20 April 2017

Selenium diode of Over voltage Protection of Semiconductor

  • The metal oxide varistor or selenium diode is used to protect semiconductor device against transient over voltage or high dv/dt
  • The MOV is called as voltage dependent non linear resistor. 
  • The resistance of the non linear resistor decreases as the voltage across it increases. It is always connected across the semiconductor device.
  • The characteristic of selenium diode is shown in the figure A. 
  • The forward breakover voltage of this diode is very low but is has comparatively higher reverse breakdown voltage. This diode operates in the reverse biased condition. 
  • When overvoltage appears across semiconductor, it operates.
  • As the selenium diode operates, the voltage across it remains constant but current increases sharply. There are two types of selenium diodes : Polarized and Non – polarized
  • The symbol of both types of selenium diodes are shown in the figure A. The polarized type diode operates only in one direction whereas non – polarized diode operates in both directions.


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