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I am trying to design a SMPS for a project (I have to make a custom one for integration purpose).

This SMPS have universal input (85-265V AC at 50 or 60 Hz) and an output of ideally 53V (but it can be between 51 and 55V, it does not really matter much).

I am not really familiar with SMPS design, so I used the WEBENCH TI tool to get a quick design that I can integrate in the project (it does not have to be perfect yet, it is just for a prototype).

My question is: how do I select and off the shelf transformer (from mouser, digikey or else) to meet the design requirement (again nothing as to be perfect) because I do not want to other custom design transformer for something that will likely change in a couple of weeks (and I do not know one thing about winding one).

Here are the parameters from TI calculation tool:

Transformer repart part 1

Transformer report part 2

Menu to select an alternate transformer parameters

PS: I want to precise thatI tried several time to do it by myself, but I think that I do not understand the system weel enough to make a proper selection. For example, I do not know how the inductance affect the output voltage and current.

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    \$\begingroup\$ You are extremely unlikely to find an off-the-shelf transformer for a high-frequency SMPS from online shops. Most of what they sell are "iron" (i.e. line-frequency) transformers which will not operate well at tens or hundreds of kilohertz. For SMPS you really need ferrite. (Note that WebBENCH already suggested CUSTOM...) \$\endgroup\$
    – Adam Lawrence
    Feb 21, 2020 at 22:11
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    \$\begingroup\$ Do you have to go through safety and electromagnetic compliance testing with this design? In all the countries you are going to sell this? Or is it OK if your design electrocutes someone or burns down a building? Just asking if you have taken all the aspects of making a mains input power supply into account. If you can't buy an off-the-shelf power supply module that has been pre-certified, perhaps ask a design house how much it would cost to have a design that can be integrated on your board with a guarantee that it is safe and even have them make the tests for the certifications? \$\endgroup\$
    – Justme
    Jul 13, 2021 at 12:21

3 Answers 3

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A flyback design ? Appears to be.

There are very few 'off the shelf' SMPS transformers, on account of the multitude of varying design parameters, unlike line frequency transformers.

There are a number of design resources online, my favourite of which is Power Integration's power supply design tool that provides transformer design assistance (rather well in fact). It's entirely generic in its application, so you don't need to use a PI part to make good use of the tool.

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You have answered your own question. Find a Split Primary (no tap in the center) transformer with a turn ratio that your program spit out :)

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  • \$\begingroup\$ There is more to it than that... Volt-seconds for starters, inductance, target switching freq etc... \$\endgroup\$
    – user16222
    Mar 15, 2021 at 8:10
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Off-the-shelf parts have limited selection. If you can't find one that is close enough, your only recourse is a custom build.

Considering the application is connected to mains (it must be safety rated), I would strongly encourage engaging with a custom design service, or an electrical engineer, to design and build samples. The basic calculations are fine as a starting point.

EMI performance also depends on the windup (particularly if internal shields should be used, but also tricks like aux winding extension can be used to effect), and this will need to be verified by a test engineer before release to production.

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