14 April 2017

Snubber Circuit

  • The SCR is turned on due to transient or high dv / dt voltage across it in spite of switch S is kept open. 
  • The SCR may damage due to this type of surge voltage
  • The transient voltage is generated due to inductive load and SCR is protected against such transient voltage. 
  • The snubber circuit is connected across SCR in order to reduce effect of transient voltage. This RC circuit is called as snubber circuit.

  • When SCR T1 is in turned off condition, the charging of capacitor is done through path (+) (+) Vdc – S – D – C – Vdc (-). 
  • The capacitor is connected across DC supply due to low forward resistance of diode D therefore the voltage across SCR T1 reduces. 
  • When the voltage across capacitor is equal to supply voltage, the diode D becomes reverse biased.   
  • When the SCR T1 is turned on, the discharging of capacitor is done through path (+) C – R – SCR T1 – C (-).   
  • The resistance R limit the discharging current and protects the SCR against overload current. 
  • The RC circuit and diode D is used as snubber circuit as shown in the figure A. 
  • It protects SCR against dv / dt and transient voltage. The alternative circuit of the snubber circuit is shown in the Figure C.

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