This document discusses voltage divider biasing of BJT transistors. It explains the steps to analyze a voltage divider bias circuit: 1) replace capacitors with open circuits, 2) simplify the circuit using Thevenin's theorem, and 3) identify the base-emitter and collector-emitter loops. Equations for the bias point currents and voltages are derived from loop analyses. A simulation circuit is provided to experimentally determine the bias point parameters. The full experiment can be accessed online for hands-on practice of voltage divider bias analysis.

1. 1
BJT
Voltage Divider Biasing

2. Objectives
2

At the end of the module the student would be
able to explain

Study Voltage Divider Bias

3. Voltage Divider Bias Circuit
3

Provides good Q-point stability
with a single polarity supply
voltage

1st step: Locate capacitors and
replace them with an open circuit

2nd step: Simplified circuit using
Thevenin Theorem

3rd step: Locate 2 main loops
which;
 BE loop
 CE loop

4. Voltage Divider Bias Circuit
4

1st step: Locate capacitors and replace them with
an open circuit

5. Voltage Divider Bias Circuit
5
■ 2nd step: : Simplified circuit using Thevenin
Theorem
From Thevenin Theorem;
Thevenin Theorem;
RTH = R1 // R2 =
VTH =
R1 ×R2
R1 +R2
R2
VCC
R1 +R2

6. Voltage Divider Bias Circuit
6
■ 3rd step: : Locate 2 main loops.
BE Loop
2
CE Loop
2
1

7. Voltage Divider Bias Circuit
7

BE Loop Analysis
VTH − I B RTH − VBE − I E RE = 0
Recall; I E = ( β + 1) I B
1
Substitute for IE
VTH − I B RTH − VBE − ( β + 1) I B RE = 0
∴IB =
VTH − VBE
RRTH + ( β + 1) RE

8. Voltage Divider Bias Circuit
8

CE Loop Analysis
VCC − I C RC − VCE − I E RE = 0
2
Assume;
I E ≈ IC
Therefore;
∴VCE = VCC − I C ( RC + RE )

9. Voltage Divider Bias Circuit
9

Build the circuit as shown below and find out
the following parameters IC , IB , VB, VE and VC

10. Voltage Divider Bias Circuit
10

11. Simulation and Results
11


Run DC analysis with Default Settings
Observe the output on voltmeters and
ammeters

12. Access it Online
12

You can access this experiment from the link below
http://www.docircuits.com/public-circuit/380/bjt-voltage-divider-bias