| 摘要 |
The output signal of a micro-phone and a transmission resistant signal is designed to be fed to a hand free circuit for preventing noise. Power (Bt) is applied to the micro-phone (3) through a resistor R2, a diode D1, a resistor R1. A gene diode D2 for maintaining constant voltage and a transistor TR1 are connected parallely with each other between the connection point of the diode D1 and the resistor R2, and ground connection. The electric potential of the connection point remains constant when TR1 is off, and ground connection when TR1 is off, and ground connection when TR1 is ON. The transmission resistant signal is applied to the base terminal of TR1 so that the transistor TR1 for switching is ON with the action of the transmission resistant signal.
|
