Diode Switching Circuits
Diodes are useful for more duties than just changing AC to DC. The circuit in Fig. 7 uses a silicon diode to switch audio from point “A” to point “B” by applying a positive voltage to the bias circuit. The switching bias voltage can come from a mechanical switch or any logic output.
The switching circuit in Fig. 8 steers a single audio signal to a choice of two outputs. When a positive voltage is applied to the anode of either diode, through R2 or R3, its internal resistance goes from near infinity as an open switch, to a low of a few ohms when closed. If both switches are closed the audio will be switched to both outputs A and B.
The diode-switching circuit in Fig. 9 uses a positive voltage to switch input “B” to the output circuit and a negative voltage to switch input “A” to the output. All three of the diode switching circuits can handle audio levels up to 2- volts peak-to-peak, and operate with a bias voltage of 9 to 16.
Copyright by Bill Bytheway, K7TTY February 2012