Question

a)

Transistors of a certain type are specified to have β values in the range 50

to 150. Find the range of their α values.

b)

Measurement of

a

npn BJT in a particular circuit shows the base current to

be 14.46 μA, the emitter current to be 1.460 mA, an

d the base

–

emitter voltage

to be 0.7 V. For these conditions, calculate α, β, and

𝐼

𝑆

.

c)

Consider

a

npn transistor with

𝑉

𝐵𝐸

= 0.7 V at

𝐼

𝐶

= 1 mA. Find

𝑉

𝐵𝐸

at

𝐼

𝐶

=

0.1 mA

.

Answer 1

The relationship between α and β is given by

$\alpha = \frac{\beta}{\beta +1}$

Part a

With β = 50

$\alpha = \frac{50}{50 +1} = 0.9804$

Part b

With β = 150

$\alpha = \frac{150}{150 +1} = 0.993$

α value ranges between 0.98 and0.99