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Pulse Transformers

Discussion in 'General Electronics Discussion' started by Chris6100, Apr 24, 2012.

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  1. Chris6100

    Chris6100

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    Apr 20, 2012
    Hello,
    Can a pulse transformer such as http://uk.farnell.com/murata-power-solutions/1001c/transformer-pulse-encaps-1-1/dp/1087805 be used to isolate a circuit from the mains?

    I am designing a power supply and looked at transformerless solutions but since this is for a prototype I would ideally like the design reasonably isolated for safety. All other transformers I've come across seem to be either massive or cannot supply something similar to a 1:1 turns ratio.
     
  2. duke37

    duke37

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    Jan 9, 2011
    The quick answer is no.
    Mains is a sine wave at 50 or 60Hz and nothing like a pulse.
    To get isolation you will need a transformer, either a 'massive' iron cored transformer or a high frequency ferrite cored transformer fed by a switching circuit. The pulse transformer MAY work in the latter case.
     
  3. Chris6100

    Chris6100

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    Apr 20, 2012
    Yeah I thought that would be the case but thought I'd check anyway! Thank you!
     
  4. Chris6100

    Chris6100

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    Apr 20, 2012
    I've been researching various designs and was intending to make a smps. I seem to be unable to find suitable parts to make one that can provide around 200VDC from a 230V mains AC supply. It also needs to supply a current of around 1-2A. The Forward type topology seemed a reasonable place to start but could somebody possibly guide me in the right direction with regard to an example design or the sort of parts I could expect to use.

    Additionally, what sort of physical size would I be to expect here? Ideally I would like it to fit in a box about 20x20cm and 3 or 4cm high.

    Are there any other PSU designs which might fit my spec?
     
  5. Chris6100

    Chris6100

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    Apr 20, 2012
  6. TedA

    TedA

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    Sep 26, 2011
    Chris,

    If you really need 2A @ 200V, that's 400W. The pulse transformer you mentioned is no doubt much too small for this power, and it lacks agency approval for this application.

    A SMPS running off the mains is not a trivial design challenge.

    You can get a good idea about what's involved by looking at a PC power supply of the same total power rating. Indeed, the xppower unit's guts will generally resemble what you see inside the PC supply.

    You have not given us any idea about considerations such as how many you plan to make, what your safety approval environment might be, how much time you have, and so-on.

    If you need an agency-approved device for production, your best bet would be to locate an off the shelf unit that will do the job. Failing this, several power supply manufacturers offer custom design and manufacturing to your requirements.

    If you just want one example for your basement project, you might start with a PC or other off the shelf SMPS and modify it.

    Ted
     
  7. davenn

    davenn Moderator

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    1,884
    Sep 5, 2009
    those are just standard SMPS units used for laptops, LCD screens etc where low voltage and higher current (4+ Amps) is required in a small package

    I think part of the problem here is that you havent really defined why you want a "pulse transformer" which is nothing like this link.

    Are you calling something a pulse transformer when you are really just referring to a SMPS ?? ie. an error in definitions ?

    Dave
     
  8. Chris6100

    Chris6100

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    Apr 20, 2012
    Thanks for the replies. The pulse transformer was the wrong spec and is not suitable for this project. I was just looking at different devices and came across the pulse transformer which had a high isolation voltage. Unfortunately the constant voltage is is low.

    For now I will just be making one because it is for a one off company project. I need to make it as quickly as possible although there are no imminent deadlines. I have designed many linear supplies with a higher power rating and I am aware the smps will not be a trivial task but as far as I'm aware it is the only way to get a power supply small enough with the power rating of between 200 and 400 watts. If this project prooves to be successful them more will need to be made.
     
  9. duke37

    duke37

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    Jan 9, 2011
    You could look at TV and computer power supplies, possibly take one and rewind the transformer output to the voltage you require. You will need fast high voltage rectifiers and low ESR capacitors.

    An push-pull inverter would be easier to design, could be run at a lower frequency and would be easier on the rectifiers and capacitors. A simple one could be made without voltage regulation.
     
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