Patent ID: 7420356

Claim:
A current direction detection circuit for detecting a reverse flow of current in a ground side output transistor, through which current flows from a grounded input terminal to an output terminal, comprising: a monitoring transistor having a control terminal and an output terminal arranged to be connected, respectively, with a control terminal and an output terminal of the ground side output transistor; an impedance element having one terminal connected with the input terminal of the monitoring transistor and the other terminal grounded; first and second constant-current sources; a diode-connected reference transistor arranged between the first constant-current source and ground potential; and a sensing transistor arranged between the second constant-current source and the impedance element, the sensing transistor having a control terminal connected with a control terminal of the reference transistor; wherein a voltage between the second constant-current source and the sensing transistor is output as a control signal to control the ground side output transistor and monitoring transistor.