Electronic Ballast with inverter protection circuit

• US 5,883,473 A
• Filed: 12/03/1997
• Issued: 03/16/1999
• Est. Priority Date: 12/03/1997
• Status: Expired due to Term

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Li, Edward, Sodhi, Sameer
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Lee, Wilson
• Application Number:
  US08/984,444
• Time in Patent Office: 468 Days
• Field of Search: 315/DIG. 5, 315/DIG. 7, 315/225, 315/291, 315/307, 315/219, 315/308, 315/119, 315/209 R, 315/224
• US Class Current: 315/225
• CPC Class Codes: H05B 41/2855 against abnormal lamp operating conditions
• CPC Class Codes: H05B 41/2985 against abnormal lamp operating conditions
• CPC Class Codes: Y10S 315/05 Starting and operating circuit for fluorescent lamp
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

An electronic ballast (10) comprising an AC-to-DC converter (100), an inverter (200), an output circuit (400), a high-voltage detection circuit (500), and a no-load detection suit (600). The inverter (200) includes an inverter control circuit (300) that monitors the lamp(s) via the high-voltage detection circuit (500) and the no-load detection circuit (600), and that terminates inverter switching in response to various lamp-fault conditions such as "diode-mode" behavior. Inverter control circuit (300) also provides for automatic ignition of a replaced lamp and may be economically implemented as a single integrated circuit.

Claims

1. An electronic ballast for powering a gas discharge lamp, comprising:

an AC-to-DC converter having a pair of input connections adapted to receive a source of alternating current, and a pair of output connections;

an inverter, comprising;

first and second input terminals coupled to the output connections of the AC-to-DC converter, wherein the second input terminal is coupled to a circuit ground node;

an inverter output terminal;

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

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

an inverter control circuit, comprising;

a DC supply input;

a first drive output coupled to the first inverter switch;

a second drive output coupled to the second inverter switch;

a high-voltage detect (HVD) input; and

a no-load detect (NLD) input;

a startup circuit coupled between the AC-to-DC converter and the DC supply input of the inverter control circuit, the startup circuit being operable to provide power for initiating operation of the inverter control circuit; and

a bootstrap circuit coupled between the inverter output terminal and the DC supply input of the inverter control circuit, the bootstrap circuit being operable to provide steady-state operating power to the inverter control circuit;

an output circuit, comprising;

a set of output wires comprising first, second, third, and fourth output wires adapted to being coupled to the gas discharge lamp, wherein the first output wire is coupleable to the second output wire through a first filament of the lamp, and the third output wire is coupleable to the fourth output wire through a second filament of the lamp;

a DC blocking capacitor coupled between the inverter output terminal and a first node;

a DC path resistor coupled between the first input terminal of the inverter and the first node;

a resonant inductor coupled between the first node and the first output wire; and

a resonant capacitor coupled between the second and third output wires;

a high-voltage detection circuit coupled between the second output wire and the HVD input of the inverter control circuit;

a no-load detection circuit coupled between the fourth output wire and the NLD input of the inverter control circuit;

wherein the inverter control circuit is operable to;

(a) provide an ignition period following initial application of electrical power to the ballast, wherein, regardless of the signals applied to the NLD and HVD inputs, the inverter switches are switched on and off in a complementary fashion for at least a first predetermined period of time;

(b) continue to provide complementary switching of the first and second inverter switches when the lamp is operating normally;

(c) terminate switching of the inverter switches in response to each of the following conditions;

(i) failure of the lamp to ignite and operate normally within the ignition period;

(ii) removal of the lamp;

(iii) failure of the lamp to conduct current in a substantially normal fashion; and

(iv) opening of at least one filament of the lamp; and

(d) provide a relamping period, wherein complementary switching of the inverter switches is;

(i) automatically resumed for at least a second predetermined period of time following replacement of a defective or failed lamp with a new lamp; and

(ii) terminated in response to failure of the new lamp to ignite and begin operating normally within the relamping period; and

wherein the inverter control circuit further comprises a driver circuit coupled to the first and second drive outputs, the driver circuit having a shutdown input, wherein the driver circuit is operable to provide complementary switching of the inverter switches when a logic "0" is applied to the shutdown input, and to terminate switching of the inverter switches when a logic "1" is applied to the shutdown input.

