| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a switching power supply device that is capable of achieving zero watt at the time of no load without using a signal from the outside. <P>SOLUTION: A switching power supply device includes: a no-load detection circuit Z4 that detects a no-load state based on a pulse voltage induced by a secondary winding S of a transformer T; a first feedback circuit Z3 that feeds back the no-load state detected by the no-load detection circuit Z4 from a secondary side to a primary side to thereby stop an on/off operation of a switching element Q1 by a control circuit Z1; and a second feedback circuit Z5 that feeds back the no-load state detected by the no-load detection circuit Z4 from the secondary side to the primary side to thereby stop an operation of an activation circuit Z2 that activates the control circuit Z1. When an output voltage Vout from a secondary-side rectifying and smoothing circuit (smoothing capacitor C2, diode D1) falls below a preset voltage, the second feedback circuit Z5 releases the operation stop of the activation circuit Z2. <P>COPYRIGHT: (C)2013,JPO&INPIT |
