Ballast with protection circuit for quickly responding to electrical disturbances

• US 6,720,739 B2
• Filed: 09/17/2001
• Issued: 04/13/2004
• Est. Priority Date: 09/17/2001
• Status: Expired due to Term

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Original Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Inventors: Konopka, John G.
• Primary Examiner(s): Clinger, James
• Assistant Examiner(s): Tran, Chuc
• Application Number:
  US09/953,593
• Publication Number:
  US 20030052621A1
• Time in Patent Office: 939 Days
• Field of Search: 315/225, 315/119, 315/227, 315/307, 315/308, 315/291, 315/127, 315/293, 315/219, 315/209.R, 315/DIG.5, 315/DIG.7
• US Class Current: 315/225
• CPC Class Codes: H05B 41/2851 for protecting the circuit against abnormal operating conditions
• CPC Class Codes: H05B 41/2855 against abnormal lamp operating conditions
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A ballast (10,20) for powering a gas discharge lamp load (30) comprises a protection circuit (300,600) operable to monitor an electrical signal (40) in the ballast and disable the ballast for at least a predetermined period of time in response to a disturbance wherein at least a portion (44) of the electrical signal (40) exhibits a time-rate-of-change that exceeds the time-rate-of-change of the signal during normal operation of the ballast and gas discharge lamp load. Protection circuit (300,600) is capable of disabling the ballast within a response time that is less than twice the period of the electrical signal. In a preferred embodiment that is suitable for ballasts with driven-type inverters, protection circuit (300) comprises a latching device (310) and a triggering circuit (330). In a preferred embodiment that is suitable for ballasts with self-oscillating type inverters, protection circuit (600) comprises a pull-down circuit (640) and a negative voltage source (610).

Claims

1. A ballast for powering a gas discharge lamp load, the ballast comprising a protection circuit operable to:

(i) monitor an electrical signal within the ballast; and

(ii) disable the ballast for at least a predetermined period of time in response to a disturbance wherein at least a portion of the electrical signal exhibits a time-rate-of-change that substantially exceeds the time-rate-of-change of the signal during normal operation of the ballast and gas discharge lamp load, wherein the protection circuit is further operable to disable the ballast within less than 100 microseconds after occurrence of the disturbance.

2. The ballast of claim 1, wherein the protection circuit is operable to disable the ballast in response to at least one of:

disconnection of a lamp from the ballast; and

an arcing condition at an output of the ballast.

3. The ballast of claim 1, wherein:

during normal operation of the ballast and gas discharge lamp load, the electrical signal is a periodic signal having a period; and

the protection circuit is operable to disable the ballast within a response time that is less than twice the period of the electrical signal.

4. The ballast of claim 1, wherein the ballast and protection circuit are further operable such that the ballast is reenabled after the predetermined period of time elapses.

5. The ballast of claim 1, wherein the predetermined period of time is less than one second.

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

an inverter operable to provide a high frequency voltage at an inverter output;

an output circuit coupled to the inverter output and having output connections adapted for connection to the gas discharge lamp load;

a protection circuit coupled to the inverter and the output circuit, wherein the protection circuit is operable to;

(i) monitor a signal within the output circuit; and

(ii) disable the inverter for at least a predetermined period of time in response to a disturbance wherein at least a portion of the signal exhibits a time-rate-of-change that substantially exceeds the time-rate-of-change of the signal during normal operation of the ballast and gas discharge lamp load, wherein;

during normal operation of the ballast and gas discharge lamp load, the high frequency voltage at the inverter output is a substantially periodic signal having a period; and

the protection circuit is operable, in response to a disturbance in the signal within the output circuit, to disable the inverter within a response time that is less than at least one of;

twice the period of the high frequency voltage at the inverter output; and

100 microseconds.

7. The ballast of claim 6, wherein the inverter and protection circuit are operable such that the inverter is reenabled after the predetermined period of time elapses.

