EP3257332A1

EP3257332A1 - Dimmer system

Info

Publication number: EP3257332A1
Application number: EP16748468.2A
Authority: EP
Inventors: Gregory BULL; Warren HERFT; Dean Williams
Original assignee: Lumitech Pty Ltd
Current assignee: Lumitech Pty Ltd
Priority date: 2015-02-09
Filing date: 2016-02-09
Publication date: 2017-12-20
Also published as: WO2016127198A1; AU2016218927A1

Abstract

A premises including a dimming system for large area lighting may be upgraded to use LEDs incorporating a driver without upgrading the legacy dimming system. The driver receives a control signal from the legacy dimming system, e.g. a chopped mains waveform, and determines a signal level from the control signal The signal level is used as an input to modulate a pulse width of a pulse width modulated signal having a frequency greater than the human fusion flicker rate. The pulse width modulated, signal is provided to the LEDs. The width of the pulse determines the average current to the LED element and hence the light level output of the LEDs.

Description

DIMMER SYSTEM

CROSS REF RENCE. TO RELATED APPLICATIONS

[000 ! j This application is related to and claims the priority benefit of Australian Provisional Application No, 2015900402 filed 9 February 2015, the entire contents of which are herei incorporated by reference.

FIELD OF THE INVENTION

[0002] This disclosure relates to lighting systems and i particular to dimmer systems for dimming light emitting diode (LED)s i large facil ities.

BACKGROUND OF THE INVENTIO

[0003] Man facilities, such as school halls, theatres, stages, and simila such venues have run lightin systems using conventional incandescent bulbs. These venues would often employ a form of dimming system, of which the Philips Dynalite system was one common example out of several commercially available systems. Prior art or legacy dimming systems typically employed a TRJAC or THY ISTOR to chop the mains waveform thereby reducing th average current through the bulb filament which in turn reduces the light output from the bulb. Such dimming systems were effective in dimming the conventional bulbs from 100% power to 0% and back again, or anywhere in between, with an eve distribution of power to the bulbs.

[0004] For a. premises to reduce its power consumption and achieve higher envitOnmental ratings, it is desirable for the premises to replace high consumption incandescent bulbs with towe consumption LEDs. However, a problem with LEDs is that th installed (legacy) dimming systems are not able to dim the LEDs to anytliing less than about 30% power before the LEDs become unstable. Fo venues where complete or near darkness is required, such as any performance or entertainment venue, movie theatre, stage, etc. this is not acceptable. However, to install a replacement dimming system can require a major re-fit of the premises which is beyond the budget of many establishments..

jOOOSj What is required is an improved system for enhancing the capability of a legacy dimming system with LED lighting systems. SUMMARY OF THE INVENTION^'

{0006] In one aspect, there is provided a driver circuit for a light emitting diode (LED), the driver circuit including a power supply that derives power from a legacy dimming circuit to produce an output voltage, an input level detector that detects a signal level from the legacy diiniiiing circuit, and a pulse generator that produces a pulse signal having a widt that is dependent on the detected signal level, wherein .the pulse signal is coupled with the output voltage to power the LED,

{0007j in one aspect, there is provided a lighting system for a premises, the lighting system including at least one dimmin control panel at least one legacy dimmin circuit, at least one light emitting diode (LED) element including at least one LED, and at least one driver for the at least one LED element, the at least one driver including a power supply that derives power from the legacy dimming circuit to produce an output voltage, an input level detector that detects a signal level from the legacy dimming circuit, and a pulse generator that produces a pulse signal having a width that is dependent on the detected signal level, wherein the pulse signal is coupled with the output vol tage of the power suppl to power the LED.

