BJT charactrestics....

[Deepthi Palavelli]

Hi..!
Is there any difference between beta(a.c) nb beta(d.c)?
How we calculate beta(d.c) in terms of beta(a.c)?



Thanhs in advance.!

 

[ArNvC]

A Bipolar Junction Transistor (BJT) when operated with DC inputs, the levels of its collector current Ic and base current Ib are related by the term beta (β), and expressed as:

β(dc) = Ic/Ib

For alternating potentials beta AC is expressed as:

β(ac) = ∆Ic/∆Ib│V(ce) = constant. As a general rule β(ac)>β(dc). To amplify an ac voltage, the transistor must operate at ranges of different values, hence the difference. So your calculation will depend on the ranges of Ic and Ib.

 

[John Steave]

The Bipolar Transistor tutorial, we saw that the most common circuit configuration for an NPN transistor is that of the Common Emitter Amplifier circuit and that a family of curves known commonly as the Output Characteristic Curves, relate the transistors Collector current ( Ic ), to the output or Collector voltage ( Vce ), for different values of Base current ( Ib ).

the Collector current, Ic of the transistor is also equal to the DC gain of the transistor (Beta), times the Base current (β x Ib), if we assume a Beta (β) value for the transistor of say 100, (one hundred is a reasonable average value for low power signal transistors) the Base current Ib flowing into the transistor will be given as:
β(dc) = IC/IB
This bias reference voltage can be easily calculated using the simple voltage divider formula. And try to **broken link removed** for completely known about BJT Characteristics.

 

[Kalyan_Acharjya]

beta (D.C) for static case and beta (A.C) for dynamic case....in dynamic you always considered in range. i.e ranges of Ic and Ib (in CE Amplifier) with respect to constant Vce. Generally beta (A.C)>beta (D.C) ,but not huge difference in their values. You considered for DC analysis or Ac Analysis...thats the important.