Patent ID: 7514908
Filing Date: 2009-04-07
Classification: G05F,H02M,H03F,H03K,Y02B

Abstract:
1. A switching power source comprising: an inductor; a capacitor which has one end thereof connected to one end of the inductor and another end thereof connected to a ground potential of the circuit and forms an output voltage; a switching element which is connected to another end of the inductor and controls a current which is made to flow into the inductor based on an input voltage; an element which brings another end of the inductor into a predetermined potential when the switching element assumes an OFF state; a driving circuit which drives the switching element; a booster circuit which includes a bootstrap capacity which has one end thereof connected to another end of the inductor and a MOSFET which has a source-drain route thereof connected between another end of the bootstrap capacity and an external power source terminal, and is capable of generating a boosted voltage which is used as an operating voltage of the driving circuit on another end of the bootstrap capacity; a level shifting circuit which forms a switching control signal which allows the MOSFET to assume an ON state when the element is in a conductive state and allows the MOSFET to assume an OFF state when the element is not in a conductive state; and a PWM control circuit which forms a PWM signal and controls an operation of the switching element through the driving circuit, wherein the MOSFET is configured to connect another source/drain region and a substrate gate such that a junction diode between one source/drain region and the substrate gate is directed in the direction opposite to the direction toward the external power source terminal from other end of the bootstrap capacity, and prevents the flow of the current toward the external power source terminal from another end of the bootstrap capacity by the junction diode when the boosted voltage is generated by allowing the MOSFET to assume an OFF state in response to the PWM signal.