Switching power supply for enabling switching element to be soft-started in burst mode, image forming apparatus and soft start method of switching element

摘要

A switching power supply comprises a transformer; a switching element; a power supply control section which outputs a first gate voltage of a first pulse width consecutively for plural times when the switching element is driven in a burst mode in which the switching element is intermittently driven; a drive time control section which, based on the first gate voltage input consecutively for plural times when the switching element is driven, outputs a second gate voltage to the switching element consecutively for plural times and gradually increases a pulse width of the second gate voltage to a first pulse width from a second pulse width narrower than the first pulse width; and a switching section to which a switches an input destination of the first gate voltage output by the power supply control section from the switching element to the drive time control section in the burst mode.