DC BIASING OF BJT

Feb 25 • General • 4464 Views • 2 Comments on 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 :

  1. The input and voltage  characterstics are non -linear in nature
  2. For hand based calculation basis simple models are required .
  3. 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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2 Responses to DC BIASING OF BJT

  1. Rachita Mishra says:

    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

  2. Fauzia Neshat says:

    Relevant information about DC BIASING OF BJT. go through the article it will be helpful.

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