Multisim problem? or Have I made a mistake?

Discussion in 'Electronics Resources' started by bytraper, Oct 16, 2011.

  1. bytraper

    Thread Starter Active Member

    Sep 28, 2010
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    4
    Hi Guys.

    Ive built a circuit in multisim which is supposed to give a 1v-p-p triangle waveform output, but instead I get nothing. In real life, the circuit works fine, but in multisim its dead.

    Can anyone see where I've made the error?

    [​IMG]
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Change R4 and R15 to 1MEG from 1m. The simulator sees 1M as "one milliOhm", or 1/1000 Ohm, or 0.001 Ohm.
     
  3. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    Thanks Sarge,
    I can't believe it was so simple... I was about to throw the whole digital simulation idea in the bin!
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I guarantee that you are not the first to be "bitten" by this, nor will you be the last!

    it's really too bad that they couldn't differentiate Mega from milli by case, but that would be inconsistent with everything else.
     
  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    That must be a quirk in multisim. I know mine I can use standard prefixes.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Joe,
    What simulator are you using?
    LTSpice, PSPICE Student, Tina-TI and Circuitmaker need MEG spelled out; "M" or "m" means milli.
     
  7. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Multisim 11.0 Power Pro can tell the difference between m and M.
     
  8. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    He's right, I can use MEG or a capital M.

    Is there a way to simulate current load?
     
  9. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Do you mean a constant current load? One that increases it's impedance when voltage increases? What exactly would that be good for?

    Or do you mean a constant output power? So when voltage increases, current decreases?
     
  10. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    Um, I'm trying to design a current limiter with a 0.003 ohm resistor.

    But I need to be able to increase the load on the simulated mosfet to increase the resistance so I can work out the correct resistor combinations for the inverting op-amp.

    does that make sense?
     
  11. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Tina and Tina-TI uses standard prefixes. I have Tina Educational ... where I can introduce "problems" for troubleshooting.

    I use from f to T or scientific notation ... 1e-15 shows up as 1f and 1e12 shows up as 1T on the resistor I had in a schematic. Outside of those ranges it will show the scientific notation ... 1e-18 for example.

    On edit ... added page from Tina's quick start user guide
     
    Last edited: Oct 19, 2011
  12. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    It just occurred to me I can just use an inductor of different size to generate a dummy current load...
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    I don't have Multisim; but in LTSpice you can place a current symbol, give it a value of current to sink or source, and check a box to indicate that it is a load. Checking the load box causes the current source to stop sinking or sourcing current when the voltage across it is near zero.
     
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