Patent ID: 7403365
Filing Date: 2008-07-22
Classification: H02M

Abstract:
1. An over-current detection circuit for a power-supply device contained in a buck type DC-DC converter comprising: a pair of power semiconductor switching components; a driving means for the pair of power semiconductor switching components; a pulse-width modulation type oscillator for supplying a driving signal to the driving means; and an error amplifier for supplying an error signal with respect to a reference voltage to the oscillator, wherein, separately from a high side power semiconductor switching component that is one of the pair of power semiconductor switching components, a sense power semiconductor switching component having a 1/m size of the high side power semiconductor switching component is provided, wherein the circuit comprises a means for causing the sense power semiconductor switching component to be normally on, and a means for detecting an over-current by comparing, in a comparator, the ON-voltage obtained by causing a current that is 1/m of an over-current value to flow through the sense power semiconductor switching component, that is, the reference voltage for over-current detection, and a voltage obtained by applying the ON-voltage when the high side power semiconductor switching component is on to a sample-and-hold circuit comprised of a switch and a capacitor, wherein m refers to a positive integer.