Output Characteristics Of Transistor

In the last post, we studied and implemented the input characteristics of the bjt transistor(bc547). In this post, we will be focusing on the output characteristics of the BJT transistor(bc547). Why it is important to understand?. We will be seeing it in great depth.

The output characteristic of the BJT transistor is plotted between the output current(Ic) and the output voltage(Vce) keeping the base current(Ib) constant.
Consider 2 Cases for understanding output characteristics of BJT
CASE:-1:-When Ib=10uA and Vce & Ic are varying

The input current Ib is fixed and Vce and Ic keep on varying. As Vce has increased Ic also increases but by a very small amount this is because the collector terminal(N-type) region is connected to the positive terminal. Since it is reverse biased therefore depletion region(D2) between collector and base increases. As depletion region D2 increases, electrons present in the emitter terminal suffers little resistance to migrate to the collector terminal.

Let's say if Vce=1v and there are 100e-(electrons) in the emitter terminal(N-Type region) out of that 100e- only 30e- will migrate to the collector terminal.

Now if Vce=2v and there are 100e-(electrons) in the emitter terminal(N-Type region) out of that 100e- only 45e- will migrate to the collector terminal i.e. collector current Ic increases in this case.

Similarly, as Vce increases Ic also increases, at some point where Vce=Vce(max) the base is totally vanished(nullified) causing undesired collector current to flow and the transistor enters into breakdown region.

The concept will be more clear by watching the video present below:-

VIDEO:-

CASE:-2:-When Ib=20uA and Vce & Ic are varying

In this case, as Ib is increased we see that Ic also increases by some amount. Again as Vce increases Ic also increases and the transistor works the same as discussed above.

Let's do it practically:-

@ Here is the OBSERVATION TABLE of an output characteristic considering the above conditions:-

@ GRAPHICAL REPRESENTATION:-

@ CONCLUSION:-

*As Input current(Ib) increases output current(Ic) also increases.

*Also if output voltage(Vce) increases output current(Ic) also increases if Vce=Vcc then the transistor will enter into breakdown region.

@ Now the question arises why we are studying output characteristics ?

So here is the explanation,

Just look at the above diagram clearly here you can see 3 regions 

Region:-1:- Cutoff Region:-

In the cutoff region, the input current(Ib) is almost negligible. From the above output characteristics, we can say that as Ib=0 therefore Ic=0 but still some current flows due to minority charge carriers. There is a negligible effect of Vce on Ic(i.e. if Vce is increased Ic is almost constant). Thus we can say that in the cutoff region transistor acts as an open circuit(switch off case). You can assume this phenomenon as the tap is closed i.e. no water(current) is flowing.

Region:-2:- Saturation Region:-

In saturation region,the input current(Ib) is high or is at it's peak value since Ib is high Ic is also high but Vce is very low in this region. Thus transistor behaves like a short circuit(switch on the case). You can assume this phenomenon as the tap is open i.e. maximum water(current) is flowing.

Region:-3:- Linear or Active Region:-

In the linear region, you can assume that the transistor is partially on or you can say that is partially off. This region is responsible for the application of amplification. Now you can assume this phenomenon as you are trying to block(partially open) the water coming from the pipe, what you will see is that water will come out with great force(Amplification). For best amplification transistor should be biased properly. So in the next post, we will learn what is biasing, why it is needed, and how to bias a transistor?  

Thus by learning output characteristics we can conclude that a single transistor can be operated in 3 different regions as mentioned above.

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