Input Characteristic Of Transistor

In an earlier blog, we understood some basics of transistors and we saw that the power gain was more in CE configuration also it has high gain therefore

from now onwards we will be studying only CE configuration to understand the BJT transistor in little depth.

Also, we will be taking NPN transistors because the current flows very easily and quickly in NPN transistors while the current flow is a little less and slow for PNP transistors the reason we had discussed in earlier blog.
So the main aim of this blog is to focus on the input characteristics of the BJT transistor using CE configuration.
@  INPUT  CHARACTERISTIC  OF  BJT  TRANSISTOR(bc547) :-

The input characteristic is obtained by plotting the Input base current(Ib) versus Input base voltage(Vbe) keeping the Output voltage(Vce) constant.

For understanding input characteristics of CE configuration in detail , consider 2 cases

# Case :-1 :- Vce=0v[Constant] but Ib and Vbe is varying

When we apply some voltage to the base of the transistor then the electrons present in the emitter region moves towards the base or p-region. When the electrons enter the base region then these electrons are attracted to the base terminal of the transistor because base-emitter terminals together form the forward bias p-n junction diode. As the electrons move from emitter to base therefore the current flows from base to emitter. Practically the electrons flow from emitter to base only if Vbe is greater than or is equal to 0.7 volts but depending upon temperature and many other factors this value may vary. Therefore the input characteristic of the BJT transistor is the same as that of a p-n junction diode.

VIDEO :-

# Case:-2 :- Vce=1v but Ib and Vbe is varying 

Here we are keeping Vce=1v constant and Vbe varying. Since Vce=1v i.e. collector and the base junction is reverse biased which means we had applied positive voltage to the n region(collector) of the transistor, therefore, the depletion region(D2) of the base-collector region increases causing a reduction in the base region. Now if we increase base voltage or in other words if we increase Vbe the base-emitter region acts like a forward-biased p-n junction diode and therefore the electrons move from the N-type region(Emitter) to the p-type region(base). When electrons enter the p-region which is reduced due to an increase in depletion region (D2)  most of the electrons move to the collector region this is because the collector(n-type region)terminal (Vce=1) is at a higher potential than the base terminal(Vbe) giving rise to more current(Ic) in collector region and less current at the base terminal(Ib)

For example, suppose if we consider that there are 100 e- (electrons) in the emitter region now when we keep Vce=1v and if we increase Vbe then it will act like pn junction which is forward biased and therefore this 100e- will enter the p-type region. Now, 94e- will move to the collector region while the remaining 6e- will move to the base terminal giving rise to less current(Ib) at the base terminal and more current(Ic) at the collector terminal.

VIDEO  :-

Now let's do it practically, just perform the practical as discussed in the above cases you may obtain some values as shown below:-
Observation Table :-

 Note :-The input current Ib is in microamperes (uA) and the input voltage Vbe is in volts(v)

Graphical Representation :-

CONCLUSION:- The input characteristics of  BJT(bc547)Transistor is the same as forwarding bias p-n junction diode and the input current Ib decreases with an increase in output voltage Vce.

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