| 摘要 |
PURPOSE:To stably control output, by determining an ON-period with oscillator output voltage for determining oscillating cycles with the integrating circuit of a condenser and a resistor. CONSTITUTION:By a switching power source, DC input voltage Ei is ON/OFF- controlled with a main transistor (hereinafter, Tr) Q1, and AC voltage obtained from the secondary winding of a main transformer T1 is rectified and smoothed into DC output voltage Vo, which is outputted. This control circuit block 2 is provided with an integrating circuit 9 consisting of a resistor R2 and a condenser C2 for applying a reference voltage source Vref and determining oscillating cycles, and a circuit 9 consisting of resistor R4, R5 for dividing this voltage, and a divided voltage is applied to a current-detecting terminal Cs. This voltage is compared with signal voltage or the like fed back by an optical transmission element PH1, and the ON-period of the TrQ1 is determined. Then, the maximum value of time ratio can easily be determined, and circuit elements can be reduced.
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