Question

The collector and emitter current levels for a transistor with common base dc current gain of 0.99 and base current of 20 μA are respectively 
1. 2 mA and 1.98 mA
2. 1.98 μA and 2 mA 
3. 1.98 mA and 2 mA
4. 2 mA and 1.98 μA 

Answer 1

Correct Answer - Option 3 : 1.98 mA and 2 mA

Concept:

Collector current can be calculated as:

Ic = βIb ----(1)

where β is common emitter DC gain and 

\(β=\frac{\alpha}{1-\alpha}\) -----(2)

Emitter current can be calculated by:

Ie = Ib + Ic -----(3)

Calculation:

Given:

α = 0.99

I_b = 20 μA

From equation (1) and (2), 

I_c can be calculated:

\(\beta=\frac{0.99}{1-0.99}=99\)

I_c = 99 × 20

I_c = 1.98 mA

From equation (3)

I_e can be calculated as:

I_e = 1.98 + 0.02 = 2 mA.