8. The ballast of claim 6, wherein the predetermined period of time is less than one second.

9. An electronic ballast, comprising:

an inverter having first and second output terminals, the second output terminal being coupled to circuit ground, the inverter being operable to provide a high frequency voltage between the first and second output terminals;

an output circuit coupled to the output terminals of the inverter, the output circuit comprising;

first and second output connections adapted for connection to a lamp load comprising at least one gas discharge lamp;

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

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

a direct current blocking capacitor coupled between the second output connection and circuit ground;

a protection circuit having an input coupled to the output circuit, and an output coupled to the inverter, the protection circuit being operable to monitor a signal within the output circuit and, in response to occurrence of a disturbance in the signal, to disable the inverter for a predetermined period of time, wherein a disturbance is deemed to have occurred when at least a portion of the signal has a time-rate-of-change that substantially exceeds the time-rate-of-change of the signal during normal operation of the ballast and lamp load, wherein the protection circuit further comprises;

a latching device coupled between the output of the protection circuit and circuit ground, the latching device having a control terminal and being operable to;

(i) turn on and couple the output of the protection circuit to circuit ground in response to a voltage at the control terminal reaching a predetermined triggering voltage; and

(ii) remain on for as long as the amount of current flowing through the latching device from the output of the detection circuit to circuit ground exceeds a predetermined holding current; and

a triggering circuit coupled to the input of the protection circuit, the control terminal of the latching device, and circuit ground, the triggering circuit being operable, in response to a disturbance, to provide sufficient voltage at the control terminal to turn on the latching device.

10. The ballast of claim 9, wherein:

the output circuit further comprises a current-sensing resistor interposed between the resonant capacitor and the circuit ground node; and

the input of the protection circuit is coupled to the current-sensing resistor.

11. The ballast of claim 9, wherein:

the inverter further comprises a pair of inverter switches and a drive circuit coupled to the pair of inverter switches, the drive circuit having a supply input for receiving a direct current (DC) supply voltage, the drive circuit being operable to switch the inverter switches on and off in a substantially complementary manner as long as the DC supply voltage is greater than a predetermined value;

the output of the protection circuit is coupled to the supply input of the drive circuit; and

the protection circuit is operable, in response to a disturbance, to turn the drive circuit off by coupling the supply input of the drive circuit to the circuit ground node for a limited period of time.

12. The ballast of claim 9, wherein:

during normal operation of the ballast and gas discharge lamp load, the high frequency voltage at the inverter output is a substantially periodic signal having a period; and

the triggering circuit is operable, in response to a disturbance, to provide sufficient voltage at the control terminal to turn on the latching device within a response time that is less than at least one of;

twice the period of the high frequency voltage at the inverter output; and

100 microseconds.

13. The ballast of claim 9, wherein the latching device is a silicon-controlled rectifier having an anode coupled to the protection circuit output, a cathode coupled to circuit ground, and a gate terminal, wherein the gate terminal is the control terminal.

14. The ballast of claim 13, wherein the triggering circuit comprises:

a capacitor coupled between the input of the protection circuit and a first node, wherein the first node is coupled to the control terminal of the latching device; and

a resistor coupled between the first node and circuit ground.

15. The ballast of claim 9, wherein the output circuit further comprises:

third and fourth output connections adapted for connection to the at least one gas discharge lamp, wherein the lamp includes;

a first filament coupled to the first and third output connections; and

a second filament coupled to the second and fourth output connections; and

first and second auxiliary windings magnetically coupled to the resonant inductor, wherein;

the first auxiliary winding is coupled between the first and third output connections; and

the second auxiliary winding is coupled between the second and fourth output connections.

16. The ballast of claim 15, wherein the input of the protection circuit is coupled to the fourth output connection.

17. The ballast of claim 15, wherein:

the inverter further comprises a pair of inverter switches and a drive circuit coupled to the pair of inverter switches, the drive circuit having a supply input for receiving a direct current (DC) supply voltage, the drive circuit being operable to switch the inverter switches on and off in a substantially complementary manner as long as the DC supply voltage is greater than a predetermined value;

the output of the protection circuit is coupled to the supply input of the drive circuit; and

the protection circuit is operable, in response to a disturbance, to turn the drive circuit off by coupling the supply input of the drive circuit to circuit ground for a limited period of time.

