Load Control Device for a Light-Emitting Diode Light Source

• US 20140009085A1
• Filed: 07/05/2013
• Published: 01/09/2014
• Est. Priority Date: 07/06/2012
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Veskovic, Dragan
• Granted Patent: US 9,253,829 B2
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 3/33538 of the forward type H02M3/3353, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33546 with automatic control of the output voltage or current H02M3/33561 takes precedence
• CPC Class Codes: H02M 3/33553 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H05B 44/00 Circuit arrangements for operating electroluminescent light sources for operating light emitting diodes H05B45/00
• CPC Class Codes: H05B 45/00 Circuit arrangements for operating light-emitting diodes [LED]
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/30 Driver circuits
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A load control device for controlling the intensity of a light source (e.g., a light-emitting diode light source) reduces visible flickering in the light source when a target intensity of the light source is dynamically changing. The load control device includes a load regulation circuit operable to conduct a load current through the electrical load and to control the amount of power delivered to the electrical load. The load control device also includes a controller for adjusting the average magnitude of the load current to a target current. The controller pulse-width modulates the magnitude of the load current between a first current less than the target current and a second current greater than the target current. When the target current is dynamically changing, the controller is operable to adjust to the average magnitude of the load current towards the sum of the target current and a supplemental signal.

Claims

1. A load control device for controlling the amount of power delivered to an electrical load, the load control device comprising:

a load regulation circuit operable to conduct a load current through the electrical load and to control the amount of power delivered to the electrical load;

a controller coupled to the load regulation circuit for adjusting the average magnitude of the load current to a target current, the controller operable to pulse-width modulate the magnitude of the load current between a first current less than the target current and a second current greater than the target current;

wherein, when the target current is dynamically changing, the controller is operable to adjust to the average magnitude of the load current towards the sum of the target current and a supplemental signal.

2. The load control device of claim 1, wherein the supplemental signal comprises a periodic ramp signal.

3. The load control device of claim 2, wherein the controller sets a peak magnitude of the periodic ramp signal to a maximum ramp signal magnitude when the target current is dynamically changing.

4. The load control device of claim 3, wherein the controller is operable to decrease the peak magnitude of the periodic ramp signal from the maximum ramp signal to zero amps across a period of time after the target current reaches a steady-state value.

5. The load control device of claim 3, wherein the controller is operable to decrease a ramp period of the periodic ramp signal to zero seconds across a period of time after the target current reaches a steady-state value.

6. The load control device of claim 2, wherein the controller comprises a microprocessor and the periodic ramp signal is a digital signal.

7. The load control device of claim 1, wherein the load regulation circuit comprises an LED drive circuit for an LED light source.

8. The load control device of claim 7, wherein the LED drive circuit comprises a forward converter.

9. The load control device of claim 1, wherein the supplemental signal comprises a sawtooth waveform.

10. The load control device of claim 1, wherein the controller is operable to adjust the average magnitude of the load current to the target current when the target current is at a steady-state value.

11. The load control device of claim 1, wherein the controller is operable to adjust a duty cycle of the pulse-width modulated load current to adjust the average magnitude of the load current between the first current and the second current.

12. A method for controlling the amount of power delivered to an electrical load, the method comprising:

conducting a load current through the electrical load;

adjusting the average magnitude of the load current to a target current by pulse-width modulating the magnitude of the load current between a first current less than the target current and a second current greater than the target current; and

adjusting the average magnitude of the load current towards the sum of the target current and a supplemental signal when the target current is dynamically changing.

13. The method of claim 12, wherein the supplemental signal comprises a periodic ramp signal.

14. The method of claim 13, further comprising:

setting a peak magnitude of the periodic ramp signal to a maximum ramp signal magnitude when the target current is dynamically changing.

15. The method of claim 14, further comprising:

decreasing the peak magnitude of the periodic ramp signal from the maximum ramp signal to zero amps across a period of time after the target current reaches a steady-state value.

16. The method of claim 14, further comprising:

decreasing a ramp period of the periodic ramp signal to zero seconds across a period of time after the target current reaches a steady-state value.

17. The method of claim 12, wherein the supplemental signal comprises a sawtooth waveform.

18. The method of claim 12, wherein the electrical load comprises an LED light source.

19. The method of claim 12, further comprising:

adjusting the average magnitude of the load current to the target current when the target current is at a steady-state value.

20. The method of claim 12, further comprising:

adjusting a duty cycle of the pulse-width modulated load current to adjust the average magnitude of the load current between the first current and the second current.