| 摘要 |
PURPOSE:To eliminate a noise by a simple consitution without malfunction by controlling a gain by detecting a decrease in Zener diode current and by sending a control signal to a gain control circuit when the current decreases below a prescribed value. CONSTITUTION:To electric power source 1 including a ripple, Zener diode 3 is connected via current limiting resistance 2 to form a shunting regulator for a tuning voltage and its output voltage is adjusted by selection resistance VR4 and applied to tuner 5. To diode 3, the base of switching transistor TR 20 and resistance 21 are connected and in normal operation, the emitter-base voltage of TR20is clipped at a saturation level by the across voltage of resistance 21. As the electric power source is turned off and the voltage at power terminal 6 drops, the current of diode 3 starts to decrease and when TR20 reaches the saturation voltage between the emitter and base, TR20 is turned off and diode 23 is turned on to control the gain of gain control circuit 9 through monostable multivibrator 10, so that a noise can be controlled without malfunction. |
