LED light source 302. For example, the control circuit 340 may use a constant PWM frequency f_DIM(e.g., about 500Hz) to generate the dimming control signal V_DIM。

When using PWM dimming techniques in the current load control mode, the control circuit 340 may be configured to respond to the load current feedback signal V_ILOADTo control the load current I_LOADPeak amplitude of (I)_PKSo as to make the load current I_LOADAverage amplitude of (I)_AVEIs kept constant (e.g. at the target lamp current I_TRGTAt (c). When using the CCR dimming technique during the current load control mode, the control circuit 340 may control the dimming control signal V_DIMDuty cycle of DC_DIMMaintaining high-end dimming duty cycle DC_HE(e.g., about 0% so that the FET Q332 may be always on) and the target load current I may be adjusted_TRGT(via peak current control signal V_IPKDuty cycle of DC_IPK) To control the intensity of the LED light source 302.

When operating in the current load control mode, the control circuit 340 may be configured to determine or learn a value representative of the load voltage V generated across the LED light source 302_LOADAnd/or store the learned magnitude in a memory (e.g., memory 150) as the learned load voltage V_LEARNED. For example, when the control circuit controls the intensity of the LED light source 302 to the high-end intensity L_HEThe control circuit 340 may use the bus voltage feedback signal V from the flyback converter circuit 320_BUS-FBDetermining (e.g. measuring) bus voltage V_BUSAnd/or storing the measurement in a memory as a learned load voltage V_LEARNED. The control circuit 340 may be configured, for example, during a start-up routine (e.g., when power is first supplied to the LED driver 300) and/or after a start-up routine (e.g., when the bus voltage V is_BUSIs in a steady state condition) determines (e.g., measures) the bus voltage V_BUSThe amplitude of (c).

The control circuit 340 may respond to the learned load voltage V when the LED light source 302 is turned on_LEARNEDTo control the flyback converter circuit 320 to control the bus capacitor C_BUSA rate of charging to ensure that the LED light source 302 is quickly illuminated after receiving a command to turn on the LED light source 302 and/or after supplying power to the LED driver 300 to turn on the LED light source. When a command to turn on the LED light source 302 has been received and/or power has been supplied to the LED driver 300 to turn on the LED light source, the control circuit 340 may be configured to respond to the learned load voltage V_LEARNEDTo control the flyback converter circuit 320 using open loop control until the bus voltage V_BUSReaches or exceeds the bus voltage threshold V_TH-BUS(e.g., charging threshold V)_TH-CH). The control circuit 340 may be configured to retrieve the learned load voltage V from the memory_LEARNEDAnd can be based on the learned load voltage V_LEARNEDDetermining a bus voltage threshold V_TH-BUSValue of (e.g., V)_TH-BUS＝η·V_LEARNED) Where η is a constant, which may be, for example, about 0.85.

The control circuit 340 may also be configured to learn the load voltage V based on the learned load voltage_LEARNEDAn operating parameter of the flyback converter circuit 320 is determined. For example, the operating parameter of the power converter circuit 320 may be at the bus capacitor C_BUSOn-time t for controlling FET Q312 while charging_ONWhich may be referred to as a "preload" on-time t_ON-PRE. FIG. 4 is a graph showing a learned load voltage V_LEARNEDPreloaded on-time t with FET Q312_ON-PREA plot of an example relationship 400 therebetween. As shown in FIG. 4, the relationship 400 may be, for example, a linear relationship. Relationship 400 may be an exampleSuch as stored in memory as an equation or table. The relationship 400 ranges from a minimum learned load voltage V_LEARNED-MINMinimum preload on-time t (e.g., about 15 volts)_ON-MIN(e.g., about 159.6 musec) to a maximum learned load voltage V_LEARNED-MAX(e.g., about 38 volts) maximum preload on-time t_ON-MAX(e.g., about 169.9 μ sec). The preload on-time t of the relationship 400 may be selected_ON-PRESuch that the on-delay period of the LED driver 300 may be approximately the same for different LED light sources having different resulting load voltages.

The control circuit 340 may be configured to control the bus capacitor C_BUSIs charging and bus voltage V_BUSIs less than the bus voltage threshold V_TH-BUSWhile using open loop control to control the on-time t of the FET Q312_ONControl to preload on-time t_ON-PRE. At bus voltage V_BUSReaches or exceeds the bus voltage threshold V_TH-BUSThen, the control circuit 340 may use closed loop control (e.g., by feeding back the signal V in response to the bus voltage)_BUS-FBOn-time t of the amplitude adjustment FET Q312_ON) The flyback converter circuit 320 is initially controlled to convert the bus voltage V_BUSTowards the target bus voltage V_BUS-TRGTAnd (6) adjusting.

Fig. 5A and 5B illustrate bus voltage V of an LED driver (e.g., LED driver 300) when the LED driver turns on two different LED light sources_BUS1、V_BUS2An example waveform of (a). For example, FIG. 5A shows the first learned load voltage V having about 38 volts when turned on_LED1First bus voltage V of LED light source_BUS1And fig. 5B shows the second learned load voltage V having about 15 volts when turned on_LED2Second bus voltage V of LED light source_BUS2Waveform 510 of (a). Fig. 5A and 5B each show the bus voltage V when the LED driver is first powered to turn on the LED light source_BUSMagnitude over time.

At time t₀Control circuitry (e.g., control electronics) for the LED driver after power is appliedWay 340) may execute a startup routine (e.g., startup mode) until time t₁At this point, the control circuit begins to control the power converter circuit (e.g., flyback converter circuit 320) to generate the bus voltage V thereacross_BUS1、V_BUS2The bus capacitor of (2) is charged. As shown in fig. 5A, at time t₂First bus voltage V_BUS1May exceed a charging threshold, e.g. bus voltage threshold V_TH-BUSWhich may depend on the first learned load voltage V_LED1(e.g., V)_TH-BUS＝0.85·V_LED1). When the bus capacitor is at time t₁And t₂Is charged continuously for a first charging period T_CHARGE1The control circuit may control the power converter circuit using open loop control having a load voltage V according to the first learning_LED1Determined operating parameters (e.g., as described above). When at time t₂First bus voltage V_BUS1Exceeding the bus voltage threshold V_TH-BUSThereafter, the control circuit may control the power converter circuit using closed loop control to convert the first bus voltage V_BUS1Is adjusted towards the target bus voltage. The control circuit may be controlled from time t₂Beginning to use closed loop control to control power converter circuit control loop delay period T_DELAYUntil the LED light source is at time t₃And (4) switching on. Thus, the LED light source may be at time t from the control circuit₁Switch-on delay period T when starting to control power converter circuit_TURN-ON1And then switched on.

