The Silicon Controlled Rectifier (SCR) is one of the most important semiconductor devices that exist. It was invented by General Electric in 1961 for use in power transmission and distribution, but today it has many applications.

So what is an SCR?

It is a three-terminal device that can be switched on and off like a transistor. The main difference between an SCR and a transistor, however, is that the current through the SCR cannot be reversed once it has been turned on.

How does it work?

An SCR consists of four layers: two PN junctions (Junction A and Junction B) separated by an N-region, and two P regions (P+ and P-) on either side of the N region. A positive voltage applied between Junction A and one of the outer terminals will turn it on.

If another external terminal is also given a negative voltage with respect to Junction A, then current can flow around the outside loop, through the load, and back into Junction B.

The SCR has infinite resistance until it is turned on by applying a positive voltage between its gate terminal (G) and either of its two main terminals (MA or MB). Once the device begins to conduct current, however, there is no turning off unless an external circuit can remove enough current from the gate to reduce the voltage below the turn-off threshold.

Applications of Silicon Controlled Rectifiers

The SCR is used extensively in power transmission and distribution, motor control, and other industrial applications where it is important to be able to turn devices on or off without having to worry about reversing the current flow. In recent years, SCRs have also found their way into consumer electronics, where they are used for such things as power supplies, motor controllers, and lighting.

So there you have it - a brief introduction to Silicon Controlled Rectifiers. Stay tuned for future posts that will explore this topic in more detail!