| 摘要 |
<p>PURPOSE:To decrease the number of diodes of a limitter circuit and make a constant current feeding circuit compact by clamping voltage of an electric current limitter transistor TR of a constant current feeding circuit of two-wire channels by another TR suitably. CONSTITUTION:To a telephone exchange a constant current feeding circuit 3 of a PCM terminal office device is connected by two-wire channels T, R. The circuit 3 comprises a differential amplifier 4 for detecting a voltage change of the channels T, R, drivers 5, 6 for controlling the change of electric current flowing through the channels T, R, and an electric current limitting circuits 7, 8 making a sum of the electric current constant passing through the amplifier 4. These circuits 7, 8 comprise transistors TRQ11, TRQ12 for controlling the electric current, TRQa, TRQb connected to bases of the TRQ11, TRQ12, and resistances Ra-Rd connected between emitter collectors of TRQa, TRQb. Values of the resistances Ra-Rd are selected, voltages of the TRQ11, Q12 are clamped suitably, the number of diodes of the circuits 7, 8 are decreased and the circuit 3 is made compact.</p> |
