What is SCR (thyristor)? | Working of SCR (thyristor)

Hello friends, in today’s article I am going to tell you what is SCR (thyristor), the working of SCR (thyristor), the characteristic curve of SCR (thyristor), if you also want to know then keep reading this article completely. so let’s start

What is SCR (thyristor)

Silicon Controlled Rectifier (SCR)Construction– It is a four-layer (P1, N1, P2, N2) and three junctions (J1, J2, J3) semiconductor device.. The concentration of impurity is kept high in P1 and N2 layer and the concentration of impurity in the P2 and N1 layer is kept low. Therefore, for this reason, the width of the depletion layer at the junctions J1 and J3 are kept less than that of junction J2.

If SCR is made from Ge instead of silicon, then for this the value of α at room temperature is approximately equal to 0.5. Due to which this device becomes ON without applying a voltage to the room temperature. The planetary device is made only from silicon materials and it is a unilateral device.

Working of SCR (thyristor)

To understand the working of silicon control rectifier, it is necessary to pay attention to the following points

1. Reverse Blocking Mode – Thyristor is in reverse bias when the cathode is made positive to the anode and switch ‘S’ is open. In this situation, a very small amount of current flows, which is called backward leakage current. If the value of the reverse bias voltage is increased, a small amount of current will now flow through it in a large amount. This causes a breakdown, it is called Reverse Breakdown Voltage (VBR) and an avalanche is formed at the junctions J1 and J3, due to which the reverse bias voltage suddenly increases. The back and long regions are shown by PQ in figure (b) and the rear bias, the thyristor acts as an open switch.

2. Forward Blocking Mode – When the gate circuit is open and the value of the voltage between them is increased by making the anode positive to the cathode. Then in the thyristor, the junctions J1 and J3 are in forwarding bias and J2 in reverse bias. In this mode very little current flows which are called forward leakage current, which is shown in figure (b). In Figure (b) OM represents the forward blocking mode of the thyristor.

3. Forward Conduction Mode – When the gate circuit is kept closed and voltage is provided by keeping the gate terminal positive relative to the cathode, it attracts electrons from the cathode (N-type) side. Kar Junction to J2. At the same time, the anode is kept positive to the cathode, so that junctions J1 and J3 are in a forward bias state and electrons are responsible for moving near the junctions J1 and J3. Therefore, as soon as the voltage between the anode and the cathode is increased, the thyristor turns into a rapid conduction state due to the electrons reaching the three junctions J1, J2, and J3. This is called forward avalanche breakdown.

The voltage at which this breakdown occurs is called the Forward Breakdown Voltage. That is, by providing the gate voltage, fast current starts flowing through the thyristor, the minimum anode current at which the thyristor turns on is called latching current. Similarly, when the thyristor is turned on (ON), the minimum anode current as far as the thyristor can remain on (ON) is called holding current (IH).

As per figure (b), after the breakdown occurs as soon as the gate current is applied, the thyristor turns on (ON) at point M and is transferred to point N and works in a forward conduction state from point N to K.

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Now you must have known what is SCR (thyristor), the working of SCR (thyristor), the characteristic curve of SCR (thyristor).