ILLUMINATION DEVICE INCLUDING LEDS AND A SWITCHING POWER CONTROL SYSTEM

• US 20100320922A1
• Filed: 06/23/2010
• Published: 12/23/2010
• Est. Priority Date: 06/23/2009
• Status: Active Grant

• Current Assignee: Ilumisys Incorporated (Altair Engineering Incorporated)
• Original Assignee: Altair Engineering Incorporated
• Inventors: Palazzoló, Francis, Ivey, John
• Granted Patent: US 8,421,366 B2
• Time in Patent Office: Days
• US Class Current: 315/210
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 47/19 via wireless transmission
• CPC Class Codes: H05B 47/195 the transmission using visible or infrared light

Abstract

Disclosed herein is an illumination device including light-emitting diodes, an alternating current input, a full-wave rectifier coupled to the alternating current input and configured to produce a rectified voltage output and a power converter, the power converter having a switching element electrically coupled to the rectified voltage output of the full-wave rectifier. An improvement of the illumination device includes a feedback circuit configured to determine an average current across the light-emitting diodes and to invert a signal representing the average current to provide a switching signal to the switching element such that, for a range of operating points, increasing a current drawn into the power converter will decrease LED power and decreasing the current drawn into the power converter will increase LED power.

Claims

1. In an illumination device including light-emitting diodes, an alternating current input, a full-wave rectifier coupled to the alternating current input and configured to produce a rectified voltage output and a power converter, the power converter having a switching element electrically coupled to the rectified voltage output of the full-wave rectifier, an improvement comprising:

a feedback circuit configured to determine an average current across the light-emitting diodes and to invert a signal representing the average current to provide a switching signal to the switching element such that, for a range of operating points, increasing a current drawn into the power converter will decrease LED power and decreasing the current drawn into the power converter will increase LED power.

2. The device of claim 1 wherein the alternating current input comprises a conventional ballast for a fluorescent bulb.

3. The device of claim 2, further comprising:

protection circuitry electrically coupled between the ballast and the full-wave rectifier.

4. The device of claim 1, wherein the light-emitting diodes are coupled to the rectified voltage output of the full-wave rectifier and the single switching element is a low-side switch electrically coupled between the light-emitting diodes and a sense resistor.

5. The device of claim 4, further comprising:

an inductor in series with the light-emitting diodes and located between the light-emitting diodes and a connection point of the low-side switch and the light-emitting diodes.

6. The device of claim 5, further comprising:

a diode in series with the inductor and the light-emitting diodes and electrically coupled to the rectified voltage output, a diode located between the connection point and the rectified voltage output.

7. The device of claim 4 wherein the current sensed by the sense resistor is a peak current occurring when the low-side switch is closed.

8. The device of claim 1 wherein the feedback circuit is configured to calculate the average current from the peak current obtained from at least one of a sense resistor and the emitted light output.

9. The device of claim 1 wherein the feedback circuit comprises a pulse width modulator and a control system for the pulse width modulator, the control system including an input coupled to the rectified voltage output and a second input coupled to a sense resistor.

10. The device of claim 1 wherein the single switching element is a high-side switch connected between the rectified output voltage and the light-emitting diodes.

11. The device of claim 10, further comprising:

an inductor connected in series with the light-emitting diodes at a connection point between the light-emitting diodes and the high-side switch; and

wherein a sense resistor is connected in series with the inductor and the light-emitting diodes and is coupled to ground.

12. The device of claim 11, further comprising:

a diode connected to a connection point between the high-side switch and the inductor such that the recirculation diode is reverse-biased when the high-side switch is closed;

and wherein the recirculation diode is in parallel with the light-emitting diodes.

13. The device of claim 11 wherein the feedback circuit comprises a pulse width modulator and a control system for the pulse width modulator, the control system including a first input coupled to the rectified voltage output and a second input coupled to a sense resistor.

14. The device of claim 1, further comprising:

a remote signal receiver configured to receive a remote signal indicating a desired brightness level for the light-emitting diodes; and

a dimming circuit responsive to the remote signal receiver and configured to provide a control signal to the feedback circuit indicating the desired brightness level.

15. The device of claim 14, wherein the remote signal receiver comprises one of an infrared receiver and a radio frequency antenna.

16. The device of claim 1, wherein feedback circuit is configured to output a duty cycle with a value greater than the duty cycle used to achieve a maximum value of current through the light-emitting diodes.

17. An illumination device having at least one LED and a power converter with a switching element for connection to an existing fluorescent lamp fixture including a conventional ballast, an improvement to the illumination device comprising:

a feedback circuit operable to provide a switching signal to the switching element according to a duty cycle, the feedback circuit configured to;

increase the value of the duty cycle to decrease an output current signal through the LEDs; and

decrease the value of the duty cycle to increase the output current signal through the LEDs.

18. The device of claim 17, wherein feedback circuit is further configured to output a value of the duty cycle greater than a predetermined value, the predetermined value representative of the duty cycle adapted to attain a maximum value of current through the at least one LED;

and

19. The device of claim 18, wherein the predetermined value is greater than 0.2.

20. A method of controlling a feedback circuit for an illumination device having at least one LED and a power converter with a switching element;

determining an average current across the at least one LED;

inverting a signal representing the average current such that, for a range of operating points, increasing a current drawn into the power converter will decrease LED power and decreasing the current drawn into the power converter will increase LED power; and

providing the switching signal to the switching element.