| 摘要 |
A current supply circuit for supplying a speech current via subscriber's lines to a telephone set, in which a pair of constant-current circuits, each so constituted as to hold the potential between the base and the emitter of a control transistor therein to be consant, is connected across the subscriber's lines so that the control transistors are connected in series to a DC power source. A constant-voltage circuit is connected across the bases of the control transistors for making the voltage of the base-emitter paths of each of the control transistors to be constant. At least one of the constant-current circuits may be connected across the subscriber's lines via a light emitting diode of a photo coupler.
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