Input Characteristic Of Transistor

In earlier blog we understood some basics of transistors and we saw that the was more in CE configuration also it has high gain therefore from now on wards 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 transistor while the current flow is 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 bjt transistor using CE configuration.
@ INPUT CHARACTERISTIC OF BJT TRANSISTOR(bc547) :-

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

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

When we apply some voltage to the base of transistor then the electrons present in the emitter region moves towards base or p-region.When the electrons enters the base region then these electrons are attracted to the base terminal of the transistor because base emitter terminals together forms the forward bias p-n junction diode.As the electrons moves from emitter to base therefore the current flows from base to emitter.Practically the electrons flows 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 bjt transistor is same as that of a p-n junction diode.

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

For example suppose if we consider that there are 100 e- (electrons) in 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 remaining 6e- will move to the base terminal giving rise to less current(Ib) at base terminal and more current(Ic) at collector terminal.

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

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

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

Originally published at https://www.practical-buddy.xyz on May 11, 2020.