SCR (silicon Controlled Rectifier) is a three junction ,three terminal, four layer and unidirectional device which act as electronic switch.It contains three electrodes (terminals) cathode (C), anode (A) and Gate (G)(control electrode).it offers high resistance to supply across anode and cathode at OFFstate. It conducts and allow the current flow in one direction only so it termed as unidirectional device and also known as Reverse Blocking Thyristor.SCR can be switched ON by applying a positive triggering pulse (of right character) to gate,then it act as low resistive path to for current flow.when SCR switched on Gate losses complete control on the conduction,and SCR conducts even after the gate current removed.Then way used to switch off SCR is known as commutation.
