LED BASED LIGHTING APPLICATION

• US 20110248640A1
• Filed: 09/03/2009
• Published: 10/13/2011
• Est. Priority Date: 09/05/2008
• Status: Active Grant

• Current Assignee: eldoLAB Holding B.V. (Acuity Brands, Inc.)
• Original Assignee: eldoLAB Holding B.V. (Acuity Brands, Inc.)
• Inventors: Welten, Petrus Johannes Maria
• Granted Patent: US 9,271,345 B2
• Time in Patent Office: Days
• US Class Current: 315/210
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/3575 by means of dummy loads or bleeder circuits, e.g. for dimmers
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The present invention relates to a lighting application, the lighting application can e.g. comprise an LED assembly comprising a serial connection of two or more LED units, each LED unit comprising one or more LEDs, each LED unit being provided with a controllable switch for substantially short-circuiting the LED unit. The lighting application further comprises a control unit for controlling a drive unit and arranged to receive a signal representing a voltage level of the supply voltage, and control the switches in accordance with the signal. The invention further provides for an LED driver that enables to operate a TRIAC based dimmer at an optimal holding current and an LED driver comprising a switchable buffer, e.g. a capacitor.

Claims

1. A lighting application comprising

an LED assembly comprising two or more LED units, each LED unit comprising one or more LEDs, the LED assembly further comprising a switch assembly comprising one or more controllable switches for modifying a topology of the LED assembly, the LED assembly, in use, being powered from a supply voltage,

a control unit comprising an input terminal arranged to receive a signal representing a voltage level of the supply voltage or a load current of the LED assembly, and an output terminal for providing a control signal to the switch assembly to control the switch assembly in accordance with the signal, thereby modifying the topology of the LED assembly.

2. The lighting application according to claim 1 further comprising

a drive unit for powering the LED assembly, the drive unit, in use, being powered from the supply voltage.

3. The lighting application according to claim 2 wherein the drive unit comprises a linear regulator or a switching regulator for powering the LED assembly.

4. A lighting application according to claim 1 wherein

the LED assembly comprises a serial connection of two or more LED units and wherein the switch assembly comprises two or more controllable switches for substantially short-circuiting the resp. two or more LED units,

5. The lighting application according to claim 1 wherein the control unit is further arranged to

determine a maximum number of LED units and/or which LED units that can be powered by the supply voltage based on the signal,

control the switches according to the maximum.

6. The lighting application according to claim 1 wherein the supply voltage comprises a dimmer circuit output voltage.

7. The lighting application according to claim 1 wherein the supply voltage comprises a periodic voltage.

8. The lighting application according to claim 7 wherein the control signal is synchronized with the periodic voltage.

9. The lighting application according to claim 1 further comprising a waveform analyser arranged to assess the supply voltage and provide the signal to the control unit.

10. The lighting application according to claim 9 wherein the waveform analyser is arranged to determine a zero crossing of the supply voltage.

11. The lighting application according to claim 7 further comprising a memory unit for storing waveform information obtained, in use, by the waveform analyser.

12. The lighting application according to claim 8 wherein the control unit is arranged to apply a duty cycle modulation of a current provided to the LED assembly by controlling the switch assembly.

13. The lighting application according to claim 12 wherein a duty cycle period of the duty cycle modulation is selected such that a period of the supply voltage divided by the duty cycle period results in an integer value.

14. A method of powering an LED assembly connectable to a power source, the LED assembly comprising two or more LED units, the LED assembly further comprising a switch assembly comprising one or more controllable switches for modifying a topology of the LED assembly, the LED assembly, in use, being powered by the power source, the method comprising the steps of

detecting a voltage output level of the power source,

providing a control signal to the switch assembly to control the switch assembly based on the voltage output level, thereby modifying the topology of the LED assembly

15. The method according to claim 14, the method further comprising the steps of

comparing the voltage output level to a required voltage for powering the LED assembly to determine a maximum number of LED units that can be powered by the power source,

control the switch assembly of the LED assembly in accordance with the maximum.

16. The method according to claim 14 further comprising the step of adjusting a duty cycle of the LED units in accordance with the voltage output level while maintaining a colour set point.

