PURPOSE: To detect a line current with high accuracy by providing a transistor to correct the voltage between the base and the emitter of a voltage-current conversion transistor in a voltage-current conversion circuit.
CONSTITUTION: An A-line current IA and a B-line current IB are converted to voltages by resistors RA1, RB1 respectively, and thus voltages VA, VB are generated. The voltage-current converter 1 on the A-side outputs an output current IA2 proportionate to the input voltage VA, while the voltage-current converter 2 on the B-side outputs an output current IB2 proportionate to the input voltage VB. A detection output part 3 for sum current outputs an output voltage VOUT proportionate to the sum current I21 of the currents IA2, IB2. In this case, in the converter 1, the TRQ3 is provided for correcting the VBE of the transistors TRQ4, Q8 for voltage-current conversion, and by correcting the VBE of the TRQ4, Q8, a voltage-current conversion difference is eliminated. In such a way, a highly accurate detection of a current can be executed.
KITANO JUNJIRO
INABE YASUNOBU
NIPPON TELEGRAPH & TELEPHONE