- #1

likephysics

- 640

- 4

## Homework Statement

Given, β=100, Is = 6E-16

See attachment.

a) Find min value of Rb such that the BJT is in active region

b) For the Rb found, what is the base-collector voltage if β=200

## Homework Equations

## The Attempt at a Solution

Assuming, VCE min for active region operation as 0.75V, I got Ic = 0.87mA

since β=100, Ib = 0.0087mA

Vbe = Vt ln (Ic/Is) = 0.728V

using Ib = (Vth-Vbe)/Rth {thevenin equivalent}, I got Rbmin as 7K. The voltage divider voltage is 0.75v and Rth is 2.1k.

But now, when I plug in Ib = Vth-Vbe/Rth, I get 0.00104mA. Which Ib is correct?

I can't figure out how to calculate the beta change. Where do I use the beta?

Ib is 0.0087mA, with new beta Ic will be 1.74mA. which will make IcRc = 3.48v, which doesn't make sense.