Types of Diode


  1. Diode is a Non-Linear device.
  2. The ac component present in the dc output of rectifier is called ripple. For full wave rectifier ripple frequency fr = 100 Hz.
  3. Inductor passes low frequency and blocks high frequency signals. Initially inductor acts as open circuit and after charging acts as short circuit.
  4. Capacitor passes high frequency and blocks low frequency signals. Initially capacitor acts as short circuit and after charging acts as open circuit.

Zener Diode

  1. Zener Diode is a special purpose diode designed to operate in breakdown region.
  2. Zener Diode is used as Voltage Regulator.
  3. To Check whether the zener diode is operating in breakdown region OR not. We find Vth across load. If Vth>Vz then zener diode will act in breakdown region otherwise not.
  4. Zener effect occurs below 4 or 5 V reverse voltage.
  5. Temperature co-efficient is negative for zener effect working diode. If temperature increase by 1 degree centigrade, breakdown voltage decrease by 1.4 mV.
  6. Avalanche effect occurs above 6 V reverse voltage.
  7. Temperature co-efficient is positive for avalanche effect working diode. If temperature increase by 1 degree centigrade, breakdown voltage increase by 2 mV.

Light Emitting Diode

  1. Light Emitting Diode (LED) is a special purpose diode which emits light when forward biased.
  2. LED is made of Gallium, Arsenic and Phosphorous.
  3. LED produces non-coherent light.


When light falls on the P-N Junction of photo diode, it is dislodges the valence electrons from their orbit producing free electrons and holes in the process.


Opto-coupler combines a LED and a photo-diode. It provides electrical isolation.


Light Amplification by Stimulated Emission of Radiation (LASER) produces coherent light (Light waves are in same phase to each other). LASER is used in communication, medical, defense etc.

Schottky Diode

  1. Schottky Diode is a special purpose diode with almost zero reverse recovery time. It is used at high frequencies where short switching time are needed.
  2. Reverse recovery time is the time a diode takes to shut off after it is suddenly switched from forward to reverse bias.
  3. Used in digital devices above 300 MHz (SMPS).
  4. It has high speed turn OFF Barrier potential 0.25 V.
  5. It has metal such as Gold, Silver or Platinum on one side of junction and doped silicon (N-type) on the other side.
  6. It has no depletion layer so no stored charges at junction.

Varactor Diode

The width of depletion layer increases with the reverse voltage. This is why the capacitance of a varactor diode can be controlled by the reverse voltage. Used in TV and Radio receivers for tuning. Tuning range of varactor depends on the doping level.

Lighting, Power line faults and transients can pollute the ac line voltage by superimposing dips and spikes.
  1. Dips are reverse voltage drops lasting microseconds or less.
  2. Spikes are very brief over-voltages up to 2000 V or more.
  3. This semiconductor device is like two back to back zener diodes with a high breakdown voltage in both directions.
  4. Used as transient suppressor for line filtering.

Tunnel Diode

Tunnel Diode exhibits negative resistance phenomenon i.e. increase in forward voltage produces a decrease in forward current.
  1. It is a voltage control device. 
  2. The negative resistance of tunnel diodes is useful in high frequency circuits called oscillators.

PIN Diode

PIN Diode operate as a variable resistor at RF and microwave frequencies.
  1. When diode is forward biased, it acts like a current controlled resistance.
  2. When diode is reverse biased, it acts like a fixed capacitor.
  3. Used in microwave communications, as RF switches, attenuators, photo-detectors and phase shifters.


Albert Malvino and David J Bates, “Electronic Principles”, 7th Edition, TATA McGRAW HILL.

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