MIXED LOAD CURRENT COMPENSATION FOR LED LIGHTING

• US 20130221871A1
• Filed: 02/22/2013
• Published: 08/29/2013
• Est. Priority Date: 02/29/2012
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Cirrus Logic Incorporated
• Inventors: King, Eric J., Melanson, John L., Baker, Daniel J.
• Granted Patent: US 9,167,662 B2
• Time in Patent Office: Days
• US Class Current: 315/254
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/385 using flyback topology

Abstract

In at least one embodiment, a system and method provide current compensation in a lighting system by controlling a lamp current to prevent a current through a triac-based dimmer from undershooting a holding current value. In at least one embodiment, at least one of the lamps includes a controller that controls circuitry in the lamp to draw more lamp current for a period of time than needed to illuminate a brightness of the lamp at a level corresponding to particular phase-cut angle of the supply voltage. By drawing more current than needed, the controller increases the dimmer current during the period of time to prevent the dimmer current from falling below the holding current value. In at least one embodiment, the period of time corresponds to a compensating pulse of the lamp current at a time when the dimmer current would otherwise fall below the holding current value.

Claims

1. A method comprising:

detecting a leading edge of a dimmer phase-cut voltage;

after detecting the leading edge, controlling a lamp current of an electronic lamp to prevent a current through a triac of the dimmer from undershooting a holding current value, wherein the holding current value represents a value that if undershot by the current through the triac of the dimmer would stop the triac from conducting; and

preventing the current through the dimmer from undershooting the holding current value.

2. The method of claim 1 wherein controlling a lamp current to prevent a current through the dimmer from undershooting a holding current value comprises:

generating a current pulse for a first duration of time as the current through the dimmer decreases.

3. The method of claim 2 wherein a lighting system includes multiple lamps coupled in parallel to receive a portion of the lamp current and wherein the first duration of time is based on current control characteristics of at least a plurality of the multiple lamps.

4. The method of claim 2 further comprising:

retrieving data from a memory in a controller of a switching power converter, wherein the data represents the first duration of time of the current pulse.

5. The method of claim 2 further comprising:

ramping down the current pulse at the end of the first duration of time.

6. The method of claim 1 wherein controlling a lamp current to prevent a current through a triac of the dimmer from undershooting a holding current value draws an amount of excess current into a switching power converter of the electronic lamp that exceeds an amount of current used to illuminate a light source of the electronic lamp at a brightness corresponding to the dimmer phase-cut voltage, the method further comprising:

dissipating power in the switching power converter that corresponds to the amount of excess current drawn.

7. The method of claim 1 wherein controlling a lamp current to prevent a current through the dimmer from undershooting a holding current value further comprises:

varying the amount of lamp current drawn to prevent the undershooting in correlation with different phase-cut angles of the dimmer phase-cut voltage.

8. The method of claim 7 wherein the correlation between the varying amount of lamp current drawn to prevent the undershooting and the different phase-cut angles is non-linear.

9. The method of claim 1 wherein controlling a lamp current to prevent a current through the dimmer from undershooting a holding current value comprises:

superimposing the lamp current on the current through the dimmer to prevent the current through the dimmer from undershooting the holding current value.

10. The method of claim 1 further comprising:

waiting for a first duration of time after detecting the leading edge before controlling the lamp current to prevent the current through the dimmer from undershooting the holding current value.

11. The method of claim 10 wherein the first duration of time after detecting the leading edge begins after the current through the dimmer has a negative change over time and before the current through the dimmer reaches the holding current value.

12. The method of claim 1 wherein the dimmer is a triac-based dimmer that conducts current provided to a non-homogenous set of light emitting diode-based lamps.

13. The method of claim 1 further comprising:

dynamically detecting an indication of a possible undershoot of the holding current value; and

upon detection of the indication, controlling the lamp current to prevent the current through a triac of the dimmer from undershooting the holding current value.

