SCR used as a Switch

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 SCRwhen in on-state; hence there is some wastage of power.
  3. It is more costly and need more care in handling.

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