| 摘要 |
PURPOSE:To stabilize an output voltage efficiently by respectively providing the error amplifier of a control circuit with a resistance determining a feedback gain and a control current output part with an output current limiting resistance. CONSTITUTION:A switching power circuit is composed of a main transformer 1, a self-oscillated feedback circuit controlling the ON-OFF state of a switching element by its feedback winding and others to obtain a DC output voltage Vout by making the output voltage of a transformer secondary winding L2 go through a magnetic amplifier MA, rectification and smoothing and the like. Then, a control current corresponding to the output voltage Vout is caused to flow through the magnetic amplifier MA by a control circuit 10. Said control circuit 10 is composed of an error amplifier 11 and a control current output part 12 and said error amplifier 11 is provided with a resistance R5 deciding a feedback gain. Also in a control current output part 12, a resistance R4 for limiting an output current is connected between the emitter of a transistor Tr2 and the positive side F point of said output voltage Vout. Thus, said feedback gain can be varied so as to be capable of operating within the most efficient range.
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