How thyristors work
Transistors are the tiny electronics components that changes the world, you'll find them in every electronics items like telephones, computers, calculators, radios and hearing aids etc. They are amazingly versatile, but that doesn't mean they can do everything. Although we can use them to switch tiny electrical current on and off (that is the basic principle behind computer memory), and transform small current into somewhat large ones(that's how an amplifier works), they are not very useful when it comes to handling much bigger currents. Another drawback is that they turn off altogether as soon as the switching current is removed, which means they are not so useful in devices such as alarms where you want a circuit to trigger and stay on indefinitely. For those sorts of jobs, we can turn to a somewhat similar electronics components called a thyristor, which has things in common with diodes, resistors and transistors. Thyristors are reasonable easy to understand. let's see the full explanation.
What are thyristors?
First of all let's know about some terminology. Some people use the term silicon-controlled rectifier (SCR) interchangeably with "thyristor". In fact, silicon-controlled rectifier is a brand name that General Electric introduced to describe one particular kind of thyristor that it made. There are various other kinds of thyristors too (including ones called diacs and triacs, which are designed to work with alternating current), so the terms aren't completely synonymous. Nevertheless, this article is about keeping things simple, so we'll just talk about thyristors in the most general terms and assume SCRs are exactly the same thing. We'll refer to them as thyristors throughout.
Three connections
So what is a thyristor? It's an electronic component with three leads called the anode (positive terminal), cathode (negative terminal), and gate. These are somewhat analogous to the three leads on a transistor, which you'll remember are called the emitter, collector, and base (for a conventional transistor) or the source, drain, and gate (in a field-effect transistor, or FET). In a conventional transistor, one of the three leads (the base) acts as a control that regulates how much current flows between the other two leads. The same is true of a thyristor, the gate controls the current that flows between the anode and the cathode.
Transistors versus Thyristors
Both transistor and thyristor are 3 terminal devices. But the three terminals of the transistor are emitter, base and collector and that of thyristor are anode, cathode and gate.
As
already mentioned, transistors and thyristors are both semiconductor devices.
They are now widely employed in switching operations because of their numerous
advantages such as noiseless operation owing to absence of moving parts, very
high switching speed (say 109 operations per second), high efficiency, low
maintenance, small size, little weight 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 over mechanical switches or electro-mechanical relays.
However, transistors and thyristors both have their own areas of applications.
