Cat-Ear Power Supply Having a Latch Reset Circuit

• US 20090273958A1
• Filed: 05/02/2008
• Published: 11/05/2009
• Est. Priority Date: 05/02/2008
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Baby, Cyril
• Granted Patent: US 7,889,526 B2
• Time in Patent Office: Days
• US Class Current: 363/127
• CPC Class Codes: H02M 7/2176 comprising a passive stage to generate a rectified sinusoidal voltage and a controlled switching element in series between such stage and the output
• CPC Class Codes: H05B 39/08 by shifting phase of trigger voltage applied to gas-filled controlling tubes also in controlled semiconductor devices in converters H02M5/00; with regulation G05F1/44

Abstract

A cat-ear power supply is operable to generate a DC voltage and draws current from an AC power source near the beginning and end of a half-cycle of the AC power source. A controllably conductive switching circuit selectively charges an energy storage capacitor to produce the DC voltage and become conductive to charge the energy storage capacitor near the beginning of the half-cycle of the AC power source. A latch circuit controls the controllably conductive switching circuit to become non-conductive in response to the magnitude of the DC voltage. A switch voltage monitor circuit controls the controllably conductive switching circuit to become non-conductive and resets the latch circuit when the magnitude of a switch voltage across the switching circuit exceeds a predetermined switch voltage threshold. The switching circuit becomes conductive to charge the energy storage capacitor near the end of the half-cycle when the magnitude of the switch voltage drops below the predetermined switch voltage threshold.

Claims

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

an energy storage capacitor;

a controllably conductive switching circuit coupled in series electrical connection with the energy storage capacitor for selectively charging the energy storage capacitor to produce the DC voltage, the controllably conductive switching circuit operable to become conductive to charge the energy storage capacitor near the beginning of a half-cycle of the AC power source;

a latch circuit coupled to the controllably conductive switching circuit, wherein the latch circuit controls the controllably conductive switching circuit to become non-conductive in response to the magnitude of the DC voltage; and

a switch voltage monitor circuit coupled to the controllably conductive switching circuit and the latch circuit, such that the switch voltage monitor circuit controls the controllably conductive switching circuit to become non-conductive when the magnitude of a switch voltage across the controllably conductive switching circuit exceeds a predetermined switch voltage threshold and also resets the latch circuit when the magnitude of the switch voltage exceeds the predetermined switch voltage threshold;

wherein the controllably conductive switching circuit is operable to become conductive to charge the energy storage capacitor near the end of the half-cycle when the magnitude of the switch voltage drops below the predetermined switch voltage threshold.

2. The power supply of claim 1, wherein the switch voltage monitor circuit comprises a switch voltage monitor semiconductor switch coupled across the latch circuit, such that the voltage across the latch circuit is controlled to substantially zero volts when the magnitude of the switch voltage exceeds the predetermined switch voltage threshold.

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

a voltage regulation circuit coupled to the latch circuit and the energy storage capacitor, and operable to cause the latch circuit to control the controllably conductive switching circuit to become non-conductive when the magnitude of the DC voltage exceeds a predetermined peak voltage threshold.

4. The power supply of claim 3, wherein the latch circuit comprises a first latch semiconductor switch coupled in series electrical connection with a first resistor, the switch voltage monitor semiconductor switch of the switch voltage monitor circuit coupled in parallel with the series combination of the first latch semiconductor switch and the first resistor, the first latch semiconductor switch rendered conductive when the magnitude of the DC voltage exceeds the predetermined peak voltage threshold.

5. The power supply of claim 4, wherein the latch circuit comprises a second latch semiconductor switch coupled in series electrical connection with a second resistor, the series combination of the second latch semiconductor switch and the second resistor coupled in parallel with the series combination of the first latch semiconductor switch and the first resistor, the second latch semiconductor switch rendered conductive in response to the first latch semiconductor switch being rendered conductive.

