Soft-start method of switching power supply, output control circuit and switching power supply

摘要

PROBLEM TO BE SOLVED: To suppress the overshoot and the undershoot of an output voltage during the soft start of a switching regulator.;SOLUTION: After the switching power source is started, the input voltage of the switching regulator is switched in response to the switching pulse with a fixed pulse width, so that the output voltage of the switching power source is flatly increased up to an intermediate value. Then, the input voltage is switched in response to the switching pulse with a variable time ratio which is determined by a pulse width modulation control, to increase the output voltage from the intermediate value to a target value. The switching pulse is the fixed pulse which is used to flatly increase the output voltage with no pulse width modulation control, before performing the pulse width modulation control. Thus, the overshoot or the undershoot is hard to occur with the output voltage.;COPYRIGHT: (C)2005,JPO&NCIPI