| 摘要 |
PROBLEM TO BE SOLVED: To protect a switching element from an overvoltage when a load is short-circuited. SOLUTION: A maximum conducting time setting means is provided that is configured to set the maximum length of the conducting time of the switching element to a prescribed time length that is shorter than the case that constant voltage control at least by a constant voltage controlling means is stopped, and to make the prescribed time length variable according to the level of a DC input voltage. Or an overload protecting means is provided that starts controlling a switching frequency for the switching element according to a state that a load current reaches a prescribed level regarded a an overcurrent. Also, an overvoltage protecting means is used together that controls the switching frequency according to a state that a voltage between the collector and the emitter of the switching element reaches a prescribed level. This structure enables the switching element to be protected from the overvoltage when a load is short-circuited. COPYRIGHT: (C)2004,JPO
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