14. The method of claim 1 wherein the electronic lamp comprises one or more light emitting diodes.

15. An apparatus comprising:

a controller, wherein the controller is configured to;

detect a leading edge of a dimmer phase-cut voltage;

after detecting the leading edge, control a lamp current of an electronic lamp to prevent a current through a triac of the dimmer from undershooting a holding current value, wherein the holding current value represents a value that if undershot by the current through the triac of the dimmer would stop the triac from conducting; and

prevent the current through the dimmer from undershooting the holding current value.

16. The apparatus of claim 15 wherein to control a lamp current to prevent a current through the dimmer from undershooting a holding current value, the controller is further configured to:

generate a current pulse for a first duration of time as the current through the dimmer decreases.

17. The apparatus of claim 16 further comprising:

the electronic lamp; and

multiple additional electronic lamps coupled in parallel with the electronic lamp to each receive a portion of the lamp current;

wherein the first duration of time is based on current control characteristics of at least a plurality of the multiple lamps.

18. The apparatus of claim 16 wherein the controller is further configured to:

retrieve data from a memory in a controller of a switching power converter, wherein the data represents the first duration of time of the current pulse.

19. The apparatus of claim 16 wherein the controller is further configured to:

ramp down the current pulse at the end of the first duration of time.

20. The apparatus of claim 15 wherein control of a lamp current to prevent a current through a triac of the dimmer from undershooting a holding current value draws an amount of excess current into a switching power converter of the electronic lamp that exceeds an amount of current used to illuminate a light source of the electronic lamp at a brightness corresponding to the dimmer phase-cut voltage, the controller is further configured to:

dissipate power in the switching power converter that corresponds to the amount of excess current drawn.

21. The apparatus of claim 15 wherein to control a lamp current to prevent a current through the dimmer from undershooting a holding current value, the controller is further configured to:

vary the amount of lamp current drawn to prevent the undershooting in correlation with different phase-cut angles of the dimmer phase-cut voltage.

22. The apparatus of claim 21 wherein the correlation between the varying amount of lamp current drawn to prevent the undershooting and the different phase-cut angles is non-linear.

23. The apparatus of claim 15 wherein to control a lamp current to prevent a current through the dimmer from undershooting a holding current value, the controller is further configured to:

superimpose the lamp current on the current through the dimmer to prevent the current through the dimmer from undershooting the holding current value.

24. The apparatus of claim 15 wherein the controller is further configured to:

wait for a first duration of time after detecting the leading edge before controlling the lamp current to prevent the current through the dimmer from undershooting the holding current value.

25. The apparatus of claim 24 wherein the first duration of time after detecting the leading edge begins after the current through the dimmer has a negative change over time and before the current through the dimmer reaches the holding current value.

26. The apparatus of claim 15 wherein the dimmer is a triac-based dimmer and triac-based dimmer conducts current provided to a non-homogenous set of light emitting diode-based lamps.

27. The apparatus of claim 15 wherein the controller is further configured to:

dynamically detect an indication of a possible undershoot of the holding current value; and

upon detection of the indication, control the lamp current to prevent the current through a triac of the dimmer from undershooting the holding current value.

28. The apparatus of claim 15 wherein the electronic lamp comprises one or more light emitting diodes.

29. The apparatus of claim 15 further comprising:

the electronic lamp; and

multiple additional electronic lamps coupled in parallel with the electronic lamp.

30. The apparatus of claim 15 further comprising:

the electronic lamp, wherein the electronic lamp includes a switching power converter coupled to the controller and further includes one or more light emitting diodes coupled to the switching power converter.

31. An apparatus comprising:

a lamp, wherein the lamp comprises;

a switching power converter;

one or more light emitting diodes coupled to the switching power converter; and

a controller, coupled to the switching power converter, wherein the controller is configured to;

detect a leading edge of a dimmer phase-cut voltage;

after detecting the leading edge, control a lamp current of the lamp to prevent a current through a triac of the dimmer from undershooting a holding current value, wherein the holding current value represents a value that if undershot by the current through the triac of the dimmer would stop the triac from conducting; and

prevent the current through the dimmer from undershooting the holding current value.