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TINA/Spice: Transformer simulation not replicating real AC/DC circuit

Daniel Sala
Prodigy 190 points
Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

Hi,

I'm trying to replicate (in TINA)  a simple transformer-based mains supply AC/DC power supply I physically made a couple of years ago (that works) with identical components - except some fine details about the transformer, I would assume - in order to learn how to use/model transformers in TINA.

The problem is that the results have no bearing on reality so I guess I have some parameters wrong somewhere or there is something about how I have drawn the schematic that affects the simulation.  Where I expect to see around 12V Dc to 17V DC and ~80mA I get only ~300nV and 2nA.

I'm also unsure as to why I need to add a GND symbol to the AC sine wave input for it to function/not give errors.

Attached below is the schematic I am working with.  Any idea as to what needs to be altered for it to simulate reasonably accurately, please?  TIA.

  • 0
    Guru 40370 points
    I think you have to use a transient analysis for this since the DC voltage depends on the non-linear behavior of the diodes.

    Also, you should isolate the grounds. Use a 1 Gohm resistor on the AC side. What would have happened to your power supply if you would have shorted the mains to the DC ground? Don't try it! 8^)
  • 0 in reply to Keith Barkley
    Prodigy 190 points

    Hi Keith,

    Thanks for the reply and suggestions, much appreciated.  "What would have happened to your power supply if you would have shorted the mains to the DC ground?" - Sadly, no doubt someone somewhere on the Internet has a dodgy circuits website that suggests this!

    I followed your advice and also found it was necessary to increase the number of turns on the primary and secondary sides to obtain a meaningful transient analysis.

    The first attempt is patently wrong somewhere, even if the results are the desired ones, as the turns ratio is grossly incorrect.  The second attempt is closer to the correct turns ratio but still incorrect, although the results are also those desired/expected.  It took a lot of fiddling and guesstimating to get to both outcomes, hence the delayed response...

    I'm under the impression that using transforrmers in simulations requires (in my case) a far greater understanding of transformers, typical real-life numbers of turns, and multiple other transformer parameters, not just the turns ratio - and much less cherry-picking arbitrary ones to achieve the desired results :).

    Attached is the schematic with the 1G between VG1 and GND and the results from the two different turns ratios that gave the output expected, in case it's of any use to anyone either troubleshooting or like myself, starting off with transformers too.

    I really appreciate your input. Thanks very much.

  • 0 in reply to Daniel Sala
    Guru 40370 points
    Yeah, I tried it in PSPICE and never got a satisfactory simulation with a transformer.
  • 0 in reply to Keith Barkley
    Prodigy 190 points

    Hi Keith,

    Okay.  I was altering other parameters in the model this afternoon for a short while after doing a little reading and feel it would be a Sisyphean task and excessively time-consuming to get the model right/realistic, if at all. I'm under the impression that transformers are very hard to emulate (and then, by people who know what they are aiming for) for simulation purposes.  And, if you say that, I'll just accept that the right output values will have to suffice as it's really the DC side of a circuit after the transformer that I'm interested in.

    Many thanks for your help with this matter.

    Best regards,

    Daniel