Dimmer decoder with adjustable filter for use with led drivers

• US 20110084623A1
• Filed: 10/14/2010
• Published: 04/14/2011
• 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: Barrow, Steven M.
• Granted Patent: US 8,736,191 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, (i) identifying at least one pulse duty cycle for at least one pulse in the sense signal during that sampling period and (ii) generating an output value identifying a duty cycle for driving one or more light emitting diodes (LEDs). The output value is based on the at least one pulse duty cycle. The method further includes filtering the output values using a filter and adjusting the filter based on a rate at which the output of the dimmer changes. The filter could be adjusted by controlling whether an additional resistor forms part of an RC filter based on a sampling state.

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;

identifying at least one pulse duty cycle for at least one pulse in the sense signal during that sampling period; and

generating an output value identifying a duty cycle for driving one or more light emitting diodes (LEDs), the output value based on the at least one pulse duty cycle;

filtering the output values using a filter; and

adjusting the filter based on a rate at which the output of the dimmer changes.

2. The method of claim 1, further comprising:

determining a sampling state identifying a size of a current sampling period, wherein the sampling state is determined based on one or more duty cycles associated with one or more prior sampling periods;

wherein adjusting the filter comprises adjusting the filter based on the sampling state.

3. The method of claim 2, wherein adjusting the filter comprises controlling whether an additional resistor forms part of an RC filter based on the sampling state.

4. The method of claim 3, wherein:

the additional resistor is removed from the RC filter in response to a determination that 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

the additional resistor is inserted into the RC filter in response to a determination that a change between duty cycles for consecutive sampling periods has not exceeded the threshold for a specified number of sampling periods.

5. The method of claim 4, wherein the additional resistor is inserted into the RC filter at an end of a delay period occurring after the determination is made that the change between duty cycles for consecutive sampling periods has not exceeded the threshold for the specified number of sampling periods.

6. The method of claim 3, wherein controlling whether the additional resistor forms part of the RC filter comprises:

controlling a switch coupled across the additional resistor, the additional resistor removed from the RC filter when the switch is closed, the additional resistor inserted into the RC filter when the switch is opened.

7. The method of claim 1, wherein filtering the output values controls how fast light output from the one or more LEDs changes between consecutive output values.

8. A system comprising:

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

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;

identify at least one pulse duty cycle for at least one pulse in the sense signal during that sampling period; and

generate an output value identifying a duty cycle for driving the one or more LEDs, the output value based on the at least one pulse duty cycle; and

a filter configured to filter the output values;

wherein the dimmer decoder is further configured to adjust the filter based on a rate at which the output of the dimmer changes.

9. The system of claim 8, wherein:

the dimmer decoder is further configured to determine a sampling state that identifies a size of a current sampling period, wherein the sampling state is determined based on one or more duty cycles associated with one or more prior sampling periods; and

the dimmer decoder is configured to adjust the filter based on the sampling state.

10. The system of claim 9, wherein:

the filter comprises an RC filter; and

the dimmer decoder is configured to control whether an additional resistor forms part of the RC filter based on the sampling state.

11. The system of claim 10, wherein:

the dimmer decoder is configured to remove the additional resistor from the RC filter in response to a determination that 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

the dimmer decoder is configured to insert the additional resistor into the RC filter in response to a determination that a change between duty cycles for consecutive sampling periods has not exceeded the threshold for a specified number of sampling periods.

12. The system of claim 11, wherein the dimmer decoder is configured to insert the additional resistor into the RC filter at an end of a delay period occurring after the determination is made that the change between duty cycles for consecutive sampling periods has not exceeded the threshold for the specified number of sampling periods.

13. The system of claim 10, wherein:

the dimmer decoder is configured to control whether the additional resistor forms part of the RC filter by controlling a switch coupled across the additional resistor;

the additional resistor is inserted into the RC filter when the switch is opened; and

the additional resistor is removed from the RC filter when the switch is closed.

14. The system of claim 8, wherein the filter is configured to control how fast light output from the one or more LEDs changes between consecutive output values.

15. An apparatus comprising:

an output configured to be coupled to a filter; and

a digital block 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;

identify at least one pulse duty cycle for at least one pulse in the sense signal during that sampling period;

generate an output value identifying a duty cycle for driving one or more light emitting diodes (LEDs), the output value based on the at least one pulse duty cycle;

provide the output value to the filter for filtering; and

adjust the filter based on a rate at which the output of the dimmer changes.

16. The apparatus of claim 15, wherein:

the digital block is further configured to determine a sampling state that identifies a size of a current sampling period, wherein the sampling state is determined based on one or more duty cycles associated with one or more prior sampling periods; and

the digital block is configured to adjust the filter based on the sampling state.

17. The apparatus of claim 16, wherein the digital block is configured to adjust the filter by controlling whether an additional resistor forms part of an RC filter based on the sampling state.

18. The apparatus of claim 17, wherein:

the digital block is configured to remove the additional resistor from the RC filter in response to a determination that 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

the digital block is configured to insert the additional resistor into the RC filter in response to a determination that a change between duty cycles for consecutive sampling periods has not exceeded the threshold for a specified number of sampling periods.

19. The apparatus of claim 18, wherein the digital block is configured to insert the additional resistor into the RC filter at an end of a delay period occurring after the determination is made that the change between duty cycles for consecutive sampling periods has not exceeded the threshold for the specified number of sampling periods.

20. The apparatus of claim 17, wherein:

the digital block is configured to control whether the additional resistor forms part of the RC filter by controlling a switch coupled across the additional resistor;

the additional resistor is removed from the RC filter when the switch is closed; and

the additional resistor is inserted into the RC filter when the switch is opened.