Claims
- 1. An electronic ballast for a gas discharge lamp, said ballast comprising:
- a series resonant, parallel loaded, half-bridge inverter for producing a high frequency pulses from direct current;
- said inverter including a half-bridge capacitor for shifting the level of said pulses to produce alternating current;
- wherein a first DC voltage occurs across said half-bridge capacitor during normal operation and a second DC voltage occurs across said half-bridge capacitor when no lamp is attached to the ballast, said first DC voltage being greater than said second DC voltage; and
- a control circuit coupled to said half-bridge capacitor for sensing the DC voltage across said half-bridge capacitor and for turning off said inverter when said second DC voltage occurs.
- 2. The ballast as set forth in claim 1 wherein said inverter includes an inductor and a resonant capacitor connected in series with said half-bridge capacitor.
- 3. The ballast as set forth in claim 1 wherein said inverter includes
- a first output terminal;
- a second output terminal;
- an inductor and a resonant capacitor connected in a series circuit;
- wherein said resonant capacitor is coupled between said first output terminal and electrical ground and wherein said half-bridge capacitor is coupled between said second output terminal and electrical ground.
- 4. The ballast as set forth in claim 1 and further including
- boost circuit having a high voltage voltage output and a low voltage output; and
- wherein said control circuit is powered by said low voltage output from said boost circuit.
- 5. The ballast as set forth in claim 4 wherein said control circuit includes:
- a first timer circuit for defining a first period during which said inverter is on;
- a second timer circuit for defining a second period during which said inverter remains off after said second DC voltage occurs;
- wherein said first timer circuit and said second timer circuit are operated in cascade and said first period and said second period are consecutive.
- 6. The ballast as set forth in claim 5 wherein said control circuit includes:
- a shut-off timer for turning off said ballast a predetermined period after power is applied to said inverter; and
- a resistive current path from said half-bridge capacitor to said shut-off timer for resetting said shut-off timer when said first DC voltage is present.
- 7. The ballast as set forth in claim 6 wherein shut-off timer is coupled to said second timer circuit and initiates said second period.
- 8. The ballast as set forth in claim 1 wherein said control circuit includes:
- a shut-off timer for turning off said ballast a predetermined period after power is applied to said inverter; and
- a resistive current path from said half-bridge capacitor to said shut-off timer for resetting said shut-off timer when said first Dc voltage is present.
- 9. The ballast as set forth in claim 8 wherein said shut-off timer includes a capacitor charged by opposing currents and the net voltage across said capacitor determines whether or not said ballast is turned off.
- 10. An electronic ballast for a gas discharge lamp, said ballast comprising:
- an AC input circuit for receiving alternating current from a power line and producing a direct current;
- an inverter coupled to said AC input circuit and having a first output terminal and a second output terminal, said inverter converting direct current into high frequency pulses;
- a capacitor coupled to one of said output terminals for shifting the level of said pulses to produce alternating current at said first output terminal and at said second output terminal, wherein there is a high DC voltage across said capacitor when a lamp is connected to said output terminals and is operating normally, otherwise there is a low DC voltage across said capacitor; and
- a control circuit coupled to said inverter and to said capacitor for sensing the DC voltage across said capacitor and for reducing said high frequency alternating current when the voltage across said capacitor is low.
- 11. The ballast as set forth in claim 10 wherein said inverter includes an inductor and a resonant capacitor connected in a series circuit and wherein said resonant capacitor is coupled to said first output terminal and said second output terminal.
- 12. The ballast as set forth in claim 10 wherein said inverter includes an inductor and a resonant capacitor connected in a series circuit and wherein said resonant capacitor is coupled to said first output terminal and to electrical ground.
- 13. The ballast as set forth in claim 10 wherein said control circuit includes:
- a first timer circuit for defining a first period during which said lamp is warmed;
- a second timer circuit for defining a second period during which said high frequency alternating current is reduced after a fault is detected;
- wherein said first timer circuit and said second timer circuit are connected in cascade and said first period and said second period are consecutive.
- 14. The ballast as set forth in claim 13 wherein said control circuit includes:
- a shut-off timer for reducing said high frequency alternating current a predetermined time after power is applied to said AC input circuit; and
- a resistive current path from said second output terminal to said shut-off timer for resetting said timer when said high voltage is present.
- 15. The ballast as set forth in claim 14 wherein shut-off timer is coupled to said second timer circuit and initiates said second period.
- 16. The ballast as set forth in claim 10 wherein said control circuit includes:
- a shut-off timer for reducing said said high frequency alternating current a predetermined time after power is applied to said AC input circuit; and
- a resistive current path from said second output terminal to said shut-off timer for resetting said timer when said high voltage is present.
- 17. The ballast as set forth in claim 16 wherein said shut-off timer includes a timing capacitor charged by opposing currents and the net voltage across said timing capacitor determines whether or not said said high frequency alternating current is reduced.
Parent Case Info
This application is a continuation of prior application Ser. No. 08/216,649 filed Mar. 22, 1994, now abandoned.
US Referenced Citations (16)
Foreign Referenced Citations (1)
Number |
Date |
Country |
8600851 |
Nov 1986 |
WOX |
Continuations (1)
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Number |
Date |
Country |
Parent |
216649 |
Mar 1994 |
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