Similarly, as shown in FIG. 5B, the second bus voltage V_BUS2May be at time t₄Exceeding the bus voltage threshold V_TH-BUS. Bus voltage threshold V in FIG. 5B_TH-BUSMay be lower than in the case of fig. 5A because of the second learned load voltage V_LED2Lower than the first learned load voltage V_LED1. The control circuit may control the power converter circuit with the operating parameter using open loop control for a time t₁And time t₄Second charging period T in between_CHARGE2. Since the control circuit can be based on the first learned load electricityPressure V_LED1And a second learned load voltage V_LED2Determining an operating parameter, thus a first charging period T_CHARGE1And a second charging period T_CHARGE2May be approximately equal. When at time t₄Second bus voltage V_BUS2Is greater than the bus voltage threshold V_TH-BUSThereafter, the control circuit may start from time t₄Beginning to use closed loop control to control power converter circuit control loop delay period T_DELAYUntil at time t₅The LED light source is switched on, so that the LED light source can be switched on for a delay time period T_TURN-ON2And then switched on. Due to control loop delay period T_DELAYMay be a constant parameter (e.g., with learned load voltage V)_LED1、V_LED2Irrelevant) and thus the first on delay period T_TURN-ON1And a second turn-on delay period T_TURN-ON2May be approximately equal.

Fig. 6 is a simplified flow diagram of an example turn-on process 600 for controlling a power converter circuit of an LED driver (e.g., flyback converter circuit 320 of LED driver 300). For example, the turn-on process 600 may be performed by a control circuit (e.g., the control circuit 340) at step 610 in response to receiving a command to turn on the LED light source and/or in response to supplying power to the LED driver to turn on the LED light source. The control circuit may retrieve the learned load characteristic (e.g., learned load voltage V) from memory at step 612_LEARNED) And may be based on the learned load voltage V at step 614_LEARNEDDetermining a charging threshold (e.g., bus voltage threshold V)_TH-BUS) Value of (e.g., V)_TH-BUS＝η·V_LEARNEDWhere η may be 0.85). The control circuit may learn the load voltage V based on the learned load voltage at step 616_LEARNEDDetermining an operating parameter (e.g., preload on-time t) of a power converter circuit_ON-PRE) And at step 618 the preload on-time t is used_ON-PREControlling the power converter circuit. When the bus voltage V is at step 620_BUSIs less than the bus voltage threshold V_TH-BUSThe control circuit may use the preload on-time t at step 618_ON-PREContinuing to control power transferA converter circuit. When the bus voltage V is at step 620_BUSIs greater than or equal to the bus voltage threshold V_TH-BUSAt this point, the control circuit may begin controlling the power converter circuit to convert the bus voltage V using closed loop control at step 622_BUSIs adjusted towards the target bus voltage and then the turn-on process 600 is exited.

Fig. 7 is a simplified block diagram of a load control device (e.g., LED driver 700) for controlling the intensity of an LED light source 702 (e.g., LED light engine). The LED light source 702 is shown as a plurality of LEDs connected in series, but may comprise a single LED or a plurality of LEDs connected in parallel, or a suitable combination thereof, depending on the particular lighting system. Additionally, the LED light source 702 may alternatively include one or more Organic Light Emitting Diodes (OLEDs). The LED driver 700 may be adapted to work with a plurality of different LED light sources, which may be rated at different magnitudes of load current and voltage.

LED driver 100 may include a hot terminal H and a neutral terminal N for receiving an AC voltage V from an AC power source (not shown)_AC. LED driver 700 may include an RFI filter and rectifier circuit 710, which may receive AC voltage V_AC. The RFI filter and rectifier circuit 710 may operate to minimize noise provided on the AC power source and generate a rectified voltage V_RECT. The LED driver 700 may include a power converter circuit 720 (e.g., a first power converter circuit) and a load regulation circuit, such as an LED drive circuit 730 (e.g., a second power converter circuit). The power converter circuit 720 may receive the rectified voltage V_RECTAnd across the bus capacitor C_BUSGenerating a variable DC bus voltage V_BUS. Power converter circuit 720 may include any suitable power converter circuit for generating an appropriate bus voltage, such as a boost converter, a buck-boost converter, a flyback converter, a single-ended primary inductor converter (SEPIC), a Cuk converter, or other suitable power converter circuit. The power converter circuit 720 may also provide electrical isolation between the AC power source and the LED light source 702 and operate as a PFC circuit to adjust the power factor of the LED driver 100 towards power factor one.

The LED driving circuit 730 may receive the bus voltage V_BUSAnd controls the amount of power delivered to the LED light source 702 to control the intensity of the LED light source. For example, the LED driver circuit 730 may include a buck converter, as will be described in more detail below. To control the amount of power delivered to the LED light source 702, the LED drive circuit 730 may be configured to control the load current I conducted through the LED light source 702_LOADIs measured.

The LED driver 700 may include a control circuit 740 for controlling the operation of the power converter circuit 720 and the LED driver circuit 730. The control circuitry 740 may include, for example, a controller or any other suitable processing device, such as a microcontroller, Programmable Logic Device (PLD), microprocessor, Application Specific Integrated Circuit (ASIC), or Field Programmable Gate Array (FPGA). The control circuit 740 may be configured to control the LED drive circuit 730 to control the load current I conducted through the LED light source_LOADTo control the amount of power delivered to the LED light source. The control circuit 740 may be configured to control the LED drive circuit 730 to switch the LED light source 702 on and off, and to adjust the present intensity L of the LED light source 702_PRESTowards the target intensity L_TRGTAdjusting (e.g., dimming), the range of target intensities may span the dimming range of the LED light source, e.g., at the low end intensity L_LE(e.g., about 0.1% to 1.0%) and the high end intensity L_HE(e.g., about 100%).

The control circuit 740 may be configured to cause the target intensity L of the LED light source 702_TRGT(and thus the current intensity L)_PRES) Fade (e.g., gradually adjust over a period of time). The control circuit 740 may be configured to control the current intensity L of the LED light source by adjusting the current intensity L_PRESGradation of intensity L from the minimum_FADE-MINSlowly increasing to the target intensity L_TRGTWhile the LED light source 702 is graded from off to on, the minimum grading intensity may be less than the low-end intensity L_LE(e.g., about 0.02%). The control circuit 740 may be configured to control the current intensity L of the LED light source by adjusting the current intensity L_PRESFrom greater than or equal to the low end intensity L_LESlowly decreases to a minimum gradual intensity L_FADE-MINAnd the LED light source 702 is ramped from on to off, at which point the control circuit 740 may turn off the LED light source.

The control circuit 740 may be coupled to a memory 712 configured to store an operating characteristic (e.g., target intensity L) of the LED driver 700_TRGTLow end intensity L_LEHigh end strength L_HEEtc.). The memory 712 may be implemented as an external Integrated Circuit (IC) or as internal circuitry of the control circuit 740. The LED driver 700 may also include a communication circuit 714, which may be coupled to, for example, a wired communication link, or a wireless communication link, such as a Radio Frequency (RF) communication link or an Infrared (IR) communication link. The control circuit 740 may be configured to determine the target intensity L of the LED light source 702 in response to digital messages received via the communication circuit 714_TRGTOr operating characteristics stored in the memory 712. In response to receiving a command to turn on the LED light source 702, the control circuitry 740 may be configured to execute a turn-on routine. LED driver 700 may also include a power supply 716 that may receive a rectified voltage V_RECTAnd generates a Direct Current (DC) supply voltage V for powering a low voltage circuit of the LED driver_CC(e.g., about 5 volts). Additionally, the power supply 716 may generate one or more additional supply voltages, for example, to power the power converter circuit 720 and/or control circuitry of the LED driver circuit 730.

