| 摘要 |
PROBLEM TO BE SOLVED: To stabilize each output voltage accuracy at a prescribed control ratio by detecting the amplitude of each output voltage, when two or more output voltages are obtained. SOLUTION: This switching power supply unit comprises an inductor L connected in series with a primary winding T1 of a transformer T, a series circuit of a capacitor 5 and a second switching element Q2 connected in parallel with the series circuit of the inductor L and the primary winding T1, a first switching element Q1 connected in series with the primary winding T1, and control circuits CT1, CT2 which alternately turn on and off the first and second switching elements Q1, Q2 with an off-period of both the switching elements and controlling the on-time of the switching elements for controlling the output. Furthermore, the unit includes an output voltage detecting circuit DT with voltage detecting resistors R2, R4 included for detecting output voltages Vo1, Vo2 respectively, and a control signal forming part with a photo diode PD1 and a shunt regulator ZD1 included for forming a control signal for the on-time at a prescribed control ratio, in response to the amplitude of Vo1, Vo2 detected by the resistors.
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