| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that overcurrent protection in a circuit 6 for supplying power from a DC power source 63 through a power switching FET 60 is performed conventionally by detecting a magnitude of a current Iand turning off the FET 60, but when the DC power source is a high voltage (e.g., 500 V), overcurrent in the case of a grounding accident becomes extremely high and it becomes too late in accordance with the conventional method.SOLUTION: When a drain current Iof the FET 60 increases, a drain-source voltage Valso increases. A drain-source voltage detection circuit 2 detects that Vreaches a first determination value and reaches a second determination value larger than the first determination value. The first and second determination values are set to values in proportion to a DC power source side voltage Vof the FET 60. An overcurrent protection signal generation circuit 7 generates an overcurrent protection signal when a time ratio (t/t) between a time tuntil reaching the first determination value and a time tuntil reaching the second determination value is smaller than a preset constant (a), and the FET 60 is turned off. |