[0008] In one aspect, there is provided a method o controlling at least one Light Emittin Diode (LED) element includin at least one LED from a legacy dimming circuit of a premises, the method including using a dri ver to:

(a) receive a control signal fro the legacy dimmin circuit;

(b) determine a signal level of the control signal;

(c) use the determined signal level to modulate the pulse width of a pulse width waveform, to produce a pulse width modulated waveform; and

(d) provide the pulse widt modulated waveform to the at least one LED element. EIEF DESCRIPTION OF THE DRAWINGS

[0009} Reference will now he made, by way of example only, to specific emhodiments and to the accompanying drawings in which:

[001© j Figur 1 shows a prior art lighting system;

[00111 Figure 2 show's a lighting system in accordance with an embodiment of the present inventi n; {0012} Figure 3 shows a schemati c of a driver system;

{0013} Figure 4 shows a specific example of a driver circuit;

{0014} Figure 5 shows how the pulse width will vary with detector DC input level;;

10015 J Figure 6 shows the power carv e as a function of input control setting;

{0016\ Figure 7 shows a venue lighting system including at least one LED and driver of an embod iment of the present invention:

{0017} Figure 8 shows an alternative circuit diagram featuring an anti-ringing circuit; and

{0018} Figure shows an alternative circuit diagram for a high power LED embodiment.

DETAILED DESCRIPTION OF THE INVENTIO

{0019} Figure 1 shows a prior art dimming arrangement HI In this arrangement, a legacy dimmin system 12, for example but not exclusively, the Philips Dynalite system, provides dimming controls to an array of lights 14 dispersed throughout the premises. The lights may he arranged in sets or banks with one di mming control signal going to a subset of the lights of the complete lighting system, i one specific example, the lighting system may be in a theatre with complex lighting system controlled from a main desk or computer. The lighting system might use many high power light dimmers to control the ight levels in the theatre itself and other areas.

{0020 j If the theatre deci des to convert these lights to LED's they wil l discover that the high power replacement LED elements require a "Driver", When the LED and it's Driver are driven from the existing leadin edge dimming system, the LED performs badly or not at all. The nature of the power source will not allo the LED Driver to operate correctly.

{0021} Some problems are ;

• overheating of the LED Dri ver and dimmer flickering at low end;

• .not^' achieving low end;

• not reducing below 25%.

J0022J The only wa the theatre could use these LED's is to run a permanent power suppl and control wiring to the new LED Dri ver; This would be a major undertaking and great expense for the theatre. {00231 Figure 2 shows an embodiment of the present invention in which a translator or driver circuit 20 is installed between the legacy dimming system 12 and an upgraded LED lighting system including LED element 22. The LED element 22 is shown as a single LED b t t e person skilled in the ar will readily understan that an individual LED lighting element may be made up of multiple LCDs within the body of the LED element (as shown in Figures 8 and 9). T e LEDs within an LED element may be all of the same colour or be of multiple colours. The driver 20 translates the power from the existing dimming system 12 into a new form that the LED element 22 can respond to. The driver 20 thus negates the need to re ire the theatre for an LED upgrade.

[0024J The driver 20 is shown schematically in Figure 3. The driver 20 includes a power supply 21, a power load circuit (input level detector) 24, a Pulse Width Modulation (P W generator 26, a integrator 27 and a current limiter 28 to suit the LED 22, The power suppl 21 produces an output voltage while the integrator 27 produces a pulsed output, the width of which is determined by DC level produced by the power load circuit 24 from an incoming waveform 23 of a legacy dimming circuit. The output voltage and pulsed outpiit are coupled, via the current limiter 28 to the LED 2 to power the LED with pulsing current. Thus, the overall light output of the LED 22 detectable to a human observer is dependent on the pulse width . The _.frequency of the pulsing current is sufficiently high to prevent any observable flicker of the LED for a human observer. The frequency may be selected to be above the human fusio flicker rate which is the threshold frequenc above which the average human eye is unable to discern the fluctuation in light intensity and therefore the average human observer will not be able to discern any flicker. The human fusion flicker threshold is often considered to be approximately 60 Hz but is dependent on number of parameters of the light including, without limitation, the frequency of the modulation, the wavelength of the emitted light, the drop in amplitude from the peak level across the cycle (amplitude modulation), the ambient lighting levels, age and fatigue of the observer, etc, Furthermore, the human fusion flicker threshold is a statistical average representing the value at which half the human test population can no longer discern flicker. For audience lighting, it is- not satisfactory to subject half the audience to flickering light sources. Thus, it is preferable if the pulse signal frequency is selected to be well above the human fusion flicker threshold to accommodate a greater number of patrons. In one embodiment, the pulse signal frequency is greate than 500 Hertz (Hz). In one embodiment, the pulse signal frequency is greater than 1000 Hz. n one embodiment the pulse signal frequency is greater than 2000 Hz.

