| 摘要 |
PROBLEM TO BE SOLVED: To protect a DC/DC converter from breakdown caused by the input of an overvoltage even if a charging power supply is separated from a high voltage battery and all the power from the charging power supply is applied to the DC/DC converter. SOLUTION: A low voltage battery B2 is connected to a high voltage battery B1 which is charged by a DC power from an alternator A side with a voltage of 42 V via a DC/DC converter CN2 which steps down the DC voltage from 42 V to 14 V. A high voltage power supply line L1 and a low voltage power supply line L2 are connected to each other with a bypass line B3 in which a power MOS-FET Q1 is provided so as to detour the DC/DC converter CN2. If the high voltage power supply line L1 is disconnected from the high voltage battery B1, the power MOS-FET Q1 is turned on by a potential on the bypass line L3 which is higher than the allowable input voltage of the DC/DC converter CN2 via a Zener diode ZD and a transistor Q2.
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