Snubber Circuit

• The SCR may be 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 (+) V_dc – S – D – C – V_dc (-). 
• 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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