| 摘要 |
PROBLEM TO BE SOLVED: To provide an overload protection circuit which can attain downsizing and weight reduction in electrical machinery capable of operating an overvoltage protection positively and driven by an adapter of a notebook-sized personal computer, printer, or fax even if the output capacity of a DC power source is roughly equal to the maximum electric power consumption. SOLUTION: This overvoltage protection circuit 25 is provided with a Zener diode 13 which runs current with overvoltage in a current passage involving a DC-DC converter 16 connected to DC power supply 1, an NPN transistor 18 which turns current passing through the Zener diode 13 to be triggered and develops a short cut in the current passage to which overvoltage is applied, a fuse 21 fused by the short-cut of the current passage to shut off a short-circuit passage, and a PNP transistor 17 in which the fuse 21 is connected to a trigger terminal and fused to shut off the current passage under overvoltage.
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