The control circuitry 740 may include digital control circuitry, such as a processor 742, which may be, for example, a microprocessor, a Programmable Logic Device (PLD), a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or other suitable processing device or controller. Control circuit 740 may also include analog control loop circuit 750. The processor 742 and the analog control loop circuit 750 may operate together to control the LED driver circuit 730 to vary the load current I_LOADIs adjusted to the target current I_TRGT. Target current I_TRGTMay depend on the target intensity L_TRGT(e.g., the target intensity L_TRGTA function of). Processor 742 may generate target current control signal V_I-TRGTWhich may have a current level indicative of the target current I_TRGTDC amplitude or duty cycle. Processor 742May be based on the target intensity L of the LED light source 702_TRGTTo control the target current control signal V_I-TRGTDC amplitude or duty cycle.

The control circuit 740 may further include a latch circuit 760 that may generate a drive signal V for controlling the operation of the LED drive circuit 730_DR(e.g., for rendering the switching transistor of the LED driver circuit 730 conductive and non-conductive to pass the load current I_LOADTowards the target current I_TRGTAdjustment). Processor 742 may generate frequency control signal V_FREQWhich can set the operating frequency f of the LED driving circuit 730_OP. Responsive to a frequency control signal V_FREQThe latch circuit 760 may control the driving signal V_DRSuch that the switching transistor of the LED driver circuit 730 is turned on to initiate a cycle of the LED driver circuit, at which point the LED driver circuit may begin conducting the inductor current I_LThe inductor current is conducted through an inductor (not shown) of the LED driver circuit 730. The analog control loop circuit 750 may generate a peak current threshold V_TH-PKWhich may be used by latch circuit 760 in response to inductor current I_LTo render the switching transistor of the LED driving circuit 730 non-conductive.

The LED driver 700 may include an amplifier circuit 770 that may receive a current feedback signal V from the LED driver circuit 730_I-FB. The amplifier circuit 770 may amplify the current feedback signal V_I-FBTo generate an instantaneous current feedback signal V_I-INSTWhich may indicate the inductor current I flowing through the inductor of LED driver circuit 730_LThe instantaneous amplitude of (c).

LED driver 700 may also include a filter circuit 780, such as a box filter circuit. Filter circuit 780 may receive instantaneous current feedback signal V_I-INSTAnd generates a filtered feedback signal, e.g. an average current feedback signal V_I-AVEWhich may indicate an inductor current I flowing through an inductor of LED drive circuit 730 (e.g., within a particular time window)_LIs measured. Processor 742 may generate filter control signal V_FILTER(e.g., filter control signal) for controlling filter powerOperation of circuit 780, e.g. to control when filter circuit 780 feeds back signal V to the instantaneous current_I-INSTAnd (6) filtering. For example, processor 742 may control filter control signal V_FILTERTo allow the filter circuit 780 to filter the window period T during each cycle of the LED driver circuit 730_FILTERInternal pair instantaneous current feedback signal V_I-INSTAnd (6) filtering. Processor 742 may control signal V at an AND frequency_FREQControlling the filter control signal V in a synchronous manner_FILTERE.g. to be within a filter window period T_FILTERBegins a cycle of the LED driver circuit 730. For example, the filter window period T_FILTERMay have the same length during each period of the LED driving circuit 730 as the frequency control signal V_FREQIs independent of the frequency of (a). Average current feedback signal V_I-AVEMay indicate the filter window period T_FILTERDuring the inductor current I_LIs measured (e.g., when filter circuit 780 is feeding back signal V to the instantaneous current_I-INSTWhen filtering is performed).

The analog control loop circuit 750 of the control circuit 740 may receive the average current feedback signal V_I-AVEAnd latch circuit 760 may receive instantaneous current feedback signal V_I-INST. The analog control loop circuit 750 may be responsive to a target current control signal V_I-TRGTAnd an average current feedback signal V_I-AVETo adjust the peak current threshold value V_TH-PKThe amplitude of (c). The latch circuit 760 may control the driving signal V_DRIn response to a frequency control signal V_FREQ(e.g., at the beginning of a cycle of the LED driver circuit 730) to turn on the switching transistor of the LED driver circuit 730. The latch circuit 760 may control the driving signal V_DRIn response to the peak current threshold V_TH-PKAnd instantaneous current feedback signal V_I-INSTWhile the switching transistor is rendered non-conductive. After rendering the switching transistor of the LED driving circuit 730 non-conductive, the latch circuit 760 may remain in a latched state and keep the switching transistor non-conductive until the next cycle of the LED driving circuit 730 begins.

Control circuit 740 may be configured to determineOr learning one or more operating characteristics of the LED light source 702 (e.g., measuring or receiving an indication of one or more operating characteristics of the LED light source 702) (e.g., learned load characteristics). For example, control circuit 740 may be configured to determine a representative load voltage V_LOADVoltage of the magnitude of (1). Load voltage V generated across LED light source 702_LOADMay depend on the load current I_LOADIs detected (e.g., control circuit 740 sets load current I_LOADRegulated target load current I_TRGT) And internal circuitry for the LED light source. Control circuit 740 may be configured to determine (e.g., measure) load voltage V_LOADAnd/or store the measurement in memory 712 as a learned load voltage V_LEARNED. The control circuit 740 may be configured to use the load voltage feedback signal V received from the LED drive circuit 730_V-LOADTo determine (e.g., measure) the load voltage V_LOADThe amplitude of (c). For example, the LED drive circuit 730 may include a resistive divider circuit (not shown) coupled across the LED light source 702 for generating the load voltage feedback signal V_V-LOADAs a scaled load voltage. Load voltage feedback signal V_V-LOADCan be received by an analog-to-digital converter (ADC) of processor 742 for learning load voltage V_LOADThe amplitude of (c).