[0025] A specific embodiment of a circuit is illustrated in Figure 4. The power supply 21 receives an input 23 from the legacy dimmer circuit and creates a circuit voltage from the dimmer signal. Typically, the dimmer signal will be a chopped mains waveform produced by a TRIAC, myristor or the like. For Australian systems, the mains waveform will be 230V AC, 50 Hz based on the mains supply but this will differ from country to country. The leading edge modulated power 2 of the dimmer circuit first encounters a transformer 41. In one embodiment, the transformer is a toroidal iron core transformer. This is to ensure that it responds as necessar to the leading edge signal 23 front the dimme circuit, as well as increasing the reliability of the circuit. The transformer is selected to prov ide a match with the forward voltage of the LED. When at foil power the secondary AC RMS voltage should be the same as or close to the LED forward voltage.

[0026] The transformer 4 isolates the circuit, particularly the LED, electrically from the mains and presents an inductive loa to the Leading Edge Dimmer reducing the voltage to 50 VAC max. it is rectified 42 and filtered with a large value capacitor 43, e.g. 4700 μΡ, after which the DC voltage rises to about 70 VDC, depending on the power level applied from the dimmer circuit, The Anode 2 1 of the LED 22 is connected to this 70V positive D power rail 406, The inductor 401 and the high speed diodes 402, 403 give a boost to the DC rail 406 at the lower end of the power range.

[0027] The output of the rectifier circuit 42 i s also used to produce a supply vol tage , e.g. 1 V supply voltage 404, which is used to power various components of the driver circuit, such as the one of more integrated circuits, op amps, etc. as will be described in more detail below.

[0028] The LED cathode 22 is switched to negative via a powe MOSFET 407 and the current through the LED i controlled by Pulse Width Modulation of the MOSFET 407 as follows.

[0029] The power load circuit 24 receives the AC output from the transformer and passes it through a separate rectifier 45 to an RC network 46 and an Optocoupler 47. This circuit creates a DC signal which follows the level sent from the dimmer circuit while isolating th potentially high voltages of the dimmer circuit. |0030| The Pulse Width Modulation generator 26 in the form of Cnios Tinier IC 405 generates a narrow 3 kilofaertz (kHz) pulse which drives an Op Amp 410. I one embodiment, the Cruos Timer is a 555 Crnos Timer chip, powered by the 12V supply voltage 404 deri ved from the rectifier circuit 42, though other ty es of tinier chips will be apparent to the person skilled in the art The Op Amp 410, using an R/C network 41 1 , creates a stable and adj ustable sawtooth wa veform of around 3 Hz at the output of the Op Amp 410.

{0031 j The signal combiner 27 uses a second Op Amp 415 to compare the 3 hz sawtoot waveform from Op Amp 410 with the DC level from the optically coupled 4? power level detection stage 24. The mag itude of the pulse signal output of Op Am 410 is fixed, but the width will depend on the DC level input Figure 5^" shows that as the D level 51 derived from the dimmer waveform 23 increases, the pulse width 52 at the output of O Amp 415 will increase proportionally. The higher the D level input, the longer withi the cycle it takes for the waveform input to reach the DC level 54 and cause the comparator to switch from high to low. That is, the higher the DC level input the longer the pulse signal output remains high, i.e. the wider the pulse signal output. A sawtooth profile is used because it has been found by the present inventors to produce more linear response and therefore easier operatio for the user. However, the person skilled in the art would readily understand that other waveforms, e.g. sine, may he used depending on the response required,

[0032] The 3 kHz pulse signal output of the op amp 410 is coupled to the LED 22 via the power MOSFET 407. Operating at this frequency, whic is a frequency well above the human tiicke fusion rate, the LED will appear to be a steady state light source with no observable flicker. The intensity of the light output of the LED 22 that is detectable by person will depend on th average time for which the LED is on and is therefore dependent on the width of the pulse signal output supplied from the op amp 410 to the power MOSFET 407. At very short pulse widths (low dut cycle), the LED 22 will be mostly off and the average light output will be very low. At long pulse widths (high duty cycle), the LED will he on for longer periods and the overall light output of the LED 22 will increase, up to 100% duty cycle at which the LED will be on constantly and will produce its maximum output.

