[PDF] Varactor Diode | Construction | Working Principle | Applications | New Topic [2023]

In this note, we will discussing about the Varactor Diode and its Construction, Working Principle, and Applications also. Welcome to Poly Notes Hub, a leading site for Diploma Engineering Notes Syllabus-Wise.

Author Name: Arun Paul.

What is Varactor Diode ?

A junction diode which acts as a variable capacitor under changing reverse bias known as a varactor diode.

Its capacitance varies as the voltage across its terminals changes. This property makes these diodes useful in electronic circuits for tuning radio frequencies, voltage-controlled oscillators, and frequency multipliers. They’re commonly employed in applications where a voltage-controlled capacitance is necessary, such as in tuning circuits for radios, televisions, and communication systems.

Construction

This is the construction of Varactor Diode –

When a PN Junction is formed, a depletion layer is created in the junction area. Since there are no charge carriers within the depletion zone, the zone acts as an insulator. The p-type material with holes(considered positive) as majority carriers and the n-type material with electrons (- ve charge) as majority carriers act as charged plates. Thus the diode may be considered as a capacitor with n-region and p-region forming oppositely charged plates and with depletion zone between them acting as a dielectric. This is illustrated in Fig (i). It is specially constructed to have high capacitance under reverse bias. Fig (ii) shows the symbol. The values of the capacitance of varactor diodes are in the picofarad (10^-12F) range.

Working Principle

Below, we discuss about the working principle of Varactor Diode –

For normal operation, a varactor diode is always reverse biased. When reverse voltage across a varactor diode is increased, the width of the depletion layer increases. Therefore, the total junction capacitance of the junction decreases. on the other hand, of the reverse voltage across the diode is lowered, the width of the depletion layer decreases. Consequently, the total junction capacitance increases. The total capacitance can be change simply by changing the reverse voltage. For this reason, this diode is sometimes called Voltage-Controlled Capacitor.

Advantages

Below, we listed some advantages of Varactor Diode –

1. Compact In Size.
2. Offers quick adjustment in Frequency Tunning.
3. Fast in Response and Lower in Cost.

Applications

Below, we listed some applications of this diode –

1. Used in Radio Systems.
2. Used in TVs.
3. Used in Communication Systems as well.