Question

Find collector current IC2, given input voltages are V1=2.078v & V2=2.06v and total current IQ=2.4mA. (Assume α=1)

(a) 0.8mA

(b) 1.6mA

(c) 0.08mA

(d) 0.16mA

This question was posed to me in an international level competition.

The query is from Operational Amplifier Internal Circuit topic in portion Operational Amplifier of Linear Integrated Circuits

Answer 1

Accurate answer is (a) 0.8mA

Paint a vivid picture of understanding with: Collector current,  IC2=αF×IQ/(1+e^Vd⁄VT),

VT = Volts equivalent of temperature = 25mv,

 ⇒ Vd = V1-V2   =2.078v-2.06v=0.018v    (equ1)

Substituting equation 1,

  ⇒ Vd/VT  = 0.018v/25mv  =   0.72v (equ2)

Substituting equation 2,

 ⇒ IC2= 1×2.4mA/(1+e^0.72)  =  2.4mA/(1+2.05)  = 0.8mA.