Patent ID: 7245116

Claim:
A power supply driver circuit including a switching power supply device that switches a power transistor passing a current through an inductance by a PWM mode to convert an input voltage and outputs the converted voltage, the circuit comprising: a current detection transistor that has a drain terminal or a collector terminal, a source terminal or an emitter terminal, and a control terminal, wherein a drain terminal or a collector terminal of the power transistor is coupled to the drain terminal or the collector terminal of the current detection transistor, and the control terminal of the current detection transistor is coupled to receive a driving voltage which is received by a control terminal of the power transistor; a current detection resistor that is coupled to the source terminal or the emitter terminal of the current detection transistor; and an operational amplifier circuit that has a pair of input terminals, one of the pair of input terminals being coupled to a connection node of the current detection resistor and the current detection transistor and the other of the pair of input terminals being applied to a voltage of same potential as a source voltage or an emitter voltage of the power transistor, wherein a feedback loop is formed so as to make the pair of input terminals of the operational amplifier circuit be at a same potential, and wherein a signal produced by the current detection resistor is outputted as a current detection signal.