Power Supply for a Load Control Device

• US 20090160409A1
• Filed: 12/05/2008
• Published: 06/25/2009
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Carmen, Daniel F.
• Granted Patent: US 8,067,926 B2
• Time in Patent Office: Days
• US Class Current: 320/166
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 5/257 using semiconductor devices only
• CPC Class Codes: H05B 39/044 continuously H05B39/042 takes precedence
• CPC Class Codes: H05B 47/185 via power line carrier transmission
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A power supply for a load control device generates a DC voltage and provides an asymmetrical output current, while drawing a substantially symmetrical input current. The power supply comprises a controllably conductive switching circuit for controllably charging an energy storage capacitor across which the DC voltage is produced. The energy storage capacitor begins charging at the beginning of a half-cycle and stops charging after a charging time in response to the magnitude of the DC voltage and the amount of time that the energy storage capacitor has been charging during the present half-cycle. The charging time is maintained substantially constant from one half-cycle to the next. The power supply is particularly beneficial for preventing asymmetrical current from flowing in a multiple location load control system having a master load control device supplying power to a plurality of remote load control devices all located on either the line-side or the load-side of the system.

Claims

1. A power supply for a load control device for controlling the amount of power delivered to an electrical load from an AC power source, the load control device operable to receive an AC voltage waveform of the AC power source, the power supply operable to generate a DC voltage, the power supply comprising:

an energy storage element;

a controllably conductive switching circuit coupled in series electrical connection with the energy storage element for selectively charging the energy storage element to produce the DC voltage, the controllably conductive switching circuit operable to become conductive after the magnitude of the AC voltage waveform exceeds approximately the magnitude of the DC voltage waveform during a half-cycle of the AC voltage waveform; and

a latching circuit coupled to the controllably conductive switching circuit, the latching circuit adapted to cause the controllably conductive switching circuit to become non-conductive in response to the magnitude of the DC voltage and the amount of time that the energy storage element has been charging during the half-cycle.

2. The power supply of claim 1, further comprising:

a first voltage-responsive current source operable to conduct a first current having a magnitude representative of the magnitude of the DC voltage; and

a second time-responsive current source operable to conduct a second current having a magnitude representative of the amount of time that the energy storage element has been charging during the half-cycle.

3. The power supply of claim 2, wherein the energy storage device charges for the length of a charging time period during the half-cycle, and the first and second current sources operate to maintain the length of the charging time period substantially the same from one half-cycle to the next.

4. The power supply of claim 3, wherein the length of the charging time period changes by approximately 20% or less from one half-cycle to the next.

5. The power supply of claim 3, wherein the length of the charging time period is approximately 1 msec±

0.2 msec.

6. The power supply of claim 2, further comprising:

a current threshold detect circuit operable to sum the first and second currents to produce a total current.

7. The power supply of claim 6, wherein the latching circuit is responsive to the current threshold detect circuit to cause the controllably conductive switching circuit to become non-conductive when the total current exceeds a predetermined current threshold.

8. The power supply of claim 1, wherein the controllably conductive switching circuit comprises a semiconductor switch.

9. The power supply of claim 8, wherein the semiconductor switch comprises a field-effect transistor.

10. The power supply of claim 1, wherein the energy storage element comprises a capacitor.

11. A power supply for a load control device for controlling the amount of power delivered to an electrical load from an AC power source, the load control device operable to receive an AC voltage waveform of the AC power source, the power supply comprising:

an output for providing the DC voltage and adapted to conduct an asymmetrical output current;

an energy storage element, the DC voltage generated across the energy storage element; and

a controllably conductive switching circuit coupled in series electrical connection with the energy storage element for selectively charging the energy storage element to produce the DC voltage, such that the power supply draws an input current from the AC power source;

wherein the controllably conductive switching circuit is controlled such that the input current is substantially symmetrical.

12. The power supply of claim 11, wherein the energy storage device charges for the length of a charging time period during the half-cycle, and the length of the charging time period is substantially the same from one half-cycle to the next.

13. The power supply of claim 12, wherein the length of the charging time period changes by approximately 20% or less from one half-cycle to the next.

14. The power supply of claim 12, wherein the length of the charging time period is approximately 1 msec±

0.2 msec.

