| 摘要 |
PROBLEM TO BE SOLVED: To prevent a synchronous output MOS transistor from breaking beyond an avalanche breakdown voltage, while cutting off a current flowing into the ground via the synchronous output MOS transistor, when a reference voltage is changed or the like, in a step-down synchronous rectification type switching regulator. SOLUTION: A detection voltage obtained by detecting an output voltage of the switching regulator is compared with the reference voltage by an error amplifier Q1. An output MOS transistor PMT1 and a synchronous output MOS transistor NMT1 are driven by a PWM pulse from a PWM comparator Q2 so as to maintain the output voltage at a fixed level. When the setting voltage is changed by changing the reference voltage and when a reverse-current detection comparator Q3 detects a reverse current of the synchronous output MOS transistor NMT1, the output pulse of the PWM comparator Q2 is inputted to a discharge MOS transistor NMT3 by a change-over switch SW1 so as to discharge the electric charges of a smoothing capacitor C1. COPYRIGHT: (C)2007,JPO&INPIT
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