Merits and demerits of collector-to-base bias, Electrical Engineering

Merits and Demerits of Collector-to-base bias:


In this type of circuit the circuit stabilizes the operating point against differences in temperature and β (that is replacement of transistor)


In this type of circuit, to keep Ic independent of β, the subsequent condition must be met:

Ic = βIb = β(Vcc - Vbe)/ Rb + Rc + βRc ≈ (Vcc - Vbe) / Rc

This is the case while

βRc >> Rb

As β-value is set (and usually not known) for a given transistor, this relation can be satisfied either through keeping Rc fairly large or making Rb very low.

If Rc is large, a high Vcc is essential that increases cost also precautions are essential while handling.

The reverse bias of the collector-base region is small If Rb is low that limits the range of collector voltage swing which leaves the transistor in active mode.

The resistor Rb causes an AC feedback, decreasing the voltage gain of the amplifier. This not desirable effect is a trade-off for greater Q-point stability.

Posted Date: 1/10/2013 7:18:45 AM | Location : United States

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