# Analysis of 4 Resistor Bias Circuit (3)

## And I_{C }= I_{E ≈ }

V_{B − VBE }R_{E }

(for large β) (5)

## Hence I_{C and IE become independent of β! }

Thus we can setup a Q-point independent of β which tends to vary widely even within transistors of identical part number (For example, β of 2N2222A, a NPN BJT can vary between 75 and 325 for I_{C = 1 mA and VCE = 10V) }

27

# 4 Resistor Bias Circuit -Example

## A 2N2222A is connected as shown with R_{1 = 6.8 kΩ, R2 = 1 kΩ, RC = 3.3 kΩ, }

V R BE = 0.7V. E = 1 k Ω a n d V C C

## = 30V. Assume

## Compute V_{CC }

and I_{C for β = i)100 }

and ii) 300

28

14