| 摘要 |
PURPOSE:To inhibit the peak value of voltage applied to a switching element by controlling conversion frequency in response to the level of output voltage from a rectifying circuit or AC supply voltage. CONSTITUTION:A rectifying circuit consisting of a diode bridge 4, a choke coil 5 and a smoothing capacitor 6 is connected to a commercial power supply 1 through a fuse 2 and power switches 3a, 3b. A primary coil 12a for a transformer 12 is connected to the power supply 1 through the fuse 2 and the power switches 3a, 3b, and a DC power circuit 13 is connected to a secondary coil 12b. A feedback circuit 20, an oscillating circuit 40, a PWM circuit 50 and a base drive circuit 60 are each connected to an output terminal for the DC power circuit 13. The feedback circuit 20 compares output voltage from the rectifying circuit and the collector voltage of a transistor 7, and transmits a trigger signal corresponding to the result of the comparison over the oscillating circuit 40. Accordingly, conversion frequency by the PWM circuit 50 and the base drive circuit 60 is controlled.
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