At a Glance of CC Configuration
In our previous blog, we learn about the CB configuration of the transistor and now in our today’s blog we will learn about CC Configuration its Current amplification factor, Input characteristics and Output characteristics.
As the name suggests, this configuration has a common collector to the input and output sides.
VBB and VEE are the biasing potentials for the input and output sides, respectively.
IB is the base current, IE is the emitter current, and IC is the collector current.
For the detailed explanation of this configuration, the NPN transistor is taken however the working is in active mode. Hence, the emitter-base junction is forward bias, and the collector-base junction is reverse biased.
The output voltage VCE is equal to VBE + VBC.
In the case of output characteristics, we plot the graphical relation between the output current (IE ) and output voltage (VCE) for different values of current (IB), hence we have the visual relation between
IE Vs. VCE for various levels of base current (IB).
We learned in our previous blog on BJT that,
Ic = α IE
And α varies from 0.95 -0.98, which is nearly equal to 1, therefore we can say that the collector current is almost identical to the emitter current.
Common base characteristics for common emitter configuration are taken as Ic Vs. VCE
So for all practical purposes, the output characteristics of the common collector configuration are similar to the common-emitter configuration.
Current amplification factor in CC Configuration
ϒ denotes the current amplification factor.
It is the ratio of change in emitter current to the change in base current.
ϒ = IE / IB
However we know that,
IE = Ic + IB ——– 1
Ic = α IE + ——— 2
By putting equation 2 in equation 1 we get,
IE = α IE + ICBO + IB
(1- α) IE = IB + ICBO )
Divide the both side by (1- α), we get
IE = IB/ (1- α) + ICBO/ (1- α)
And we know that 1/ (1- α) is the current amplification factor in the common collector configuration.
IE = ϒ. IB + ϒ. ICBO
Input characteristics of CC Configuration
Common collector configuration input characteristics are drawn between collector-base voltage VBE and the base current IB when the emitter voltage VCE is constant therefore Change in output voltage VCE depends upon the changes in VBC and IB.
The input characteristics curve for the common collector configuration is shown below.
Output characteristics of CC Configuration
Output characteristics for the common base configuration are drawn between the emitter-collector voltage VCE and output current IE when the input current IB is constant. The collector current is proportional with the base current; therefore, when the input current IB is zero, then the collector current also becomes zero. Hence, no current will flows through the transistor.
If we have to operate the transistor in the active region, we need to increase the base current till it reaches to saturation region. To plot the output characteristics graph, we need to keep the base current IB constant and vary the emitter-collector voltage VCE.
The output characteristics graph for common collector configuration is as shown in the below figure.
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