| 摘要 |
PROBLEM TO BE SOLVED: To provide a step-down switching regulator in which a useless current flowing through the gate of a switching transistor is reduced under light load. SOLUTION: A switching transistor M1 and a synchronous rectification transistor M2 connected in series between an input terminal 102 and the ground apply the voltage at the joint, as a switching voltage Vsw, to one end of an inductor L1 connected to the outside of a main control circuit 100. A PWM control section 20 creates a first PWM signal Vpwm1 for controlling the duty ratio such that the output voltage Vout from a step-down switching regulator 200 approaches a predetermined reference voltage. A forced off circuit 50 monitors the switching voltage Vsw and turns the synchronous rectification transistor M2 off forcibly when it exceeds the ground potential. A minimum on time setting circuit 60 limits the duty ratio of a second PWM signal Vpwm2 such that the on time of the switching transistor M1 becomes longer than a predetermined minimum value. COPYRIGHT: (C)2007,JPO&INPIT
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