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Similarly, with the remaining electrons, the collector current is quite high and the emitter current is the sum of both the currents. The base is lightly doped and thus the base current is very low. What could be the value of alpha? ‘Low’ or ‘High’?

Alpha is the other factor that is the current gain of the transistor from the collector to the emitter terminal.

It is a dimensionless quantity as is the ratio of two currents. Thus this value goes as high as 200 for standard transistors.

This factor-beta makes the transistor work as an amplifier.

This is called DC current gain and represented as ,

The current in an NPN transistor is given by the ratio of collector current to that of the base.

From the above analysis, we can say that.

It has a higher value than the base current. The current flowing in the collector region because of the remaining electrons flow is the collector current, I C. The current produced due to the recombination of the electrons and hole is known as the base current, I B. The few electrons coming from the emitter get recombined with the holes but maximum electrons cross the base region and enter the collector region. The base region is very lightly doped and is a p-type semiconductor, therefore has a few holes as the charge carriers. In an n-type semiconductor the majority charge carriers are the electrons and thus, start moving towards the base junction, thus the name emitter current, I E. Please note that the depletion region behaves as the opposition to the flow of current, therefore, the thinner the layer the more the current flow in that region.

The depletion region of the emitter-base region is smaller as compared to the collector-base region. Similarly, for the collector-base region, the positive supply of V CC is connected to the n-type semiconductor and thus made reverse biased. Now we must understand here how to make a junction forward or reverse biased?Īs the n-type of semiconductor comes first when talking about the emitter-base region therefore, the negative of the voltage supply gets connected with it to make it in forward bias. Also, the collector-base junction is reverse biased and V EE is the supply for this region.

The emitter region is always connected to the negative supply and the collector with the positive one.Īs shown in the fig, the base-emitter junction is made forward biased with a supply voltage as V CC. Here, the base region has the control for ON/OFF of the transistor based on the input given to it. The emitter is moderately doped with the least doping in the base region (lightly doped p-semiconductor). The three terminals emitter, base, and collector are all doped differently.