Ballast with protection circuit for preventing inverter startup during an output ground-fault condition

• US 6,657,400 B2
• Filed: 07/19/2002
• Issued: 12/02/2003
• Est. Priority Date: 09/28/2001
• Status: Expired due to Fees

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Original Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Inventors: Konopka, John G., Sodhi, Sameer, Prasad, Himamshu V.
• Primary Examiner(s): Vu, David
• Application Number:
  US10/198,878
• Publication Number:
  US 20030062850A1
• Time in Patent Office: 501 Days
• Field of Search: 315/224, 315/244, 315/DIG.5, 315/DIG.7
• US Class Current: 315/224
• CPC Class Codes: H05B 41/2851 for protecting the circuit against abnormal operating conditions
• CPC Class Codes: Y10S 315/05 Starting and operating circuit for fluorescent lamp

Abstract

A ballast (10) for powering a gas discharge lamp load includes an inverter (200) and a protection circuit (400) for preventing start up of the inverter (200) in response to a ground fault condition wherein one or more of the ballast output connections (302,306) is coupled to earth ground.

Claims

1. A ballast for powering a gas discharge lamp load, comprising:

a circuit ground having a nonzero average voltage with respect to earth ground;

an inverter having a DC voltage supply and an inverter output, wherein the inverter is operable to commence operation when a voltage provided by the DC voltage supply reaches a predetermined start up threshold;

first and second output connections adapted for connection to the gas discharge lamp load;

a protection circuit coupled to the DC voltage supply of the inverter, the circuit ground, and one of;

(i) the inverter output; and

(ii) the first output connection, wherein the protection circuit is operable, in response to a fault wherein the first output connection is coupled to earth ground prior to start up of the inverter, to prevent start up of the inverter by preventing the voltage provided by the DC voltage supply from reaching the predetermined start up threshold.

2. The ballast of claim 1, wherein the protection circuit prevents start up of the inverter by coupling the DC voltage supply to the circuit ground.

3. The ballast of claim 1, wherein the protection circuit comprises:

an input coupled to one of;

(i) the inverter output; and

(ii) the first output connection;

an output coupled to the DC voltage supply of the inverter;

a first resistor coupled between the input and a first node;

a second resistor coupled between the first node and the circuit ground;

an electronic switch having a collector, a base coupled to the first node, and an emitter coupled to the circuit ground; and

a third resistor coupled between the output and the collector of the electronic switch.

4. The ballast of claim 1, wherein the protection circuit is operable to prevent start up of the inverter when the first output connection is coupled to earth ground via an impedance of less than about 100,000 ohms.

5. The ballast of claim 1, wherein:

the protection circuit is further coupled to the second output connection; and

the protection circuit is further operable, in response to a fault wherein the second output connection is coupled to earth ground prior to start up of the inverter, to prevent start up of the inverter by preventing the voltage provided by the DC voltage supply from reaching the predetermined start up threshold.

6. The ballast of claim 5, wherein the protection circuit prevents start up of the inverter by coupling the DC voltage supply to the circuit ground.

7. The ballast of claim 5, wherein the protection circuit comprises:

a first input coupled to one of;

(i) the inverter output; and

(ii) the first output connection;

a second input coupled to the second output connection;

an output coupled to the DC voltage supply of the inverter;

a first resistor coupled between the first input and a first node;

a second resistor coupled between the first node and the circuit ground;

an electronic switch having a collector, a base coupled to the first node, and an emitter coupled to the circuit ground;

a third resistor coupled between the output and the collector of the electronic switch; and

a fourth resistor coupled between the second input and the first node.

8. The ballast of claim 5, wherein the protection circuit is operable to prevent start up of the inverter when at least one of the first and second output connections is coupled to earth ground via an impedance of less than about 100,000 ohms.

9. The ballast of claim 5, wherein:

the ballast further comprises a third output connection adapted for connection to the gas discharge lamp load;

the protection circuit is further coupled to the third output connection; and

the protection circuit is further operable, in response to a fault wherein the third output connection is coupled to earth ground prior to start up of the inverter, to prevent start up of the inverter by preventing the voltage provided by the DC voltage supply from reaching the predetermined start up threshold.

10. The ballast of claim 9, wherein the protection circuit prevents start up of the inverter by coupling the DC voltage supply to the circuit ground.

11. The ballast of claim 9, wherein the protection circuit comprises:

a first input coupled to one of;

(i) the inverter output; and

(ii) the first output connection;

a second input coupled to the second output connection;

a third input coupled to the third output connection;

an output coupled to the DC voltage supply of the inverter;

a first resistor coupled between the first input and a first node;

a second resistor coupled between the first node and the circuit ground;

an electronic switch having a collector, a base coupled to the first node, and an emitter coupled to the circuit ground;

a third resistor coupled between the output and the collector of the electronic switch;

a fourth resistor coupled between the second input and the first node; and

a fifth resistor coupled between the third input and the first node.

12. The ballast of claim 9, wherein the protection circuit is operable to prevent start up of the inverter when at least one of the first, second, and third output connections is coupled to earth ground via an impedance of less than about 100,000 ohms.