[0033] The MOSFET 407 source has a resistor 48 which allows a voltage to develop across it proportional to the LED current. If the current is above the LED's rating it lowers the voltage at the comparator input and stabtlises the power. A current limiting resistor 409 limits the current of the circuit.

[0034 j Figure 6 shows the power response curve as a function of the settings from the control desk. At very low desk settings (i.e. control settings from the control panel of the legacy dimming circuit) the input waveform 23 is little more than a spike. Fortunately the LED is also only just startin to light and does not require much current. As the desk setting moves from "0" to above (e.g. on a scale of 1 to 10) and beyond, there is^•tmtnedtately generated 12 volts to run the circuit 20 via the supply voltage 404, and a fast rising DC voltage to about 70 volts on the power rail 406.

[0035] At the instant enough power is sent to the LED to operate, the PWM generator 26 comes to life and attempts to drive the output. The PWM width- is controlled b the input level voltage with the higher the input level the wider the Pulse Width becomes, The circuit is adjusted so that the maximum input level is equal to the point that the current limiter 409 is set to, for the particular LED.

[0036] The example circuit of Figure 4 is designed to output 700mA at 50 Volts to the LED element 22 and the specific component values indicated, as may he read from Figure 4, reflect this circuit design. A person skilled in the art would readily understand that the component values ma be adjusted for different circuit characteristics, in particularly the linearity of the output, and that additional components ma be added while other components may be deleted depending on the ultimate circuit requirements, LED to be dri ven, output of the legacy dimmer circuit, etc. For example, the circuit may b modified for suitability with LED elements having a forward voltage drop of 36V, 42V, 50V, etc.

[0037] The driver circuit derives a DC signal level from the AC signal of the legac dimmer circuit and uses the DC signal to generate output pulses of varying widt from 100% to zero dependent on the DC signal level, thereby enabling the LED lamp to dim evenly and smoothly from 00% to zero and back. Because there is al ays more energy available than the LED could ever need, it is possible to create a linear output to the LED.

[0038] LED lighting systems are more efficient to operate and have reduced maintenance requirements. For example, the typical life span of a hi gh powered halogen light is 1000 hours compared to 50,000 hours for an equi valent LED. The system herein described in the preferred embodiments enables the venue to tap into the efficiency and maintenance benefits of modem LED li ghting without replacing their current legacy dimming system.

|003 | An additional advantage is that the LED driver that is sometimes provided by the LED manufacturer is not needed, thereby reducing installation costs.

{004ff| Figure 7 shows a schematic of venue lighting system 70 incorporating the upgraded LED system herein described. As can be seen in Figure 7, the venue includes a legacy dimming system having a plurality of dimmer circuits 72 that are driven from a mains supply 73 and receive control signals from a control panel 74 at a control desk. The venue lighting system 70 may include legac lighting systems, e.g. high powered halogen lamps, as well as LED elements, each LED element having one or more LEDs. The LEDA single dimmer circuit, e.g. dimmer 76 may control a bank of halogen lamps 77. A second dimmer 78 may control a bank of lights that includes non-LEDs, e-.g» halogen lamp 79 as well as LEDs 80. Each LED 80 will include a driver circuit 20 of the type described above that is able to effectively control and dim the respective LED using the signal from the dimmer circuit,

[0041] Figure 7 demonstrates the flexibility and adaptability of the presently described driver circuit. Because the driver circuits herein described integrate with the legacy dimmer circuits of the venue, the venu operator may partiall upgrade the venue lighting system without having to do an entire- upgrade at once. Furthermore, a single dimmer circuit may include LEDs as well as non-LBD lights allowing halogens to remain in use where such lights remain beneficial while using LEDs wherever suitable.

