| 摘要 |
PROBLEM TO BE SOLVED: To obtain a voice signal superimposing circuit that ensures stable impedance in a voice signal frequency band without the need for a high inductance. SOLUTION: The voice signal superimposing circuit is provided with a constant voltage control IC 2 that converts voltage received from a power supply into a desired voltage, a smoothing inductor 3 connected to the output terminal of the constant voltage control IC 2, a smoothing capacitor 4, a Schottky diode 5 acting like a feedback path of a load current when a switching transistor(TR) 21 in the constant voltage control IC 2 is turned off. The voice signal superimposing circuit divides output voltage by using detection resistors Ra, Rb, feeding back the divided voltage to the constant voltage control IC 2, comparing the feedback voltage with a reference voltage by a voltage comparator in the constant voltage control IC 2 to control the ON/OFF of the switching TR 21, thereby making the output voltage stable and superimposing a voice signal onto the constant voltage power supply. Then an output with the voice signal superimposed on the desired power supply voltage is obtained by applying the voice signal to the input terminal of the voltage comparator in the constant voltage control IC 2.
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