How an SCR functions as a switch ?

Thyristor Circuit Symbol
Thyristor Circuit Symbol

We have seen that SCR operates either in on-state or in off-state and no other state in between, that is SCR behaves like a mechanical switch. As such it is called electronic switch.

An SCR has following advantages over a mechanical switch or electro-mechanical relay:

  1. Noiseless operation owing to absence of moving parts.
  2. Very high switching speed (say 109 operations per second).
  3. High efficiency.
  4. Low maintenance.
  5. Small size and trouble free service for long period.
  6. Large control current range (say from 30 A to 100 A) with small gate current of few mA.
  7. Long life as no wear and tear is involved.

However, SCR suffers from the following drawbacks:

  1. Cut-off current is not exactly zero.
  2. There is some voltage drop across SCR when in on-state; hence there is some wastage of power.
  3. It is more costly and need more care in handling.


  1. Yang Jin Hyung

    I want to cut a electric power source(220VAC) in case of any signal or bias is inputted in gate of SCR.

    Is it possible? If you have any solution, let me know the circuit and recommended SCR part number.


    • Veer sachin

      Can we maked ON OFF SWITCH circuit using Triac( like switchboard ) for ac

  2. this site v v useful for electronics students who never maintain proper notes for studies!

  3. mohd arshad

    it is very easy to clear concept about electronics and my special thanks for mr feedburner.

  4. Ganesh Kumar Shetty

    I want to switch an electrical circuit of 230V A.C using a SCR by applying 1.5vots D.C to its gate. Please tell me what should be the value of SCR.

  5. lawrence mugambi

    THANK U for your updates.I would request u to update with circuits for building a simple robot.