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Switch mode power supplys

  1. Jan 26, 2016 #1
    I am looking into different methods of power supply's when I found out about switch mode power supply's. These are the type of supply's that you have in your phone charger (or at least i believe so).

    The type of supply I need, is something that can supply a voltage of 2.5 volts @ 70 amps, and plugs right into the wall. To do this, I would use whats called a buck converter (because it lowers the voltage). So I was looking on amazon for things that would work for me, and I found nothing anywhere. so I decided to lower my expectations, and just look for any buck converter that would work with a input of 120 volts dc from the wall, after it was rectified, and filtered, and I could find nothing.

    Then I tried looking into building my own power supply, given a switch ic, which I looked for, and still found nothing, that could handle an input of 120 volts. What I was wondering, was how come basically every single thing powered by the wall outlet is powered by these, if none of them can handle an input of 120 volts? And how do I find one that can.

    Also, how would I create my power source that can step down the main wall outlet power to 2.5 volts @ over 30 amps at least? Also, why is it that I could not find any switch ic that could handle 120 volts, if every phone charger has one that can? Do they not sell them to the public?

    Why is it that I could not find a Built buck converter on amazon that could handle an input of 120 volts? Could I modify a 30 volt one to work with 120 volts, or put something between the filtered dc wall current and the buck converter to do this? Thanks for the help, it is really appreciated.
     
    Last edited by a moderator: Jan 26, 2016
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  3. Jan 26, 2016 #2

    Averagesupernova

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    Take a look at this thread: https://www.physicsforums.com/threads/smps-float-capacitor-question.838254/
    A lot of discussion about switchers in general. I don't think you can expect an off the shelf IC to do what you want. That is not how electronics generally works. Notice in the schematic in the referenced thread that the IC is not really driving anything with serious power. The output transistors are what have to take the heat.
     
  4. Jan 26, 2016 #3

    berkeman

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    Welcome to the PF.

    What is the application? In general you would not use a Buck DC-DC converter with 120Vrms wall power because a Buck converter does not provide any safety isolation. It can only be used in low-voltage applications, or in applications where there are no user-accessible parts in the low-voltage section.

    Instead you would use a Flyback or Forward Converter or some other isolated switching power supply topology. You may be able to find an off-the-shelf power supply to satisfy your application, although the combination of low voltage at 2.5V and high current at 70A is unusual... :smile:
     
  5. Jan 26, 2016 #4
    So, if they don't use buck converters, for example, in wall usb phone chargers, then what do they use, and would it be capable of supplying the sufficient amperage I need? Also, how would I go about building one?
     
  6. Jan 26, 2016 #5

    berkeman

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    The USB wall charger probably uses a Flyback topology converter to make 5V at 1A.

    Why do you want 2.5V at 70A?
     
  7. Jan 26, 2016 #6
    I am trying to charge a 630 Farad capacitor, with a 2.5 volt rating as fast as humanly possible. Hopefully within a 15 second time span.
     
  8. Jan 26, 2016 #7

    berkeman

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    Why?
     
  9. Jan 26, 2016 #8
    well, I am using the supercapcitor to power some of my projects, and would like to be able to charge it from the wall, and charge it as quickly as possible. I think it would be awesome if I could fully charge it in under 15 seconds.
     
  10. Jan 26, 2016 #9

    berkeman

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    Well, based on your questions, you probably shouldn't be trying to work with such high power projects yet. I'd recommend that you work on low-voltage projects for a while (like using a 12V, 1A power brick that is already safety approved to power your projects). It's good that you want to learn about electronics, but this project sounds too dangerous for your level of understanding right now. This thread is closed.
     
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