13. The ballast of claim 1, wherein the ballast further comprises an output circuit, comprising:

a resonant inductor coupled between the inverter output and the first output connection;

a resonant capacitor coupled between the first output connection and the circuit ground; and

a direct current (DC) blocking capacitor coupled between the second output connection and the circuit ground.

14. The ballast of claim 1, further comprising a full-wave rectifier circuit, comprising:

first and second input terminals adapted to receive a source of alternating current, wherein the second input terminal is at the same electrical potential as earth ground; and

first and second output terminals coupled to the inverter, wherein the second output terminal is coupled to the circuit ground.

15. The ballast of claim 14, wherein the DC voltage supply includes a start up resistor coupled to a source of full-wave rectified alternating current.

16. The ballast of claim 14, wherein the DC voltage supply includes a start up resistor coupled to the first input terminal of the inverter.

17. The ballast of claim 14, wherein the DC voltage supply includes a start up resistor coupled to a source of half-wave rectified alternating current.

18. The ballast of claim 14, wherein the DC voltage supply includes a start up resistor coupled to the second input terminal of the full-wave rectifier circuit.

19. The ballast of claim 14, wherein the rectifier circuit is operable to provide a half-wave rectified AC voltage between the second output terminal and earth ground.

20. A ballast for powering a gas discharge lamp load, comprising:

a full-wave rectifier circuit, comprising;

first and second input terminals adapted to receive a conventional source of alternating current (AC); and

first and second output terminals, wherein;

the second output terminal is coupled to a circuit ground node; and

a half-wave rectified AC voltage is present between the circuit ground node and earth ground;

an inverter, comprising;

first and second input terminals coupled to the first and second output terminals of the rectifier circuit;

an inverter output;

a first inverter switch coupled between the first input terminal and the inverter output;

a second inverter switch coupled between the inverter output and the circuit ground node;

a driver circuit coupled to the first and second inverter switches and operable to commutate the inverter switches in a substantially complementary fashion, the driver circuit including a DC supply input and operable to commence commutation of the inverter switches when a voltage at the DC supply input exceeds a predetermined start up threshold; and

a DC supply circuit coupled to, and operable to provide the voltage at, the DC supply input of the driver circuit;

an output circuit coupled to the inverter output, the output circuit including first and second output connections adapted for connection to the gas discharge lamp load; and

a protection circuit, comprising;

a first input coupled to one of;

(i) the inverter output; and

(ii) the first output connection;

an output coupled to the DC supply input of the driver circuit;

a first resistor coupled between the input and a first node;

a second resistor coupled between the first node and the circuit ground;

an electronic switch having a collector, a base coupled to the first node, and an emitter coupled to the circuit ground; and

a third resistor coupled between the output and the collector of the electronic switch.

21. The ballast of claim 20, wherein the protection circuit further comprises:

a second input coupled to the second output connection; and

a fourth resistor coupled between the second input and the first node.

22. The ballast of claim 21, wherein:

the output circuit further comprises a third output connection adapted for connection to the gas discharge lamp load; and

the protection circuit further comprises;

a third input coupled to the third output connection; and

a fifth resistor coupled between the third input and the first node.

23. The ballast of claim 20, wherein the DC voltage supply includes a start up resistor coupled to one of:

(i) the first output terminal of the full-wave rectifier circuit;

(ii) the first input terminal of the inverter; and

(iii) the second input terminal of the full-wave rectifier circuit.

24. A ballast for powering a gas discharge lamp load, comprising:

a full-wave rectifier circuit, comprising;

first and second input terminals adapted to receive a conventional source of alternating current (AC); and

first and second output terminals, wherein;

the second output terminal is coupled to a circuit ground node; and

a half-wave rectified AC voltage is present between the circuit ground node and earth ground;

an inverter, comprising;

first and second input terminals coupled to the first and second output terminals of the rectifier circuit;

first and second output terminals adapted for connection to the gas discharge lamp load;

a first inverter switch coupled between the first input terminal and the second output terminal;

a second inverter switch coupled between the second output terminal and the circuit ground node;

a third inverter switch coupled between the first input terminal and the first output terminal;

a fourth inverter switch coupled between the first output terminal and the circuit ground node;

a driver circuit coupled to the first, second, third, and fourth inverter switches and operable to commutate the inverter switches, the driver circuit including a DC supply input and operable to commence commutation of the inverter switches when a voltage at the DC supply input exceeds a predetermined start up threshold; and

a DC supply circuit coupled to, and operable to provide the voltage at, the DC supply input of the driver circuit;

a protection circuit, comprising;

a first input coupled to the first output terminal of the inverter;

an output coupled to the DC supply input of the driver circuit;

a first resistor coupled between the input and a first node;

a second resistor coupled between the first node and the circuit ground;

an electronic switch having a collector, a base coupled to the first node, and an emitter coupled to the circuit ground; and

a third resistor coupled between the output and the collector of the electronic switch.

25. The ballast of claim 24, wherein the protection circuit further comprises:

a second input coupled to the second output terminal of the inverter; and

a fourth resistor coupled between the second input and the first node.

26. The ballast of claim 24, wherein the DC voltage supply includes a start up resistor coupled to one of:

(i) the first output terminal of the full-wave rectifier circuit;

(ii) the first input terminal of the inverter; and

(iii) the second input terminal of the full-wave rectifier circuit.