How an SCR functions as a switch ?
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:
- Noiseless operation owing to absence of moving parts.
- Very high switching speed (say 109 operations per second).
- High efficiency.
- Low maintenance.
- Small size and trouble free service for long period.
- Large control current range (say from 30 A to 100 A) with small gate current of few mA.
- Long life as no wear and tear is involved.
However, SCR suffers from the following drawbacks:
- Cut-off current is not exactly zero.
- There is some voltage drop across SCR when in on-state; hence there is some wastage of power.
- It is more costly and need more care in handling.