| 摘要 |
PURPOSE:To simplify a circuit composition of the title unit,by using a comparator means, and by controling the width of pulse. CONSTITUTION:On a switching power unit an AC power source 1 is rectified by a diode bridge 2, and the rectified power is converted to pulse by a control transistor 4 via a transformer 5, and after that, via a rectifier diode 6 or the like, the output of specified voltage is generated from an output end 9. In order to keep output voltage to be a specified value with the control circuit of the power unit, the circuit is composed of an output voltage detecting circuit 10, an input voltage drop detecting means 11, a reset means 12, a control IC 13, a soft start means 14, an excess current detecting means 15, a surge voltage absorbing means 16, and the like. The reset means 12 is connected to the input voltage drop detecting means 11 in series, and this output is directed to an error amplifier Q3 for input via the excess current detecting means 15. In this case, when the input voltage drop detecting means 11 is worked, then a part of the excess current detecting means 15 is worked via the reset means 12, and on excess current, the output of pulse is stop-controlled.
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