Control circuit 740 may be configured to determine when target intensity L is reached_TRGTAt or near the low end intensity L_LETime-determining (e.g. measuring) load voltage V_LOADThe amplitude of (c). For example, the control circuit 740 may be configured to ramp the LED light source 702 from on to off (e.g., when the load current I is turned on) when the control circuit 740_LOADIs within a range from a maximum learning threshold I_LEARN-MAXTo a minimum learning threshold I_LEARN-MINWhile within the measurement window) determines (e.g., measures) the load voltage V_LOADThe amplitude of (c). Maximum learning threshold I_LEARN-MAXAnd a minimum learning threshold I_LEARN-MINMay be the rated (or maximum) current I of the LED light source 702_RATEDA function of (2), e.g. 0.0020I respectively_RATEDAnd 0.0002I_RATED。

The control circuit 740 may be configured such thatBy learned load voltage V_LEARNEDTo control the LED driver circuit 730. For example, the control circuit 740 may be configured to respond to the learned load voltage V when the LED light source 702 is turned on_LEARNEDTo control the LED driver circuit 730. The control circuit 740 may be configured to charge (e.g., "precharge") an output capacitor (not shown) of the LED drive circuit 730 before attempting to turn on the LED light source 702. In response to receiving a command to turn on the LED light source 702 and/or in response to supplying power to the LED driver 700 to turn on the LED light source, the control circuit 740 may precharge the output capacitor until the load voltage V_LOADReaches or exceeds a pre-charge voltage threshold V_TH-PCIt may be, for example, a learned load voltage V_LEARNEDFor example, as will be described in more detail below. Precharging the output capacitor may allow, for example, for ramping to the low-side intensity L_LEThe LED driver 700 quickly and consistently turns on the LED light sources 702.

The control circuit 740 may be configured to learn the load voltage V according to the learned load voltage_LEARNEDAn operating parameter (e.g., a preload parameter) is determined and used to control the LED driver circuit 730 to precharge an output capacitor of the LED driver circuit 730 before turning on the LED light source 702 (e.g., as will be described in more detail below). For example, control circuit 740 may be configured to determine a target current control signal V to use_I-TRGTAccording to the learned load voltage V_LEARNEDThe output capacitor of the LED driver circuit 730 is precharged. In addition, processor 742 may generate an enable control signal V_START-UPFor controlling the analog control loop circuit 750 while precharging the output capacitor of the LED driving circuit 730 to maintain the output of the analog control loop circuit 750 at a predetermined voltage.

At a load voltage V_LOADReaches or exceeds a pre-charge voltage threshold V_TH-PCThereafter, processor 742 may control enable control signal V_START-UPTo allow the analog control loop circuit 750 to respond to the current feedback signal V_I-FBAnd closed loop control is used to control the LED driver circuit 730 to adjust the load current I_LOADTowards the target current I_TRGTAnd (6) adjusting.

Fig. 8 is a simplified schematic diagram of a load control device, such as an LED driver 800 (e.g., LED driver 700 of fig. 1), for controlling the intensity of an LED light source 802. LED driver 800 may include a memory for storing bus voltage V_BUSBus capacitor C_BUSThe bus voltage may be generated by a first power converter circuit (e.g., power converter circuit 720 of LED driver 700). The LED driver 800 may include a second power converter circuit, such as an LED driver circuit 830, which may be configured to control the load current I conducted through the LED light source 802_LOADThe amplitude of (c). LED driver 800 may also include control circuit 840, which may be a hybrid analog-to-digital control circuit (e.g., control circuit 740 of LED driver 700). The control circuit 840 may include a processor 842, a low pass filter circuit 844, an analog control loop circuit (which may include an integrator circuit 850, for example), and a latch circuit 860. The latch circuit 860 may generate the driving signal V_DRWhich may be provided to the LED driver circuit 830. The LED driver 800 may further include an amplifier circuit 870 and a filter circuit 880 (e.g., a box filter circuit) for generating the instantaneous current feedback signal V, respectively_I-INSTAnd an average current feedback signal V_I-AVE。

As shown in fig. 8, the LED driving circuit 830 may include a buck converter. The LED driver circuit 830 may include a switching transistor, such as a Field Effect Transistor (FET) Q832, which may be responsive to a drive signal V_DRIs controlled to control the load current I_LOADThe amplitude of (c). The LED driver circuit 830 may also include an inductor L834, a switching diode D835, an output capacitor C836, and a feedback resistor R838. Drive signal V_DRMay be coupled to the gate of FET Q832 by a gate drive circuit 839. When the FET Q832 is on, the inductor L834 may sink an inductor current I_LSlave bus capacitor C_BUSConducted through the parallel combination of output capacitor C836 and LED light source 802. Inductor L834 may couple inductor current I when FET Q832 is non-conductive_LConducted through a switching diode D835 and an output capacitor C836 and LED light sources 802. The LED light source 802 may conduct an inductor current I_LAnd the output capacitor C836 may conduct the inductor current I_LOf the transient component of (a). Load current I_LOADMay be approximately equal to the inductor current I_LIs measured.

The current feedback signal V may be generated across a feedback resistor R838 of the LED drive circuit 830_I-FBAnd the current feedback signal may be related to the inductor current I_LIs proportional to the amplitude of the signal. Current feedback signal V_I-FBMay be received by amplifier circuitry 870. The amplifier circuit 870 may include an operational amplifier U872, and may be configured as a non-inverting amplifier circuit. The operational amplifier U872 may have a non-inverting input that may receive the current feedback signal V_I-FB. The amplifier circuit 870 may also include a resistor R874 coupled between the inverting input terminal and circuit common of the operational amplifier U872, and a resistor R876 coupled between the inverting input terminal and output terminal of the operational amplifier U872. The amplifier circuit 870 may be configured to generate the instantaneous current feedback signal V_I-INSTWhich may be a current feedback signal V_I-FBAnd may indicate the inductor current I_LThe instantaneous amplitude of (c).

The filter circuit 880 may feed back the signal V to the instantaneous current_I-INSTFiltering to generate an average current feedback signal V_I-AVEWhich may indicate the inductor current I_LIs measured. The filter circuit 880 may include a controllable switch circuit 882 and a low pass filter circuit (e.g., a third order low pass filter circuit) including resistors R884, R886, R888 and capacitors C885, C887, C889. Processor 842 may generate filter control signal V_FILTERFor rendering the controllable switch circuit 882 conductive and non-conductive. When the controllable switch circuit 882 is conductive, the filter circuit 880 may be configured to couple the instantaneous current feedback signal V_I-INSTFiltering to generate an average current feedback signal V_I-AVE. When the controllable switch circuit 882 is non-conductive, the capacitors C885, C887, C889 of the filter circuit 880 may feed the average current feedback signal V_I-AVEIs maintained during the time period indicating the previous conduction of the controllable switch circuit 882_LIs measured.

Processor 842 may generate a Pulse Width Modulation (PWM) signal V_PWMWhich may be received by a low pass filter circuit 844 of the control circuit 840. The low pass filter circuit 844 may be configured to generate the target current control signal V_I-TRGTWhich may have an indicated target current I_TRGTDC amplitude of (d). For example, the low pass filter circuit 844 may include a resistor-capacitor (RC) circuit having a resistor R846 and a capacitor C848. The processor 842 may be configured to control the pulse width modulated signal V_PWMTo adjust the target current control signal V_I-TRGTThe amplitude of (c).

