| 摘要 |
PROBLEM TO BE SOLVED: To prevent the main current from flowing to the body diode of an FET for synchronous rectifying in a DC-DC converter using a synchronous rectifier circuit. SOLUTION: The main circuit 10 of a DC-DC converter is constituted of capacitors C1 and C2 having a half-bridge constitution, a primary circuit of FETs Q1 and Q2 which are alternately ON-driven with pause periods in between, and the primary winding n1 of a transformer T1 connected to the primary circuit. The circuit 10 is also constituted of the secondary windings n21 and n22 of the transformer T1, FETs Q3 and Q4 for synchronous rectifying connected to the windings n21 and n22, an inductor L1, and a capacitor C0. During the 'ON' period of the FET Q1, the simultaneous turning on of the FET Q4 for synchronous rectifying with the FET Q3 is prevented by short-circuiting the gate of the FET Q4 to the source of the FET Q4 by turning on FETs Q9 and Q7 and, when the FET Q1 is turned off, the FET Q4 is ON-driven by supplying a pulse from a one-shot multivibrator 4 by means of a delay circuit 3 after a preset short time elapses.
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