Question

A transistor of α = 0.99 and V_BE = 0.7 V is connected in the common-emitter configuration as shown in the figure. If the transistor is in the saturation region, find the value of collector current.

Answer 1

V_cc = 12 V

α = 0.99

V_BE = 0.7 V

I_C =?

Applying Kirchoff’s voltage law,

V_BE + (I_C + I_B) 1k + 10k.I_B + (I_C + I_B) 1k = 12 ………(1)

I_B = `"I"_"C"/β`

β = `α/(1 - α) = 0.99/(1 - 0.99)` = 0.99

I_B = `"I"_"C"/99`

I_C = β I_B

I_C = 99 I_B

I_C = `"I"_"C"/99`

V_BE = 0.7 V

Substitute in equation (1)

`0.7/10^3 + (99 "I"_"B" + "I"_"B") + 10 "I"_"B" + (99 "I"_"B" + "I"_"B") = 12/10^3`

100 I_B + 10 I_B + 100 I_B = `(12 - 0.7)/10^3`

210 I_B = `11.3/10^3`;

I_B = 0.054 × 10⁻³ A

I_C = 99 I_B = 99 × 0.054 × 10⁻³ A

I_C = 5.34 × 10⁻³ A

I_C = 5.34 mA