q why we need biasingneed for biasing baising is

Question

Q. Why we Need biasing?

Need for biasing : Baising is necessary to establish the quiescent operating point so that the device operates with the linear region without exceeding the maximum power dissipation curve.

Operating point or quiescent point: It is fixed in the active region of the transistor characteristics within the maximum constraints it either shortens the life time of the device or destroys the device. The operating point is fixed for a particular value of base current IB , collector current IC and collector emitter voltage drop VCE. If any of these parameters change them, the quiescent point tends to change.

Factors affecting Q-point

· Change in ß

· Changes  in temperature

Effect of change in temperature on V_BE

VBE  decreses by 2.5mV per degree C in temperature the base current IB is fixed bias .with the increase in temperature the base-emitter voltage  VBE  decreases which inturn increases the difference between VBE and collector biasing voltage VCC and therefore base current IB increases.even a small increase in IB increase collector current IC to a larger extent and V_CC drops .Hence the Q-point fixed on these two parameters  varies.