CN106604479A - Non-isolated LED dimming circuit with PWM and DIM dimming - Google Patents

Abstract

The invention discloses a non-isolated LED dimming circuit with PWM and DIM dimming, relates to the technical field of LED dimming, and includes an LED lighting circuit and a dimming circuit. The dimming circuit includes a high-voltage to low-voltage module and a demagnetization time detection module, a switch control module, a peak detection module, and a dimming signal input terminal, the demagnetization time detection module adjusts the closing time of the high-voltage MOS tube according to the input DC signal to adjust the demagnetization time, and the peak detection module adjusts the discharge of the inductor in the LED dimming circuit peak value, the switch control module controls the gate of the high-voltage MOS tube according to the input PWM signal, the output signal of the demagnetization time detection module and the signal of the peak detection module to adjust the current of the LED lamp, and outputs a 5V voltage, which can be given to the control system. MCU, bluetooth module, and radar module provide power supply, no additional power supply is needed, the chip isolation is high, and the two control channels can be used separately without affecting each other.

Description

Non-isolated LED dimming circuit with PWM and DIM dimming

technical field

The invention relates to the technical field of LED dimming, in particular to an LED dimming circuit with PWM and DIM dimming.

Background technique

There are two commonly used methods for dimming existing LED lamps:

1. Linear dimming;

Linear dimming is mainly based on the principle of simple voltage division. Its advantages are simple application and no interference. The disadvantages are inflexibility and low efficiency. At the same time, it may cause chromatographic shift and excessive heat to increase the temperature.

2. PWM dimming method

An LED is a diode, which can be switched on and off quickly. Its switching speed can be as high as more than microseconds. It is unmatched by any light-emitting device. Therefore, as long as the power supply is changed to a pulse constant current source, the brightness can be changed by changing the pulse width.

LED lighting driver chips generally require two dimming methods, PWM dimming and analog dimming. There are various implementation methods. Analog dimming and PWM dimming use different interfaces, which are incompatible with each other, and the peripheral circuits are complex.

Contents of the invention

The technical problem to be solved by the present invention is to solve the above-mentioned differences in the prior art, and provide a new LED dimming circuit compatible with DC dimming and PWM dimming.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a non-isolated LED dimming circuit with PWM and DIM dimming, including LED lighting circuit and dimming circuit; the lighting circuit includes LED lamp tube, lamp tube An LC oscillating circuit composed of resistors, capacitors and inductors is also connected; the dimming circuit includes a high voltage to low voltage module, a demagnetization time detection module, a switch control module, a peak detection module and a dimming signal input terminal; the dimming signal input The terminal is used to input DC signals and PWM signals; the high-voltage to low-voltage module is connected to the node between the LED lamp tube and the inductor of the LED lighting circuit, and outputs the working voltage for external devices or controllers; the switch control module includes several A group of control channels, each channel is connected to a dimming signal input terminal and the gate of a high-voltage MOS transistor, and the drain of the high-voltage MOS transistor is connected to a lighting circuit. When the high-voltage MOS transistor is turned off, the inductor performs demagnetization discharge; the demagnetization The time detection module detects the demagnetization time of the inductance of the lighting circuit, and adjusts the closing time of the high-voltage MOS tube according to the input DC signal to adjust the demagnetization time; the peak detection module is used to detect the source voltage of the high-voltage MOS tube, and according to the detected source The pole voltage controls the closing of the high-voltage MOS tube through the switch control module to adjust the peak value of the inductor discharge in the LED dimming circuit; the switch control module controls the high voltage according to the input PWM signal, the output signal of the demagnetization time detection module and the signal of the peak detection module. The gate of the MOS tube.

Further, the peak detection module includes a peak detection comparator, one end of the peak detection comparator is connected to the source of the high-voltage MOS transistor, and the input base voltage is input. When the source voltage of the high-voltage MOS transistor reaches the reference voltage, the peak detection comparator outputs The control signal is sent to the switch control module to close the high-voltage MOS tube.

Further, the output terminal of the high voltage to low voltage module is also connected to a 5V voltage generating module, and the 5V voltage generating module is provided with a port for connecting to the MCU control system.

