Patent ID: 7466037

Claim:
A power supply controlling circuit, connected between a power source and a load, for controlling a current which is supplied from the power source to the load by controlling a control transistor; comprising: a reverse current detecting circuit which detects a reverse current flowing from the load to the power source; and a reverse current preventing circuit which disconnects a line between the power source and the load when the reverse current is detected by the reverse current detecting circuit; wherein the reverse current preventing circuit is disposed between the power source and the control transistor and includes a reverse current preventing transistor in which a body diode is formed, and the reverse direction of the body diode is a direction from the control transistor side to the power source side; and the reverse current preventing circuit further includes a driving circuit which receives and is driven by an output of the reverse current detecting circuit and which receives a power source from a connection point of the reverse current preventing transistor and the control transistor, wherein the power source voltage received from the connection point drives the reverse current preventing transistor.