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Electronic ballast for high-intensity discharge lamp

  • US 6,124,681 A
  • Filed: 04/12/1999
  • Issued: 09/26/2000
  • Est. Priority Date: 03/09/1999
  • Status: Expired due to Fees
First Claim
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1. An electronic ballast for a high-intensity discharge (HID) lamp, comprising:

  • a power source converting circuit for producing a rectified voltage by rectifying a conventional alternating current (AC) voltage, for providing a start voltage by transforming the rectified voltage, and for converting the rectified voltage into a boosted direct current (DC) voltage whose level is higher than a peak of the rectified voltage and which has a corrected high power-factor by high-frequency switching the rectified voltage; and

    a high-frequency driving circuit, initiating an operation thereof by the start voltage, for producing a charge voltage by using the boosted DC voltage, for flowing a discharge current due to the charge voltage by alternately executing a high-frequency switching operation, and for providing a driving power to the HID lamp while generating a resonance with an energy transferred by the discharge current,wherein the high-frequency driving circuit comprises a charging section for producing the charge voltage by using the boosted DC voltage;

    a half-bridge switching section for flowing the discharge current by discharging the charge voltage in a way of half-bridge through a pair of switching devices which are alternately executing the high-frequency switching operation and for enhancing amounts of currents flowing through the pair of the switching devices by transformers provided to each of the switching devices, whereby an amount of the discharge current increases; and

    a lamp driving section for providing the driving power to the HID lamp while generating the resonance with the energy transferred by the discharge current,wherein the charging section includes first and second capacitors which are connected serially with each other and have an identical capacitance, andwherein the half-bridge section comprises first and second switching sections and a first transformer section connected between the first switching section and the second switching section for providing base driving currents to both first and second switching sections by means of a mutual induction;

    wherein the first switching section comprises a first bipolar transistor with a grounded emitter that includes a first free-whirling path and provides a discharging path for the first capacitor when the first bipolar transistor is turned on, a start capacitor for charging the start voltage, a DIAC for providing a charge voltage of the start capacitor as a base current of the first bipolar transistor so as to initially turn on the first bipolar transistor, and a second transformer section connected between a collector and a base of the first bipolar transistor for enhancing the base driving current of the first bipolar transistor based on a variation of a collector current of the first bipolar transistor; and

    wherein the second switching section comprises a second bipolar transistor with a collector connected to the second capacitor that includes a second free-whirling path and provides a discharging path for the second capacitor when the second bipolar transistor is turned on, and a third transformer section connected between an emitter and a base of the second bipolar transistor for enhancing the base driving current of the second bipolar transistor based on a variation of an emitter current of the second bipolar transistor.

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