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