2. The electronic ballast of claim 1, wherein the inverter control circuit further comprises:

an internal reference source for providing a reference voltage;

a first comparator having a non-inverting input coupled to the HVD input, an inverting input coupled to the internal reference source, and an HVD output, the first comparator being operable to provide at the HVD output;

(i) a logic "1" when the voltage at the HVD input exceeds the reference voltage; and

(ii) a logic "0" when the voltage at the HVD input is less than the reference voltage;

a second comparator having an inverting input coupled to the NLD input, a non-inverting input coupled to the internal reference source, and an NLD output, the no-load comparator being operable to provide at the NLD output;

(i) a logic "0" when the voltage at the NLD input exceeds the reference voltage; and

(ii) a logic "1" when the voltage at the NLD input is less than the reference voltage.

3. The electronic ballast of claim 2, wherein the inverter control circuit further comprises a protection logic circuit operable to receive the HVD and NLD outputs from the first and second comparators and to provide a shutdown signal to the shutdown input of the driver circuit, wherein:

(a) the shutdown signal is a logic "0" in response to each of the following conditions;

(i) during the ignition period following initial application of power to the ballast;

(ii) when the HVD output is a logic "0" and the NLD output is a logic "0"; and

(iii) when the NLD output is a logic "1" and the HVD output changes from a logic "0" to a logic "1"; and

(b) the shutdown signal is a logic "1" in response to each of the following conditions;

(i) when the HVD output is a logic "1"; and

(ii) when the NLD output is a logic "1" and the HVD output is not changing from a logic "0" to a logic "1".

4. The electronic ballast of claim 3, wherein the reference voltage provided by the internal reference source is adjusted in dependence on the shutdown signal, wherein the reference voltage is at a first level when the shutdown signal is a logic "0", and at a second level when the shutdown signal is a logic "1", the second level being less than the first level.

5. The electronic ballast of claim 1, wherein the inverter control circuit is implemented as a single integrated circuit.

6. The electronic ballast of claim 1, wherein the high-voltage detection circuit is operable:

(a) to provide a logic "1" at the HVD input of the inverter control circuit in response to failure of the lamp to conduct current in a substantially normal fashion while both lamp filaments are intact; and

(b) to provide a logic "0" at the HVD input of the inverter control circuit in response to each of the following conditions;

(i) the lamp conducting current in a substantially normal fashion;

(ii) removal of the lamp; and

(iii) at least one lamp filament being open.

7. The electronic ballast of claim 1, wherein the high-voltage detection circuit comprises:

a first resistor coupled between the second output wire and a second node;

a second resistor coupled between the second node and a third node;

a third resistor coupled between the third node and the circuit ground node;

a first diode having an anode coupled to the third node and a cathode coupled to the HVD input of the inverter control circuit;

a first capacitor coupled between the HVD input and the circuit ground node; and

a fourth resistor coupled between the HVD input and the circuit ground node.

8. The electronic ballast of claim 7, wherein the high-voltage detection circuit further comprises:

a second diode having a cathode coupled to the second node and an anode coupled to a fourth node;

a second capacitor coupled between the fourth node and the circuit ground node;

an electronic switch having an emitter lead coupled to the DC supply input of the inverter control circuit, a collector lead, and a base lead;

a fifth resistor coupled between the emitter lead and the base lead of the electronic switch;

a first zener diode having an anode coupled to the fourth node and a cathode coupled to the base lead of the electronic switch; and

a sixth resistor coupled between the collector lead of the electronic switch and the HVD input of the inverter control circuit.

9. The electronic ballast of claim 8, wherein the electronic switch comprises a PNP-type bipolar junction transistor.

10. The electronic ballast of claim 1, wherein the no-load detection circuit is operable:

(a) to provide a logic "1" at the NLD input of the inverter control circuit in response to both lamp filaments being intact; and

(b) to provide a logic "0" at the NLD input of the inverter control circuit in response to each of the following conditions;

(i) removal of the lamp; and

(ii) at least one lamp filament being open.

11. The electronic ballast of claim 1, wherein the no-load detection circuit comprises:

a seventh resistor coupled between the fourth output wire and the circuit ground node;

a third diode having an anode coupled to the fourth output wire and a cathode coupled to the NLD input of the inverter control circuit;

a third capacitor coupled between the NLD input and the circuit ground node; and

an eighth resistor coupled between the NLD input and the circuit ground node.

12. The electronic ballast of claim 11, wherein the no-load detection circuit further comprises a fourth diode having a cathode coupled to the fourth output wire and an anode coupled to the circuit ground node.

