Switching power supply unit and electronic apparatus using the same

摘要

A switching power supply unit includes a transformer including a primary winding, a secondary winding, and a feedback winding; an input power supply and a first switching element that are connected in series with the primary winding; a control circuit provided between one end of the feedback winding and a control terminal of the first switching element; a rectification circuit connected to the secondary winding; and an output voltage detection circuit for detecting output voltage output from the rectification circuit and for sending a feedback signal to the control circuit. The control circuit includes an on-period control circuit for stabilizing the output voltage by turning off the first switching element in an on-state in accordance with the feedback signal. The control circuit also includes an off-period control circuit for stabilizing the output voltage by delaying turning on of the first switching element in accordance with the feedback signal.