Average current feedback signal V generated by filter circuit 880_I-AVEAnd a target current control signal V generated by a low-pass filter circuit 844_I-TRGTMay be received by the integrator circuit 850. The integrator circuit 850 may include an operational amplifier U852 having a control signal V coupled to a target current_I-TRGTAnd is coupled to the average current feedback signal V via a resistor R854_I-AVEThe inverting input terminal of (1). The integrator circuit 850 may include a capacitor C856 coupled between the inverting input and the output of the operational amplifier U852, such that the integrator circuit 850 may be configured to feed back the average current signal V_I-AVEAnd a target current control signal V_I-TRGTThe error between is integrated. The integrator circuit 850 may generate a peak current threshold V having a DC magnitude_TH-PKThe DC amplitude can be increased or decreased depending on the control signal V at the target current_I-TRGTAmplitude of and average current feedback signal V_I-AVEThe amount of error in between. The integrator circuit 850 may include a controllable switching circuit 858 coupled in parallel with a capacitor C856. In response to an enable control signal V received from processor 842 during an enable routine_START-UPControllable switching circuit 858 may become conductive and non-conductive (e.g., as will be described in more detail below).

Latch circuit860 may receive the peak current threshold V generated by the integrator circuit 850_TH-PKAnd an instantaneous current feedback signal V generated by the amplifier circuit 870_I-INST. The latch circuit 860 may include a comparator U862 configured to provide an instantaneous current feedback signal V_I-INSTAmplitude of and peak current threshold V_THAre compared. Comparator U862 can generate a latch control signal V at an output terminal_LATCH. When the instantaneous current feedback signal V_I-INSTIs less than the peak current threshold value V_THAt the amplitude of (3), the comparator U862 can latch the control signal V at the output terminal_LATCH(e.g. towards the supply voltage V_CC) The drive is high. When the instantaneous current feedback signal V_I-INSTIs greater than the peak current threshold V_TH-PKAt the amplitude of (3), the comparator U862 can latch the control signal V at the output terminal_LATCHDriven low (e.g., toward circuit common).

Processor 842 may generate frequency control signal V_FREQWhich can set the operating frequency f of the LED driving circuit 830_OP. The latch circuit 860 may include a PWM control circuit 866, which may receive the latch control signal V from the comparator U262_LATCHAnd receives a frequency control signal V from processor 842_FREQ. The PWM control circuit 866 may generate the drive signal V_DRWhich may be received by the gate drive circuit 839 of the LED drive circuit 830. When the frequency control signal V_FREQWhen driven high at the beginning of a cycle of the LED driver circuit 830, the PWM control circuit 866 may drive the drive signal V_DRIs driven high, which may turn on the FET Q832 of the LED driver circuit 830. When the instantaneous current feedback signal V_I-INSTExceeds the peak current threshold signal V_THAt the amplitude of (c), the comparator U862 may latch the control signal V_LATCHDrive low, which may cause the PWM control circuit 866 to drive the drive signal V_DRIs driven low. The PWM control circuit 866 may output the drive signal V_DRUntil the processor 842 again holds the frequency control signal V low at the end of the current cycle of the LED driving circuit 830 and at the beginning of the next cycle_FREQIs driven by an amplitude ofHigh.

The processor 842 may use open loop control to control the target current I according to the LED light source 802_TRGTControl frequency control signal V_FREQFrequency and pulse width modulation control signal V_PWMDuty cycle of (and thus the target current control signal V)_I-TRGTAmplitude of). FIG. 9A shows a frequency control signal V_FREQE.g., the operating frequency f of the LED driving circuit 830_OP) And a target current I_TRGTAn example plot of the relationship 900 between. FIG. 9B is the target current control signal V_I-TRGTAmplitude of (d) and target current I_TRGTAn example plot of the relationship 910 between. For example, the target current I_TRGTCan be in the high end intensity L_HEHigh side current I of_HE(e.g., about 150mA) and a low end intensity L_LEAt low side current I_LE(e.g., about 150 μ A).

Processor 842 may operate in first and second modes of operation depending on target current I_TRGTWhether less than or greater than the approximate transition current I_TRAN(e.g., about 16.8 mA). At the low end intensity L_LENear (e.g., when the target current I_TRGTLess than the approximate transition current I_TRANIn some embodiments), the processor 842 may operate in a first mode of operation during which the processor 842 may be operating at a target current I with respect to_TRGTMinimum operating frequency f_MINAnd maximum operating frequency f_MAX(e.g. linearly) adjusting the frequency control signal V_FREQWhile maintaining the target current control signal V_I-TRGTIs constant (e.g. at a minimum voltage V)_MINAt (c). At high end intensity L_HENear (e.g., when the target current I_TRGTGreater than or equal to the approximate transition current I_TRANIn some embodiments), the processor 842 may operate in a second mode of operation during which the processor 842 may be operating at a current relative to the target current I_TRGTMinimum voltage V of_MINAnd a maximum voltage V_MAX(e.g. linearly) adjusting the target current control signal V_I-TRGTWhile maintaining the frequency control signal V_FREQIs constant (e.g., at the maximum operating frequency)Rate f_MAXAt (c). For example, the maximum operating frequency f_MAXMay be about 140kHz with a minimum operating frequency f_MINMay be about 1250 Hz. For example, the maximum voltage V_MAXMay be about 3.3V, and the minimum voltage V_MINMay be about 44 mV.

Fig. 10A and 10B show example waveforms illustrating the operation of the LED driver 800 shown in fig. 8. FIG. 10A shows a graph illustrating the current when the target current I is_TRGTLess than the transition current I_TRANAn example waveform of the operation of LED driver 800. Processor 842 may generate frequency control signal V_FREQTo set the operating frequency f of the LED driving circuit 830_OP. For example, the operation period T of the LED driving circuit 830_OPCan be equal to the frequency control signal V_FREQA period of time. Processor 842 may be based on target current I_TRGTSetting the operating frequency f_OP(and thus setting the operating period T)_OP) (e.g., as shown in FIG. 9A). Processor 842 may generate frequency control signal V_FREQTo have a predetermined on-time T_FREQ-ONWhich may have the same length (e.g., as the frequency control signal V) in each cycle of the LED driver circuit 830_FREQFrequency or target current I_TRGTIrrelevant).

Processor 842 may control signal V with respect to frequency_FREQGenerating the filter control signal V in a synchronous manner_FILTER. For example, processor 842 may simultaneously apply filter control signal V_FILTERAnd a frequency control signal V_FREQAre all driven high to start the period of the LED driving circuit 830 (e.g., at time t in fig. 10A)₁). At time t₁The PWM control circuit 866 of the latch circuit 860 may output the driving signal V_DRIs driven high (e.g. towards the supply voltage V)_CC) Thereby turning on the FET Q832 of the LED driver circuit 830. At this point, inductor L834 of LED driver circuit 830 may begin to conduct inductor current I_L. When the instantaneous current feedback signal V_I-INST(which may be related to the inductor current I_LProportional to) exceeds the peak current threshold signal V_THAt the amplitude of (V), the PWM control circuit 866 may drive the voltage V_DRIs driven low (e.g., toward circuit common), as at time t of fig. 10A₂This may cause the FET Q832 of the LED driver circuit 830 to become non-conductive as shown. Drive signal V_DRMay be characterized by an on-time T_ONAnd may be equal to the operation period T_OPAs shown in fig. 10A. PWM control circuit 866 may cause LED Q832 to conduct during each operating cycle of LED drive circuit 830 for a duration of drive signal V_DROn-time T of_ONLength of (d). Inductor current I_LMay have a peak amplitude I_PKAs shown in fig. 10A. Inductor current I_LMay be at time t₂Starts to decrease until the inductor current I_LAt time t₃Dropping to zero amps.

