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In several projects so far, I have been using old "fashioned" transformer based power supplies. However, this time around I want to use a switching mode power supply. The supply will be used to power some 5V micro controller and supporting electronics. The power requirements are equivelent to that of a old usb phone charger (which for several reasons is not going to be used.)

After some research on the internet I found a very neat tool by NXP, which helps with most of the complicated mathematics involved: http://nxp.transim.com/fb/design.aspx So far i have been using the default specifications (universal mains, 5V, 5W, integrated FET, TEA1721)

Unfortunately i get stuck at the part where i have to choose the transformer (the bottom 3 choices from the "design" tab).

For instance, i want to use the following transformer: http://nl.farnell.com/bi-technologies-tt-electronics/hm42-10001lftr/transformer-gate-drive-300uh/dp/2192063 The tool proceeds to ask questions such as: Winding ratio, primary inductance and last asks the specific transformer you use.

The datasheet of the transformer(sorry, cant post more than 2 links) i was planning to use (and also several other transformers out there) do not answer there questions. Because of this I get the feeling that when designing a SMPS also a specific transformer is designed.

So the above boils down to: where can I find the data required to completely fill out the design tool?

Any help is much appreciated, thanks in advance!

Kind Regards, Victor

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2 Answers 2

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For instance, i want to use the following transformer: http://nl.farnell.com/bi-technologies-tt-electronics/hm42-10001lftr/transformer-gate-drive-300uh/dp/2192063

You can't use the transformer you want to - it isn't rated for doing what you want.

Unfortunately i get stuck at the part where i have to choose the transformer (the bottom 3 choices from the "design" tab).

What's wrong with the design page that it produced: -

enter image description here

It tells you: -

  1. The core (E16/8/5, Ferroxcube, 3C90, 570µm)
  2. The gapping (0.57 mm)
  3. How many turns for primary, auxiliary and secondary
  4. How to wind them
  5. The wire gauges

It even gives you options for using different ferrite cores - see radio buttons.

What were you expecting? You want something easier? Yes, well go to premier magnetics and choose a design for 5V and 1A (such as this one) and they do the job for you using a Power Integrations part: -

enter image description here

They'll sell you the transformer and provide all the info for the other magnetics. If you are still insistent on using the NXP tool then start learning about transformers so you can take the premier magnetics transformer and feed the data back into the tool.

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  • \$\begingroup\$ Thanks for the reply. What i was looking for is to just take a off the shelf transformer and put that into the design tool to calculate the value's of the components around it. Not instructions on how to wind a transformer yourself. \$\endgroup\$
    – user43487
    Commented May 27, 2014 at 16:54
  • \$\begingroup\$ The transformer you wanted to use was way off mark. What you should do is allow the software to give you the inductance and turns ratios then go to somewhere like premier magnetics and see what matches most closely. Try this premiermag.com/pdf/pol.pdf. They have about 50 transformers that will do 5V. \$\endgroup\$
    – Andy aka
    Commented May 27, 2014 at 17:48
  • \$\begingroup\$ And, if you follow the link thru for a 5V 1A supply it'll take you to here: premiermag.com/pdf/pol-05010.pdf and, if you scroll down it will give you the full circuit diagram and values using a chip from power integrations. It really can't be much easier. \$\endgroup\$
    – Andy aka
    Commented May 27, 2014 at 17:56
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Take a loook on "Cookbook: For Do It-Yourself Transformer Design", from Wurth Elektronik document. It contains some math stuff regarding this kind of design. Also see Webench, an on-line tool from TI - it save you from have to specify each transformer parameter.

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  • \$\begingroup\$ thanks for your reply, i did have a look at webench, however it does not answer the questions, it just spits out a "custom" transformer part \$\endgroup\$
    – user43487
    Commented May 26, 2014 at 16:14

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