| 摘要 |
In a discharge bulb control, a time constant circuit comprised of a capacitor and a resistor is used to determine an electric power to be supplied to a discharge bulb. During a warm-up period of the discharge bulb, the capacitor is charged to produce a voltage which varies, toward a predetermined voltage, with an electric current flowing thereto so that the electric power is increased gradually. After the warm-up control, the time constant for charging the capacitor is reduced to maintain the capacitor voltage at the predetermined voltage. Even with the current leakage occurring in the capacitor after the warm-up control, the electric power is controlled by the predetermined voltage which is not influenced by the current leakage. Thus, the electric power applied to the discharge bulb after the warm-up control can advantageously be maintained at the required level.
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