PWM / PFM control circuit and switching power supply circuit

摘要

PROBLEM TO BE SOLVED: To provide a switching power-supply circuit that achieves a smooth transition of a control mode by reducing a ripple voltage when shifted from PFM control in a lightload state to PWM control in a heavyload state.;SOLUTION: A PWM/PFM control circuit has a differential-time generation means 9 which forms a differential-time signal S7 showing a differential time corresponding to a difference between a pulse width of a PWM control signal S3 and a pulse width of a PFM control signal S4 on the condition that the pulse width of the PWM control signal S3 is smaller than that of the PFM control signal S4. It is composed so as to control an oscillation frequency of a reference signal S6, which serves as a reference for forming the PWM control signal S3, to be low corresponding to the differential time on the basis of the differential time signal S7.;COPYRIGHT: (C)2008,JPO&INPIT