Circuits and methods for reducing flicker in an LED light source

• US 9,084,319 B2
• Filed: 11/02/2012
• Issued: 07/14/2015
• Est. Priority Date: 11/02/2012
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sullivan, Timothy Roy, Herrington, Daniel Ross
• Primary Examiner(s): HOUSTON, ADAM D
• Application Number:
  US13/667,964
• Publication Number:
  US 20140125239A1
• Time in Patent Office: 984 Days
• Field of Search: 315/200.R, 315/250
• US Class Current: 1/1
• CPC Class Codes: B64G 1/222 for deploying structures between a stowed and deployed state
• CPC Class Codes: B64G 1/44 using radiation, e.g. deployable solar arrays
• CPC Class Codes: B64G 1/66 Arrangements or adaptations of apparatus or instruments, not otherwise provided for
• CPC Class Codes: H01Q 1/08 Means for collapsing antennas or parts thereof collapsible loop antennas H01Q7/02; means for collapsing H-antennas or Yagi antennas H01Q19/04
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 15/161 Collapsible reflectors
• CPC Class Codes: H02S 30/20 Collapsible or foldable PV modules
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

Method and circuits for balancing a first waveform used to drive an LED are disclosed herein. The first waveform has a first cycle with a first amplitude and a second cycle with a second amplitude. An embodiment of the method includes adjusting the first amplitude of the first cycle to match the second amplitude of the second cycle, the result being a second waveform. The LED is driven with the second waveform.

Claims

1. A method of balancing a first waveform used to drive an LED, the first waveform having a first cycle with a first amplitude and a second cycle with a second amplitude, the method comprising:

adjusting the first amplitude of the first cycle to match the second amplitude of the second cycle, the result being a second waveform; and

driving the LED with the second waveform.

2. The method of claim 1, wherein the first amplitude is greater than the second amplitude and wherein the adjusting comprises attenuating the first cycle so that the first amplitude matches the second amplitude.

3. The method of claim 1 and further comprising determining if the first amplitude is within a predetermined value of the second amplitude and skipping the adjusting if the first amplitude is within a predetermined value of the second amplitude.

4. The method of claim 1, wherein the first waveform is rectified from a sinusoidal waveform being attenuated by a first conduction angle during the first cycle and a second conduction angle during the second cycle.

5. The method of claim 1, wherein the first cycle has a DC component and wherein the adjusting is performed by changing the DC component of the first cycle.

6. The method of claim 5, wherein the adjusting is performed by a DC to DC converter.

7. The method of claim 1, wherein the first amplitude is less than the second amplitude and wherein the adjusting comprises amplifying the first cycle so that the first amplitude matches the second amplitude.

8. The method of claim 1, wherein the first cycle has a peak associated therewith, the second cycle has a peak associated therewith, and wherein the amplitudes are based on the peaks.

9. The method of claim 1, wherein the first cycle has a trough associated therewith, the second cycle has a trough associated therewith, and wherein the amplitudes are based on the troughs.

10. An LED driver comprising:

an input for receiving an input current, the input current having a first cycle having a first conduction angle and a second cycle having a second conduction angle;

a decision circuit, wherein the decision circuit determines when the amplitude of the first cycle is within a predetermined value of the amplitude of the second cycle; and

a converter, wherein the converter adjusts the amplitude of the first cycle to be substantially equal to the amplitude of the second cycle when the amplitude of the first cycle is not within the predetermined value of the amplitude of the second cycle.

11. The LED driver of claim 10 and further comprising a rectifier connected to the input, wherein the rectifier rectifies the input current, and wherein the decision circuit acts on the rectified current.

12. The LED driver of claim 10, wherein the converter is a DC to DC converter.

13. The LED driver of claim 10, wherein the first cycle has a DC component and wherein the converter adjusts the DC component of the first cycle.

14. The LED driver of claim 10 and further comprising a balancing circuit, wherein the balancing circuit receives data from the decision circuit indicating that the first cycle needs to be adjusted and outputs data to the converter as to the amount to adjust the first cycle.

15. The LED driver of claim 14, wherein the converter, balancing circuit, and decision circuit are integrated into a single circuit.

16. The LED driver of claim 10, wherein the decision circuit determines whether the amplitude of the first cycle is lower than the amplitude of the second cycle and adjusts the cycle with the greater of the two amplitudes to the lower amplitude.

17. The LED driver of claim 10, wherein the first cycle has a peak associated therewith, the second cycle has a peak associated therewith, and wherein the amplitudes are based on the peaks.

18. The LED driver of claim 10, wherein the first cycle has a trough associated therewith, the second cycle has a trough associated therewith, and wherein the amplitudes are based on the troughs.

19. The LED driver of claim 10, wherein the LED driver is located in a bulb.

20. A method of balancing a first current waveform used to drive an LED, the waveform having a first cycle with a first amplitude and a second cycle with a second amplitude, the method comprising:

rectifying the first current waveform;

determining whether the first amplitude and the second amplitude have a difference that is greater than a predetermined value;

determining the amount that the greater of the first amplitude and the second amplitude has to be attenuated when the difference between the first amplitude and the second amplitude is greater than a predetermined value;

adjusting the greater of the first amplitude and the second amplitude to the lower of the first amplitude and the second amplitude, the resulting waveform being a second current waveform; and

driving the LED with the second current waveform.