Fixed bias or base bias method of stabilization in Hindi ( fixed bias stability factor) HD

FIXED BIAS OR BASE BIAS METHOD OF STABILIZATION Stability factor for fixed bias configuration Common emitter biasing circuit In this circuit E-B junction is forward biased by battery VBB In this circuit C-B junction is reverse biased by battery VCC Since VBE required to forward bias the transistor is very less And it is very difficult to have a battery of such a small value. Resistance RB is connected in series with VBB and thus, RB is adjusted according to value of battery VBB Since, it is always convenient to have electronic circuit which works on single battery Fixed bias or base bias method The circuit is modified to be used with single battery VCC This forms fixed bias circuit or base bias circuit Here VCC is used to both forward bias the E-B junction and reverse bias the C-B junction A zero signal value of IB is provided by supply VCC By selecting proper value of RB the required valued of base current IB is made to flow And output current IC depends on input current IB IC=βIB By circuit analysis _=_/_ Since, supply VCC is fixed, therefore, IB also fixed therefore this circuit is called fixed bias circuit _=_−⁡〖_ 〗 _=(_−_)/_ IC and VCE are operating point values ADVANTAGES OF FIXED BIAS CIRCUIT 1. Simple circuit as it uses few components. 2. It provides max flexibility, because the biasing conditions are easily set by changing the value of RB. 3.No loading of source VCC as no emitter resistance, RE is used. DISADVANTAGES OF FIXED BIAS CIRCUIT Poor stability 1. There is no means to stop self increase of IC due to increase in temperature. So, thermal stability is not provided. 2. If β increases due to transistor replacement then, Ic also increases by factor β Therefore there is a chance of thermal runaway Stability factor Since Stability factor S is very high equal to S= β+1. Thus, this circuit is rarely used The modified circuit for fixed bias method is collector to base bias method