13. The electronic ballast of claim 1, wherein the bootstrap circuit comprises:

a fourth capacitor coupled between the inverter output terminal and a fifth node;

a second zener diode having a cathode coupled to the fifth node and an anode coupled to the circuit ground node; and

a fifth diode having an anode coupled to the fifth node and a cathode coupled to the DC supply input of the inverter control circuit.

14. The electronic ballast of claim 1, wherein the AC-to-DC converter comprises:

a full-wave rectifier circuit coupled between the input and output connections of the AC-to-DC converter; and

a bulk capacitor coupled across the output connections of the AC-to-DC converter.

15. The electronic ballast of claim 14, wherein the startup circuit comprises:

a pull-down resistor coupled between the DC supply input of the inverter control circuit and one of the output connections of the AC-to-DC converter; and

a filtering capacitor coupled between the DC supply input and the circuit ground node.

16. An electronic ballast for powering at least two gas discharge lamps, comprising:

an AC-to-DC converter having a pair of input connections adapted to receive a source of alternating current, and a pair of output connections;

an inverter, comprising;

first and second input terminals coupled to the output connections of the AC-to-DC converter, wherein the second input terminal is coupled to a circuit ground node;

an inverter output terminal;

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

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

an inverter control circuit, comprising;

a DC supply input;

a first drive output coupled to the first inverter switch;

a second drive output coupled to the second inverter switch;

a high-voltage detect (HVD) input; and

a no-load detect (NLD) input;

a startup circuit coupled between the AC-to-DC converter and the DC supply input of the inverter control circuit, the startup circuit being operable to provide power for initiating operation of the inverter control circuit; and

a bootstrap circuit coupled between the first node and the DC supply input of the inverter control circuit, the bootstrap circuit being operable to provide steady-state operating power to the inverter control circuit;

an output circuit, comprising;

a first set of output wires comprising first, second, third, and fourth output wires adapted to being coupled to a first gas discharge lamp, wherein the first output wire is coupleable to the second output wire through a first filament of the first lamp, and the third output wire is coupleable to the fourth output wire through a second filament of the first lamp;

a second set of output wires comprising fifth, sixth, seventh, and eighth output wires adapted to being coupled to a second gas discharge lamp, wherein the fifth output wire is coupleable to the sixth output wire through a first filament of the second lamp, and the seventh output wire is coupleable to the eighth output wire through a second filament of the second lamp, the eighth output wire being coupled to the fourth output wire;

a DC blocking capacitor coupled between the inverter output terminal and a first node;

a DC path resistor coupled between the first input terminal and the first node;

a first resonant inductor coupled between the first node and the first output wire;

a second resonant inductor coupled between the first node and the fifth output wire;

a first resonant capacitor coupled between the second and third output wires; and

a second resonant capacitor coupled between the sixth and seventh output wires;

a high-voltage detection circuit coupled between the HVD input of the inverter control circuit and at least the second and sixth output wires;

a no-load detection circuit coupled between the eighth output wire and the NLD input of the inverter control circuit;

wherein the inverter control circuit is operable to;

(a) provide an ignition period following initial application of electrical power to the ballast, wherein, regardless of the signals applied to the NLD and HVD inputs, the inverter switches are switched on and off in a complementary fashion for at least a first predetermined period of time;

(b) continue to provide complementary switching of the inverter switches as long as at least one operational lamp is present with both of its filaments intact and each of the failed lamps has at least one open filament;

(c) terminate switching of the inverter switches in response to each of the following conditions;

(i) all of the lamps failing to ignite and operate normally within the ignition period;

(ii) removal of all of the lamps;

(iii) at least one of the lamps conducting current in a substantially abnormal fashion;

(iv) all of the lamps having at least one open filament; and

(d) provide a relamping period, wherein complementary switching of the inverter switches is automatically resumed for at least a second predetermined period of time following replacement of a defective or failed lamp with a new lamp; and

wherein the inverter control circuit further comprises a driver circuit coupled to the first and second drive outputs, the driver circuit having a shutdown input, wherein the driver circuit is operable to provide complementary switching of the inverter switches when a logic "0" is applied to the shutdown input, and to terminate switching of the inverter switches when a logic "1" is applied to the shutdown input.

