Transistor Biasing

Biasing of the transistor:

1. We know that for normal operation of the transistor the first junction i.e. the emitter base junction should be forward biased and the collector base junction to be reverse bias.

2. But the transistor can be biased in some other way also.

a. Forward- Reverse biasing: Also called as FR biasing. It’s the normal operation of the transistor where emitter base is forward and collector base is reverse bias.

b. The transistor is said to be in the active region.

c. This kind of biasing is used for amplification.

1. Forward- forward biasing: Also called as FF biasing. In this both the junctions are forward biased.

2. The transistor is in the saturation region. Here the collector current is independent of the emitter current.

3. The transistor acts as a closed switch.

a. Reverse- Reverse Biasing: Here both the junction are reverse biased.

b. Here there is no flow of current through the transistor.

c. It acts as open switch

d. It is in cut-off region.

1. Reverse- Forward Biasing: Here the emitter base junction is reverse bias and the collector base junction is forward biased.

2. Then the transistor works in inverted mode of operation.

3. The design is conceptually significant

biasing_transistor

Very good question indeed... thank you for asking this question.

To start with, I would like to remind that a transistor is a three terminal device with the three terminals being the emitter, base and the collector.

When the emitter-base junction is forward biased and the base collector junction is reverse biased, this three terminal device is called as a transistor since it sustains the so called transistor action.

However when this three terminal device is biased in some other configuration, it does not sustain transistor action and thus in strict sense should not be called a transistor. This device may function as a closed switch, open switch etc. but not as the transistor.

The term 'transistor' is suitable only when the device is able to sustain transistor action(forward-reverse configuration). In all other cases, it must be named as per the functionality it offers (a switch etc.).