steps for basing a transistor and simulation with multisim | applied electronics engineering

# steps for basing a transistor and simulation with multisim

By Applied Electronics - Monday, August 8, 2016 No Comments
Voltage divider biasing is one of the good technique to bias a transistor. Biasing a transistor is the process of calculating the value of resistors R1, R2 and Re given the output DC voltage and AC voltage gain. For example, in the circuit diagram below, let the source voltage Vs be 10V, let the output DC voltage Vc be 5V. Let also the AC voltage gain be 10 and beta of the transistor be 100.

The steps for biasing a transistor using voltage divider biasing is given below.

1. Assign the collector resistor some value say 1KOhm, that is Rc = 1kOhm

2. Calculate the value of Re using the AC voltage gain formula as follows,

Av = Rc/ Re
or,
Re = Rc/ Av = 1kOhm/10
hence,
Re = 100Ohm

3. Find Ve using the following formula

Av = Vr/Ve = Vs - Vc/ Ve
or,
Ve = Vs-Vc/Av = 10V-5V/10
or,
Ve = 0.5V

3. Find Vb

Vb = Ve+0.7
Vb = 0.5V+0.7V
or,
Vb = 1.2V

4. Find Ic

Ic =  Vr/ Rc = Vs-Vc/Rc = 10V-5V/1KOhm
or,
Ic = 5mA

5. Find Ib

hfe =  Ic/ Ib
or,
Ib = Ic/ hfe
or,
Ib = 5mA/ 100
or,
Ib = 0.05mA

6. Find I2

I2 = 10*Ib
or,
I2 = 10*0.05mA
or,
I2 = 0.5mA

7. Find R2

R2 = Vb/ I2
or,
R2 = 1.2V/ 0.5mA
or,
R2 = 2.4KOhm

8. Find R1

R1 = Vs- Vb/ I2+Ib
or,
R1 = 10V - 1.2V/ 0.5mA +0.05mA
or,
R1 = 16KOhm

Simulation

We can use multisim software(see online multisim simulator) to check this transistor biasing circuit. Following is the simulation result from multisim.

The probe placed at the collector predicts correct values as predicted and calculated.