Transistors are mainly used for switching and amplification applications.

Transistor (Bipolar Junction Transistor - BJT): This three-layer semiconductor device is similar to 2 diodes back to back. It has 3 contacts: Base (B), Emitter (E), and Collector (C).











In a transistor, we push/pull current into the Base and then that turns on the collector circuit. Saying this, Base is the control of this current-controlled electronic switch. So, as we change the Base current, the Collector and Emitter current changes dramatically (gets amplified).

We forward bias the base-emitter junction and reverse bias the base-collector junction. This means, we put a positive voltage on the base and we drive current into the base which makes this transistor gets turned-on (current flows from R1 to R2).



NPN Transistor showing two different depletion regions (shaded) when the Base-Emitter diode region is forward biased. When the +ve and -ve charges flow across the depletion region, there is a potential energy g…