| 摘要 |
PROBLEM TO BE SOLVED: To suppress output fluctuating due to abrupt increase in the output voltage for stable operation. SOLUTION: A switching power supply unit is provided with a current- limiting circuit, which when an inverter 3 is controlled to the stop side due to abrupt increase in output voltage, operates to suppress increase in pull-in current due to an error amplifier 9. The current-limiting circuit comprises a current limiting transistor 12 and a base bias circuit. The current-limiting transistor 12 is inserted and connected by emitter and collector, in a line which connects a power line of output voltage and the output of the error amplifier 9 via a current-limiting resistor R4 and a photocoupler light-emitting portion 11a. The base bias circuit divides a voltage, obtained by rectifying a voltage produced in a secondary winding L2 of a transformer 4 and applies the obtained voltage to the base of the current-limiting transistor 12. In response to drop in the voltage produced in the secondary winding, due to the stop-side operation of an inverter element 5, the current-limiting transistor 12 is operated in the off direction, and thereby the pull-in current of the error amplifier 9 is limited. COPYRIGHT: (C)2004,JPO
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