| 摘要 |
<p>PURPOSE:To eliminate any special consideration as to the dielectric strength for mounting by separating completely a DC current suply circuit connected to a subscriber line while keeping the circuit symmetrically spaced to the upper and lower parts. CONSTITUTION:When a line resistance up to a subscriber telephone set TEL is small, the voltage drop of a resistor R1 is increased, a voltage at the positive input of an operational amplifier OP1 is reduced and collector current of a transistor (TR1), i.e., supply current I is increased. When the supply current I is increased to a certain value, however, that is, the positive input voltage of the operational amplifier OP1 is decreased to a value, then a forward voltage impressed to a diode D1 is larger, the current is increased rapidly, the terminal voltage of the diode D1 is made almost constant, resulting that the positive input voltage of the operational amplifier OP1 is made almost constant and then the supply current I is made almost constant. The similar operation is conducted as to the lower half circuit and the semi-constant current characteristic is realized by the cooperation of both circuits.</p> |
