Claims
- 1. An electronic ballast for driving a hot cathode discharge lamp, comprising:
- a DC voltage source;
- a chopper comprising chopper switching means which is connected in series with an inductor across said DC voltage, said switching means being driven to turn on and off for providing a periodically interrupted voltage which is smoothed by a capacitor to produce a smoothed DC voltage as a chopper output;
- an inverter comprising inverter switching means which is coupled to said chopper output to produce therefrom a high frequency AC voltage as an inverter output to be applied to cathodes of said discharge lamp;
- an inverter controller which allows said inverter to operate selectively in a normal mode of providing said inverter output of a first level and in a limited mode of providing said inverter output of a second level which is substantially constant and which is lower than said first level and is determined to give a preheating current to said cathodes; and
- delay means for delaying the start-up of said inverter from the start-up of the chopper in such a manner as to enable said inverter to operate only after said chopper output increases to a predetermined level, said delay means initiating said inverter to operate in the limited mode before the chopper output reaches a steady state level,;
- wherein:
- said inverter controller controls said inverter to operate in said limited mode after the start-up of said inverter for a predetermined period to preheat said discharge lamp after which said inverter controller controls said inverter to operate in said normal operation mode for lighting said discharge lamp,
- said inverter controller controls said inverter to switch from said limited mode to said normal mode only after said chopper output reaches said steady state level, and
- said inverter provides said inverter output of said first level in said normal mode from said chopper output which is boosted to a steady level.
- 2. An electronic ballast as set forth in claim 1, wherein said inverter comprises a resonant circuit which provides a resonance voltage as said inverter output to said discharge lamp, and said inverter switching means capable of varying a frequency of said inverter output over a range including a resonance frequency of said resonant circuit, said inverter controller operating in said normal operation mode for producing said inverter output of a first frequency around said resonance frequency and operating in said limited operation mode for producing said inverter output of a second frequency higher than said first frequency.
- 3. An electronic ballast as set forth in claim 1, wherein said delay means provides a start-up signal to said inverter controller for initiating said limited operation mode at a timing dependent upon an ambient temperature such that the limited operation mode is initiated earlier as said ambient temperature becomes lower.
- 4. An electronic ballast as set forth in claim 3, further including a timer which starts counting a predetermined time duration upon said chopper output reaching the steady state level, said time producing an end signal upon termination of said time duration for switching said inverter from said limited operation mode to said normal operation mode such that said normal operation mode is initiated irrespective of the ambient temperature.
- 5. An electronic ballast as set forth in claim 3, wherein said delay means comprises a thermistor of positive temperature coefficient and a capacitor which are connected across the chopper output to charge said capacitor up to a threshold level at differing rates depending upon ambient temperature, said capacitor energizing said inverter controller to enable said inverter to operate in said limited operation mode upon charged up to said threshold level.
- 6. An electronic ballast as set forth in claim 1, wherein said inverter controller includes a voltage detector for said chopper output, said inverter controller including a timer which counts a predetermined time period after said chopper output is detected by said voltage detector to increase to a predetermined level and which issues a stop signal at the end of said time period to switch said inverter controller for operating said inverter in from the limited mode to said normal mode.
- 7. An electronic ballast as set forth in claim 1, wherein said delay means comprises a voltage detector for said chopper output and provides a pre-heating start signal when said chopper output reaches a predetermined level selected to be lower than said steady state level and provides a pre-heating end signal after said chopper output reaches said steady state level, said inverter controller causing said inverter to operate in said limited mode in response to said pre-heating start signal and allowing said inverter to operate in said normal mode in response to said pre-heating end signal.
- 8. An electronic ballast as set forth in claim 1, wherein said delay means comprises a secondary winding coupled to said inductor of said chopper, said secondary winding being connected through a resistor to a capacitor for charging said capacitor by a voltage induced at said secondary winding in response to the start-up of said chopper, said capacitor providing an operating voltage to said inverter controller such that said inverter controller is enabled to operate said inverter in said limited mode in a delayed manner after the start-up of said chopper.
- 9. An electronic ballast as set forth in claim 1, further including a dummy load which is connected to the chopper output in parallel with said inverter.
- 10. An electronic ballast as set forth in claim 9, further including switch means which disconnects said dummy load from said chopper in response to said chopper output reaching said steady state level.
- 11. An electronic ballast as set forth in claim 9, wherein said dummy load is a heater disposed around said discharge lamp for heating said cathodes.
- 12. An electronic ballast as set forth in claim 10, wherein said switch means is actuated by timer means to disconnect said dummy load after a predetermined time period which is selected to be not less than a time period required for said chopper to produce said steady state chopper output from the start-up of said chopper.
- 13. An electronic ballast as set forth in claim 1, wherein said inductor of said chopper includes a pair of secondary windings which produce induced voltages to be fed respectively to said cathodes for preheating said cathodes.
- 14. An electronic ballast as set forth in claim 13, further including switch means which disconnects said secondary windings from said cathodes in response to the chopper output reaching the steady state level.
Priority Claims (1)
Number |
Date |
Country |
Kind |
5-004557 |
Jan 1993 |
JPX |
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RELATED PATENT APPLICATIONS
This is a continuation of U.S. patent application Ser. No. 08/105,539, filed Aug. 12, 1993.
US Referenced Citations (7)
Continuations (1)
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Number |
Date |
Country |
Parent |
105539 |
Aug 1993 |
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