34.fixed bias without re

1. BJT
Fixed Biasing
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2. Objectives
At the end of the module the student would be
able to explain
Study Fixed Biasing
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3. Fixed Base Bias Circuit
This is common
emitter (CE)
configuration
1st step: Locate
capacitors and
replace them with
an open circuit
2nd step: Locate 2
main loops which;
BE loop
CE loop
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4. Fixed Base Bias Circuit
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1st step: Locate capacitors and replace them with an open
circuit

5. Fixed Base Bias Circuit
5
1
2
1
2
BE Loop CE Loop
2nd step: Locate 2 main loops.

6. Fixed Base Bias Circuit
BE Loop Analysis
V
CC – I
BR
B – V
BE = 0
Therefore,
I
B = (V
CC – V
BE)/R
B
6
1
IB

7. Fixed Base Bias Circuit
CE Loop Analysis
V
CC
– I
C
R
C
– V
CE
= 0
V
CE
= V
CC
– I
C
R
C
But I
C
= βI
B
V
CE
= β
DC
((V
CC
- V
BE
)/R
B
)
7
2
IC

8. Fixed Base Bias Circuit
DISADVANTAGE
Unstable – because it is too dependent on β and
produce width change of Q-point
For improved bias stability , add emitter resistor to
dc bias.
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9. Fixed Base Bias Circuit
Let us construct this circuit and find the
following parameters IC, IB, VCE, VB, VC, VBC.
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10. Fixed Base Bias Experiment
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11. Simulation and Results
Run DC analysis with default settings
Observe the outputs on the voltmeters and
ammeters
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12. Access it Online
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You can access this experiment from the link below
http://www.docircuits.com/public-circuit/378/bjt-fixed-bias-without-re