17. The electronic ballast of claim 16, wherein the inverter control circuit further comprises:

an internal reference source for providing a reference voltage;

a first comparator having a non-inverting input coupled to the HVD input, an inverting input coupled to the internal reference source, and an HVD output, the first comparator being operable to provide at the HVD output;

(i) a logic "1" when the voltage at the HVD input exceeds the reference voltage; and

(ii) a logic "0" when the voltage at the HVD input is less than the reference voltage;

a second comparator having an inverting input coupled to the NLD input, a non-inverting input coupled to the internal reference source, and an NLD output, the no-load comparator being operable to provide at the NLD output;

(i) a logic "0" when the voltage at the NLD input exceeds the reference voltage; and

(ii) a logic "1" when the voltage at the NLD input is less than the reference voltage.

18. The electronic ballast of claim 17, wherein the inverter control circuit further comprises a protection logic circuit operable to receive the HVD and NLD outputs from the first and second comparators and to provide a shutdown signal to the shutdown input of the driver circuit, wherein:

(a) the shutdown signal is a logic "0" in response to each of the following conditions;

(i) during the ignition period following initial application of power to the ballast;

(ii) the HVD output is a logic "0" and the NLD output is a logic "0"; and

(iii) the HVD output changing from a logic "0" to a logic "1" while the NLD output is a logic "1"; and

(b) the shutdown signal is a logic "1" in response to each of the following conditions;

(i) the HVD output is a logic "1"; and

(ii) the NLD output is a logic "1" and the HVD output is not changing from a logic "0" to a logic "1".

19. The electronic ballast of claim 18, wherein the reference voltage provided by the internal reference source is adjusted in dependence on the shutdown signal, wherein the reference voltage is at a first level when the shutdown signal is a logic "0", and at a second level when the shutdown signal is a logic "1", the second level being less than the first level.

20. The electronic ballast of claim 16, wherein the inverter control circuit is implemented as a single integrated circuit.

21. The electronic ballast of claim 16, wherein the high-voltage detection circuit is operable:

(a) to provide a logic "1" at the HVD input of the inverter control circuit in response to failure of at least one of the lamps to conduct current in a substantially normal fashion while both of its lamp filaments are intact; and

(b) to provide a logic "0" at the HVD input of the inverter control circuit in response to each of the following conditions;

(i) all of the lamps conducting current in a substantially normal fashion;

(ii) removal of all lamps;

(iii) each lamp having at least one open filament; and

(iv) each of the failed lamps having at least one open filament.

22. The electronic ballast of claim 16, wherein the high-voltage detection circuit comprises:

a first resistor coupled between the second output wire and a second node;

a ninth resistor coupled between the sixth output wire and the second node;

a second resistor coupled between the second node and a third node;

a third resistor coupled between the third node and the circuit ground node;

a first diode having an anode coupled to the third node and a cathode coupled to the HVD input of the inverter control circuit;

a first capacitor coupled between the HVD input and the circuit ground node; and

a fourth resistor coupled between the HVD input and the circuit ground node.

23. The electronic ballast of claim 22, wherein the high-voltage detection circuit further comprises:

a second diode having a cathode coupled to the second node and an anode coupled to a fourth node;

a second capacitor coupled between the fourth node and the circuit ground node;

an electronic switch having an emitter lead coupled to the DC supply input of the inverter control circuit, a collector lead, and a base lead;

a fifth resistor coupled between the emitter lead and the base lead of the electronic switch;

a first zener diode having an anode coupled to the fourth node and a cathode coupled to the base lead of the electronic switch; and

a sixth resistor coupled between the collector lead of the electronic switch and the HVD input of the inverter control circuit.

24. The electronic ballast of claim 23, wherein the electronic switch comprises a PNP-type bipolar junction transistor.

25. The electronic ballast of claim 16, wherein the no-load detection circuit is operable:

(a) to provide a logic "1" at the NLD input of the inverter control circuit in response to at least one of the lamps having both filaments intact; and

(b) to provide a logic "0" at the NLD input of the inverter control circuit in response to each of the following conditions;

(i) removal of all lamps; and

(ii) each lamp having at least one open filament.

26. The electronic ballast of claim 16, wherein the no-load detection circuit comprises:

a seventh resistor coupled between the fourth output wire and the circuit ground node;

a third diode having an anode coupled to the fourth output wire and a cathode coupled to the NLD input of the inverter control circuit;

a third capacitor coupled between the NLD input and the circuit ground node; and

an eighth resistor coupled between the NLD input and the circuit ground node.

27. The electronic ballast of claim 26, wherein the no-load detection circuit further comprises a fourth diode having a cathode coupled to the fourth output wire and an anode coupled to the circuit ground node.

