Question

1. Explain briefly the operation of a bi-polar transistor as a switch.

Answer 1

Transistor works in three regions

1) active region

2) cut off region

3 ) saturation region

In active region transistor work as an amplifier.

In cuttoff region transistor work like open switch, and in saturation region it's works like short circuit or closed switch.

Based on supply voltage to the base terminal the transistor works like a switch. When sufficient input voltage give to the base terminal ( vin>0.7) the transistor goes to switch on state. When base has high potential then it creates a bridge to electrons to pass the emitter junction to collector junction just like as a switch.

Also when base terminal has low potential or 0 voltage then transistor goes to open circuit or switch off condition. This is happens in cut off region. In cut off region transistor does not have the sufficient energy to pass the electrons from emitter junction to collector junction.

In npn transistor , giving supply means we injects the electrons into the p type semi conductor to break the potential barrier which is formed by p type semi conductor in transistor. If we break the barrier then transistor goes to on otherwise it's in off state like a switch.