AU2016218927A1 - Dimmer system - Google Patents

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

PCT/AU2016/000033 WO 2016/127198

DIMMER SYSTEM

CROSS REFERENCE TO RELATE» APPLICATIONS

[0001} This application is islated to and claims the priority benefit of Australian Provisional Application Mo. 2015900402 filed 9 February2015, the entire contents of which are herein incotpnrated by reference.

FIELD OF THE INVENTION

[0002] This disclosure relates to lighting systems and in particular to dimmer systems tor dimming light emitting diode (LED)s in large facilities.

BACKGROLMD OF Til E INVENTION {0003j Many facilities, such as school halls, theatres, stages, and similar such venues have run lighting 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 TR’IAC or THYRISTOR to chop the mains waveform thereby reducing the 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 hi between, with an even distribution of power to the bulbs. |0004| lor a premises to reduce its power consumption and achieve higher environmental ratings, it is desirable for the premises to replace high consumption incandescent bulbs with tower consumption LEDs. However, a problem with LEDs is that the; installed (iegac>) dimming systems are not able to dim the LEDs to anything less than about 10% power before the LEDs become unstable. For 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.

[000551 What is required is an improved system for enhancing the capability of a legacy dimming system with LED lighting systems. 1 PCT/AU2016/000033 WO 2016/127198

SUMMARY OF THE INVENTION

[0006] in one aspect, there is provided a driver circuit for a light emitting diode (LED), the driver circnlt including a power supply that derives power from a legacy dimniiiig circuit to produce an output voltap, an input level detector that detects a signal level from the legacy dimming circuit, ami 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 voltage to power the LED, |0007j In cate aspect, there is provided a lighting system for a premises, the lighting system including at least one dimming control 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 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 supply to power the LED.

[0008} In one aspect, there is provided a method of controlling at least one Light Emitting Diode (LED) element including at least one LED from a legacy dimming circuit of a premises, the method including using a driver to: (a) receive a control signal from the legacy dimming 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 wa veform; and (d) provide the pulse width modulated waveform to the at least one l,ED element.

BRIEF DESCmFMN OF THE DRAWINGS |0009j Reference will now be made, by way of example only, to specific embodiments and to the accompanying drawings jn which: jOOIOj Figure 1 shows a prior art lighting system; [0011] Figure 2 shows a lighting system in accordance with an embodiment of the present invention; PCT/AU2016/000033 WO 2016/127198 (0012J Figure 3 shows a schematic of a driver system; 10G13J Figure 4 shows a specific example of a driver circuit; |00141 Figures shows how the pulse width will vary with detector DC' inpu t level; j 00151 Figure 6 shows the power curve as a function of input control setting; (0016j Figure 7 shows a venue lighting system including at least one LED and driver of an embodiment of the present invention: (00171 Figure 8 shows an alternative circuit diagram featuring an anti-ringing circuit; and (0018! Figure 9 shows an alternative circuit diagram for a high power LED embodiment

DETAILED DESCRIPTION OF THE: INVENTION (0019( Figure 1 shows a prior art dimming arrangement 10, In this arrangement, a legacy dimming 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 fee arranged in sets or banks with one dimming control signal going to a subset of the tights of the complete lighting system. In one specific example, the lighting system may fee in a theatre with a complex lighting system controlled from a main desk or computer. The lighting system might use many high power light dimmers to control the light levels in the theatre itself and other areas, [0020} 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 "Driver1'. When the LED and it's Driver are driven from the existing leading edge dimming system, the LED performs badly or not at all. The nature of the power source will not allow the LED Driver to operate correctly, (002! j Some problems are : * overheating of ihe LED Driver and dimmer flickering at low end; * not achieving low end; * not reducing below 25%.

