Varactor Diode

Varactor Diode

What is Varactor Diode?

This is a P-N junction diode operating at high frequencies. Its capacitance depends on the voltage  across it, whereas in normal diodes, an attempt is made to keep the internal capacitance value to a minimum because the value of internal capacitance changes according to the given signal voltage. Varactor diode can be used for amplifying and switching at high frequencies.

Symbol of Varactor Diode

Varactor Diode

The effective capacitance of the varactor diode depends on the reverse bias voltage charged on it. Therefore, this device can also be used in place of the gang capacitor in the tuning circuit of the radio receiver. This type of circuit can also be used in the remote control tuning circuit of receivers.

Working of Varactor Diode

Working of Varactor diode is similar to the parallel plate capacitor so let us consider a parallel plate capacitor having two plates separated by distance d same in varactor diode case so see below image for more clarity

so if the diode is conduction stage then depletion layer is thin so as per the formula of Parallel plate capacitor which given as below

C=EA/d

so if distance between plates are reduces the capacitance increases and vice versa.

If you understand the working of parallel plate capacitor you can easily understand varactor diode. Varactor diode is used in voltage controlled oscillator.