Further, the high-voltage to low-voltage module includes a high-voltage JFET, the source of the high-voltage JFET is connected to the drain of the MOS transistor M2, and is also connected to the drain of the MOS transistor M1 through a resistor, and the gate of the MOS transistor M2 is connected to the gate of the MOS transistor M1, and The drain of the MOS transistor M2 is connected to the gate, the source of the MOS transistor M2 outputs a DC voltage for external equipment, the source connected to the MOS transistor M2 is connected to the hysteresis comparator, the hysteresis comparator inputs the reference voltage, and the hysteresis comparator then Connect the control circuit to regulate the gate of the MOS transistor M2.

Further, the demagnetization time detection module includes an amplifier, a logic control module and a capacitor, the input terminal of the amplifier is connected to the gate of the high-voltage MOS transistor, the amplifier is connected to the logic control module to generate a control signal, and the control signal controls the current for charging the capacitor. A time control signal is generated to control the off time of the gate of the high voltage MOS transistor.

From the above technical solution, it can be seen that the present invention has the following advantages: when multi-channel dimming is set, one driver chip can meet the use requirements, and the high-voltage MOS tube and the corresponding switch channel are added before; the peripheral circuit is simplified, and only a few A resistor and capacitor; the port is multiplexed, and only one input port is used to realize the DIM and PWM dimming functions. Compatible with PWM and DIM dimming. The PWM dimming ratio is from 0.1% to 100%. It is convenient for the design and application of various schemes; the output voltage is 5V, which can provide power for the MCU, Bluetooth module, and radar module of the control system, without additional power supply; the chip has high isolation, and multi-channel control can be used independently without affecting each other.

Description of drawings

Fig. 1 is the functional block diagram of the dimming circuit of the present invention;

Fig. 2 is the circuit schematic diagram of the middle and high voltage to low voltage module of the present invention;

Fig. 3 is the schematic diagram of demagnetization time detection module;

Fig. 4 is the schematic diagram of peak detection module;

Figure 5 is a current waveform diagram of the inductor when the DC signal is not connected;

Fig. 6 is a current waveform diagram of the inductor when a DC signal is connected.

detailed description

Hereinafter, with reference to the accompanying drawings, the specific implementation manner of the present invention will be described in detail by taking lighting circuits such as two LEDs as an example, without limitation.

As shown in Figure 1, the non-isolated LED dimming circuit with PWM and DIM dimming of the present invention includes an LED lighting circuit and a dimming circuit; the lighting circuit includes two LED lamps, and a capacitor is connected in parallel at both ends of each lamp tube. The resistor and the inductor are provided with a Schottky tube between the inductor and the LED lamp. The inductor discharges through the Schottky tube and the LED lamp, and this discharge time is the demagnetization time.

The dimming circuit includes a high-voltage to low-voltage module, a demagnetization time detection module, a switch control module, a peak detection module, and two dimming signal input terminals; each dimming signal input terminal is compatible with DC signal and PWM signal input; the high-voltage to low-voltage module is connected The output end of the LED lighting circuit, that is, the node connected between the LED lamp and the inductor, the high-voltage to low-voltage module directly generates a low-voltage 7.5V voltage, and outputs the working voltage for external devices or controllers, and then generates the module through the 5V voltage to obtain the The required 5V voltage. The 7.5V voltage can supply power to the Bluetooth receiving control module, the infrared receiving control module, etc., and the 5V voltage can supply power to the radar receiving control module and MCU control system.

The specific structure of the high-voltage to low-voltage module is shown in Figure 2. The high-voltage to low-voltage module includes a high-voltage JFET. The source of the high-voltage JFET is connected to the drain of the MOS transistor M2, and is also connected to the drain of the MOS transistor M1 through a resistor. The MOS transistor M2 and The gate of the MOS transistor M1 is connected, and the drain of the MOS transistor M2 is connected to the gate. The source of the MOS transistor M2 outputs a DC voltage for external equipment, and the source connected to the MOS transistor M2 is connected to the A hysteresis comparator, the hysteresis comparator inputs the reference voltage, and the hysteresis comparator is connected to the control circuit to regulate the gate of the MOS transistor M2. The high voltage at the end of the inductor is converted into a medium voltage after passing through the high voltage JFET, about 20 to 30V, and then converted into a low voltage 7.5V after passing through the MOS transistors M1 and M2. When VDD exceeds 7.5V, the signal S is passed through the hysteresis comparator. Pull it low to turn off the MOS transistor M2. When the VDD voltage is lower than 7.5V, the signal S outputs a high-impedance state, and the MOS transistor M2 is turned on to charge VDD. The input terminal of the control circuit can also intervene in the DVR signal. When the voltage of the DN1 port connected to the module is low, the signal S is pulled down, and the MOS transistor M2 is turned off to prevent the VDD voltage from flowing back to the DN1 terminal.