6. The power supply of claim 5, wherein the first latch semiconductor switch comprises a PNP bipolar junction transistor having a base coupled to the junction of the second latch semiconductor switch and the second resistor, the second latch semiconductor switch comprising an NPN bipolar junction transistor having a base coupled to the junction of the first latch semiconductor switch and the first resistor, the base of the first latch semiconductor switch further coupled to the voltage regulation circuit, such that the voltage across the latch circuit is maintained at a substantially low voltage after the magnitude of the DC voltage exceeds a predetermined peak voltage threshold.

7. The power supply of claim 2, wherein the switch voltage monitor semiconductor switch comprises an NPN bipolar junction transistor, the switch voltage monitor circuit further comprising a zener diode adapted to be coupled between the AC power source and a base of the transistor, such that the transistor is rendered conductive when the voltage across the zener diode exceeds a breakover voltage of the zener diode.

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, further comprising:

a voltage regulation circuit coupled to the latch circuit and the energy storage capacitor, and operable to cause the latch circuit to control the controllably conductive switching circuit to become non-conductive when the magnitude of the DC voltage exceeds a predetermined peak voltage threshold.

11. The power supply of claim 1, wherein the load control device is operable to receive an AC line voltage of the AC power source, and the magnitude of the switch voltage is representative of the magnitude of the AC line voltage.

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

a controllably conductive device adapted to be coupled in series electrical connection between the source and the load, the controllably conductive device having a control input for controlling the controllably conductive device between a non-conductive state and a conductive state;

a controller operatively coupled to the control input of the controllably conductive device for controlling the semiconductor switch between the non-conductive state and the conductive state;

a cat-ear power supply for generating a DC voltage, the power supply comprising a controllably conductive switching circuit for selectively charging an energy storage capacitor to produce the DC voltage, the controllably conductive switching circuit operable to become conductive to charge the energy storage capacitor near the beginning of a half-cycle of the AC power source, the power supply further comprising a latch circuit for controlling the controllably conductive switching circuit to become non-conductive in response to the magnitude of the DC voltage, and a switch voltage monitor circuit for controlling the controllably conductive switching circuit to become non-conductive and also resetting the latch circuit when the magnitude of a switchvoltage across the controllably conductive switching circuit exceeds a predetermined switch voltage threshold;

wherein the controllably conductive switching circuit is operable to become conductive to charge the energy storage capacitor near the end of the half-cycle when the magnitude of the switch voltage drops below the predetermined switch voltage threshold.

13. The load control device of claim 12, wherein the controllably conductive device comprises a bidirectional semiconductor switch.

14. The load control device of claim 13, wherein the bidirectional semiconductor switch comprises two FETs in anti-series connection.

15. The load control device of claim 14, wherein the controller is operable to control the FETs using a reverse-phase control dimming technique.

16. The load control device of claim 12, further comprising:

a neutral terminal coupled to the power supply, the neutral connection adapted to be coupled to the neutral side of the AC power source, such that the power supply is operable to draw current from the AC power source through the neutral terminal.

17. The load control device claim 12, wherein the load control device is operable to receive an AC line voltage of the AC power source, and the magnitude of the switch voltage is representative of the magnitude of the AC line voltage.

18. 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 line voltage of the AC power source, the power supply operable to generate a DC voltage, the power supply comprising:

an energy storage capacitor;

a controllably conductive switching circuit coupled in series electrical connection with the energy storage capacitor for selectively charging the energy storage capacitor to produce the DC voltage, the controllably conductive switching circuit operable to become conductive to charge the energy storage capacitor near the beginning of a half-cycle of the AC power source;

a latch circuit coupled to the controllably conductive switching circuit, wherein the latch circuit controls the controllably conductive switching circuit to become non-conductive in response to the magnitude of the DC voltage; and

a switch voltage monitor circuit coupled to the controllably conductive switching circuit, such that the switch voltage monitor circuit controls the controllably conductive switching circuit to become non-conductive when the magnitude of the AC line voltage exceeds a predetermined line voltage threshold;

characterized in that the switch voltage monitor circuit is further coupled to the latch circuit such that the latch circuit is reset when the magnitude of the AC line voltage exceeds the predetermined line voltage threshold, and the controllably conductive switching circuit is operable to become conductive to charge the energy storage capacitor near the end of the half-cycle when the magnitude of the AC line voltage drops below the predetermined line voltage threshold.