| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a single-ended forward-type switching power supply device having a synchronization rectification circuit and being capable of protecting a load and inner circuit elements with certainty in the case of an output short circuit and the like. <P>SOLUTION: A switching power supply device has: a MOS-type FET main switching element 14 and a commutation side switching element 24; a synchronization rectification driving circuit 32 keeping the commutation side switching element 24 in an off state when an on-time of the main switching element 14 becomes short; a PWM control circuit 16 performing pulse width modulation based on an error signal ΔVo of an output voltage Vo, and making a driving pulse V16 be at a low level when a switching current signal of a current detection circuit 38 reaches a first reference voltage Vr1; a variable resistive element 46 provided between gate and source terminals of the main switching element 14; and a variable control circuit 48 reducing a resistance value of the variable resistive element 46 to suppress a voltage Vg14 between the gate and source terminals of the main switching element 14 when the switching current signal reaches a second reference voltage Vr2. <P>COPYRIGHT: (C)2012,JPO&INPIT |
