To reduce circuit loss in an overcurrent detector for an inverter for use in a washing machine, an air conditioner, a refrigerator, or the like or a semiconductor switch of a power factor improvement circuit or the like.
The overcurent detector includes: a current detection resistor for detecting a current in one direction flowing through a load; a diode having a cathode terminal connected to a high potential side of the current detection resistor; a bias circuit including a DC power supply and a bias current adjustment resistor and supplying a constant bias current to the current detection resistor in the same direction as the direction for detecting the current via the diode; and a photo coupler connected so that a current branched from a current path flowing from the DC power supply to the current detection resistor flows to a photodiode at a primary side in parallel with a series circuit of the diode and the current detection resistor. In the overcurrent detector, the photo coupler 7 is normally biased so as to be turned off, and turned on when a current not less than a prescribed current value flows through the current detection resistor to transmit an overcurrent state to a secondary side of the photo coupler.
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Daisuke Nagano
Kentaro Fujii