28. The electronic ballast of claim 16, wherein the bootstrap circuit comprises:

a fourth capacitor coupled between the inverter output terminal and a fifth node;

a second zener diode having a cathode coupled to the fifth node and an anode coupled to the circuit ground node; and

a fifth diode having an anode coupled to the fifth node and a cathode coupled to the DC supply input of the inverter control circuit.

29. The electronic ballast of claim 16, wherein the AC-to-DC converter comprises:

a full-wave rectifier circuit coupled between the input and output connections of the AC-to-DC converter; and

a bulk capacitor coupled across the output connections of the AC-to-DC converter.

30. The electronic ballast of claim 29, wherein the startup circuit comprises:

a pull-down resistor coupled between the DC supply input of the inverter control circuit and one of the output connections of the AC-to-DC converter; and

a filtering capacitor coupled between the DC supply input and the circuit ground node.

31. An electronic ballast for powering at least two fluorescent lamps, comprising:

an AC-to-DC converter having a pair of input connections adapted to receive a source of alternating current, and a pair of output connections;

an inverter, comprising;

first and second input terminals coupled to the output connections of the AC-to-DC converter, wherein the second input terminal is coupled to a circuit ground node;

an inverter output terminal;

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

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

an inverter control circuit, comprising;

a DC supply input;

a first drive output coupled to the first inverter switch;

a second drive output coupled to the second inverter switch;

a high-voltage detect (HVD) input; and

a no-load detect (NLD) input;

a startup circuit coupled between the AC-to-DC converter and the DC supply input of the inverter control circuit, the startup circuit being operable to provide power for initiating operation of the inverter control circuit; and

a bootstrap circuit coupled between the first node and the DC supply input of the inverter control circuit, the bootstrap circuit being operable to provide steady-state operating power to the inverter control circuit;

an output circuit, comprising;

a first set of output wires comprising first, second, third, and fourth output wires adapted to being coupled to a first fluorescent lamp, wherein the first output wire is coupleable to the second output wire through a first filament of the first lamp, and the third output wire is coupleable to the fourth output wire through a second filament of the first lamp;

a second set of output wires comprising fifth, sixth, seventh, and eighth output wires adapted to being coupled to a second fluorescent lamp, wherein the fifth output wire is coupleable to the sixth output wire through a first filament of the second lamp, and the seventh output wire is coupleable to the eighth output wire through a second filament of the second lamp, the eighth output wire being coupled to the fourth output wire;

a DC blocking capacitor coupled between the inverter output terminal and a first node;

a DC path resistor coupled between the first input terminal of the inverter and the first node;

a first resonant inductor coupled between the first node and the first output wire;

a second resonant inductor coupled between the first node and the fifth output wire;

a first resonant capacitor coupled between the second and third output wires; and

a second resonant capacitor coupled between the sixth and seventh output wires;

a high-voltage detection circuit coupled between the HVD input of the inverter control circuit and at least the second and sixth output wires;

a no-load detection circuit coupled between the eighth output wire and the NLD input of the inverter control circuit; and

wherein the inverter control circuit further comprises;

a driver circuit coupled to the first and second drive outputs, the driver circuit having a shutdown input, wherein the driver circuit is operable to provide complementary switching of the inverter switches when a logic "0" is applied to the shutdown input, and to terminate switching of the inverter switches when a logic "1" is applied to the shutdown input;

an internal reference source for providing a reference voltage that is adjusted in dependence on the shutdown signal, wherein the reference voltage is at a first level when the shutdown signal is a logic "0", and at a second level when the shutdown signal is a logic "1", the second level being less than the first level;

a first comparator having a non-inverting input coupled to the HVD input, an inverting input coupled to the internal reference source, and an HVD output;

a second comparator having an inverting input coupled to the NLD input, a non-inverting input coupled to the internal reference source, and an NLD output; and

a protection logic circuit operable to receive the HVD and NLD outputs from the first and second comparators and to provide a shutdown signal to the shutdown input of the driver circuit, wherein;

(a) the shutdown signal is a logic "0" in response to each of the following conditions;

(i) during an ignition period following initial application of power to the ballast;

(ii) at least one operational lamp is present with both of its filaments intact, and each of the failed lamps has at least one open filament; and

(iii) during a relamping period following replacement of a defective or failed lamp with a new lamp; and

(b) the shutdown signal is a logic "1" in response to each of the following conditions;

(i) all of the lamps failing to ignite and operate normally within the ignition period;

(ii) removal of all of the lamps;

(iii) at least one of the lamps conducting current in a substantially abnormal fashion; and

(iv) each of the lamps having at least one open filament.