Load control device for a light-emitting diode light source

• US 9,888,535 B2
• Filed: 11/18/2016
• Issued: 02/06/2018
• Est. Priority Date: 11/08/2013
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Chitta, Venkatesh, Hayes, Jeffrey S., Stevens, Jr., Robert D.
• Primary Examiner(s): TRAN, THUY V
• Application Number:
  US15/355,230
• Publication Number:
  US 20170071039A1
• Time in Patent Office: 445 Days
• Field of Search: 315224, 315276, 315291, 315308, 315360
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0035 using burst mode control
• CPC Class Codes: H02M 1/0058 by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826
• 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 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer
• CPC Class Codes: H05B 44/00 Circuit arrangements for operating electroluminescent light sources for operating light emitting diodes H05B45/00
• CPC Class Codes: H05B 45/10 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 45/327 Burst dimming
• CPC Class Codes: H05B 45/345 Current stabilisation; Maintaining constant current
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: H05B 45/50 : responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• CPC Class Codes: Y02B 70/10 : Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A method for controlling an amount of power delivered to an electrical load may include controlling an average magnitude of a load current towards a target load current that ranges from a maximum rated current to a minimum rated current in a normal mode, and controlling the average magnitude of the load current below the minimum rated current in a burst mode. The burst mode may include at least one burst mode period that comprises a first time period associated with an active state and a second time period associated with an inactive state. During the burst mode, the method may include regulating a peak magnitude of the load current towards the minimum rated current during the active state, and stopping the generation of at least one drive signal during the inactive state to control the average magnitude of the load current to be less than the minimum rated current.

Claims

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

receiving a load current feedback signal that indicates an average magnitude of a load current through the electrical load;

generating at least one drive signal for controlling the load current;

adjusting an operational characteristic of the at least one drive signal in response to the load current feedback signal in order to control the amount of power delivered to the electrical load towards a target amount of power;

controlling the average magnitude of the load current towards a target load current that ranges from a maximum rated current to a minimum rated current in a normal mode; and

controlling the average magnitude of the load current below the minimum rated current in a burst mode, wherein the burst mode includes at least one burst mode period that comprises a first time period associated with an active state and a second time period associated with an inactive state;

wherein, during the burst mode, the method further comprises adjusting the operational characteristic of the at least one drive signal to regulate a peak magnitude of the load current towards approximately the minimum rated current in response to the load current feedback signal during the active state, and stopping generating the at least one drive signal while maintaining the operational characteristic of the at least one drive signal constant during the inactive state to control the average magnitude of the load current to be less than the minimum rated current when in the burst mode.

2. The method of claim 1, further comprising:

adjusting a burst duty cycle to maintain the average magnitude of the load current below the minimum rated current;

wherein a duration of the first time period associated with the active state is determined based on the burst duty cycle.

3. The method of claim 2, further comprising:

during the burst mode, regulating the peak magnitude of the load current to the minimum rated current during the active state in a first burst mode period and to the minimum rated current plus a current offset during the active state in a second burst mode period.

4. The method of claim 3, wherein the current offset ranges from a minimum current offset to a maximum current offset based on the burst duty cycle and the target amount of power.

5. The method of claim 4, further comprising:

increasing 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.

6. The method of claim 2, wherein adjusting a burst duty cycle further comprises adjusting the burst duty cycle in response to the target amount of power during the burst mode.

7. The method of claim 2, wherein adjusting a burst duty cycle further comprises adjusting the burst duty cycle linearly with respect to the target amount during the burst mode.

8. The method of claim 2, wherein controlling the average magnitude of the load current below the minimum rated current in a burst mode further comprises controlling the average magnitude of the load current below the minimum rated current in the burst mode when the target amount of power is less than a transition amount of power that is associated with the minimum rated current.

9. The method of claim 2, further comprising:

regulating the average magnitude of the load current by adjusting the burst duty cycle and the target load current during the burst mode.

10. The method of claim 1, wherein the operational characteristic of the at least one drive signal comprises a duty cycle or an operating frequency of the at least one drive signal.

11. The method of claim 1, further comprising:

adjusting a duty cycle of the at least one drive signal 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; and

adjusting the duty cycle of the at least one drive signal 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 during the burst mode.

12. The method of claim 1, further comprising:

increasing 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.