[0022( The only way the theatre could use these LED's is to run a permanent power supply and control wiring to the new LED Dri ver. This would he a major undertaking and great expense for the theatre. PCT/AU2016/000033 WO 2016/127198 [0023j 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 but the person skilled in the art will readily understand that an individual LED lighting element may be made up of multiple LEDs within the body of the LED element (as shown in Figures 8 and 9). The 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 ferm that the LED element 22 can respond to. The driver 20 thus negates the need to rewire 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 \Vhdth Modulation (PWM) generator 26, an integrator 27 and a current limiter 28 to suit the LED 22. The power supply 21 produces an output voltage while the integrator 27 produces a pulsed output, the width of which is determined by a DC level produced by the power load circuit 24 from an incoming waveform 23 of a legacy dimming circu it. The output voltage and pulsed output are coupled, via foe current limiter 28 to the LED 22 to power the LED with a pulsing current. Thus, foe overall light output of foe 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 foe human toto flicker rate which is the threshold frequency 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 a 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 foe 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 fo accommodate a greater number of patrons. In one embodiment, foe pulse signal frequency is greater than 500 Hertz (Hz). In 4 PCT/AU2016/000033 WO 2016/127198 one embodiment, the puke signal frequency is greater than 1000 Hz. In 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 front 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 TRLAC, thyristor or the like, For Australian systems, the mains waveform will be 230VAC, 50 Hz based on the mains supply but this will differ from country to country/ The leading edge modulated power 29 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 necessary to tire leading edge signal 23 from the dimmer circuit, as well as increasing the reliability of the circuit. The transformer is selected to provide a match with the Ibnvaid voltage of the: TED, When: at foil power the secondary AC RMS voltage should be the same as or close to th e TED forward voltage .

[0026] The transformer 41 isolates the circuit, particularly the TED. electrically from the mains and presents an inductive load to the Leading Edge Dimmer reducing the voltage to 50 MAC' max. ft is rectified 42 and filtered with a large value capacitor 43, e.g. 4700 μΕ. after which the DC voltage rises to about 70 VDC. depending on the power level applied from the dimmer circuit. The Anode 221 of the LED 22 is: connected to this 70 V positive DC power mi 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.

[00271 The output of the rectifier circuit 42 is also used to produce a supply voltage, c.g. 12V supply voltage 404, which is used to power various components of the dri ver circuit, such as the one or more integrated circuits, op amps, etc. as will be described in more detail below. (0028] The TED cathode 222 is switched to negative via a power MDSFET 407 and the current through the LED is 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 Optoeoupler 47. This circuit creates a DC signal which follows the level sent from the dimmer circuit while isolating the potentially high voltages of the dimmer circuit. 5 PCT/AU2016/000033 WO 2016/127198 {0030) The Pulse Width Modulation generator M m the form of Cmos Timer IC 405 generates a narrow 3 kilohertz (kHz) pulse which drives an Op Amp 410. It one embodiment, the Cmos Timer is a 555 Cmos Timer chip, powered by the I2M supply voltage 404 derived from the rectifier circuit 42, though other types of tuner chips will be apparent to the person skilled in the art. The Op Amp 410, using an R/C network 411, creates a stable and adjustable sawtooth waveform of around 5 KHz at the output of the Op Amp 410. |003i| The signal combiner 27 uses a second Op Amp 415 to compare the 3Khz sawtooth waveform from Op Amp 410 with the DC level from the optically coupled 47 power level detection stage 24. The magnitude of the pulse signal output of Op Amp 410 is fixed, but the width will depend on the DC level input. Figure 5 shows that as the DC level 51 derived from the dimmer waveform 23 increases, the pulse width 52 at the output of Op Amp 415 will increase: proportionally. The higher the DC level input, the longer within 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 a more linear response and therefore easier operation for the user. However, the person skilled in the art would readily understand that other waveforms, eg. sine, may be 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 MOS 1 l· 1 407 . Operating at this frequency, which is a frequency well above the human flieker 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 a person will depend on the average time for which the LED is on and is therefore dependent on the width of fhe pulse signal output suppHcdfrom the op amp 410 to foe power MOSFET 407. At very short pulse widths (low duty cycle),: the LED 22 will be mostly off and the average light output will fee very low, At long pulse widths (high duty cycle), the LED will fee 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 PCT/AU2016/000033 WO 2016/127198 lowers the voltage at the comparator input and stabilises the power. A current limiting resistor 409 limits the current of the circuit.

