Explain Vceq & Icq in Collector-Base Bias Config.

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Discussion Overview

The discussion revolves around the concepts of Vceq and Icq in the context of a collector-base bias configuration in transistor circuits. Participants are seeking clarification on the definitions and calculations related to these quantities, as well as their implications in circuit analysis.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that Vceq represents the collector-emitter voltage at the quiescent point, while Icq is the collector current at this point.
  • One participant questions the equation for base resistance, suggesting it may require parentheses for clarity.
  • Another participant asserts that Vce can be expressed as Vcc - Ic*Rc, challenging the earlier definitions of Vceq.
  • There is a suggestion that neglecting Vbe in the calculations may not be justified, as biasing should not be overly simplified.
  • Participants discuss the implications of applying Kirchhoff's voltage law to derive equations related to Vceq and the base resistance.
  • One participant asks if the derived formula for Vceq is a generalized expression for the collector-emitter voltage at the quiescent point.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and calculations of Vceq and Icq, with no consensus reached on the correct expressions or assumptions involved. The discussion remains unresolved regarding the validity of certain approximations and the necessity of specific terms in the equations.

Contextual Notes

Limitations include potential missing assumptions about the circuit configuration and the conditions under which certain approximations are made, such as neglecting Vbe in comparison to Vcc.

ranju
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the base resistance in collector to base bias configuration is given by
Rb=Vcc-Vbe-IcRl / Ib
now , in a question only the value of Vceq is given & they found Rb as Rb=Vceq/Ib.!
what is Vceq over here..?? and another quantity Icq is used..what are these two quantities..please explain a bit..
 
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ranju said:
the base resistance in collector to base bias configuration is given by
Rb=Vcc-Vbe-IcRl / Ib
Isn't this equation needing a set of paentheses? Here, borrow a spare pair of mine: ( )

now , in a question only the value of Vceq is given & they found Rb as Rb=Vceq/Ib.!
what is Vceq over here..?? and another quantity Icq is used..what are these two quantities..please explain a bit..
Vceq would be the value of Vce at the quiescent point, the "Q point".
Icq is the value of collector current at the Q point

The Q point is the DC operating point that your bias arrangement sets.

BTW, it is not correct to use lower-case subscripts for these DC bias points, you should be using upper-case. There is a strict convention to follow. VCEq is the quiescent C-E voltage.

I hope that answers your questions.
 
that means VCEq = Vcc-Vbe-IcRL...?
 
ranju said:
that means VCEq = Vcc-Vbe-IcRL...?
Sketch your circuit. Mark on it a closed loop. You won't be able to draw any closed loop to confirm your quoted guess. So your guess must be wrong.

Apply Kirchoff's voltage law to any complete loop on the schematic to find that loop's equation.
 
This is the given circuit with which I was referring to ..
Here in the solution , they took RB=VCEQ / IB
and if we apply KVL we ger RB= VCC-VBE-ICRL / IB
we can neglect VBE in comparison to VCC , so is VCEQ=VCC-ICRL...??
 

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ranju said:
This is the given circuit with which I was referring to ..
Here in the solution , they took RB=VCEQ / IB
Approximately.

and if we apply KVL we ger RB= VCC-VBE-ICRL / IB
Approximately. But what happened to those extra parentheses I leant you?

we can neglect VBE in comparison to VCC
There is no good reason for doing so, biasing need not be quite so rough and ready.

so is VCEQ=VCC-ICRL...??
Approximately. So what is being neglected in making this approximation?
 
so is that a generalised formula for CE voltage at quiscient point...this what I was asking...
 

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