LTSpice - simulating the switching of an inductor

Discussion in 'General Electronics Chat' started by atferrari, Jan 18, 2015.

  1. atferrari

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    Using LTSpice to simulate the switching of an inductor as per attached .asc file.

    I understand that the emitter current (Q2), at the moment it is turned on, should be positive starting from 0 mA.

    LTSpice insists in showing a negative current which contradicts the sense of the one through L2, which is positive, starting from 0.

    BTW, current through D2 is consistent with that of L2.

    At lost here...

    Inductor 01.png
     
  2. SgtWookie

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    Capacitive coupling from the base to the emitter of a fast rising signal. Try changing your rise/fall times of V2 to 1uS instead of 10nS
     
  3. Jony130

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    If current is leaving the node simulation gives this current a minus sign. Probe a collector current.
     
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  4. atferrari

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    No changes SW even with higher rise/fall times. What makes me doubt is that collector current IS positive but emitter's is not. :( Electrons, where do they go? :oops:
     
  5. Jony130

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    Simply, the emitter current is leaving the node (emitter is sourcing the current). And all "sourcing" currents are negative in LTspice.
     
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  6. atferrari

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    Gracias Jony.

    I was trying to understand how an inductor behaves and suddenly this!
     
  7. Jony130

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  8. atferrari

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    Thanks Jony. Finished the reading. I think I got the basics clear now.
     
  9. SgtWookie

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    You might also head over to Ronald Dekker's site: http://dos4ever.com/
    and check out the "Flyback Converters for Dummies" section: http://dos4ever.com/flyback/flyback.html
    It's a very useful introduction to inductors; I've sent lots and lots of folks there to read up on them. The bonus is, there's a project that relates exactly to what you're interested in doing.
     
  10. killivolt

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    Hey Sgt. Got any models of TIP32c and TL431
     
  11. Jony130

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  12. atferrari

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    Thanks for sharing that Sarge.
     
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  13. SgtWookie

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    There is a model of the TL431 in LTSpice's Misc folder.
    I believe I'd retrieved a TIP32 model from ONSemi's (formerly Motorola) site:
    http://www.onsemi.com/PowerSolutions/supportDoc.do?type=models
    Might as well get the TIP31 models while you're at it so you'll have the complements. ;)
     
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  14. killivolt

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    Thanks, Sgt.

    I like your signature; my thoughts exactly.

    Best wishes;

    kv
     
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