Electronics

The Varactor Diode

The varactor also termed to as varicap, is a diode that behaves like a variable capacitor, with the PN junction working like the dielectric and plates of a common capacitor. Because of this, the symbol of the varactor is as shown below:

Symbol for varactor
Figure 1.0 Symbol for varactor

A varactor diode employs a PN junction in reverse bias and has a structure such that the capacitance of the diode varies with the reverse voltage. A voltage controlled capacitance is useful in tuning applications. The typical capacitance values are small, in the order of picofarads.

The figure below shows a typical tuning circuit where the DC voltage control Vc changes the capacitance of the varactor to form a resonant circuit.

Figure 1.1 A varactor tuner circuit

Varactors are being used to replace the old variable capacitor tuning circuits as in television tuners.

Also read: Optoelectronics

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John Mulindi

John Mulindi is an Industrial Instrumentation and Control Professional with a wide range of experience in electrical and electronics, process measurement, control systems and automation. In free time he spends time reading, taking adventure walks and watching football.

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