Day 6- Beta of a BJT

In this experiment, we will figure out the Beta(gain) of the npn bipolar junction transistor
the basic schematic of the transistor is sown

With the relationship of
Ic=a*Ie
Ic=B*Ib
B=a/(1-a)

In this experiment, we set up the circuit as shown below

with a NPN type 2N3904 transistor

we will R1 (variable resistance box) and R2 of 100ohm(measured 98.2ohm) in the circuit

We will measure the change in R1 respect to the change in Ib and Ie

Measured V         Rb(Theoretical)         Rb(actual)            Ib                   Ie

6.05 V                       530 k ohm           529 k ohm          0.011 mA      1.36 mA

6.05 V                       265 k ohm           263 k ohm          0.021 mA      2.81 mA

6.05 V                       176 k ohm           176.6 k ohm       0.033 mA      4.18 mA

6.05 V                       132 k ohm           132.5 k ohm       0.046 mA      5.56 mA

6.05 V                       106 k ohm           106.4 k ohm       0.058 mA      6.98 mA

we can plot the graph with logger pro with Ie vs. Ib graph




Since we know that Ie=(1+beta)Ib
and we know the slope of the line is 116.2
116.2-1 will be the beta value of 115.2

According to the textbook, transistor has some saturated value that after the value, the transistor will acts like open and close switch. Since the kind of transistor we are using(BJT) is usually use as parts in amplifier, we do not want it function as switch. Instead, we want it to act like flow controller that control the desire current we want.  Thus, we are only interesting in the linear portion of the graph of the transistor.