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BJTFixed Biasing
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Objectives At the end of the module the student
would be able to explain Study Fixed Biasing
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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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Fixed Base Bias Circuit4
1st step: Locate capacitors and replace them with an open circuit
Fixed Base Bias Circuit5
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1
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BE Loop CE Loop
2nd step: Locate 2 main loops.
Fixed Base Bias Circuit BE Loop Analysis VCC – IBRB – VBE = 0Therefore, IB = (VCC – VBE)/RB
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1
IB
Fixed Base Bias CircuitCE Loop AnalysisVCC – ICRC – VCE = 0VCE = VCC – ICRC
But IC = βIB
VCE = βDC((VCC - VBE)/RB)
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2
IC
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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Fixed Base Bias Circuit
Let us construct this circuit and find the following parameters IC, IB, VCE, VB, VC, VBC.
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Fixed Base Bias Experiment10
Simulation and Results Run DC analysis with default settings Observe the outputs on the voltmeters and
ammeters
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Access it Online12
You can access this experiment from the link belowhttp://www.docircuits.com/public-circuit/378/bjt-fixed-bias-without-re