Switch type step-down DC-DC converter and circuit for power conversion

摘要

PROBLEM TO BE SOLVED: To provide a switching type step-down DC-DC converter and a power conversion circuit capable of stably obtaining a high-side drive voltage at a proper level and of reducing a power loss.SOLUTION: A step-down DC-DC converter has a bootstrap circuit in which a bootstrap diode and a bootstrap capacitor are connected between a high-potential power supply output end and a connection point between a high-side switch element and a low-side switch element. The bootstrap circuit includes: a voltage detection circuit that detects a voltage between both ends of the bootstrap capacitor to determine whether or not the detection voltage is equal to or more than a first threshold voltage; and a cut-off circuit that is inserted in a current path between the high-potential power supply output end and the connection point, of the bootstrap circuit, and that blocks the current path when the detection voltage is equal to or more than the first threshold voltage.SELECTED DRAWING: Figure 1