Load control device having a variable drive circuit

• US 7,619,365 B2
• Filed: 04/10/2006
• Issued: 11/17/2009
• Est. Priority Date: 04/10/2006
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Davis, Gregory T., Hausman, Donald F. Jr., Orchowski, Neil
• Primary Examiner(s): Owens; Douglas W
• Assistant Examiner(s): A, MINH D
• Application Number:
  US11/401,062
• Publication Number:
  US 20070236152A1
• Time in Patent Office: 1,317 Days
• Field of Search: 315/307, 315/291, 315/112, 315/117, 315/118, 315/209.R, 315/246
• US Class Current: 315/112
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 5/293 using semiconductor devices only
• CPC Class Codes: H03K 2217/0009 AC switches, i.e. delivering AC power to a load
• CPC Class Codes: H05B 39/048 with reverse phase control
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A load control device for controlling the amount of power delivered to an electrical load from a source of AC power comprises a controllably conductive device and a variable gate drive circuit. The controllably conductive device is coupled in series electrical connection between the source and the electrical load to control the amount of power delivered to the load. The variable drive circuit is thermally coupled to the controllably conductive device and provides a continuously variable impedance in series with the control input of the controllably conductive device. The impedance of the variable drive circuit is operable to decrease as a temperature of the controllably conductive device increases and vice versa. Preferably, the variable drive circuit comprises an NTC thermistor. Accordingly, the switching times of the controllably conductive device, i.e., the times when the controllably conductive device is changing between the conductive and non-conductive states, remain constant, or alternatively decrease, as the temperature of the controllably conductive device increases.

Claims

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

a first controllably conductive device operable to conduct current from the source to the load during a positive half-cycle of the AC power source, the first controllably conductive device having a first control input to render the first controllably conductive device conductive and non-conductive;

a second controllably conductive device operable to conduct current from the source to the load during a negative half-cycle of the AC power source, the second controllably conductive device having a second control input to render the second controllably conductive device conductive and non-conductive;

a control circuit operable to independently render the first and second controllably conductive devices conductive and non-conductive;

a first variable drive circuit coupled in series electrical connection with the first control input of the first controllably conductive device to provide a first impedance in series with the first control input; and

a second variable drive circuit coupled in series electrical connection with the second control input of the second controllably conductive device to provide a second impedance in series with the second control input;

wherein the first impedance of the first variable drive circuit is operable to change substantially only in response to a first temperature of the first controllably conductive device and the second impedance of the second variable drive circuit is operable to change substantially only in response to a second temperature of the second controllably conductive device.

2. The load control device of claim 1, wherein the first variable drive circuit is operable to decrease the first impedance as the first temperature of the first controllably conductive device increases and operable to increase as the first temperature of the first controllably conductive device decreases;

and

wherein the second variable drive circuit is operable to decrease the second impedance as the second temperature of the second controllably conductive device increases and operable to increase as the second temperature of the second controllably conductive device decreases.

3. The load control device of claim 2, wherein the first and second variable drive circuits are each operable to provide a continuously variable impedance in series with the control input of the respective controllably conductive device.

4. The load control device of claim 3, wherein the first and second variable drive circuits are thermally coupled to the first and second controllably conductive devices, respectively.

5. The load control device of claim 4, wherein each variable drive circuit comprises a thermistor.

6. The load control device of claim 5, wherein the thermistor of each variable gate drive circuit comprises an NTC thermistor.

7. The load control device of claim 6, wherein each variable drive circuit further comprises a first resistor coupled in series electrical connection with the control input of the controllably conductive device and in parallel electrical connection with the NTC thermistor.

8. The load control device of claim 7, wherein each variable drive circuit further comprises a second resistor coupled in series electrical connection with the NTC thermistor;

wherein the series combination of the second resistor and the NTC thermistor is coupled in parallel electrical connection with the first resistor.

9. The load control device of claim 3, wherein each controllably conductive device comprises a semiconductor switch.

10. The load control device of claim 9, wherein the first controllably conductive device comprises a first FET and the second controllably conductive device comprises a second FET, the first and second FETs coupled in anti-series connection.

11. The load control device of claim 10, wherein the first FET and the second FET are independently controlled.

12. The load control device of claim 9, wherein the first controllably conductive device comprises a first IGBT and the second controllably conductive device comprises a second IGBT, the first and second IGBTs coupled in anti-series connection.

13. The load control device of claim 2, wherein each variable drive circuit is operable to provide at least three discrete steps of impedance in series with the control input of the respective controllably conductive device.

14. The load control device of claim 13, wherein each variable drive circuit is operable to provide at least ten discrete steps of impedance in series with the control input of the respective controllably conductive device.

15. The load control device of claim 2, wherein the electrical load comprises a lighting load and each variable drive circuit is operable to provide a plurality of discrete steps of impedance in series with the control input of the respective controllably conductive device such that the number of discrete steps of impedance is great enough to prevent perceptible flicker in the lighting load as the impedance of each of the variable gate drive circuits is changed from one step to the next.

16. A load control device, for controlling the amount of power delivered to an electrical load from a source of AC power, comprising:

a plurality of controllably conductive devices adapted to be coupled in series electrical connection between the source and the electrical load, each controllably conductive device having a control input for rendering the respective controllably conductive device to be conductive or non-conductive, the plurality of controllably conductive devices including two semiconductor switches comprising a first FET and a second FET coupled in anti-series connection; and

a variable drive circuit coupled to the control inputs of the controllably conductive devices to provide a continuously variable impedance in series with the control inputs of the controllably conductive devices, the variable drive circuit thermally coupled to the controllably conductive devices, such that the variable drive circuit is operable to control the impedance in response to temperatures of the controllably conductive devices, the variable drive circuit operable to decrease the impedance as the temperatures of the controllably conductive devices increase and operable to increase the impedance as the temperatures of the controllably conductive devices decrease;

wherein the variable drive circuit comprises an NTC thermistor, a first resistor coupled in series electrical connection with the control inputs of the controllably conductive devices and in parallel electrical connection with the NTC thermistor, and a second resistor coupled in series electrical connection with the NTC thermistor, the series combination of the second resistor and the NTC thermistor coupled in parallel electrical connection with the first resistor, the variable drive circuit directly connected to both of the control inputs of the two semiconductor switches.