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# Numericals on Transistors - Questions & Answers [Solved]

Numerical on current , amplification factors of transistors

1. Generalized expression for collector current:

IC = α IE +IC0[1-e(Vc/VT)]

Where VC is the negative and is very large as compared to VT . the physical interpretation is that the P-N junction diode current crossing the collector junction is supplemented by the fraction α of the current IE .

2, Current amplification factor:

a. The alpha factor is the current amplification factor and is the ratioof the collector current to the emitter current

α =Δ IC/ΔIE , where VCB should be constant,

This value of alpha is always less than 1

b. The beta factor β is the current gain factor (transport factor) of the common emitter circuit and is defined as the ratio of collector current to the base current.

β =Δ IC/ΔIB

c. Relationship between α and β

α = β/1+ β and β= α/1- α

1. In a certain transistor , collector current is 0.98 mA and base current is 20mA. Determine the value of 1. Emitter current, 2. Current amplification factor 3. Current gain factor

Solution: for emitter current , please draw the circuit of common base configuration , gives weigtage, the as per Kirchhoff’s law find emitter current.

Other two factor can be found out by direct formulas

2. Determine the values of emitter current and collector current of the transistor having α=0.98 and collector to base leakage current ICB0 = 4µA . the base current is 50 µA.

Solution: collector current is given as: IC= αIE+ICB0 and IE=IC+IB .

Thus using this two answer can be found out.

3. The BJT has IB = 10 µA, β= 99 and IC0 = 1 µA. what is collector current IC ?

Solution: IC= αIE+ICB0 and β= α/1- α will provide you with the answer.

**Some basics:**1. Generalized expression for collector current:

IC = α IE +IC0[1-e(Vc/VT)]

Where VC is the negative and is very large as compared to VT . the physical interpretation is that the P-N junction diode current crossing the collector junction is supplemented by the fraction α of the current IE .

2, Current amplification factor:

a. The alpha factor is the current amplification factor and is the ratioof the collector current to the emitter current

α =Δ IC/ΔIE , where VCB should be constant,

This value of alpha is always less than 1

b. The beta factor β is the current gain factor (transport factor) of the common emitter circuit and is defined as the ratio of collector current to the base current.

β =Δ IC/ΔIB

c. Relationship between α and β

α = β/1+ β and β= α/1- α

**Numerical**1. In a certain transistor , collector current is 0.98 mA and base current is 20mA. Determine the value of 1. Emitter current, 2. Current amplification factor 3. Current gain factor

Solution: for emitter current , please draw the circuit of common base configuration , gives weigtage, the as per Kirchhoff’s law find emitter current.

Other two factor can be found out by direct formulas

2. Determine the values of emitter current and collector current of the transistor having α=0.98 and collector to base leakage current ICB0 = 4µA . the base current is 50 µA.

Solution: collector current is given as: IC= αIE+ICB0 and IE=IC+IB .

Thus using this two answer can be found out.

3. The BJT has IB = 10 µA, β= 99 and IC0 = 1 µA. what is collector current IC ?

Solution: IC= αIE+ICB0 and β= α/1- α will provide you with the answer.

It is nice.. Easy to understand for beginners

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