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Varactor Diode (Varicap Diode)

 

Varactor Diode

Varactor Diode (Varicap Diode)

Definition

A varactor diode is a reverse-biased PN junction diode that acts as a voltage-controlled capacitor.

Working Principle

  • Operates only in reverse bias
  • Depletion region acts as an insulator
  • P and N regions act like capacitor plates
Condition Effect
Increase in reverse voltage Depletion layer widens → Capacitance decreases
Decrease in reverse voltage Depletion layer narrows → Capacitance increases

Key Formula

C ∝ 1 / √V

Where:
C = Capacitance
V = Reverse Voltage

Applications

  • Tuning circuits (Radios, TVs)
  • Voltage Controlled Oscillators (VCO)
  • Frequency Modulation (FM)
  • Phase-Locked Loops (PLL)
  • RF Filters

Summary

  • Always used in reverse bias
  • Acts as variable capacitor
  • Used in frequency tuning
  • Capacitance controlled by voltage
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