Wall Warts ER

Discussion in 'General Electronics Chat' started by Austin Clark, May 20, 2012.

  1. Austin Clark

    Thread Starter Member

    Dec 28, 2011
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    Can wall adapters (wall warts) be modeled as a voltage source with equivalent series resistance? Or is the model more complex?
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    It's all depends on the purpose of this model.
    As first approximation and for low frequency should do the job.
     
  3. Austin Clark

    Thread Starter Member

    Dec 28, 2011
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    And if it isn't? What if you wanted a accurate detailed model?
     
  4. #12

    Expert

    Nov 30, 2010
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    You would plug it in and measure it.
     
  5. Austin Clark

    Thread Starter Member

    Dec 28, 2011
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    Sounds tedious, and that wouldn't be reasonable. There got to be a model that makes sense mathematically and physically.
     
  6. #12

    Expert

    Nov 30, 2010
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    I disagree. Measuring real circuits and seeing what they do is so reasonable that people do it every day.

    Most of the requests on this site are for practical, working circuits, as opposed to detailed mathematical models of things that can be analysed in a dozen different ways. Your requests are so general that a proper answer would require several pages on a dozen different aspects of each circuit. Being more specific would help.

    A seemingly simple wall wart can be modeled as a DC supply with a resistance in series. It can be modeled with respect to the magnetics inside it and how they vary from ideal. It can be modeled in the frequency spectrum. Even the wire from the wall wart to the circuit board can be modeled as a high frequency delay line.

    I suggest you get started. You have a lot of work ahead of you!
     
  7. Austin Clark

    Thread Starter Member

    Dec 28, 2011
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    Ugh, you're probably right. But still, any input on the problem? It doesn't seem like the voltage source with a series resistor model is very accurate, why not?
     
  8. #12

    Expert

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    Have you measured one? How does it vary from the model of a voltage source with a series resistance, and by how much does it vary? Is that enough to say the simple model is not useable?
     
  9. Austin Clark

    Thread Starter Member

    Dec 28, 2011
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    I got this from the forum. It's a bunch of wall-wart data. Theoretically, using the series resistor model, the current drawn and the voltage dropped should be proportional. Sometimes, on some of the data collected, that seems to be fairly accurate, but some are just all over the place. Maybe it has to do with the fact that some wall-warts are regulated and/or have internal circuitry involved, thus giving them complex load characteristics. That's sorta the mystery I'm trying to solve.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Certainly if it's regulated or not makes a difference in the model.

    A non-regulated one can likely be fairly accurately modeled for most purposes as an ideal voltage source in series with a resistor.

    A regulated one can likely be modeled as an ideal voltage source in series with a (typically very small) resistor with a switch-over to a current limit at some over-current point. At that point the current stays relatively constant and the voltage drops directly with any reduction in the load resistance beyond the limit point.
     
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  11. Wendy

    Moderator

    Mar 24, 2008
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    One thing you are missing, most wall warts are different. The huge numbers of types, starting with simple transformers and ending with high power switching regulated types, means there is no universal model.

    You are better dealing with the approximation in the end.
     
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