Load control device for a light-emitting diode light source

Patent metadata

Field	Value
Publication number	US-9247608-B2
Application number	US-201414536491-A
Country	US
Kind code	B2
Filing date	Nov 7, 2014
Priority date	Nov 8, 2013
Publication date	Jan 26, 2016
Grant date	Jan 26, 2016

Abstract

A load control device for controlling the amount of power delivered to an electrical load is able to operate in a burst mode to adjust the amount of power delivered to the electrical load to low levels. The load control device comprises a control circuit that operates in a normal mode to regulate an average magnitude of a load current conducted through the load to a target load current that ranges from a maximum rated current to a minimum rated current. The control circuit operates in the burst mode to regulate the average magnitude of the load current below the minimum rated current. During the burst mode, the control circuit regulates a peak magnitude of the load current to the minimum rated current during a first time period, and stops regulating the load current during a second time period, such that the average magnitude of the load current is below the minimum rated current.

First claim

What is claimed is:

1. A load control device for controlling an amount of power delivered to an electrical load, the load control device comprising:
a load regulation circuit configured to control a magnitude of a load current conducted through the electrical load to control the amount of power delivered to the electrical load; and
a control circuit coupled to the load regulation circuit and configured to adjust an average magnitude of the load current, wherein the control circuit is configured to operate in a normal mode to regulate the average magnitude of the load current to a target load current that ranges from a maximum rated current to a minimum rated current, the control circuit further configured to operate in a burst mode to regulate the average magnitude of the load current below the minimum rated current;
wherein, during the burst mode, the control circuit is configured to regulate a peak magnitude of the load current to the minimum rated current during a first time period using a control loop, and to stop regulating the load current during a second time period resulting in the average magnitude of the load current being below the minimum rated current, the control circuit configured to freeze the control loop during the second time period.

2. The load control device of claim 1 , wherein the control circuit is configured to control the load regulation circuit in an active state in which the control circuit regulates the peak magnitude of the load current to the minimum rated current during the first time period, the control circuit further configured to control the load regulation circuit in an inactive state in which the control circuit stops regulating the load current during the second time period.

3. The load control device of claim 2 , wherein the control circuit is configured to adjust a burst duty cycle defining when the load regulation circuit operates in the active state and the inactive state to adjust the average magnitude of the load current below the minimum rated current when operating in the burst mode.

4. The load control device of claim 3 , wherein the control circuit is configured to adjust the average magnitude of the load current to control the amount of power delivered to the electrical load to a target amount of power.

5. The load control device of claim 4 , wherein the control circuit is configured to adjust the burst duty cycle in response to the target amount of power when operating in the burst mode.

6. The load control device of claim 5 , wherein the control circuit is configured to adjust the burst duty cycle linearly with respect to the target amount of power when operating in the burst mode.

7. The load control device of claim 4 , wherein the control circuit is configured to operate in the burst mode when the target amount of power is less than a transition amount of power.

8. The load control device of claim 4 , further comprising:
a current sense circuit configured to provide a load current feedback signal that indicates the magnitude of the load current to the control circuit;
wherein the control circuit is configured to regulate the average magnitude of the load current to the target load current in response to the load current feedback signal in the normal mode, the control circuit further configured to regulate the peak magnitude of the load current to the minimum rated current in response to the load current feedback signal in the active state of the burst mode.

9. The load control device of claim 3 , wherein, during the burst mode, the control circuit is configured to regulate the average magnitude of the load current by adjusting the burst duty cycle and the target load current.

10. The load control device of claim 9 , wherein, during the burst mode, the control circuit is configured to regulate the peak magnitude of the load current to the minimum rated current during the first time period in a first burst mode period and regulate the peak magnitude of the load current to the minimum rated current plus a current offset during the first time period in a second burst mode period.

11. The load control device of claim 10 , wherein the current offset ranges from a minimum current offset to a maximum current offset based on the burst duty cycle and a target intensity.

12. The load control device of claim 11 , wherein the control circuit is configured to increase the magnitude of the load current from an initial current to the minimum rated current plus the current offset over a ramp time period at a beginning of the first time period.

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

14. The load control device of claim 13 , wherein the LED drive circuit comprises a forward converter.

15. The load control device of claim 1 , wherein the control circuit is configured to increase the magnitude of the load current from an initial current to the minimum rated current over a ramp time period at a beginning of the first time period.

16. An LED driver for controlling an intensity of an LED light source, the LED driver comprising:
an LED drive circuit configured to conduct a load current through the LED light source and to control the intensity of the LED light source; and
a control circuit coupled to the LED drive circuit for adjusting an average magnitude of the load current to control the intensity of the LED light source to a target intensity, wherein the control circuit is configured to operate in a normal mode to regulate the average magnitude of the load current to a target load current that ranges from a maximum rated current to a minimum rated current, the control circuit further configured to operate in a burst mode to regulate the average magnitude of the load current below the minimum rated current;
wherein, during the burst mode, the control circuit is configured to control the LED drive circuit in an active state during a first time period in which the control circuit regulates a peak magnitude of the load current to the minimum rated current using a control loop, the control circuit further configured to control the LED drive circuit in an inactive state during a second time period in which the control circuit freezes the control loop to stop regulating the load current, such that the average magnitude of the load current is below the minimum rated current.

17. The LED driver of claim 16 , wherein the control circuit is configured to adjust a burst duty cycle defining when the LED drive circuit operates in the active state and the inactive state to adjust the average magnitude of the load current below the minimum rated current when operating in the burst mode.

18. The LED driver of claim 17 , wherein the control circuit is configured to adjust the burst duty cycle in response to the target intensity when operating in the burst mode.

19. The LED driver of claim 18 , wherein the control circuit is configured to adjust the burst duty cycle linearly with respect to the target intensity when operating in the burst mode.

20. The LED driver of claim 17 , further comprising:
a current sense circuit configured to provide a load current feedback signal that indicates a magnitude of the load current to the control circuit;
wherein the control circuit is configured to regulate the average magnitude of the load current to the target load current in response to the load current feedback signal in the normal mode, the control circuit further configured to regulate the peak magnitude of the load current

Assignees

• Lutron Electronics Co

Inventors

• Chitta Venkatesh
• Hayes Jeffrey S
• Stevens Jr Robert D

Classifications

• H05B45/345

  Current stabilisation; Maintaining constant current · CPC title

• H05B45/327

  Burst dimming · CPC title

• H05B45/14

  using electrical feedback from LEDs or from LED modules · CPC title

• H05B45/10

  Controlling the intensity of the light · CPC title

• H05B45/395

  Linear regulators · CPC title