Hitachi, Ltd.

Fujitsu Corporation

Oki Electric Industry Co., Ltd.

Nippon Electric Co., Ltd.

Nippon Telegraph and Telephone Public Corporation

Takaaki Osaki

Hideo Mizutani

Michio Tokunaga

Koichi Hasegawa

Ryoichi Okada

A current supply circuit for a telephone exchange is disclosed in which a current-supplying current amplifier series-connected between a power supply and a load amplifys an output current of an input current supply circuit, and a driving current amplifier for driving the current-supplying current amplifier is controlled by an output of an output voltage detector parallel-connected with the load in a negative-feedback fashion to set the differential mode output impedance of the current supply circuit at a large or small value in accordance with frequency and to set the common mode output impedance at a small value; and in which a part of the output voltage detector for connecting the load to the driving current amplifier includes a diode for preventing a direct current from flowing in a opposite direction to that of a direct current from the power supply in order to suppress, independently of the state of the load, a current which flows from the load side into the driving current amplifier, whereby an increase in current is restricted and an on-off control can be conducted in a short time without impairing an essential function of the current supply circuit.

Current supply circuit for telephone exchange

Growing community of inventors

Yokohama, Japan

Takaaki Osaki