[0042] Figure 8 shows an alternative embodiment for a driver circuit 800 for an LED element 820 of one or more LEDs 822 having a forward voltage of 50 Volts. It has been discovered by the present inventors that certain high power LED's can make a tiny noise when driven by PWM systems_* While the phenomenon is largely unresearched and unexplained, one possible explanation is that the LED junction may warp as the power mshes in enough to create the noise. Square edged pulses can be faintly heard (if within the audio range) up close to some LED's. Wit many such lamps together in a large installation such as a theatre or auditorium, the noise can become quite audible and noticeable to the audience.

[0043] The circuit 800 of Figure 8 is similar to the driver circuit of Figure 4 but includes the addition of an anti-ringing filter 810. The anti-ringing filter 810 includes an RC filter that performs a dual role. First, it turns the squar edged pulse int a more rounded pulse which stops the ringing noise. Secondly, it creates a lower depth of modulation on output further reducing the risk of flicker or strobing.

|0044| The circuit 800 of Figure 8 further includes valle filling circuitry 830 that improves the power factor and increases the efficiency of the circuit The drive level adjustment is shown- located after the rectifier 45 which has also been found to improve the efficiency of the circuit

{0045] In one embodiment, the circuit 800 uses an LM3 I I comparator 815 to achieve a narrow pu!sewidth which provides a better response time at a operatin frequency greater titan 2kHz than the circuit of Figure 4 which shows an L .3-58 comparator.

[0046] The other components of Figure 8 are largely identical or similar to the components of Figure 4 and thus no further description of the components is considered necessary herein,

[0047J The frequency of the PWM although much higher tha humans can see has bee selected for the embodiment of Figure 8 to be less than 3Khz and specifically is set at approximate! 2200 Hz. The reasoning is that harmonics generated by frequencies above 3khz ca start to produce Radio Frequenc Interference which may be undesirable. The power MOSFETs are limited to their switching speed and different devices perform better or worse at higher frequencies. Other PWM dimming system frequency's hav been tested by the present inventors at 500 cycles per second (CPS), 1000 CPS, 4000 CPS, 12000 CPS, and 40000 CPS.

[0048J Figure 9 shows an embodiment of a driver circuit 900 for a higher powered LED element 920 with a forward voltage of 212V. The circuit 900 operates using the same pulse width modulation circuit principles of the previous embodiments but the specific devices and components may differ in power ratings and transformer type and arrangement The transformer 941 outputs first voltage from a first secondary 942 at the higher level e.g.. 195VRMS, for powering the highe powered LED element 920. The transformer 941 also outputs a lower voltage through an additional secondary 943, e.g. at 50VRMS that ca be further reduced to 12 V DC for powering the remainder of the dri ver circuit, including the PWM and input level detector components. The circuit 900 may operate at similar frequencies, e.g. 2200 Hz, as for the previousl described embodiments.

[0049] The circuit 900 includes the additio of LED temperature limiting. In some environments, the high power LED, e.g. operating at 200 Watts, has been found to get hot enough that temperature limiting becomes preferable in order to prevent early LED failure. The temperature .uniting circuit 950 includes a temperature sensor 951 that produces an output that couples with the drive input to the optoeoupler 947 of the input level detection circuit. Once the temperature sensor 951 reaches a threshold temperature, it will begin to reduce the output of the signal level detector, thereby reducing the average power of the LEDs and thus their operating temperature. Adj stment components 952 may be used to adjust the threshold temperature at which the temperature limiting circuit begins operating as well as the linearity of the temperature adjustment ¾^e threshold temperature will be dependent on the LED manufacturers recommendation and etnironmentai factors, e.g. amount o cooling available, fire risk, etc. and thus no specific example of the threshold temperature is provided herein, jOOSOj Although embodiments of the present invention have been illustrated in the accompanied drawings and described in the foregoing description, it will be ^'understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit o the invention as set forth and defined b any claims that follow.