17. An LED driver for powering an LED assembly comprising at least one LED, the LED driver comprising a converter for converting a periodic input voltage to a supply current for powering the LED assembly, the LED driver further comprising a control unit arranged to determine a minimal holding current by, in use, gradually reducing the supply current until a value of the input voltage substantially reduces to zero and subsequently control the converter to operate at a supply current at least equal to the minimal holding current.

18. The LED driver according to claim 17 wherein the step of determining a minimal holding current comprisesoperating the converter to reduce the supply currentmeasuring a value of the input voltage at the reduced supply currentrepeating steps 1 and 2 until the supply voltage substantially reduces to zero.

19. The LED driver according to claim 17 wherein the control unit comprises an output terminal for outputting a control signal to the converter for gradually reducing the supply current and an input terminal for receiving a signal representing the value of the input voltage.

20. The LED driver according to claim 17 wherein the supply voltage comprises a TRIAC dimmer output voltage.

21. The LED driver according to claim 17 wherein the LED driver comprises input terminals for receiving the supply voltage.

22. The LED driver according to claim 17 further comprising an input capacitance arranged between the input terminals.

23. The LED driver according to claim 17 wherein the control unit is arranged to determine a dimming level from the supply voltage.

24. The LED driver according to claim 17 wherein the minimal holding current is maintained during at least an entire period of the input voltage in order to determine the dimming level.

25. The LED driver according to claim 17 wherein the control unit is arranged to determine the minimal holding current at least once every 10 periods of the input voltage.

26. The LED driver according to claim 17 wherein a trailing end of a period of the periodic input voltage is applied to determine the minimal holding current.

27. A lighting application comprising an LED driver according to claim 17, the lighting application further comprising an LED assembly comprising at least one LED, the lighting application further comprising a variable load, in use controlled by the control unit, the variable load being connected in series with the LED assembly.

28. The lighting application according to claim 27 wherein the variable load comprises a switchable resistance.

29. The lighting application according to claim 27 wherein a load characteristic of the variable load is varied during a part of the periodic input voltage of the LED driver while the input voltage is monitored.

30. The lighting application according to claim 29 wherein the part is a trailing part.

31. An LED driver for powering an LED assembly comprising at least one LED, the LED driver comprising a converter for converting a periodic input voltage to a supply current for powering the LED assembly, the converter having input terminals for receiving the periodic input voltage, the LED driver further comprising an input buffer for providing a current to the terminals and a control unit, the LED driver further comprising a switching element for opening and closing a current path from the input buffer to the input terminals and wherein the control unit is further arranged to control the switching element based on an input signal representing the periodic input voltage.

32. The LED driver according to claim 31 wherein the input buffer comprises a capacitor or capacitor assembly.

33. The LED driver according to claim 31 wherein the switching element comprises a first switch for connecting and disconnection a first terminal of the input buffer to a first terminal of the input terminals.

34. The LED driver according to claim 31 or wherein the switching element is further arranged to open and close a current path from the input buffer to a supply terminal, in use, connected to the periodic supply voltage.

35. The LED driver according to claim 31 further comprising a rectifier for rectifying an AC input voltage to obtain the periodic input voltage, the rectifier having AC input terminals for receiving the AC input voltage, the switching element comprising a first switch for connecting a terminal of the input buffer to either a first or a second terminal of the AC input terminals.

36. The LED driver according to claim 35 wherein the switching element comprises a second switch for connecting a further terminal of the input buffer to an input terminal of the converter.

37. The LED driver according to claim 31, wherein the control unit is arranged to synchronise synchronize an on/off duty-cycle of the supply current with the periodic input voltage.

38. The LED driver according to claim 31, wherein the control unit is arranged to control the LED driver to apply a reduced supply current to the LED assembly when the LED assembly is powered from the input buffer.

39. The LED driver according to claim 31, wherein the input buffer comprises a capacitor and wherein the switching element enables the periodic supply voltage and a voltage over the capacitor to be added.

40. The LED driver according to claim 31, further comprising a filter capacitor.

41. The LED driver according to claim 40 wherein the switching element is arranged to interrupt a current path from the input buffer to the filter capacitor thereby disabling, in use, the input buffer to discharge to the filter capacitor.