15. The power supply of claim 12, wherein the input current has a DC component of less than approximately 0.3 V.

16. The power supply of claim 11, further comprising:

a latching circuit coupled to the controllably conductive switching circuit;

wherein the controllably conductive switching circuit is operable to become conductive after the magnitude of the AC voltage waveform exceeds approximately the magnitude of the DC voltage, and the latching circuit is operable to cause the controllably conductive switching circuit to become non-conductive, such that the energy storage element stops charging after the energy storage element has been charging for a switching time.

17. The power supply of claim 16, wherein the latching circuit is adapted to cause the controllably conductive switching circuit to become non-conductive in response to the magnitude of the DC voltage and the amount of time that the energy storage element has been charging during the half-cycle.

18. The power supply of claim 11, wherein the energy storage element comprises a capacitor.

19. A multiple location load control system for controlling the power delivered to an electrical load from an AC power source, the system comprising:

a main load control device comprising a power supply operable to draw an input current from the AC power source and to generate a link voltage; and

a remote load control device comprising a power supply, the main load control device and the remote load control device adapted to be coupled in series electrical connection between the AC power source and the electrical load, such that the main load control device and the remote load control device are both operable to conduct a load current from the AC power source to the electrical load without a neutral connection to the neutral side of the AC power source, the remote load control device adapted to be further coupled to the main load control device through an accessory wiring, the main load control device operable to provide the link voltage on the accessory wiring to allow the power supply of the remote device to charge, such that an output current of the power supply of the main load control device is asymmetrical;

wherein the input current of the power supply of the main load control device is substantially symmetrical.

20. The load control system of claim 19, wherein the power supply of the main load control device draws current from the AC power source for the length of a main power supply charging time during each half-cycle of the AC power source, and the length of the main power supply charging time is substantially the same from one half-cycle to the next.

21. The load control system of claim 20, wherein the length of the main power supply charging time changes by approximately 20% or less from one half-cycle to the next.

22. The load control system of claim 20, wherein the length of the main power supply charging time is approximately 1 msec±

0.2 msec.

23. The load control system of claim 20, wherein the input current of the power supply of the main load control device has a DC component of less than approximately 0.3 V.

24. The load control system of claim 20, wherein the power supply of the remote load control device draws current from the power supply of the main load control device during a remote power supply charging time during every other half-cycle of the AC power source.

25. The load control system of claim 19, wherein the power supply of the main load control device comprises an energy storage element, the power supply operable to stop charging the energy storage element each half-cycle of the AC power source in response to both the magnitude of the DC voltage and the amount of time that the energy storage element has been charging during the half-cycle.

26. The load control system of claim 19, wherein the electrical load comprises a magnetic low-voltage (MLV) lighting load.

27. A method for generating a DC power supply voltage for use in a load control device for controlling the amount of power delivered to an electrical load from an AC power source, the method comprising the steps of:

beginning to charge an energy storage element for generating the DC power supply voltage during a half-cycle of the AC power source;

generating a first control signal representative of the magnitude of the DC power supply voltage;

generating a second control signal representative of the amount of time that the energy storage element has been charging during the half-cycle; and

causing the energy storage element to stop charging in response to both the first and second control signals.

28. The method of claim 27, wherein the step of generating a first control signal comprises conducting a first current having a magnitude representative of the magnitude of the DC power supply voltage, and the step of generating a second control signal comprises conducting a second current having a magnitude representative of the amount of time that the energy storage element has been charging during the half-cycle.

29. The method of claim 28, further comprising the steps of:

summing the first and second currents to produce a total current; and

determining if the total current exceeds a predetermined current threshold.

30. The method of claim 29, wherein the step of causing the energy storage element to stop charging further comprises causing the energy storage element to stop charging if the total current exceeds the predetermined current threshold.

31. The method of claim 27, wherein the energy storage device charges for the length of a charging time period during the half-cycle, and the length of the charging time period is substantially the same from one half-cycle to the next.

32. The method of claim 31, wherein the length of the charging time period changes by approximately 20% or less from one half-cycle to the next.

33. The method of claim 31, wherein the length of the charging time period is approximately 1 msec±

0.2 msec.