BJT transistor

Discussion in 'Homework Help' started by PsySc0rpi0n, Apr 1, 2014.

  1. PsySc0rpi0n

    Thread Starter Well-Known Member

    Mar 4, 2014
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    I'm now about to start the analysis of the BJT transistors.

    I don't understand yet how they work. I'm reading some info about it as we speak!

    We will be analysing 2N2222!

    If you have any tutorial I can read, please post it!
     
  2. MrChips

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    Oct 2, 2009
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  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Psy,
    You may find LTSpice will also help with your studies with BJT.

    E
     
    Last edited: Apr 2, 2014
  4. PsySc0rpi0n

    Thread Starter Well-Known Member

    Mar 4, 2014
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    Ok, i need to know how to simulate the attached circuit...

    My teacher is asking to:

     
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  5. PsySc0rpi0n

    Thread Starter Well-Known Member

    Mar 4, 2014
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    Ahhh... I got it now...

    They want a current power source to inject current thru the BJT base point... Ok. Let me do those changes in my previous circuit!


    PS: Just help me on this:

    Where do i have to place the probes to check the voltage drop between C and E?
    And can i make 2 power sources vary at the same time at the Simulation command?
     
  6. ericgibbs

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    Please post your latest asc file when you are ready.
     
  7. PsySc0rpi0n

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    Teacher wants to plot Ic(Vce) and Ib must go up to 150μA in steps of 30μA and Vce must go up to 20V in steps of 0.1V

    Am i doing anything wrong?
     
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  8. MrChips

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    You can do this by hand, tedious but doable.

    Set Ib. Increase Vcc in 10 steps. Measure Icc at each Vcc.

    Step up Ib.
    Do this for five Ib settings.

    Total 5 x 10 = 50 data points.

    Plot the curves by hand or any graphing program.
     
  9. ericgibbs

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    hi,
    Did your tutor say you must have the 100K and the 220R resistors in your circuit.??

    Also why are you using DECades for the two varying parameters.?
     
  10. PsySc0rpi0n

    Thread Starter Well-Known Member

    Mar 4, 2014
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    So, how am i supposed to get the characteristic curve (Ic(Vce)) for this 2N2222???

    Well, in the thorical part he doesn't asks spoecifically for any resistor but for the same point at the laboratorial work, he gave us a schematic that has both resistors!

    And yes, i used DECade sweeps for both power sources! But i have also tried linear!
     
    Last edited: Apr 2, 2014
  11. Jony130

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    First of all remove all resistors from you circuit. Next change your sweep type from decade to linear one. Also first source need to be V1 voltage then Ib.
     
  12. PsySc0rpi0n

    Thread Starter Well-Known Member

    Mar 4, 2014
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    Nice... I got it...

    But i need to know why do i have to remove all resistors and why does it has to be linear and not decade, or better, what is the difference between the different type of sweeps, and lastly why does the Vce need to be the first to be sweeped????
     
  13. Jony130

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    In this case RB resistor has no influence on the circuit, because you use current source.
    Rc resistor have influence on Ic current for low V1 voltage values. Because Ic current cannot be greater than V1/Rc. And we use Vce first because we want Vce on the X axis.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    The Decade and Octave sweep generate the defined number of logarithmic points for each decade or octave of the variable parameter. The List sweep uses an arbitrary list for the parameter.

    The type of sweep to get the display specified by the teacher is called a Linear sweep (Start point, Stop point, Step Increment).

    The Source order determines which parameters are used for the X and Y axes. To display the normal characteristic curves of a transistor in Spice you need Vc first and Ib second.
     
  15. ericgibbs

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    hi Psy,
    You should have by now realised, no resistors and use linear variable plots , in X, Y format.

    Post your asc file when ready, we can look it over.

    Dont use a battery for the supply, use Voltage source.
    E
     
  16. PsySc0rpi0n

    Thread Starter Well-Known Member

    Mar 4, 2014
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    Ok, thanks for explanations!

    Here goes my asc file and plot for the first question!

    Now, for the next question, i have to calculate Early Voltage!
     
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  17. ericgibbs

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    Looks OK.

    Run this asc and then press Cntr L keys for Gain values at 5V and 10V.

    Its just a demo of the .measure option.:)

    E
     
  18. PsySc0rpi0n

    Thread Starter Well-Known Member

    Mar 4, 2014
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    Why do you choose 2N2222A? What is the interest of those points where you measured currents?
     
  19. shteii01

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    Feb 19, 2010
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    That looks good.

    Early Voltage is not really complicated. You have five Vbe plots. Take one Vbe plot, take the section that is straight line, figure out the equation of that straight line, now extend the straight line until it intersect the Vce axis. Now do that for the other four plots of Vbe. The point where all the plots intersect Vce axis is the negative Early voltage. So just drop the minus sign and all that is left is the value of the Early voltage.

    Here is illustration from my textbook.

    [​IMG]
     
  20. shteii01

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    I included the picture that shows what I mean.
     
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