Thyristor- Types & Modes Of Thyristor

Earlier than going deep into the workings of a thyristor, let’s perceive why it’s wanted after we have already got a tiny element named transistor that may assist us in switching and amplification.

Whereas a transistor can carry out switching, they don’t seem to be good at dealing with giant quantities of the present. One other drawback with the transistor is that they get turned OFF after we take away the switching present.

After we need to set off and the switching present is eliminated, we want another gadget because right here the transistor fails. To resolve each of the above issues, a thyristor is required. Moreover dealing with a large amount of present, it might also run repeatedly even when the switching present is removed.

A thyristor is a four-layer solid-state semiconductor gadget that incorporates Three PN junctions in sequence having Three terminals referred to as anode, cathode, and gate. Like a diode, a thyristor is a unidirectional gadget as properly however not like a diode, it may be used as an open circuit swap.

Working Principle of a Thyristor

In a thyristor, the silicon wafer is doped with 4 alternate P and N sorts, which appears like two transistors related to back-to-back

Right here, the P (cathode) and the N (anode) are joined in sequence, thus we get three terminal pins: anode, gate, and cathode.

After we forward bias the anode and cathode i.e. anode and cathode related to the optimistic and adverse terminals of a battery, the primary PN junction and final PN junction (j1 and j3 ) develop into forwarding biased as a result of break of the depletion layer. The junction j2 stays as reversed biased as no present is offered to the gate.

After we provide a present to the gate, then the j2 junction layer begins breaking and the present begins flowing within the circuit. When an adequate optimistic sign present or pulse is utilized to the gate terminal, it triggers the thyristor right into a conducting state.

A thyristor can solely be totally on or off, which means it can not lie in between On and Off states much like transistors. This makes a thyristor unsuitable as an analog amplifier, however helpful as a switching gadget.

Modes Of thyristor

Its three working modes:

Forward blocking mode

Junctions j1 and j3 are in ahead working state whereas j2 is in reverse biased state and doesn’t permit the present to move.

Forward conduction mode

Right here a optimistic voltage is utilized to the gate terminal, inflicting the j2 depletion area to interrupt down. Resulting from this, present begins flowing within the circuit and ends in swap ON mode.

Reverse blocking mode

Right here we give adverse voltage to anode and optimistic voltage to cathode whereas the gate is stored in an open circuit, causing j1 and j3 to be in reverse bias and j2 in ahead bias. As j1 and j2 are reverse biased, the move of the present is not possible.

Types Of Thyristor

There are usually 3 different kinds of thyristor:

1. Silicon Controlled Rectifier – SCR
   It has the power to regulate large present and is usually used as excessive frequency swap in {an electrical} circuit.
2. Gate Turn OFF Thyristor – GTO
   They’re utilized in inverters, AC drives, induction heater and so forth.
3. Insulated Gate Controlled Bipolar Transistor – IGBT
   They’re utilized in SMPS, motor management, induction heating, and so forth.

We use thyristor as switching circuit the place now we have to control motors and function ON/OFF lamps.

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