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

controlling an average magnitude of a load current through the electrical load in a normal mode and in a burst mode, wherein the burst mode comprises at least one burst mode period that comprises a first time period associated with an active state and a second time period associated with an inactive state, and a duration of the first time period associated with the active state is determined based on a burst duty cycle; and

during the normal mode, adjusting a target load current based on a targeted amount of power to be delivered to the electrical load to regulate the average magnitude of the load current while holding the burst duty cycle constant;

wherein, during the burst mode, the method further comprises, based on the target amount of power, adjusting the burst duty cycle and adjusting the target load to regulate the average magnitude of the load current, wherein adjusting the target load current comprises;

determining a current offset that ranges from a minimum current offset to a maximum current offset based on the burst duty cycle and the target amount of power; and

adjusting the target load current by the current offset.

14. The method of claim 13, further comprising:

during the burst mode, decreasing the target load current during consecutive burst mode periods while holding the burst duty cycle constant to decrease the average magnitude of the load current; and

decreasing the burst duty cycle and increasing the target load current in a succeeding burst mode period to decrease the average magnitude of the load current during the burst mode.

15. The method of claim 13, further comprising:

during the burst mode, increasing the target load current during consecutive burst mode periods while holding the burst duty cycle constant to increase the average magnitude of the load current; and

increasing the burst duty cycle and decreasing the target load current in a succeeding burst mode period to increase the average magnitude of the load current during the burst mode.

16. The method of claim 13, wherein determining the current offset based on the burst duty cycle and the target amount of power comprises determining the current offset based on a fractional portion of an ideal burst duty cycle during the burst mode.

17. The method of claim 13, further comprising:

in the normal mode, regulating the average magnitude of the load current to the target load current that ranges from a maximum rated current to a minimum rated current; and

in the burst mode, controlling the average magnitude of the load current below the minimum rated current.

18. The method of claim 13, wherein the normal mode is characterized by the burst duty cycle being equal to approximately 100%.

19. The method of claim 13, further comprising:

stopping regulating the load current during the second time period.

20. The method of claim 13, further comprising:

increasing the load current from an initial current to a minimum rated current plus the current offset over a ramp time period at a beginning of the first time period.

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

adjusting an average magnitude of a load current in a normal mode and in a burst mode;

regulating the average magnitude of the load current between a maximum rated current and a minimum rated current in the normal mode;

regulating the average magnitude of the load current below the minimum rated current in the burst mode by regulating a peak magnitude of the load current towards a target load current during a first time period of the burst mode and stopping regulating the load current during a second time period of the burst mode; and

increasing the load current from an initial current to the target load current over a ramp time period at a beginning of the first time period of the burst mode.

22. The method of claim 21, further comprising:

receiving a load current feedback signal that indicates the average magnitude of the load current;

generating at least one drive signal for controlling the load current; and

adjusting an operational characteristic of the at least one drive signal in response to the load current feedback signal.

23. The method of claim 22, further comprising:

during the burst mode, adjusting the operational characteristic of the at least one drive signal to regulate the peak magnitude of the load current towards approximately the minimum rated current in response to the load current feedback signal during at least a portion of the first time period.

24. The method of claim 23, further comprising:

stopping generating the at least one drive signal during the burst mode to control the average magnitude of the load current to be less than the minimum rated current; and

maintaining the operational characteristic of the at least one drive signal constant during the second time period of the burst mode.

25. The method of claim 24, further comprising:

maintaining the operational characteristic of the at least one drive signal constant while increasing the load current from the initial current to the target load current over the ramp time period during the burst mode.

26. The method of claim 25, further comprising:

adjusting the operational characteristic of the at least one drive signal to regulate the peak magnitude of the load current towards approximately the minimum rated current in response to the load current feedback signal after the ramp time period during the first time period of the burst mode.

27. The method of claim 26, further comprising:

waiting for a wait time period after the ramp time period; and

after the wait time period, adjusting the operational characteristic of the at least one drive signal to regulate the peak magnitude of the load current towards approximately the minimum rated current in response to the load current feedback signal.

28. The method of claim 21, wherein the target load current comprises one of the minimum rated current or the minimum rated current plus a current offset.

29. The method of claim 28, wherein the current offset ranges from a minimum current offset to a maximum current offset based on a burst duty cycle and a target amount of power to be delivered to the electrical load.