| 摘要 |
PURPOSE:To limit the current to a power supply transistor(TR) by connecting a base of a TR of an output stage of an operational amplifier to ground through a diode. CONSTITUTION:A base of a TR 30 being a component of an output stage circuit 12 of an operational amplifier 10 is connected to ground through a diode D14. Then a voltage level impressed to the base of the TR 30 is a voltage across the diode D14 or below. Then an output voltage of the operational amplifier 10 is dropped further more than the voltage across the diode D14 because of the base-emitter voltage of the TR 30. Thus, the output voltage of the operational amplifier 10 is limited and when a line B of the earth side connecting to a telephone set 62 is grounded, the overcurrent flowing from the base to the collector of the power supply TR 54 is prevented. |
