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Class A-B amplifier simulation help

Discussion in 'Circuit Simulation & PCB Design' started by neptune, Oct 16, 2011.

  1. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    alec,
    Run the simulation until it completes.

    Place the cursor on the transistor so that it changes into a 'finger pointer'.

    Press and Hold down the ALT key, while the key is held down left click the mouse. While the ALT key is down the cursor is a thermometer.

    NOTE: the transistor MUST be of a manufactured type, a LTS generic transistor will not [ and cannot ] show the 'thermometer cursor'

    Lets know how it goes... no magic..

    EDIT:
    avi file, change extension from txt to avi
     

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    Last edited: Nov 23, 2011
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Thanks for the avi, Eric.
    Tried that for a 2N2222 and a 2N2905. No joy. If I left click the mouse while Alt is down the hand cursor just reverts to a cross.
    My system clearly doesn't behave as yours does for transistors yet, strangely, does so for resistors and caps. Version difference? (I'm running LTS version 4.12u on XP SP2).
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    This is my target "C:\Program Files\LTC\LTspiceIV\scad3.exe", I am using XP Pro SP2

    This has worked on my PC's since 'years ago', the latest LTS upgrade was about a week ago.
     
  4. dave

    Dave New Member

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  5. alec_t

    alec_t Well-Known Member Most Helpful Member

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    My target is the same as yours, Eric, and my last LTS update was 3 Nov. So the only difference seems to be that you have the Pro version of XP. I can't believe that would account for why I can't 'do' transistor power directly. Weird. I guess I can live with that :).
     
    Last edited: Nov 23, 2011
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Alec,
    Post me a working 'noddy' test asc file with a 2N2222 on it, I will try it out.
     
  7. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Here y'are !
     

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  8. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    It works fine in all my 3 PC's ????

    EDIT:
    Searched a lot of info, its well documented as a feature.
    Checked my Windows\scad3.ini nothing special about it?
    Check page 38 of this pdf
     

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    Last edited: Nov 23, 2011
  9. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Thanks for checking. Can't see anything wrong with my scad3.ini either.
    Do you mean power measuring, or the problem I have?
     
  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    alec
    I posted, its well documented as a feature. not a problem.:rolleyes:

    If you posted your scad3.exe, I could try that on a PC.

    Is your keyboard and driver the 'usual' type ? 102key

    http://en.wikipedia.org/wiki/IBM_PC_keyboard
     
    Last edited: Nov 23, 2011
  11. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Update: I've just re-installed LTS using a fresh download. All now working OK for power measurement, so I guess my scad3.exe (or perhaps the model library) must have got corrupted somehow. Thanks for your persistence on this.
     
  12. winter1620

    winter1620 New Member

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    Is there anyone that can help me build an AB amplifier with the characteristics attached to these in LTspice, at least the schematic please...
     
  13. unclejed613

    unclejed613 Well-Known Member

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    hmmm looks like a homework assignment.... i won't design it for you, but i guess a couple hints can't hurt....

    this is going to look very much like an op amp with MOSFETs as the output devices.... lateral MOSFETs judging by the rail voltage requirement (vertical MOSFETs require quite a bit more voltage on the gates for conduction), or maybe depletion mode FETS rather than enhancement mode.... that's about as much as i can say without giving away the farm.....

    another hint is: you have probably covered all the material in class already that you need to complete this project.
     
  14. winter1620

    winter1620 New Member

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    o_O I don't quite understand this though, so when I do the schematic, how many transistors should i need to place?
     
  15. unclejed613

    unclejed613 Well-Known Member

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    i would guess about 5, but i'd rather you go through your notes and look for clues on how to do this. i can't draw a schematic for you, because your instructor wants your solution to be YOUR solution. look at op amp circuits, and draw your own conclusions.... your project has a diff amp for input and complementary MOSFETs running in class AB mode with 5 volts total supply voltage(makes you have to select the right type of FET, and bias network, and this might be the most difficult hurdle), 40db open loop gain (not too ambitious a target), 1Mhz GBW.... it can be done, and has been done in the past... but your instructor wants YOUR solution, not mine.... remember YOU will completely understand how YOUR solution works, but may not fully understand MY solution, and your instructor will know it's not your solution because you don't completely understand it. yeah, it might be nice to have a pre-fabricated schematic that works, but you must completely comprehend the "why" of how it works...

    even if you don't come up with a "perfect solution", if you have complete understanding of how it works, that's the whole point of the project (plus the object lesson of "there is no such thing as a perfect solution in engineering").
     
    Last edited: Apr 29, 2014
  16. alec_t

    alec_t Well-Known Member Most Helpful Member

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    BTW, it would have been better if you had started your own thread for this, instead of hijacking an ancient one.
     
  17. winter1620

    winter1620 New Member

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    unclejed613, Thanks for the advice and help.

    alec_t, yeah I know, srry bout that though, I'm new here and didn't know where I could have post something similar as to what I was doing for this homework. Thanks.
     
  18. alec_t

    alec_t Well-Known Member Most Helpful Member

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    There is a 'Homework Help' forum on this site.
     

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