| 摘要 |
PURPOSE:To make a small change in switching frequency due to a fluctuation in load, by starting a control circuit at the turn-on of a switching element, and forbidding the switching element from an on-state based on a lowest point detection signal while a control signal is generated for a given time. CONSTITUTION:A mono-multi circuit (MM) is driven for turning on a switching element Q1 and generating a pulse signal as a forbidding pulse with a given pulse width. During the pulse generation from the mono-multi circuit (MM), a detection pulse of a zero-cross detection circuit (ZCD) is ignored by a control circuit (CTL) so as to forbid a zero-cross detection signal. When a pulse added to a switching element (Q1) is generated from the control circuit (CTL), a D-type flip-flop circuit (FF) synchronizes the rise of the pulse with a first edge of zero-cross signal after the forbidden time is over, and then the switching element (Q1) is turned on. |
