Special Purpose Diodes

There are few diodes which are designed to serve some special purposes. There are many of such kinds like Transient voltage suppression diodes, Gold doped diodes, Super barrier diodes, Point contact diodes, Peltier diodes etc. But other than these, there are few prominent diodes, which have got many applications. Let us go through them.

Varactor Diode

A junction diode has two potentials on both sides where the depletion region can act as a dielectric. Hence there exists a capacitance. The Varactor diode is a special case diode that is operated in reverse bias, where the junction capacitance is varied.

The Varactor diode is also called as Vari Cap or Volt Cap. The following figure shows a Varactor diode connected in reverse bias.

If the reverse voltage applied is increased, the width of the dielectric region increases, which reduces the junction capacitance. When the reverse voltage decreases, the width of the dielectric decreases, which increases the capacitance. If this reverse voltage is completely null, then the capacitance will be at its maximum.

The following figure shows various symbols used for Varactor diode which represents its function.

Though all diodes have this junction capacitance, the Varactor diode is mainly manufactured to make use of this effect and increase the variations in this junction capacitance.

Applications of Varactor diode

This diode has many applications such as −

• It is used as a Voltage variable capacitor.
• It is used in variable LC tank circuit.
• Used as Automatic frequency control.
• Used as Frequency Modulator.
• Used as RF Phase shifter.
• Used as frequency multiplier in local oscillator circuits.