Claims

What is claimed is:

1 , A driver cireuit for a light emitting diode (LED) element i ncluding one or more LEDs, the driver circuit including:

(A) a power supply that deri ves power from a legacy dimming circuit to produce an output voltage;

(B) an input level detector that detects a signal level from the legacy dimming circuit; and

(C) a pulse generator that prod ces a pulse signal ving a widt that is dependent on the detected signal level, wherein the pulse signal is coupled wit th output voltage to power the LED element.

2. The driver circuit of claim I wherein the pulse signal has a frequency higher than a

threshold frequenc at which flicker is observed for a average human observer.

3. The driver circuit of claim 2 wherein the pulse signal has a frequenc of greater than 500

\ \ 7.

4, The driver circuit of claim 3 wherein the pul e signal has a frequenc of greater tha

2000 Hz.

5. The dri ver of claim 1. wherein the input level detector produces a direct current (DC) signal from an incoming ^'waveform of the legacy dimming circuit and provides the DC signal to the pulse generator.

6. The driver circuit of claim 5 wherein the in ut level detector in l des at least one

optoeoupler that electrically isolates the pulse generator from the legacy dimming circuit.

7. The driver circuit of claim 5 wherein the pulse ge erator includes at least one integrated circuit that outputs a signal waveform and at least on comparator that compares the signal waveform output of the integrated circuit with the DC signal to produce a pulse signal output, wh erei n the widt of the pulse si gnal output is depen dent on the DC s ignal

8. The driver circuit of claim 7 wherein th pulse signal output is coupled to the LED.

9. The driver circuit of claim 1 wherein the light output of the LED is dependent on the pulse width,

10. The driver circuit of claim 1 wherein the power supply includes at least one transformer^' that isolates the LE from a mains supply and t educes a voltage from the legacy dimmer circuit to a maximum voltage.

1 1. The driver circuit of claim 10 wherein the at least one transibrmer produces a circuit voltage for powering the input level detector and the pulse generator.

1.2. The driver circuit of claim 1 including an anti-ringing filter,

13. The driver circuit of claim 1 including a temperature limiting circuit that operates to reduce the detected signal level above a threshold temperature.

1.4; A lighting system for a premises, the lighting system including at least one dimming contral panel, at least one legacy dimming circuit, at least one light emitting diode (LED) element including at least one LED, and at least one driver for the at least one LED element, the at least one dri ver including a power supply that derives power from th legacy dimming circuit to produce an output voltage, an input level detector that detects a signal level from the legacy dimming Circuit, and a pulse generator that produces a pulse signal having a widt that is dependent on the detected signal level, wherein the pulse signal is coupled with, the output voltage of the power supply to power the LED.

15. The lighting system of claim 14 wherein the legacy dimmin circuit includes at least one of a triac or a thyfistor that produces a chopped mains waveform to the at least one driver.

16. The lighting system of claim 1.5 wherein the input level detector determines the signal level from the ehorjijed mains waveform.

17. The lighting system of claim .14 ncluding a plurality of dri vers each connected to the at least one legacy dimming circuit.

18 The lighting system of clai m 17 including at l east one incandescent lamp connected to the at least one legacy dimming circuit.

1 . The lighting system of claim 1.4 wherein the input level detector produces a direct current (DC) signal from an incoming waveform, of the at least one legacy dimming circuit and provides the DC signal to the pulse generator.

20. The lighting system of claim 14 wherein the pulse si gnal has a frequency of greater than 500 Hz.

21. A method of controlling at least one Light Emitting Diode (LED) element including at least one LED from a legacy dimmin g ci rcuit of a premises, the method incl uding:

(A) using a driver to:

(a) receive a control signal from the legacy dimming circuit;

(h) determine a signal level of the control signal;

(c) use the determined signal level to modulate the pulse width of a pulse width waveform to produce a pulse widt modulated waveform; and

(d) provide the pulse width modulated waveform to the at least one LED

element. The method of claim 21 including derivtng power for the at least one LED element from the control signal .

The method of claim 21 wherein the control signal includes a chopped mains waveform and wherein determining the signal level includes determining a direct current level of the chopped mains waveform.

The method of claim 21 including varying the control signal of the legacy dimming signal to vary the light output of the at least one LED element.