| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a switching power supply device that releases a disabled state of a switching element immediately after a turnoff of an AC power supply in the event of an overvoltage protection action. <P>SOLUTION: The switching power supply device comprises: an input rectifying/smoothing circuit 10; a transformer 20; a switching element 80; and an output rectifying/smoothing circuit 130 for rectifying/smoothing a secondary winding voltage to produce a DC output voltage. A control circuit 190 for controlling on/off the switching element includes a low input protection circuit 160b connected to an overvoltage protection circuit 180b for detecting a voltage depending on the DC output voltage, and configured to prevent an on duty of the switching element from damagingly excessively widening and detect a voltage depending on an AC input voltage. The overvoltage protection circuit outputs an overvoltage disabling signal to disable the on/off action of the switching element when the voltage depending on the DC output voltage becomes equal to or higher than a first threshold, and the low input protection circuit outputs a signal to release the overvoltage disabling signal to the overvoltage protection circuit when the AC input voltage drops until the voltage depending on the AC input voltage becomes lower than a second threshold. <P>COPYRIGHT: (C)2013,JPO&INPIT |
