| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply device that immediately releases an operation prohibition state of a switching element after overvoltage protection operation and after turning off an AC power supply. SOLUTION: The switching power supply device includes: a switching element 80 connected through a primary winding of a transformer 20 to an output end of an input rectifying/smoothing circuit 10 that rectifies and smoothes an alternating current input voltage and outputs a direct current input voltage; an output rectifying/smoothing circuit 130 that rectifies and smoothes a voltage induced in a secondary winding of the transformer and outputs a direct current output voltage; and a control circuit 190 that controls ON and OFF of the switching element. The control circuit includes overvoltage protection circuits 180a and 160a that detect a voltage corresponding to the direct current output voltage and a voltage corresponding to the alternating current input voltage, outputs an overvoltage operation prohibition signal for prohibiting ON and OFF operations of the switching element when the voltage corresponding to the direct current output voltage rises to a first threshold value or more, and releases the overvoltage operation prohibition signal when the alternating current input voltage drops and the voltage corresponding to the alternating current input voltage falls down below a second threshold value. COPYRIGHT: (C)2009,JPO&INPIT
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