| 摘要 |
PROBLEM TO BE SOLVED: To protect a power line with reliability, even if the core of a multiple- light lamp load is disconnected, when the core disconnection is detected by a core disconnection detecting means, changing a first prescribed value to a lower value to reduce a current which passes through the power line. SOLUTION: When a core disconnection detection signal S4 is not outputted from a microcomputer 106 as a core disconnection detecting means and an SW transistor Tr3 is off, a reference voltage obtained by dividing a supply voltage VB through resistors R2 and R3 is supplied to the positive input end of a compactor CP. If a core disconnection detection signal S4 is outputted from the microcomputer 106 and the SW transistor Tr3 is turned on, a reference voltage obtained by the supply voltage VB through a resistor R2 and the combined resistance of resistors R3 and R4 si supplied to the positive input end of the comparator CP. This reference voltage is reduced to a value smaller than the value of the reference voltage divided by the resistors R2 and R3, so as to reduce a current IL which passes through the power line.
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