VARIABLE LOAD CIRCUITS FOR USE WITH LIGHTING CONTROL DEVICES

• US 20100013405A1
• Filed: 09/04/2007
• Published: 01/21/2010
• Est. Priority Date: 09/04/2006
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Thompson, Stephen, Lopez, Clive, Booth, Graham
• Granted Patent: US 8,169,154 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations
• CPC Class Codes: H05B 45/3575 by means of dummy loads or bleeder circuits, e.g. for dimmers
• CPC Class Codes: H05B 45/397 Current mirror circuits
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A variable load circuit (2) is provided for use with a dimmer (1). A low wattage load such as a LED (3) is provided in series with the dimmer and the variable load circuit is provided in parallel with the LED. The variable load circuit has two different load characteristics: when the applied voltage from the dimmer is below a threshold, the variable load circuit presents a fixed load (24), and when the applied voltage is above a threshold the variable load circuit presents a variable load so as to act as a constant current sink. The variable load is provided by a secondary load portion (25) which may or may not act in combination with the fixed load (24), and the secondary load portion (25) is switched in or out of the variable load circuit by a trigger circuit portion (26).

Claims

1. A variable load circuit for use with a lighting control device, which variable load circuit is arranged to operate with two different load characteristics during a half cycle of an applied alternating signal, wherein the variable load circuit comprises means responsive to the applied alternating signal arranged to allow current flow in response to voltage applied during one portion of the half cycle of the applied alternating signal, and to allow the variable load circuit to act as a constant current sink during another portion of the half cycle, wherein the variable load circuit is arranged to operate independently of any external load, connected to the variable load circuit.

2. A variable load circuit according to claim 1, wherein during said one portion of the applied alternating signal the variable load circuit acts as a substantially fixed resistive load.

3. A variable load circuit according to claim 1, wherein the variable load circuit is arranged to present different load characteristics during first and third portions of the half cycle of the applied alternating signal than during a second portion of the half cycle of the applied alternating signal.

4. A variable load circuit according to claim 1, comprising a fixed load circuit portion, which includes at least one resistor arranged to act as a fixed load.

5. A variable load circuit according to claim 1, comprising a secondary load circuit portion that is arranged to operate during part of the half cycle of the applied alternating signal.

6. A variable load circuit according to claim 5, wherein the secondary load circuit portion comprises a first switch arranged to switch the secondary load circuit in and out of the variable load circuit.

7. A variable load circuit according to claim 5, wherein the fixed load circuit portion and secondary load circuit portion together act as a constant current sink during a portion of the half cycle.

8. A variable load circuit according to claim 5, wherein the secondary load circuit portion acts as a constant current sink during a portion of the half cycle.

9. A variable load circuit according to 6u ;

an) of claims 6, wherein the first switch is a first transistor, and wherein the variable load circuit comprises a trigger circuit portion to provide a current or voltage to a trigger terminal of the first transistor when a voltage above a threshold voltage is applied to the variable load circuit.

10. A variable load circuit according to claim 5, wherein the fixed load circuit comprises a transistor.

11. A variable load circuit according to claim 6, wherein the secondary load circuit portion comprises a second switch and a third switch, which second switch and third switch are arranged to form a constant current sink when the first switch allows current to pass through the secondary circuit portion.

12. A variable load circuit according to claim 11, wherein the switch in the fixed load circuit portion and the third switch are a single Field Effect Transistor (FET).

13. A variable load circuit according to claim 12, comprising a charge storage portion to keep the FET on during part of the half cycle of the applied alternating signal when relatively little or no voltage is applied to the variable load circuit.

14. A variable load circuit according to claim 12, wherein a voltage limiting means is provided between a gate contact of the FET and a source contact of the FET.

15. A variable load circuit according to claim 1 further comprising a rectifier for rectifying an AC input to the variable load circuit.

16. A variable load circuit according to claim 1 comprising no more than two terminals for external connections.

17. A variable load circuit according to claim 1 wherein the means responsive to the applied alternating signal are arranged to allow a greater current flow in response to voltage applied during said one portion of the half cycle than in response to voltage applied during said another portion of the half cycle.

18. A variable load circuit according to claim 1 wherein during said one portion of the half cycle, the absolute value of the voltage of the applied alternating signal is below a threshold, and during said another portion of the half cycle, the absolute value of said voltage is above a threshold.

19. A lighting control apparatus comprising a lighting control device and a variable load circuit, wherein the lighting control device is connected to the variable load circuit and is arranged to supply an alternating signal to the variable load circuit, and the variable load circuit is arranged to operate with two different load characteristics during a half cycle of the applied alternating signal, wherein the variable load circuit comprises means responsive to the applied alternating signal arranged to permit current to flow in response to voltage applied during one portion of the half cycle of the applied alternating signal, and to allow the variable load circuit to act as a constant current sink during another portion of the half cycle, wherein the variable load circuit is arranged to operate independently of any external load, connected to the variable load circuit.

20. A variable lighting control apparatus according to claim 19, wherein the lighting control device requires a minimum current to pass for correct operation and the variable load circuit is arranged to pass at least the minimum current during the second portion of the half cycle of the applied alternating signal.

21. A variable lighting control apparatus according to claim 19, wherein the lighting control device is arranged to charge during a first portion of the half cycle of the applied alternating signal and the variable load circuit is arranged to pass sufficient current during the first portion of the half cycle of the applied alternating signal to allow the lighting control device to charge.

22. A variable lighting control apparatus according to claim 19 wherein the lighting control device is arranged in series with the variable load circuit.

23. A variable lighting control apparatus according to claim 19 wherein the lighting control apparatus is connectable to a light for control of said light.

24. A variable lighting control apparatus according to claim 23 wherein the variable load circuit is arranged in parallel with the light, when said light is connected to the lighting control apparatus.

25. A variable load circuit for use with a lighting control device, which variable load circuit is arranged to operate with two different load characteristics during a half cycle of an applied alternating signal, wherein the variable load circuit is arranged to allow greater current flow in response to voltage applied during a first portion of the half cycle of the applied alternating signal than in response to voltage applied during a second portion of the applied alternating signal, and wherein the variable load circuit is arranged to act as a constant current sink during the second portion of the applied alternating signal, wherein the variable load circuit is arranged to operate independently of any external load, connected to the variable load circuit.