| 摘要 |
<p>PURPOSE:To suppress a power supply noise by controlling the transistor of a current supply circuit by obtaining a DC voltage containing no signal component by extracting the middle point potential between speaking lines in a circuit used for a telephone switching unit, etc. CONSTITUTION:In the circuit which supplies a speaking current to speaking lines A and B of the telephone switchboard via couples of transistors Ths Q1 and Q2, and Q3 and Q4 connected in series to battery E and the earth and between lines A and B, resistances R11 and R12 equal in value are connected between lines A and B and a middle point potential is detected by those resistances R11 and R12. Then, this middle point potential is coupled with the circuit composed of resistances R9 and R10, and R3 and R7 controlling base potentials of Trs Q2 and Q4, and capacitors C3 and C4 are connected to resistances R3 and R7 respectively. In this constitution, it is prevented that a signal component generated between speaking lines A and B appears between the middle point between resistances R11 and R12 and the earth or battery E.</p> |
