The Fixed Bias Circuit The Thermal Stability Factor : SIco SIco = ∂Ic ∂Ico General Equation of SIco Comes out to be SIco ═ β 1- β (∂Ib/∂IC) Vbe, β RC Rb RC Applying KVL through Base Circuit we can write, Ib Rb+ Vbe= Vcc Diff w. This can be written as: The Thermal Stability Factor : SIco SIco = ∂Ic ∂Ico This equation signifies that Ic Changes SIco times as fast as Ico Differentiating the equation of Collector Current IC = (1+β)Ico+ βIb & rearranging the terms we can write SIco ═ 1+β 1- β (∂Ib/∂IC) It may be noted that Lower is the value of SIco better is the stability Vbe, βįixed Bias Circuit Fixed Bias with Emitter Resistor Collector to Base Bias Circuit Potential Divider Bias Circuit Stability Factor S:- The stability factor S, as the change of collector current with respect to the reverse saturation current, keeping β and VBE constant. The goal is to set the Q-point such that that it does not go into saturation or cutoff when an a ac signal is applied.Ħ The Thermal Stability of Operating Point (SIco) The dc operating point between saturation and cutoff is called the Q-point. The selection of a proper quiescent point generally depends on the following factors: The amplitude of the signal to be handled by the amplifier and distortion level in signal The load to which the amplifier is to work for a corresponding supply voltage The operating point of a transistor amplifier shifts mainly with changes in temperature, since the transistor parameters - β, ICO and VBE (where the symbols carry their usual meaning)-are functions of temperature.ĥ The DC Operating Point For a transistor circuit to amplify it must be properly biased with dc voltages. The maintenance of operating point stable is called Stabilisation. It is desired that once selected the operating point should remain stable. The circuit used for transistor biasing is called the biasing circuit.Ĥ BIAS STABILITY Through proper biasing, a desired quiescent operating point of the transistor amplifier in the active region (linear region) of the characteristics is obtained. The later method is more efficient and is frequently used. HOW A TRANSISTOR CAN BE BIASED? A transistor is biased either with the help of battery or associating a circuit with the transistor. WHY BIASING? If the transistor is not biased properly, it would work inefficiently and produce distortion in output signal. For faithful amplification it is essential that:- Emitter-Base junction is forward biased Collector- Base junction is reversed biased Proper zero signal collector current The proper flow of zero signal collector current and the maintenance of proper collector emitter voltage during the passage of signal is called transistor biasing. The process of raising the strength of weak signal without any change in its general shape is referred as faithful amplification. of Physics, D.A.V (PG) College, Bulandshahr, U.P., India.Ģ Transistor Biasing The basic function of transistor is amplification.
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