The switch control module connection includes two sets of independent control channels, each channel is connected to a dimming signal input terminal and the gate of a high-voltage MOS transistor, and the drain of the high-voltage MOS transistor is connected to a lighting circuit, which is connected between the LED and the inductor. The nodes between them; the switch control module controls the MOS gate according to the input PWM signal, the output signal of the demagnetization time detection module and the signal of the peak detection module.

The structure of the peak detection module is shown in Figure 4, including two peak detection comparators, which are respectively connected to the sources of two high-voltage MOS transistors, and the input terminal inputs a reference voltage (the reference voltage of this chip is 0.4V, and other Voltage), after the system is powered on, the source voltage of the MOS tube rises slowly. When it reaches the reference voltage, the peak comparator sends a control signal to the switch control module, and then turns off the high-voltage MOS tube. At this time, the inductor starts to demagnetize and discharge. , the demagnetization time detection module turns on the high-voltage MOS tube, and so on. The peak detection module can adjust the peak value of the discharge of the inductor by setting the reference voltage, and control the closing of the high-voltage MOSFET, thereby controlling the peak current of the inductor. The peak current is set as Ip=VREF/RCS, where VREF is the internal reference voltage, and RCS is the CS1 port or The external sampling resistor of the CS2 port, (generally we set this resistor to be the same).

The demagnetization time detection module detects the inductance demagnetization time of the lighting circuit, and adjusts the closing time of the high-voltage MOS tube according to the input DC signal; the specific structure of the demagnetization time detection module is shown in Figure 3, and the demagnetization time detection module includes an amplifier and a logic control module And the capacitor, connect the DC power to the logic control module through the port DIM1, and then connect the amplifier to the logic control module to generate a control signal K, which controls the current for charging the capacitor, and generates a time control signal TOFF to the switch control module to extend the high-voltage MOS Tube closing time. When the source voltage of the high-voltage MOS tube reaches VREF, the peak detection module turns off the high-voltage MOS tube. This time is a fixed value (when the inductance remains unchanged and the LED load remains unchanged), and the inductance begins to demagnetize at this time (that is, the high-voltage MOS tube off time), control the delay magnetic time to control the conduction duty cycle of the high-voltage MOS tube, to control the average current, thereby adjusting the brightness of the LED lamp.

When the DIM signal connected to the dimming signal input terminal does not work, the inductor discharge current is shown in Figure 5. In the figure, CS represents the source voltage of the high-voltage MOS transistor, and VREF is the set reference voltage. When the inductor current is 0, the demagnetization ends. At this time, the demagnetization detection module turns on the high-voltage MOS transistor through the switch control module according to the signal feedback of the gate of the high-voltage MOS transistor. When the CS voltage reaches the VREF voltage, the peak detection module is closed. High-voltage MOS tube, at this time the system enters the demagnetization detection state, and so on. The demagnetization time is the time TFF when the inductor current drops from the set value to 0, and the discharge ends.

When the DIM signal is connected, the discharge current of the inductor is shown in Figure 6. After the demagnetization of the inductor is completed, the DIM signal can delay the turn-on time TDF of the high-voltage MOS tube, and the demagnetization time TFF (DIM does not work). Time TDF, so the total demagnetization time is TFF+TDF, so as to adjust the average current of the inductor discharge, and then adjust the brightness of the LED lamp.

The working principle of the system is as follows:

1. Since the chip integrates a 500V high-voltage device, a "high-voltage to low-voltage" module is used inside the circuit to directly generate a low-voltage 7.5V voltage and provide power to the chip, so that no external start-up resistor is needed, and then the 5V voltage is generated by the module. Get the required 5V voltage. Port DIM1 and port DIM2 have built-in pull-up resistors, compatible with PWM dimming and DC voltage analog dimming. The analog dimming range of the DIM port is 1V-3V. When the voltage of the DIM port is lower than 1V, the LED current is 0. When the voltage of the DIM port is higher than 3V, the current brightness of the LED is 100%. DIM can also use PWM dimming, input a square wave with a duty cycle of 0-100%, then the LED current can be adjusted from 0-100%, and the amplitude of the input square wave is 0V-5V.

