| 摘要 |
PURPOSE:To reduce remarkably power consumption and also number of elements because an output transistor (TR) flows no unnecessary large current during the standby by adding a constant current circuit to the output TR of an operational amplifier in a telephone exchange or the like. CONSTITUTION:In the operation of the operational amplifier OPA, a load current IL (flowing to a load RL) is made dependent only on a resistance ratio R/RE to a control current I0 for controlling load current by adopting Darlington connection or the like to power TRs QA, QB (amplification factor beta). In other words, the advantage using the operational amplifier is sufficiently utilized. Further, as to the operation of a constant current circuit of an output section comprising a TR Q30 and resistors RC, RB, the TR Q30 is biased by a DC bias circuit comprising TR Q11 of diode connection, a resistor R and a constant current I1. Thus, an output current IA of the TR Q30 is reduced. |
