DIMMER DECODER WITH IMPROVED EFFICIENCY FOR USE WITH LED DRIVERS

• US 20110115395A1
• Filed: 10/14/2010
• Published: 05/19/2011
• Est. Priority Date: 10/14/2009
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Lai, Chi Yuen, Herrington, Daniel R., Nederbragt, Irwin R., Barrow, Steven M., Masson, James H.
• Granted Patent: US 8,531,138 B2
• Time in Patent Office: Days
• US Class Current: 315/250
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A method includes receiving a sense signal having multiple pulses, where the sense signal is based on an output of a dimmer. The method also includes, for each of multiple sampling periods, sampling a subset of the pulses in the sense signal during that sampling period. The method further includes generating a holding current for the dimmer during the sampling of the subset of pulses in at least one of the sampling periods. In addition, the method includes, for each of the sampling periods, generating an output value identifying a duty cycle for driving one or more light emitting diodes (LEDs). The subset of pulses in each of the sampling periods includes multiple pulses during that sampling period but not one or more initial pulses at a beginning of that sampling period.

Claims

1. A method comprising:

receiving a sense signal comprised of multiple pulses, the sense signal based on an output of a dimmer;

for each of multiple sampling periods, sampling a subset of the pulses in the sense signal during that sampling period;

generating a holding current for the dimmer during the sampling of the subset of pulses in at least one of the sampling periods; and

for each of the sampling periods, generating an output value identifying a duty cycle for driving one or more light emitting diodes (LEDs);

wherein the subset of pulses in each of the sampling periods includes multiple pulses during that sampling period but not one or more initial pulses at a beginning of that sampling period.

2. The method of claim 1, wherein sampling the subset of the pulses in the sense signal during each of the sampling periods comprises:

identifying duty cycles of at least two pulses in the sense signal during that sampling period; and

selecting one of the identified duty cycles.

3. The method of claim 2, wherein sampling the subset of the pulses in the sense signal during each of the sampling periods further comprises:

shifting the selected duty cycle by a specified amount; and

saturating the shifted duty cycle at a minimum value greater than zero.

4. The method of claim 1, wherein sampling the subset of the pulses in the sense signal comprises:

determining a sampling state based on one or more duty cycles associated with one or more prior sampling periods; and

selecting a size of a current sampling period based on the sampling state.

5. The method of claim 4, wherein selecting the size of the current sampling period comprises:

selecting a first size when a change between a current duty cycle for the current sampling period and a prior duty cycle for a most-recent prior sampling period exceeds a threshold; and

selecting a larger second size when a change between duty cycles for consecutive sampling periods has not exceeded the threshold for a specified number of sampling periods.

6. The method of claim 1, wherein generating the holding current for the dimmer comprises:

generating the holding current only (i) during the sampling of the subset of pulses in each of the sampling periods and (ii) between pulses of the sense signal that are not sampled.

7. The method of claim 1, wherein generating the holding current for the dimmer comprises:

monitoring a return current provided to the dimmer; and

generating a dynamic holding current to ensure that a minimum amount of current is provided to the dimmer.

8. The method of claim 1, wherein sampling the subset of the pulses in the sense signal during each of the sampling periods comprises:

discarding a first pulse in that sampling period; and

sampling second and third pulses in that sampling period.

9. The method of claim 1, further comprising:

generating the sense signal by comparing the output of the dimmer to a threshold.

10. The method of claim 1, further comprising:

filtering each of the output values; and

generating a drive signal for a power transistor based on the filtered output values, the power transistor controlling current flow through the one or more LEDs.

11. A system comprising:

a driver configured to generate a drive signal for controlling illumination from one or more light emitting diode (LEDs); and

a dimmer decoder configured to;

receive a sense signal comprised of multiple pulses, the sense signal based on an output of a dimmer;

for each of multiple sampling periods, sample a subset of the pulses in the sense signal during that sampling period;

generate a holding current for the dimmer during the sampling of the subset of pulses in at least one of the sampling periods; and

for each of the sampling periods, generate an output value for the driver, the output value identifying a duty cycle for driving the one or more LEDs;

wherein the subset of pulses in each of the sampling periods includes multiple pulses during that sampling period but not one or more initial pulses at a beginning of that sampling period.

12. The system of claim 11, wherein the dimmer decoder is configured to, during each of the sampling periods:

identify duty cycles of at least two pulses in the sense signal during that sampling period;

select one of the identified duty cycles; and

generate the output value based on the selected duty cycle.

13. The system of claim 11, wherein the dimmer decoder is configured to:

determine a sampling state based on one or more duty cycles associated with one or more prior sampling periods; and

select a size of a current sampling period based on the sampling state.

14. The system of claim 13, wherein the dimmer decoder is configured to:

select a first size when a change between a current duty cycle for the current sampling period and a prior duty cycle for a most-recent prior sampling period exceeds a threshold; and

select a larger second size when a change between duty cycles for consecutive sampling periods has not exceeded the threshold for a specified number of sampling periods.

15. The system of claim 11, wherein the dimmer decoder is configured to generate the holding current for the dimmer by:

monitoring a return current provided to the dimmer; and

generating a dynamic holding current to ensure that a minimum amount of current is provided to the dimmer.

16. An apparatus comprising:

a comparator configured to receive an output of a dimmer and to generate a sense signal comprised of multiple pulses based on the output of the dimmer; and

a digital block configured to;

for each of multiple sampling periods, sample a subset of the pulses in the sense signal during that sampling period;

generate a holding signal for controlling a holding current for the dimmer during the sampling of the subset of pulses in at least one of the sampling periods; and

for each of the sampling periods, generate an output value identifying a duty cycle for driving one or more light emitting diodes (LEDs);

wherein the subset of pulses in each of the sampling periods includes multiple pulses during that sampling period but not one or more initial pulses at a beginning of that sampling period.

17. The apparatus of claim 16, wherein the digital block is configured to, during each of the sampling periods:

identify duty cycles of at least two pulses in the sense signal during that sampling period;

select one of the identified duty cycles; and

generate the output value based on the selected duty cycle.

18. The apparatus of claim 16, wherein the digital block is configured to:

determine a sampling state based on one or more duty cycles associated with one or more prior sampling periods; and

select a size of a current sampling period based on the sampling state.

19. The apparatus of claim 16, further comprising:

dynamic hold current generation circuitry configured to generate the holding current for the dimmer using the holding signal from the digital block.

20. The apparatus of claim 19, wherein the dynamic hold current generation circuitry is configured to generate the holding current only (i) during the sampling of the subset of pulses in each of the sampling periods and (ii) between pulses of the sense signal that are not sampled.