2. The whole system works like this: After the system is powered on, VDD reaches the turn-on voltage. At this time, the system starts to work, and the high-voltage MOS tube is turned on. The source voltage of the high-voltage MOS tube starts to rise slowly. When it reaches the internal limit value, the high-voltage MOS tube is turned off. At this time, the inductance discharges through the Schottky tube and the LED lamp, and the port DIM is connected to the MCU or other control equipment. In the case of analog dimming, the port DIM adjusts the demagnetization time through the voltage of the port DIM, thereby adjusting the current of the LED. . When the PWM waveform is input to the port DIM, the LED current is adjusted by the duty cycle of the input waveform. When the port DIM is suspended, the demagnetization time is determined by the inductor, the voltage of the LED lamp, and the current of the LED lamp.

Claims (5)

1. A non-isolated LED dimming circuit with PWM and DIM dimming, including an LED lighting circuit and a dimming circuit; the lighting circuit includes an LED lamp, and the lamp is also connected to an LC oscillator composed of a resistor, a capacitor and an inductor circuit; the dimming circuit includes a high voltage to low voltage module, a demagnetization time detection module, a switch control module, a peak detection module, and a dimming signal input terminal; the dimming signal input terminal is used to input a DC signal and a PWM signal; the The high-voltage to low-voltage module is connected to the node between the LED lamp tube and the inductor of the LED lighting circuit, and outputs the working voltage for external devices or controllers; the switch control module includes several groups of control channels, and each channel is connected to a dimming signal The input terminal is connected to the gate of a high-voltage MOS transistor, and the drain of the high-voltage MOS transistor is connected to a lighting circuit. When the high-voltage MOS transistor is turned off, the inductance is demagnetized and discharged; the demagnetization time detection module detects the demagnetization time of the inductance of the lighting circuit, and Adjust the turn-off time of the high-voltage MOS tube according to the input DC signal to adjust the demagnetization time; the peak detection module is used to detect the source voltage of the high-voltage MOS tube, and control the closing of the high-voltage MOS tube through the switch control module according to the detected source voltage Thereby adjusting the peak value of the inductor discharge in the LED dimming circuit; the switch control module controls the gate of the high-voltage MOS transistor according to the input PWM signal, the output signal of the demagnetization time detection module and the signal of the peak detection module. 2. The non-isolated LED dimming circuit with PWM and DIM dimming according to claim 1, characterized in that: the peak detection module includes a peak detection comparator, and one end of the peak detection comparator is connected to the source of a high-voltage MOS tube When the source voltage of the high-voltage MOS tube reaches the reference voltage, the peak detection comparator outputs a control signal to the switch control module to turn off the high-voltage MOS tube. 3. The non-isolated LED dimming circuit with PWM and DIM dimming according to claim 1, characterized in that: the output end of the high-voltage to low-voltage module is also connected to a 5V voltage generation module, and the 5V voltage generation module is provided with a port Used to connect to the MCU control system. 4. The non-isolated LED dimming circuit with PWM and DIM dimming according to claim 1, characterized in that: the high-voltage to low-voltage module includes a high-voltage JFET, and the source of the high-voltage JFET is connected to the drain of the MOS transistor M2. A resistor is connected to the drain of the MOS transistor M1, the gate of the MOS transistor M2 is connected to the gate of the MOS transistor M1, and the drain of the MOS transistor M2 is connected to the gate, and the source of the MOS transistor M2 outputs a DC voltage for external equipment The source connected to the MOS transistor M2 is connected to the hysteresis comparator, the hysteresis comparator inputs the reference voltage, and the hysteresis comparator is connected to the control circuit to regulate the gate of the MOS transistor M2. 5. The non-isolated LED dimming circuit with PWM and DIM dimming according to claim 4, characterized in that: the demagnetization time detection module includes an amplifier, a logic control module and a capacitor, and the input terminal of the amplifier is connected to a high-voltage MOS The gate of the tube, the amplifier is connected to the logic control module to generate a control signal, the control signal controls the current to charge the capacitor, and the time control signal is generated to control the closing time of the gate of the high-voltage MOS tube.