| 摘要 |
PROBLEM TO BE SOLVED: To high accurately control a current flowing in a load, when power source voltage is changed. SOLUTION: Voltage applied to a lamp L1 and voltage applied to a reference resistor Rr2 are monitored by a comparator CMP2, to detect changes of power source voltage, a drive signal always commanding an on-condition is given to a semiconductor chip 110 from a CPU 10 when the power source voltage is preset voltage or less, and a current is always supplied to the lamp L1 by placing a lamp driving FET of the semiconductor chip 110 always in an on- condition. While an intermittent current is allowed to flow in the lamp L1 by giving a PWM signal to the semiconductor chip 110 from the CPU 10 in accordance with a signal from the comparator CMP2, when the power source voltage exceeds the preset voltage, and an averaged current flowing in the lamp L1 is decreased.
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