BIASING IN DIODE

BIASING IN DIODE 

Connecting a p-n junction to an external d.c. voltage source is called biasing.

1. Forward biasing

2. Reverse biasing

 

1. Forward biasing

• When external voltage applied to the junction is in such a direction that it cancels the potential barrier, thus permitting current flow is called forward biasing.
• To apply forward bias, connect +ve terminal of the battery to p-type and –ve terminal to n-type as shown in figure below.
• The applied forward potential establishes the electric field which acts against the field due to potential barrier. Therefore the resultant field is weakened and the barrier height is reduced at the junction as shown in figure. 

• Since the potential barrier voltage is very small, a small forward voltage is sufficient to completely eliminate the barrier. Once the potential barrier is eliminated by the forward voltage, junction resistance becomes almost zero and a low resistance path is established for the entire circuit. Therefore current flows in the circuit. This is called forward current.

2. Reverse biasing

• When the external voltage applied to the junction is in such a direction the potential barrier is increased it is called reverse biasing.
• To apply reverse bias, connect –ve terminal of the battery to p-type and +ve terminal to n-type as shown in figure below.
• The applied reverse voltage establishes an electric field which acts in the same direction as the field due to potential barrier. Therefore the resultant field at the junction is strengthened and the barrier height is increased .

• The increased potential barrier prevents the flow of charge carriers across the junction. Thus a high resistance path is established for the entire circuit and hence current does not flow.