[0034J 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 mom than a spike. Fortunately the LED is also only just starting: to light and does not require much current. As the desk setting moves from "Ο" to above "1" (e.g. on a scale of 1 to 10) and beyond, there is immediately generated 12 volts to am the circuit 20 via the supply voltage 404, and a fast rising DC voltage to about 70 volts on the power rail 406.

[0035J At the instant enough power is sent to the LEI? to operate, the PWM generator 26 comes to life and attempts to drive the output. The PWM width is controlled by 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, tor the particular LED, [0036] The example eircuit of Figure 4 is designed to output 700mA at 50 Volts to the TED element 22 and the Specific component values indicated, as may fee read from Figure 4, reflect this circuit design. A: person skilled in the art would readily understand that the component values may fee adjusted for different circuit characteristics, in particularly the linearity of the output, and that additional components may be added while other components may be deleted depending on the ultimate circuit requirements, LED to fee dri ven, output of the legacy dimmer circuit, etc. For example, the circuit may fee modified for suitability with LED elements having a forward voltage drop of 36V, 42V, 50V, etc..

[0037j The driver circuit derives a DC signal level from the AC signal of the legacy dimmer circuit and uses the DC signal to generate output pulses of varying width from 10(¾¾ to zero dependent on the DC signal level, thereby enabling the LED lamp to dim evenly and smoothly ism 100% to zero and back. Because there is always more energy avail able 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 high powered halogen light is 1000 hours compared to 50,000 hours for an equivalent LED. The system herein described in 7 PCT/AU2016/000033 WO 2016/127198 the preferred embodiments enables the venue to tap into the efficiency and maintenance benefits of modern LED lighting; without replacing their current legacy dimming system.

[003f | An additional advantage is that the LED driver that is sometimes provided by the LED manufoeturer is not needed, thereby reducing installation costs. |0040j Figure 7 shows a schematic of a 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· legacy lighting systems, e.g. high powered halogen lamps, as well as LED elements, each LED element having one or more LEDs. The LED A 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 venue operator may partially 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-LED lights allowing halogens to remain in use where such lights I'emain beneficial while using LEDs; wherever suitable.

[0042j 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 LEDs can make a tiny noise when driven by PWM systems* While the phenomenon is largely unrescarched and unexplained, one possible explanation is that the LED junction may warp as the power rushes in enough to create the noise. Square edged pulses can be faintly heard (if within the audio range) up close to some LED's. With 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. I0043J The circuit 800 of Figure 8 is similar to the driver circuit of Figure 4 but includes the addition of an anfi-ringing filter 810. The anti-ringing filter 810 includes an RC filter that performs a dual role. First, it turns the square edged pulse into a more rounded pulse PCT/AU2016/000033 WO 2016/127198 which stops the ringing noise. Secondly, it creates a lower depth of modulation on output ftitther reducing the risk of flicker or strobing.

[0044] The circuit 800 of Figure 8 further includes valley filling circuitry 830 that improves the power factor and increases the efficiency of the circuit The drive level adfusfrneut is shown located after the rectifier 43 which has also been found to improve the efficiency of 'the· circuit [0045] in one embodiment, the circuit 800 uses an LM311 comparator 815 to achieve a narrow pulscwidth which provides a better response time at an operating frequency greater than 2kHz than the circuit of Figure 4 which shows an LM.358 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, [0047] The frequency of the PWM although much higher than humans can see has been selected for the embodiment of Figure 8 to be less than 3Kfrz and specifically is set at approximately 2200 'Hz. The reasoning is that harmonics generated 'by frequencies above 3fchz can start to produce Radio Frequency Interference which may be undesirable. The power MDSFETs are limited to their switching speed and different devices perform better or worse at higher frequencies. Other PWM dimming system frequences have been tested by the present inventors at 500 cycles per second (CPS), 1000 CPS, 4000 CPS, 12000 CPS, and 40000 CPS.