18. A ballast for powering at least one gas discharge lamp, comprising:

an inverter having a pair of output terminals and operable to provide a high frequency voltage between the inverter output terminals;

an output circuit coupled to the output terminals of the inverter, the output circuit comprising;

output connections adapted for connection to the at least one gas discharge lamp;

a resonant capacitor coupled between the inverter output terminals; and

an output transformer, comprising;

a primary winding coupled between the inverter output terminals;

a secondary winding coupled to the output connections; and

an auxiliary winding coupled to the inverter, the auxiliary winding having a first end and a second end; and

a protection circuit coupled to the inverter and the auxiliary winding of the output transformer, the protection circuit being operable to monitor a voltage signal associated with the output transformer and, in response to occurrence of a disturbance in the voltage signal, to disable the inverter for a predetermined period of time, wherein a disturbance is deemed to have occurred when at least a portion of the voltage signal has a time-rate-of-change that substantially exceeds the time-rate-of-change of the signal during normal operation of the ballast and lamps, wherein the protection circuit includes;

a first input coupled to the first end of the auxiliary winding; and

a second input coupled to the second end of the auxiliary winding.

19. The ballast of claim 18, wherein:

during normal operation of the ballast and gas discharge lamp, the high frequency voltage at the inverter output is a substantially periodic signal having a period; and

the protection circuit is operable, in response to a disturbance in the voltage signal, to disable the inverter within a response time that is less than at least one of;

twice the period of the high frequency voltage between the inverter output terminals; and

100 microseconds.

20. The ballast of claim 18, wherein the inverter and protection circuit are operable such that the inverter is reenabled after the predetermined period of time elapses.

21. The ballast of claim 18, wherein the predetermined period of time is less than one second.

22. The ballast of claim 18, wherein:

the inverter further comprises a pair of inverter switches, each inverter switch having a control input for receiving a control voltage that turns the switch on and off;

the auxiliary winding is coupled to the inverter switches and operable to provide the control voltage;

during normal operation of the ballast and lamp load, the auxiliary winding has a substantially sinusoidal voltage, thereby providing control voltages for switching the inverter switches on and off in a substantially complementary manner; and

the protection circuit is operable, in response to a disturbance, to disable the inverter by forcing the control voltage of at least one of the inverter switches to a negative value, and to maintain the control voltage at a negative value, for a limited period of time.

23. The ballast of claim 22, wherein the inverter is a push-pull type inverter.

24. The ballast of claim 22, wherein the protection circuit further comprises:

a negative voltage source coupled between the second input and circuit ground;

a pull-down circuit coupled to the first and second inputs and the negative voltage source, wherein the pull-down circuit is operable, in response to a disturbance, to couple the first input to the negative voltage source for a limited period of time.

25. The ballast of claim 24, wherein the pull-down circuit comprises:

a latching device coupled between the first input and the negative voltage source, the latching device having an anode, a cathode, and a gate, and being operable to;

(i) turn on and couple the anode to the cathode in response to a voltage between the gate and the cathode reaching a predetermined triggering voltage; and

(ii) remain on for as long as the amount of current flowing through the latching device from the anode to the cathode exceeds a predetermined holding current; and

a triggering circuit coupled to the second input, the gate, and the cathode, the triggering circuit being operable, in response to a disturbance, to provide sufficient voltage between the gate and the cathode to turn on the latching device.

26. The ballast of claim 25, wherein:

during normal operation of the ballast and lamp, the high frequency voltage at the inverter output is a substantially periodic signal having a period; and

the triggering circuit is operable, in response to a disturbance, to provide sufficient voltage between the gate and the cathode to turn on the latching device within a response time that is less than at least one of;

twice the period of the high frequency voltage at the inverter output; and

100 microseconds.

27. The ballast of claim 25, wherein the pull-down circuit further comprises a diode coupled between the first input and the anode of the latching device.

28. The ballast of claim 25, wherein the triggering circuit comprises:

a capacitor coupled between the second input and a first node; and

a resistor coupled between the first node and the cathode of the latching device.

29. The ballast of claim 25, wherein the negative voltage source comprises:

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

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

a capacitor coupled between the third node and circuit ground,

a second diode having an anode coupled to the third node, and a cathode coupled to circuit ground; and

a second resistor coupled between the third node and circuit ground.