A switching power supply includes a switching unit, a driving signal generator, and a control circuit. The driving signal generator is configured for providing a driving signal including a plurality of acting voltage parts. The plurality of acting voltage parts is used to turn on the switching unit. Each of the acting voltage parts may be one of a high level voltage and a low level voltage. The control circuit is connected between the driving signal generator and the switching unit. The control circuit turns off the switching unit when a duration of one of the plurality of acting voltage parts is longer than a preset time period.