Current detecting apparatus and its control method

摘要

To reduce errors and decrease loss, the detecting range of current is enlarged and the current is independently detectable. A rectified voltage and a rectified current are supplied from an input terminal. Resistors 1 and 2 are serially connected between the input and output terminals. A load is connected to the output terminal. Between an emitter and collector of the transistor are resistor 1 and a constant current detecting circuit 5. The transistor base is connected to a control circuit that controls the transistor switching operations. The constant current detecting circuit 5 detects current from the voltage across resistor 1. A current detecting circuit 6 detects current from the voltage across resistor 2. A signal is supplied to the control circuit when the constant current detecting circuit 5 detects small current. The control circuit supplies a signal to the transistor base that increases transistor impedance.