[0048] 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 tire specific devices and components may differ in power ratings and transformer type and arrangement. The transformer 941 outputs a first voltage from a first secondary 942 at the higher level, e g. i95VRMS, for powering the higher powered LED element 920. The transformer 941 also outputs a lower voltage through an additional secondary 943, e.g. at 50VRMS that can be further reduced to 12 V DC for powering the remainder of the driver circuit, including the PWM and input level detector components. The circuit 900 may operate at similar frequencies, e.g. 2200 Hz, as for the previously described embodiments.

[0049J The circuit 900 includes the addition of LED temperature limiting. In same environments, the high power LED;, e,g. operating at 200 Watts, has been found to get hot 9 PCT/AU2016/000033 WO 2016/127198 enough that temperature limiting becomes preferable in order to prevent eariv LEO failure. The temperature limiting circuit 930 includes a temperature sensor 951 that produces an output that couples with the drive input to the optoeoupler 947 of the input level detection circui t. 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. Adjustment 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 The threshold temperature will be dependent on the LED manufacturer· s recommendation and environmental factors, e.g. amount of cooling available, fire risk, etc. and thus no specific example of the threshold temperature is provided herein. p5t!j Although embodiments of the present invention have been illustrated in the accomphisd 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 of the invention as set forth and defined by any c1.ainis.that follow. 10

Claims (22)

1. CLAIMS What is claimed is:

   1, A driver circuit 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 produces a pulse signal having a width that is dependent on the detected signal level, wherein the pulse signal is coupled with the output voltage to power the LED element.
2. 2. The driver circuit of claim 1 wherein the pulse signal has a frequency higher than a threshold frequency at which flicker is observed for an average human observer.
3. 3. The driver circuit of claim 2 wherein the pulse signal has a frequency of greater than 500 Hz.
4. 4, The driver circuit of claim 3 wherein the pulse signal has a frequency of greater than 2000 Hz.
5. 5 . The driver 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. 6. The driver circuit of claim 5 wherein the input level detector includes at least one optocoupler that electrically isolates the pulse generator from the legacy dimming circuit.
7. 7. The driver circuit of claim 5 wherein the pulse generator includes at least one integrated circuit that outputs a signal waveform and at least one. comparator that compares the signal waveform output of the integrated circuit with the DC signal to produce a pulse signal output, wherein the width of the pulse signal output is dependent on the DC signal.
8. 8. The driver circuit of claim 7 wherein the pulse signal output is coupled to die LED.
9. 9. The driver circuit of claim 1 wherein the light output of the LED is dependent on the pulse width,
10. 10. The driver circuit of claim 1 wherein the power supply includes at least one transformer that isolates the LED from a mains supply and reduces a voltage from the legacy dimmer circuit to a maximum voltage, 1L The driver circuit of claim 10 wherein the at least one transformer produces a circuit voltage for powering the input level detector and the pulse generator.
11. 12. The driver circuit of claim 1 including an anti-ringing filter,
12. 13. The driver circuit of claim 1 including a temperature limiting circuit that operates to reduce the detected signal level above a threshold temperature.
13. 14. A lighting system for a premises, the lighting system including at least one dimming control panel, at least one legacy dimming circuit, at least one light emini ng 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 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 voltage of the power Supply to power the LED.
14. 15. The lighting system .of claim 14 wherein the legacy dimming circuit includes at least one of a triac or a thyristor that produces a chopped mains waveform to the at least one driver .
15. 16. The lighting system of claim 1.5 wherein the input le vel detector determined the signal level from the chopped mains waveform.
16. 17. The lighting system of clai m 14 includin g 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.
17. 19. The lighting system of claim 14 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.
18. 20. The lighting system of claim 14 wherein the pulse si gnal has a frequency of greater than 500¾.
19. 21. A method of controlling at least one Light Emitting Diode (LED) element including at least one LED from a legacy dimming circuit of a premises, the method including: (A) using a driver to: (a) receive a control signal from the legacy dimming circuit; (h) detemrine 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 width modulated waveform to the at least one LED element.
20. 22, The method of claim 21 including deriving power for die at least one LED element from the control signal .
21. 23, 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.
22. 24, 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.