Two Transistor Analogy of SCR

The PNPN thyristor can be considered as two transistors Q1 & Q2 connected in cascade mode as shown in above figure.Q1 & Q2 are NPN & PNP transistor such that collector of Q1 connected to the base of Q2.

The gate terminal & collector terminal of Q2 connected to the base of Q1

When small gate current is supplied to the base of Q1 the amplified collector current generates very large collector current of Q2 .this current is supplied to base of Q1 thus positive feedback is initiated and within a few microseconds saturation is immediately reach .

The current is only limited by external load connected with transistor

………………………………..1.1

Anode current is directly proportional to Gate Current

Where, =Anode Current, are =Common Base Current Gain

=Leakage Currents Of the transistor.

Application of SCR:

1) Controlled Rectifiers

2) DC To Dc Converters

3) DC To AC Converters

4) Battery Chargers

5) Lamp Dimmers

6) AC Voltage Stabilizers

7) Speed Control of AC & DC Motors