SUPPLY CIRCUIT FOR COMMUNICATION CURRENT

摘要

PURPOSE:To make samll the communication current supply source in size through the use of transistors and to avoid mutual interferrnece. CONSTITUTION:The DC current for communication of the telephone set EXT passes through, ground-resistor R2-pnp trnasistor TrQ2-terminal L1-L2-npn TrQ1- R1-DC power supply E-ground. The bias current of TrQ1,Q2 passes through, ground -R2-Q1-R0-Q2-R2-E-ground. The diodes D1,D2 and D3,D4 determine the telephone set supply current, and the resistors R1,R2,R0 control the bias current to keep TrQ1,Q2 at the active region. In practice, since TrQ1,Q2 in active region have very high impedance from the collector side, the audio signal from the telephone set can be delivered to the opposing telephone set without passing through the DC power supply side. Since the base current of TrQ1,Q2 passes through one resistor R0, the bias can be made to one state to keep the balance for the terminals L1 and L2.