Why biasing is required in transistor

Similarly In N-region negative charges i. It is observed that when surrounding temperature increases electrons minority carriers present in p-type region[Base Terminal] moves towards n-type region[collector Terminal],similarly holes minority carriers present in n-type region[collector Terminal] moves towards p-type region[Base Terminal]. When these minority carriers come close to the depletion region an electric field is generated between electrons minority carriers present in the p-region[Base Terminal] and positive charge present in the depletion region due to this the electrons from the p-region Base Terminal are transferred towards n-region Collector Terminal.

Therefore a current ICBO flows from the collector terminal to the base terminal due to minority carriers. Practically it is observed that Icbo doubles for every degree rise in temperature. Now if Ic increases that means electrons in the collector region increases due to which collector region will burn out completely.

Thus the self-destruction of unstabilized transistors is known as thermal runaway. So the main problem which affects the operating point is temperature. Hence operating point should be made independent of the temperature so as to achieve stability.

To achieve this, biasing circuits are introduced. The process of making the operating point independent of temperature changes or variations in transistor parameters is known as Stabilization. Once the stabilization is achieved, the values of I C and V CE become independent of temperature variations or replacement of transistor. A good biasing circuit helps in the stabilization of operating point.

The collector leakage current I CBO is greatly influenced by temperature variations. Therefore, the operating point needs to be stabilized i. Hence it is necessary to stabilize the operating point. The flow of collector current and also the collector leakage current causes heat dissipation. If the operating point is not stabilized, there occurs a cumulative effect which increases this heat dissipation. In order to avoid thermal runaway and the destruction of transistor, it is necessary to stabilize the operating point, i.

When it is used as an amplifier it operates in the active region and if it is used for switch application then it operates in the saturation and cutoff region, that is, it switches between these two region. So depending upon the transistor function requirement the transistor is based to operate in those aforementioned region. For amplification function, the transistor is designed to operate in the active region by proper biasing of the transistor. When it operates in the active region the B-E junction is forward biased and the C-B junction is revered biased.

So biasing is also referred as process of making the B-E junction forward biased and C-B junction a reversed biased junction.