Spice simulator does not match the actual circuit.

Discussion in 'Electronics Resources' started by birgs, Jun 3, 2012.

  1. birgs

    Thread Starter New Member

    Jun 2, 2012
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    [​IMG]


    Hi everybody,

    *I mounted this very simple circuit, which is part of a high voltage generator (and that should give continuity) but found a huge difference in charging time of C1 (220n) which should be 60 uS according to the simulator, but it was about of 10 uS in real circuit. What is wrong, since it is a very simple circuit and all inductors were made and measured by myself. Can anyone help me?.******
    Thank's for any help.
     
  2. Evil Lurker

    Member

    Aug 25, 2011
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    What kinda capacitor you using?
     
    birgs likes this.
  3. birgs

    Thread Starter New Member

    Jun 2, 2012
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    Polyester ... the most suitable in this kind of circuit ... it's a new one and accurately measured with 220N.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Likely either the circuit is wired incorrectly or the component values are incorrect. How did you measure the inductor values?
     
  5. birgs

    Thread Starter New Member

    Jun 2, 2012
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    It was measured with a ICEL LC-301 rlc meter...the FET transistor could be anyone for the amperage used here but I placed a IRFP 260N... diodes are all fast...I'm pretty sure there is nothing wrong with components or the circuit...that's what puzzles me.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    What is the current rating of L1?

    There is nothing in your circuit to limit the current through L1 expect the ON resistance of the MOSFET and the intrinsic inductor resistance which you didn't show in the model. The high current when the MOSFET is on may be saturating L1. Look at the current through the MOSFET.

    Remember the simulator uses ideal inductors, which don't saturate.
     
  7. birgs

    Thread Starter New Member

    Jun 2, 2012
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    If better analyzing the circuit, you will find that the conduction time (tON) of the MOSFET is only 4 uS, just enough time to discharge C1 previously loaded and therefore the current in L1 is limited to the intrinsic resistance (mor or less 1R) plus the inductive reactance of L1 (32R) during tOFF of the MOSFET (60uS) which is equal to 360mA.* The fact is that with 1.8mH both the simulator and the actual circuit, the charging time of C1 (220N) in both the simulator and the actual circuit should also be the same (60uS).
     
  8. crutschow

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    You didn't answer my question about the maximum current rating of the inductor.
     
  9. birgs

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    Jun 2, 2012
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    Actual Circuit- 150mA peak.

    Spice- 135mA peak.
     
    Last edited: Jun 5, 2012
  10. crutschow

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    Mar 14, 2008
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    That's the circuit current. That's not my question. My question is what is the inductor current rating? How much current is it designed to carry?
     
  11. birgs

    Thread Starter New Member

    Jun 2, 2012
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    Sorry for the misunderstanding ...

    It's still a test inductor, so it was designed to only 220mA. In the final inductor this current rating will be around 250 A.
     
    Last edited: Jun 6, 2012
  12. panic mode

    Senior Member

    Oct 10, 2011
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    is that typo or really 250A?
     
  13. birgs

    Thread Starter New Member

    Jun 2, 2012
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    I said "around" the 250A; 250A peak or 165A RMS. It will all depend on some factors. But that's for later...
     
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    post the input signal generator and the V003 test point using a dual trace oscilloscope. Trigger the scope with the input signal generator's signal.
     
  15. crutschow

    Expert

    Mar 14, 2008
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    Is this a purchased inductor or did someone build it in the lab? How is the 220mA current rating determined?
     
  16. birgs

    Thread Starter New Member

    Jun 2, 2012
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    I'll post it as soon as I provide the 2nd probe, since one of them is damaged. As my scope is a bit old and analog (Hitach V-212 20MHz) this is only possible through some shots. Wait for there, Joe Jester …


    Lab ? …. , purchaise ?..... no, no,.... it is a home-made....you are quizzing me, aren't you, crutschow? I am a stand-alone electronic technician over 20 years experience (or would be 30?) and with a little math and GOOGLE we can do a lot of things, isn't it ?. For example type in Google "How to design an inductor" and you will find a lot of URL related to the subject. I must admit that designing a transformer or an inductor is not so simple as it sounds, but also not so difficult.
     
  17. birgs

    Thread Starter New Member

    Jun 2, 2012
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    ….Although experienced, we are all subject to errors, isn't true, crutschow? ... Sory for that, guy. Specifically this inductor, correct me if I'm wrong, please …

    L1 = 60 turns 28 AWG (3A/mm2) in a FBT's Ferrite Core (Oversized Core)
    0.15mm Air Gap
    18mm Length
    18mm Diameter.
     
    Last edited: Jun 10, 2012
  18. birgs

    Thread Starter New Member

    Jun 2, 2012
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    There is the Gate Pulse Generator and the actual circuit waveforms (By the way, as to take pictures of a scope screen or whatever with a low resolution cam, I would rather a thousand times to format a few tens of Pcs !!! ). Due to a misreading of the Scope and my haste, the voltage charging period of C1 (now C6) in real circuit is not 15 uS as I said earlier but about 20 uS instead.. Even so I think it's a pretty big difference.V(n003) is now V(n011) too.


    The main question is, if both L1 (1.8mH) and the M1 gate pulses (4uS) are the same in the two circuit,*then the charging time of C6 should also be the same as well.


    Although the C6 charging time is different in both circuit, the L1 current remains about the same either one or another.


    but If the C6 voltage charging time (Compared to the same period of Spice) is shorter in real circuit, then the L1 current should be lower likewise.
     
    Last edited: Jun 12, 2012
  19. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I don't know which simulation software your using, but to charge a 0.1 uf capacitor with an average of 92 mA to 25 V is certainly less than what your software is showing.

    Now, if your charging to 25V in 20 uS, the average charging current is 125 mA.

    review this ebook page http://www.allaboutcircuits.com/vol_1/chpt_13/2.html

    My simulator's waveforms look as illustrated below.
     
    Last edited: Jun 13, 2012
  20. birgs

    Thread Starter New Member

    Jun 2, 2012
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    I'm using LTSpice IV Free Edition.
    One thing wasn't quite clear to me....in your simulation (considering you used L1=1.8 mH ), to what C6 value is your software waveforms related to, 0.1 uF or 0.22 uF ?.

    If it's 0.1 uF, then the problem is other than the Spice because replacing the 0.22 uF Spice simulator by the 0.1 uF you've mentioned earlier (and suppose had been used in your simulation), both waveforms will be matched, thus the problem remains unsolved.


    However if it's 0.22 uF, then the problem must be Spice because, although both simulators are using the same C6 value (0.22 uF), both waveforms are mismatched; mine is V(n011) 60 uS long and yours is V(n011) about 35 uS long (At least just about the same as actual circuit), thus, the problem would be solved.....
     
    Last edited: Jun 13, 2012
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