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Obtain the relation between the current amplification factors α and β of a transistor.

Aniket Singh , 9 Months ago
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Askiitians Tutor Team

Last Activity: 9 Months ago

The current amplification factors, α (alpha) and β (beta), are important parameters in the analysis of bipolar junction transistors (BJTs). These factors describe the relationship between the input current (base current, IB) and the output currents (collector current, IC, and emitter current, IE) in a transistor. There is a direct relationship between α and β:

α (alpha) is the common base current gain, which is defined as the ratio of the collector current (IC) to the emitter current (IE) while keeping the base current (IB) constant. Mathematically, it can be expressed as:

α = IC / IE

β (beta) is the common emitter current gain, which is defined as the ratio of the collector current (IC) to the base current (IB) while keeping the emitter current (IE) constant. Mathematically, it can be expressed as:

β = IC / IB

Now, let's relate α and β:

α = IC / IE
β = IC / IB

To relate α and β, you can use the equation for IE in terms of IB and IC. The sum of collector current (IC) and emitter current (IE) is the total current flowing through the transistor, which is essentially the collector current. Therefore, we have:

IC = IB + IE

Now, substitute IE in terms of IC and IB in the α equation:

α = IC / (IC - IB)

Similarly, substitute IB in terms of IC and β in the β equation:

β = IC / (IC / β)

Now, let's simplify these expressions:

α = IC / (IC - IB)

β = β

So, we've obtained the relation between α and β:

α = IC / (IC - IB)
β = β

This relationship shows that α depends on both IC and IB, while β is simply the value of β, which is a constant characteristic of the transistor. In practice, β is a known parameter for a given transistor and can be found in its datasheet, while α depends on the operating conditions and can vary with temperature and other factors.

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