Build or buy a PSU?

Discussion in 'General Electronics Chat' started by André Ferrato, Jan 14, 2016.

  1. André Ferrato

    Thread Starter Member

    Apr 5, 2015
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    Hello, i was intending to buy some power supply units from ebay to use on my future projects, but i thought, i could use this as an opportunity to learn how to make them, but i'm afraid this is not a trivial task, an psu that uses the smps technique seens rather complex to even try to do.

    So first i went to see if i could find some ready to use modules, and i found some:
    85-265 AC to DC 12V 8A
    5V 1A AC TO DC
    12V 1A AC TO DC

    They seen to be really good, taking a quick look, the boards have emi filters, fuses, thermistors... but i don't know if they can really deliver all this current.

    Even if they could not deliver this amperage, they seen to be really awesome and for this price a time saver.. is just a board ready to use(awesome!)

    So i did not found any negative points for buying.. but for building there is a lot of negative poinst rsrs. Just to start with:

    1) I don't know where to find these transformers.
    2) To make a really good smps psu requires a deep knowledge of inductors, capacitors and ic's..

    So what i should do? Go for the obvious that is buying, or embark on a wonderfull journey through the lands of power supply units?
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    Best psu is an atx from a computer, cheap easy to convert to a bench type gives out 3v, 5v, 12v at 20amps.
     
    tindel likes this.
  3. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    I thought about that also, making a bench power supply to test various projects. But the purpose of buying those modules is to make the final one, the final design, the one that is going to be converted to the PCB, so i would need a psu only for that project. I don't have a bench type to test my designs.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    Forget making your own switch mode psu, it far too much hassle for a beginner, easier to by a ready-made psu and assemble them together.
     
  5. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    I know right, but i want to know how hard it is to make one? It's like the ultimate level of electronics, or a medium level? That's what i would like to know.
     
  6. crutschow

    Expert

    Mar 14, 2008
    12,977
    3,221
    It's a least a medium level, not something a beginner should attempt.
    Layout and grounding are critical for a switching supply.
     
  7. dannyf

    Well-Known Member

    Sep 13, 2015
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    I would encourage you to think hard about your needs before deciding on a particular route.

    Possible inexpensive power supplies are abundant. For example, I use a lot of laptop power supplies myself, as I have a gazillion of them in the house. Mated to a few fixed and variable regulator, you have a nice and inexpensive power supply to experiment with.
     
  8. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    @crutschow Yes, as i thought. It seems pretty hard to do, maybe that's why there is an entire engineering area dedicated to this.

    @dannyf Whoa, that's a nice idea, use my laptop power supply for my tests.

    Have any of you guys designed your own switched mode psu?
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    You haven't said why you are focused on a switching power supply. For two of the three modules you linked to, a linear supply would not my excessively larger, and a whole lot easier for a beginner to achieve.

    Separate from that, the hardest part about an isolated switching power supply is the transformer. At the power levels you are indicating, everything else is cookbook and app notes. It still isn't trivial - the pc board layout is critical and you are dealing with offline AC. But parts from Power Integrations makes things pretty simple. Also, Pioneer Magnetics and others make power transformers specifically for some of the popular controller chip designs.

    ak
     
  10. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    @AnalogKid What is an offline AC? Also this is just a curiosity of mine, i always see those switch mode and they're so small and can take so much current. The transformers that i have here are really large compared to a switching one.

    And a "thing" about these switch mode is that they work from 85-265V, i doesn't require you to pull a switch to range the input voltage. I don't know if it's possible to do that with a linear one also, make it a electronical circuit that handles the switching, i believe it is, but i never took a time to think about it.
     
  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Offline means it is running directly of standard AC power.

    I agree, universal input is a big drawing card for switchers. There are auto-ranging circuits for linear supplies, basically a voltage comparator and a TRIAC. The low-tech way is to build a 240 V input supply with lotsa headroom, so that when it is running on 120 V it stays in regulation. Drawback is extra heat generated at 240 V operation.

    ak
     
  12. André Ferrato

    Thread Starter Member

    Apr 5, 2015
    206
    1
    Yes, it is a wonderfull feature to have in a circuit, universal input. That and efficiency is what makes me go for a switch mode.
     
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