DEEP DIMMING OF AN LED-BASED ILLUMINATION DEVICE

• US 20150282270A1
• Filed: 03/26/2015
• Published: 10/01/2015
• Est. Priority Date: 03/28/2014
• Status: Active Grant

• Current Assignee: SBC Xicato Corporation
• Original Assignee: Xicato, Inc.
• Inventors: Loveridge, Barry Mark, Hushley, Jeffrey P.
• Granted Patent: US 9,788,379 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/357 specially adapted for retrofit LED light sources
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

An LED based illumination device is dimmed by controlling an average current supplied to the LED based illumination device. The currently supplied to the LED may be supplied by an LED driver that is in communication with a dimming control engine. The dimming control engine may receive an indication of a desired average current level. The dimming control engine controls the LED driver to periodically switch a current supplied to an LED of the LED based illumination device from a high state to a low state over a switching period, wherein both a duration of the switching period is adjusted and a ratio of a time in the high state to a time in the low state is adjusted as the average current supplied to the LED based illumination device transitions from a first average current level to the desired average current level.

Claims

1. A method of controlling an average current supplied to an LED based illumination device, comprising:

receiving an indication of a desired average current level that differs from a first average current level supplied to an LED of the LED based illumination device, wherein a current supplied to the LED of the LED based illumination device is periodically switched from a high state to a low state over a switching period; and

adjusting both a duration of the switching period and a ratio of a time in the high state to a time in the low state as the average current supplied to the LED of the LED based illumination device transitions from the first average current level to the desired average current level.

2. The method of controlling the average current supplied to the LED based illumination device of claim 1, further comprising:

adjusting a value of the current supplied to the LED during the high state from a first current value to a second current value as the average current supplied to the LED based illumination device transitions from the first average current level to the desired average current level.

3. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein the switching period is determined by a number of clock pulses, and wherein the ratio of the time in the high state to the time in the low state is determined by a threshold value.

4. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein the duration of the switching period and the ratio of the time in the high state to the time in the low state are both adjusted in a same digital dimming step.

5. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein each step of the transition from the first average current level to the desired average current level changes a lumen output of the LED based illumination device by less than 0.03%.

6. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein the desired average current level supplied to the LED based illumination device is less than 0.1 percent of a maximum rated average current of the LED based illumination device.

7. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein the switching period is changed monotonically as the average current supplied to the LED based illumination device transitions from the first average current level to the desired average current level.

8. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein the ratio of the time in the high state to the time in the low state is changed monotonically as the average current supplied to the LED based illumination device transitions from the first average current level to the desired average current level.

9. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein the ratio of the time in the high state to the time in the low state is changed by changing a threshold value of a comparator circuit.

10. The method of controlling the average current supplied to the LED based illumination device of claim 1, wherein the switching period is changed by changing a preload value of a counter circuit.

11. The method of controlling the average current supplied to the LED based illumination device of claim 1, further comprising:

sensing an ambient light level during a time period when the current supplied to the LED based illumination device is at a zero state.

12. An LED based illumination device, comprising:

at least one light emitting diode (LED);

a LED driver coupled to the LED, the LED driver configured to supply a current to the LED based on a digital control signal received by the LED driver; and

a dimming control engine configured to communicate the digital control signal to the LED driver, the dimming control engine, comprising;

an amount of electronic circuitry configured to generate the digital control signal, wherein the digital control signal periodically switches between a high state and a low state, and wherein both a duration of a switching period and a ratio of a time in the high state to a time in the low state are adjusted as an average current supplied to the LED based illumination device transitions from a first average current level to a desired average current level.

13. The LED based illumination device of claim 12, further comprising:

a digital to analog converter configured to communicate an analog control signal to the LED driver to change a value of the current supplied to the LED during the high state from a first current value to a second current value as the average current supplied to the LED based illumination device transitions from the first average current level to the desired average current level.

14. The LED based illumination device of claim 12, further comprising:

a flux sensor disposed within the LED based illumination device, wherein a flux value sensed by the flux sensor is read by the dimming control engine during a time period when the current supplied to the LED is at a zero state.

15. The LED based illumination device of claim 12, wherein each step of the transition from the first average current level to the desired average current level changes a lumen output of the LED based illumination device by less than 0.03%.

16. The LED based illumination device of claim 12, wherein the desired average current level supplied to the LED based illumination device is less than 0.1 percent of a maximum rated average current of the LED based illumination device.

17. The LED based illumination device of claim 12, wherein the amount of electronic circuitry is further configured to generate an analog control signal, and wherein the LED driver is further configured to adjust the current supplied to the LED based on the analog control signal.

18. A dimming control engine, comprising:

a microprocessor configured to receive an indication of a desired average current level supplied to an LED based illumination device;

an amount of electronic circuitry configured to generate a digital control signal that periodically switches between a high state and a low state, and wherein both a duration of a switching period and a ratio of a time in the high state to a time in the low state are adjusted as an average current supplied to the LED based illumination device transitions from a first average current level to the desired average current level.

19. The dimming control engine of claim 18, further comprising:

a digital to analog converter configured to generate an analog control signal to control a value of a current supplied to the LED based illumination device during the high state from a first current value to a second current value as the average current supplied to the LED based illumination device transitions from the first average current level to the desired average current level.

20. The dimming control engine of claim 18, wherein each step of the transition from the first average current level to the desired average current level changes a lumen output of the LED based illumination device by less than 0.03%.

21. The dimming control engine of claim 18, wherein the desired average current level supplied to the LED based illumination device is less than 0.1 percent of a maximum rated average current of the LED based illumination device.