Switching power supply device and semiconductor device

摘要

In a switching power supply device which intermittently executes a switching operation, a power loss which occurs in resumption of the switching operation is reduced. A semiconductor device works as a control circuit for the switching power supply device, and includes: an intermittent oscillation control circuit which alternately gives an instruction for execution and suspension of the switching operation of a switching element; a bottom detecting circuit which detects a bottom of a ringing voltage that develops when the switching element is OFF; a bottom-monitoring time period timing circuit which times a bottom-monitoring time period starting as soon as the instruction for the execution of the switching operation is given; and a turn-on control circuit which turns ON, before the timing of the bottom-monitoring time period ends, the switching element only when the bottom of the ringing voltage is detected.

主权项

1. A semiconductor device which controls a switching power supply that causes a switching element to intermittently execute a switching operation to alternately supply and cut an input direct current (DC) voltage so as to convert the input DC voltage into a regulated output DC voltage, the semiconductor device comprising:
an intermittent oscillation control circuit which selectively gives one of an instruction for execution of the switching operation and an instruction for suspension of the switching operation, according to a level of the regulated output DC voltage; a bottom detecting circuit which detects, when the switching element is OFF, a bottom indicating a local minimum point of a ringing voltage that develops in the switching element; a bottom-monitoring time period timing circuit which times a bottom-monitoring time period for which the bottom of the ringing voltage is to be monitored, the bottom-monitoring time period starting as soon as the intermittent oscillation control circuit gives the instruction for the execution of the switching operation; and a turn-on control circuit which turns ON, while the bottom-monitoring time period is being timed, the switching element only when the bottom detecting circuit detects the bottom of the ringing voltage.