Processor 842 may be on for a predetermined on-time T_FREQ-ONAt the end (e.g., at time t in FIG. 10A)₄) Will frequency control signal V_FREQThe drive is low. Processor 842 may be in filter window period T_FILTERAt the end (e.g., at time t in FIG. 10A)₅) Control signal V of filter_FILTERThe drive is low. Processor 842 may control filter control signal V_FILTERAnd a frequency control signal V_FREQAre all driven high to operate for a period T_OPAt the end (e.g., at time t in FIG. 10A)₆) Another cycle of the LED driver circuit 830 is started.

When the target current I_TRGTLess than the transition current I_TRANThe processor 842 may control the target current control signal V_I-TRGTIs kept constant at a minimum voltage V_MINAnd according to the target current I_TRGTAt a minimum frequency f_MINWith a maximum frequency f_MAXLinearly adjusts the frequency control signal V between_FREQE.g., as shown in fig. 9A and 9B. The filter circuit 880 may be configured to filter window period T at each cycle of the LED driver circuit 830_FILTERFeedback signal V of period pair instantaneous current_I-INSTAnd (6) filtering. When the target current I_TRGTLess than the transition current I_TRANTime, filter control signal V_FILTERMay be at an operating frequency f_OPIs a characteristic periodic signal. Processor 842 may control filter control signal V_FILTERFilter window period T_FILTERIs kept constant from one period of the LED driver circuit 830 to the next period, and is compared with the frequency control signal V_FREQIs independent of the frequency of (a). Filter control signal V_FILTERMay be controlled with the frequency control signal V_FREQChanges in the frequency of (c).

Control signal V due to target current_I-TRGTAnd a filter window period T_FILTERIs kept constant, so that even the driving signal V_DRE.g., operating period T_OP) May depend on the target current I_TRGTAnd changes, the drive signal V_DROn-time T of_ONOr may be approximately the same for each cycle of the LED driver circuit 830. As a result, when the target current I is_TRGTLess than the transition current I_TRANTime, filter window period T_FILTERDuring the inductor current I_LMay be approximately the same from one cycle of the LED driving circuit 830 to the next, and is the same as the target current I_TRGTIs irrelevant. The filter window period T can be designed_FILTERTo ensure when the target current I is_TRGTLess than the transition current I_TRANAt the time of the filter window period T_FILTERInductor current I before termination_LDropping to zero amps. When the target current is less than the transition current I_TRANWhen desired, the LED driver circuit 830 may be configured to operate in a discontinuous mode of operation.

FIG. 10B shows a graph illustrating the current when the target current I is_TRGTGreater than the transition current I_TRANAn example waveform of the operation of LED driver 800. When the target current I_TRGTGreater than the transition current I_TRANThe processor 842 may be based on the target current I_TRGTAt a minimum voltage V_MINAnd a maximum voltage V_MAXLinearly adjusts the target current control signal V therebetween_I-TRGTFor example, as shown in fig. 9A and 9B. In addition, processor 842 may control frequency of signal V_FREQIs kept constant in frequencyAt a constant maximum operating frequency f_MAX(e.g., make the operation period T_OPIs kept constant for a minimum period of operation T_MIN). When the target current I_TRGTGreater than the transition current I_TRANThe processor 842 may control the filter control signal V_FILTERTo a maximum filter duty cycle (e.g., 100%). For example, when the target current I_TRGTGreater than the transition current I_TRANTime, operation period T_OPMay be equal to the filter window period T_FILTERLength of (d). As a result, as shown in FIG. 10B, when the target current I is set_TRGTGreater than the transition current I_TRANThe processor 842 may always control the filter control signal V_FILTERDriven high (e.g. filter control signal V)_FILTERIs a constant signal). When the target current I_TRGTGreater than the transition current I_TRANTime-averaged current feedback signal V_I-AVECan indicate the inductor current I_LIs measured. Additionally or alternatively, processor 842 may approximately apply filter control signal V at all times (e.g., almost all times), e.g., at a substantial duty cycle (e.g., about 90% or more)_FILTERThe drive is high.

Because the processor 842 is based on the target current I_TRGTVarying the target current control signal V_I-TRGTSo that the drive signal V_DROn-time T of_ONCan be based on the target current I_TRGTBut changes even though the driving signal V is changed_DRE.g., operating period T_OP) The same is true for keeping constant. With the target current I_TRGTIncrease peak current I of inductor current_PKIt may be increased to a point where the LED driver circuit 830 may begin operating in a continuous mode of operation. Due to the minimum operating period T_MIN(e.g., when the target current I_TRGTGreater than the transition current I_TRANTime of day operating period T_OP) May be equal to the filter window period T_FILTERSuch that the processor 842 may be configured to determine the current at the target current I_TRGTLess than the transition current I_TRANFirst operation mode when the target current I is_TRGTIs greater thanTransition current I_TRANThe LED driver 800 transitions smoothly between the second operation modes.

When the target current I_TRGTGreater than the transition current I_TRANTime, frequency control signal T_FREQPredetermined on-time T_FREQ-ONIs less than the operating period T_OPLength of (d). The processor 842 may provide the frequency control signal T at the end of each cycle of the LED driver circuit 830_FREQDriven low (e.g., at time t in FIG. 10B₇) Then driven high (e.g., at time t)₈). This causes the PWM control circuit 866 of the latch circuit 860 to stop driving the signal V_DRIs kept low and when the frequency control signal T is applied_FREQIs driven high will drive signal V_DRIs again driven high, thereby starting the next cycle of the LED driving circuit 830 (e.g., at time t)₈)。

Processor 842 of control circuit 840 may be configured to determine or learn (e.g., measure or receive an indication of) a magnitude of load voltage VLOAD (e.g., produced on capacitor C836) and/or store the measurement in a memory (e.g., memory 712) as a learned load voltage VLEARNED (e.g., a learned capacitor voltage). Load voltage V generated across LED light source 802_LOADMay depend on the load current I_LOADIs detected (e.g., control circuit 840 will measure load current I_LOADRegulated target load current I_TRGT) And internal circuitry for the LED light source. The processor 842 may be configured to receive a load voltage feedback signal (e.g., the load voltage feedback signal V of the LED driver 100) from the LED drive circuit 830_V-LOAD) Which may be a load voltage V generated by a resistor divider circuit (not shown) of the LED driver circuit 830_LOADA scaled version of (a). Processor 842 may sample the load voltage feedback signal using an analog-to-digital converter (ADC) to measure the load voltage V_LOADThe amplitude of (c).

