| 摘要 |
PROBLEM TO BE SOLVED: To provide a bootstrap circuit that can sufficiently charge a capacitor used for the bootstrap circuit even during light load or no load, and that never inhibits the original performance of a step-down converter, and to provide a step-down converter using the bootstrap circuit. SOLUTION: A CB-terminal is connected to a source terminal of a switching element Q<SB>1</SB>(13) by turning on/off the switching element Q<SB>1</SB>(13) with a PWM signal 11 via a high-side driver 12, and then by turning on/off a switch Qx(112) in synchronism with an on-period of the switching element Q<SB>1</SB>(13), and a constitution (capacitor charge/discharge path formation means) 110 for grounding the CB-terminal is added by turning on a switch Qy(114) in synchronism with an off-period of the switching element Q<SB>1</SB>(13). This allows the CB-terminal of a capacitor C<SB>B</SB>(6) used for the bootstrip circuit to be separated/isolated from the step-down capacitor circuit. COPYRIGHT: (C)2009,JPO&INPIT
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