trouble simulating ±10V > ±200V signal conditioner

Discussion in 'General Electronics Chat' started by strantor, Jan 23, 2013.

  1. strantor

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    Oct 3, 2010
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    I'm trying to turn a ±10V signal into a ±200V signal. I found this circuit in Analog AN-106 Figure 33. I simulated the circuit just as drawn in the AN, and it isn't working. See below:

    [​IMG]

    When I delete the ground on the opamp input I get a real wave out, but it's not nearly what I want (0-200V wave):

    [​IMG]

    What am I doing wrong? Is there a better circuit I should be using for this?

    (circuit attached)

    Thanks!
     
  2. crutschow

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    Mar 14, 2008
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    Change R1 to 200kΩ instead of 2m (milli) ohm for a gain of 20.

    Change V5 Input offset to 0V and amplitude to 10V.

    For a 10Hz slew response change C1 to 500pF and C2 to 0.5nF. (Note that C1 = .001uF appears to cause op amp oscillations).
     
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  3. tshuck

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    Oct 18, 2012
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    I don't typically use LTSpice, so forgive me if this is irrelevant, but you have R2 listed as "2m", where I think it should be "2M". I don't know if LTSpice uses capitalization to distinguish between milli- and mega-, but others I've used do.

    Other than that, it seems your circuit is spot on and matches with the schematic given...Now whether or not the schematic is correct is another matter entirely...
     
  4. strantor

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    Outstanding! thank you sir!
     
  5. crutschow

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    LTSpice does not recognize (capital) M as mega. It needs to be 2meg.
     
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  6. tshuck

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    Ah... Thanks. I've been meaning to get into LTSpice since it seems to be what everyone here uses...
     
  7. crutschow

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    Mainly because it's probably the best, free Spice program available.
     
  8. gootee

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    Strantor, you might also want to right-click on each diode and transistor and specify real devices, from the lists that will pop up.
     
  9. thatoneguy

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    Have you gotten it working?
     
  10. strantor

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    In simulation, yes. I'm going to breadboard it soon and see if it behaves the same in real life.
     
  11. thatoneguy

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    Can you post your working schematic/simulation to show the changes made in the event somebody else wants to make a similar circuit?
     
  12. strantor

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    Sure. All I did was perform the mods that were suggested in post #2, which got my wave output, but it was inverted, so I put the signal through an inverting amp first.
     
  13. t06afre

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    Spice, the prefix abbreviation, the full metric name, and the represented scale factors being as follows:
    F femto 10E−15
    P pico 10E−12
    N nano 10E−9
    U micro 10E−6 ​
    M milli 10E−3
    K kilo 10E+3
    MEG mega 10E+6
    G giga 10E+9
    T tera 10E+12
    Spice does not differentiate between upper and lower case, ‘MEG’ (or ‘meg’) is used for ‘mega’ instead of the standard metric upper case ‘M’.
     
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  14. strantor

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    oh yeah, the whole m, M, MEG thing turned out to be null in this case because I ended up changing the value of R2 to 190K to scale the output properly. But thank you for the clarification; now I know.
     
  15. gootee

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    If we concatenate more than one of those, will it multiply them for us? e.g. Could I use uu instead of p?
     
  16. thatoneguy

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    Some older parts (Tube era) are marked that way, though it is confusing, so not used today.
     
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  17. kubeek

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    Also you can use values like 2k2 etc.
     
  18. gootee

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    That wasn't the question. Anyway, I tried it, with LT-Spice, and uu does NOT result in pF.
     
  19. crutschow

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    Not surprising. I believe spice only looks at the first suffix letter. Anything following that is ignored. Thus 100p and 100pF for a capacitor value are both recognized as 100e-12 farads, and 10k and 10kohms for a resistor value are both recognized as 10,000 ohms.
     
  20. thatoneguy

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    I stated that the convention isn't used today (in software or by hardware manufacturers). Only some components manufactured 50 years ago and older.
     
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