FIG. 11A illustrates the learning of the load voltage V by the processor 842 when_LOADAn example waveform of the operation of LED driver 800. The processor 842 may be configured to connect the LED light source 802 from the processor 842Determining (e.g., measuring) load voltage V when the turn-on transition is off_LOADThe amplitude of (c). As shown in fig. 11A, processor 842 may ramp LED light source 802 from on to off at time t₀Will load current I_LOADFrom the initial current I_INITBegins to decrease when the load voltage V_LOADCan also be derived, for example, from the initial voltage V_INITThe decrease is started. The processor 842 may be configured to determine when the load current I is_LOADIs within a measurement window, determines (e.g., measures) the load voltage V_LOADThe range of the measured window may be at the maximum learning threshold I_LEARN-MAXAnd a minimum learning threshold I_LEARN-MINWithin (e.g., at time t as shown in FIG. 11A_WIN-STARTAnd t_WIN-ENDIn between). Maximum learning threshold I_LEARN-MAXAnd a minimum learning threshold I_LEARN-MINMay be the rated (or maximum) current I of the LED light source 802_RATEDA function of (b), e.g. 0.0020. I_RATEDAnd 0.0002. I_RATED. The processor 842 may be configured to periodically sample the load voltage feedback signal during a measurement window and process a plurality of samples to determine a learned load voltage V_LEARNED. For example, the processor 842 may be configured to process a plurality of samples of the load voltage feedback signal by calculating an average or median of the plurality of samples or filtering the samples using a digital low pass filter.

The processor 842 may be configured to measure the load voltage V when (e.g., each time) the processor 842 turns off the LED light source 802 (e.g., fades the LED light source off)_LOADAnd determining the learned load voltage V_LEARNED. The processor 842 may be configured to utilize the learned load voltage V determined when the processor 842 turned off the LED light source 802 the last time_LEARNEDTo rewrite the learned load voltage V stored in the memory_LEARNED. In addition, the processor 842 may be configured to rewrite the learned load voltage V stored in the memory_LEARNEDHandling of a learned load voltage V previously from a plurality of disconnection events_LEARNED(e.g. calculating a plurality of learned load voltagesMean or median).

The processor 842 may be configured to use the learned load voltage V, e.g., when turning on the LED light sources 802_LEARNEDTo control the LED driver circuit 830. FIG. 11B illustrates when the processor 842 causes the LED light source 802 to fade on (e.g., to fade to correspond to the target current I)_TRGTTarget intensity L of_TRGT) Example waveforms for the operation of LED driver 800. In response to receiving a command to turn on the LED light source 802 and/or in response to powering the LED driver 800 to turn on the LED light source, the processor 842 may be configured to during the precharge period T_PRE-CHARGEDuring which the output capacitor C836 of the LED driver circuit 830 is precharged before attempting to turn on the LED light source 802. The processor 842 may be configured to learn the load voltage V based on the learned load voltage_LEARNEDControlling a pulse width modulated signal V_PWMDuty cycle of (and thus the target current control signal V)_I-TRGTSuch that output capacitor C836 charges faster than normal (e.g., such as shown in fig. 9B when processor 242 responds to target current I)_TRGTControl target current control signal V_I-TRGTFaster with DC amplitude). In a precharge period T_PRE-CHARGEThe faster rate at which the output capacitor C836 charges may allow the processor 842 to quickly and consistently turn on the LED light source 802, e.g., as the LED light source is ramped to the low-end intensity L_LEThen (c) is performed.

The control circuit 840 may be configured to precharge the output capacitor C836 of the LED drive circuit 830 until the load voltage V_LOADReaches or exceeds a pre-charge voltage threshold V_TH-PC. For example, the load voltage V may be learned based on_LEARNEDTo determine a pre-charge voltage threshold V_TH-PC(e.g., V)_TH-PC＝α·V_LEARNEDWhere α is a constant, which may be, for example, about 0.90). Due to the load voltage V when the LED light source 802 is cold_LOADMay be greater than the magnitude of LED light source 802 when warm, and thus the magnitude of constant α may be less than 1 to ensure that LED driver circuit 830 does not overshoot the learned load voltage V when pre-charging output capacitor C836_LEARNED. Additionally or alternatively, use may be made ofLearned load voltage V_LEARNEDTo determine the precharge voltage threshold V_TH-PC(e.g., V)_TH-PC＝V_LEARNEDβ, where β is a constant, which may be, for example, about one volt). Additionally or alternatively, a pre-charge voltage threshold V_TH-PCMay be a fixed threshold (e.g., a predetermined threshold). The processor 842 may be configured to determine when the load voltage V is below a predetermined value_LOADDoes not exceed the precharge voltage threshold V within the timeout period_TH-PCThe precharging of the output capacitor C836 is stopped. The processor 842 may be configured to learn based on the load voltage V_LEARNEDTo select the pulse width modulation signal V_PWMSuch that the pre-charge period T of the LED driver 800_PRE-CHARGEThe light sources may be approximately the same for different LEDs having different resulting load voltages.

Processor 842 may control enable control signal V_START-UPTo be in a precharge period T_PRE-CHARGEDuring which the controllable switching circuit 858 of the integrator circuit 850 is turned on. At a load voltage V_LOADReaches or exceeds a pre-charge voltage threshold V_TH-PCThereafter, the processor 842 can control the start control signal V_START-UPSuch that the controllable switching circuit 858 of the integrator circuit 850 is non-conductive. This may allow integrator circuit 50 and latch circuit 860 to respond to current feedback signal V_I-FBAnd the LED driving circuit 830 is controlled using closed loop control to adjust the load current I_LOADIs adjusted towards the target current I_TRGT。

Fig. 12 is a simplified flow diagram of an example turn-on process 1200 for controlling a power converter circuit of an LED driver (e.g., LED driver circuit 830 of LED driver 800). For example, the turn-on process 1200 may be performed by a control circuit (e.g., control circuit 840) at step 1210 in response to receiving a command to turn on an LED light source and/or in response to supplying power to an LED driver to turn on the LED light source. The control circuit may retrieve the learned load voltage V from memory at step 1212_LEARNEDAnd may be based on the learned load voltage V at step 1214_LEARNEDSetting a precharge threshold V_TH-PCThe value of (c).At 1216, the control circuit may base the learned load voltage V on_LEARNEDSetting a pulse width modulation signal V_PWMThe duty cycle of (c). The control circuit may control the frequency control signal V at 1218_FREQIs set equal to the maximum operating frequency f_MAXAnd may initiate a control signal V at 1220_START-UPDriven high to turn on the controllable switching circuit 858. In step 1222, when the bus voltage V is_BUSIs greater than or equal to the precharge threshold V_TH-PCThe control circuit may enable the control signal V at 1224_START-UPDriven low to render controllable switching circuit 858 non-conductive and based on target intensity L at 1226_TRGTSetting a target current I_TRGT. At 1228, the control circuit may control the display by changing the intensity of the minimum fade L_FADE-MINStarting and facing the target intensity L_TRGTSlowly increasing the current intensity L of the LED light source_PRESTo begin the gradual turning on of the LED light source, and then exit the turn-on process 1200.

