| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a switching power supply unit which reduces noise and stably performs operations. <P>SOLUTION: The switching power supply unit comprises: a series circuit of primary winding P1 of a transformer T and a switching element Q1; a control circuit for turning the Q1 ON/OFF; a rectifying and smoothing circuit D, C1 for rectifying and smoothing a voltage generated in secondary winding S1 of the transformer; and an error amplifier circuit OP for outputting an error voltage of an output voltage of the rectifying and smoothing circuit and a reference voltage to the control circuit. The control circuit comprises: a signal output part FF for outputting signals for turning the Q1 ON/OFF; a bottom voltage detection part CMP1 for controlling the FF so that signals for turning the Q1 ON are outputted when it is detected that a voltage between main electrodes has become a prescribed value close to zero volt in an OFF period of the Q1; a counter 22 for counting the ON number of the Q1 by the output signals of the FF; and a delay time switching circuit 21 for controlling the FF by switching delay time so as to delay signals for turning the Q1 OFF every time the count value reaches a prescribed value. <P>COPYRIGHT: (C)2013,JPO&INPIT |
