DC BIASING OF BJT
ELECTRONICS COMPONENTS AND CIRCUITS :
DC BIASING OF BJT :
In order to turn on the transistor , DC voltage is applied to it , such that it can amplify the AC signal is termed as Biasing .
Q-point or the quiescent point is established by an DC input. There are three stages of operation that is :- 1 > Active or Linear stage Operation
2 > Operation in cutoff stage
3 > Operation in saturation stage
The DC biasing circuits of a BJT transistor are -> Fixed -bias circuit
->Emitter-Stabilized/self bias circuit
->Collector -Emitter Loop circuit
->Voltage Divider Bias Circuit
->DC Bias with voltage feedback
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The base emitter loop can be calculated by Kirchhoff’s law :
+ Vcc – IbRb – Vbe = 0
The base current can be solved by
Ib = ( Vcc – Vbe ) / Rb
For collector-emitter loop :
Collector current can be calculated by :
IC = bIB
And from Kirchhoff’s voltage law
Vce = Vcc – IcRc
The saturation values can be calculated by :
ICsat = Vcc / Rc
Vce = 0 volt
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The voltage divider bias circuit is very stable in nature . Here the voltage and current are both independent of each other .
From Kirchhoff’s voltage law analysis we get
Vce = Vcc – Ic ( Rc + Re )
The properties of DC Biasing of BJT’s are :
- The input and voltage characterstics are non -linear in nature
- For hand based calculation basis simple models are required .
- The operation mode of BJT depends on voltages at EBJ and BCJ .
For Dc Circuit analysis > all the sources ao AC are removed .
- The DC current must be in Ic and the BJT must be in active region .
- Make open circuit for all capacitors .
Similarly for AC analysis we need to do the following :
- We have to get rid of all dc sources
- Short circuit all the capacitors
- The small model for DC analysis must be removed and replaced with BJT
QUESTIONS AND ANSWERS :
QUE > What do you mean by biasing ?
ANS> In order to turn on the transistor , DC voltage is applied to it , such that it can amplify the AC signal is termed as Biasing .
QUE > What are the three stages of operation ?
ANS > There are three stages of operation that is :- 1 > Active or Linear stage Operation
2 > Operation in cutoff stage
3 > Operation in saturation stage
QUE > What are the types of DC Biasing circuits ?
ANS > The DC biasing circuits of a BJT transistor are -> Fixed -bias circuit
->Emitter-Stabilized bias circuit
->Collector -Emitter Loop circuit
->Voltage Divider Bias Circuit
->DC Bias with voltage feedback
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A bipolar junction transistor (BJT or bipolar transistor) is a type of transistor that relies on the contact of two types of semiconductor for its operation. BJTs can be used as amplifiers, switches, or in oscillators. BJTs can be found either as individual discrete components, or in large numbers as parts of integrated circuits. Dc biasing of BJT is given here
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