Claims (26)

1. A load control device for controlling the intensity of a lighting load, the load control device comprising:

a power converter circuit configured to receive a first voltage and to generate a second voltage across a capacitor; and

a control circuit operably coupled to the power converter circuit and configured to control the power converter circuit to generate the second voltage across the capacitor;

wherein the control circuit is configured to determine a learned capacitor voltage from a magnitude of the second voltage of the capacitor, the control circuit configured to determine an operating parameter associated with the power converter circuit from the learned capacitor voltage, the control circuit configured to control the power converter circuit to charge the capacitor in dependence on the operating parameter until the magnitude of the second voltage reaches a threshold.

2. The load control device of claim 1, further comprising:

a load regulation circuit configured to receive the second voltage and control a magnitude of a load current conducted through the lighting load;

wherein the control circuit is operatively coupled to the load regulation circuit and configured to control the magnitude of the load current to control the intensity of the lighting load.

3. The load control device of claim 2, wherein the power converter circuit comprises a semiconductor switch, and the control circuit is configured to turn on the semiconductor switch for an on-time during each operating cycle of the power converter circuit.

4. The load control device of claim 3, wherein the control circuit is configured to determine a preload on-time from the learned capacitor voltage and to cause the semiconductor switch to conduct the preload on-time to charge the capacitor until the magnitude of the second voltage reaches the threshold.

5. The load control device of claim 4, wherein the control circuit is configured to determine the preload on-time based on a linear relationship between the learned capacitor voltage and the preload on-time.

6. The load control device of claim 3, wherein after the magnitude of the second voltage exceeds the threshold, the control circuit is configured to adjust the magnitude of the second voltage toward a target voltage by adjusting the on-time of the semiconductor switch in response to the magnitude of the second voltage.

7. The load control device of claim 2, wherein the control circuit is configured to determine the magnitude of the second voltage when the intensity of the lighting load is at the high-end intensity.

8. The load control device of claim 2, wherein the second voltage is approximately equal to a load voltage generated across the lighting load.

9. The load control device of claim 1, wherein the power converter circuit is configured to control a magnitude of a load current conducted through the lighting load, and the control circuit is operably coupled to the power converter circuit for controlling the magnitude of the load current to control the intensity of the lighting load.

10. The load control device of claim 9, wherein the control circuit comprises: a digital control circuit configured to generate a target current control signal; and an analog control loop circuit configured to control the power converter circuit to control the magnitude of the load current in response to the target current control signal.

11. The load control device of claim 10, wherein the digital control circuit is configured to set the magnitude of the target current control signal to charge the capacitor based on the learned capacitor voltage until the magnitude of the second voltage reaches the threshold.

12. The load control device of claim 11, wherein after the magnitude of the second voltage exceeds the threshold, the digital control circuit is configured to set a magnitude of the target current control signal based on a target current of the load current, and the analog control loop circuit is configured to adjust the magnitude of the load current toward the target current.

13. The load control device of claim 9, wherein the control circuit is configured to measure the magnitude of the second voltage when the intensity of the lighting load is at the low-end intensity.

14. The load control device of claim 9, wherein the control circuit is configured to measure the magnitude of the second voltage when the power converter circuit is ramping the lighting load from on to off.

15. The load control device of claim 1, wherein the control circuit is configured to measure a magnitude of the second voltage and store a value representative of the measured voltage as the learned capacitor voltage.

16. The load control device of claim 1, wherein the control circuit is configured to determine the threshold value as a function of the learned capacitor voltage.

17. A load control device for controlling the intensity of a lighting load, the load control device comprising:

a power converter circuit configured to generate a bus voltage across a bus capacitor;

a load regulation circuit configured to receive the bus voltage and control a magnitude of a load current conducted through the lighting load; and

a control circuit operably coupled to the load regulation circuit and configured to control a magnitude of the load current to adjust an intensity of the lighting load;

wherein the control circuit is configured to measure a voltage representative of a load voltage generated across the lighting load and store a value representative of the measured voltage as a learned load voltage, the control circuit configured to determine an operating parameter of the power converter circuit from the learned load voltage, the control circuit configured to control the power converter circuit to charge the bus capacitor using open loop control in dependence on the operating parameter until a magnitude of the bus voltage reaches a threshold value.

18. The load control device of claim 17, wherein the control circuit is configured to turn on a semiconductor switch of the power converter circuit for an on-time during each operating cycle of the power converter circuit, the control circuit further configured to determine a preload on-time from the learned load voltage, and to turn on the semiconductor switch for the preload on-time to charge the bus capacitor until the magnitude of the bus voltage reaches the threshold.

19. The load control device of claim 18, wherein, after the magnitude of the bus voltage exceeds the threshold value, the control circuit is configured to adjust the magnitude of the bus voltage toward a target bus voltage by adjusting the on-time of the semiconductor switch in response to the magnitude of the bus voltage.

20. The load control device of claim 17, wherein the control circuit is configured to determine the threshold value based on the learned load voltage.

21. The load control device of claim 17, wherein the control circuit is configured to measure the bus voltage to determine the learned load voltage.

22. A load control device for controlling the intensity of a lighting load, the load control device comprising:

a load regulation circuit configured to receive a bus voltage and control a magnitude of a load current conducted through the lighting load, the load regulation circuit comprising an output capacitor configured to store a load voltage generated across the lighting load; and

a control circuit operably coupled to the load regulation circuit and configured to control a magnitude of the load current to control an intensity of the lighting load;

wherein the control circuit is configured to measure a magnitude of the load voltage and store a value representative of the measured magnitude of the load voltage as a learned load voltage, the control circuit configured to determine an operating parameter of the load regulation circuit from the learned load voltage, the control circuit configured to control the load regulation circuit to charge the output capacitor in dependence on the operating parameter until the magnitude of the load voltage reaches a threshold value.

23. The load control device of claim 22, wherein the control circuit is configured to measure the magnitude of the load voltage when the lighting load is on, and to control the load regulation circuit in accordance with the operating parameter when the control circuit is controlling the lighting load from off to on.

24. The load control device of claim 23, wherein the control circuit comprises: a digital control circuit configured to generate a target current control signal; and an analog control loop circuit configured to control the load regulation circuit to control the magnitude of the load current in response to the target current control signal, the digital control circuit further configured to set the magnitude of the target current control signal to charge the output capacitor based on the learned load voltage until the magnitude of the load voltage reaches the threshold.

25. The load control device of claim 24, wherein after the magnitude of the load voltage exceeds the threshold, the digital control circuit is configured to set a magnitude of the target current control signal based on a target current of the load current, and the analog control loop circuit is configured to adjust the magnitude of the load current toward the target current.

26. The load control device of claim 22, wherein the control circuit is configured to determine the threshold value from the learned load voltage.