What is the best way to learn how to design and make SMPS transformers?

Question

I'd like to learn about designing and making transformers for switch mode power supplies. For example if we start with an AC to isolated DC supply say 240Vac to 5V dc 1A. Is there an evaluation kit to buy? Is there a good tutorial anywhere that you have found useful? I don't want to buy a transformer I want to choose the right core and winding and understand the principles. And there are different configuration for the control circuit, I'd like to understand that too. But to begin with a simple intro scheme will do. Thanks, Peter.

clem57 · Answer

Designing Switchmode Transformers for Optimum Efficiency | Content content from Power Electronics starting point with What is an SMPS | Switch Mode Power Supply Tutorial | Radio-Electronics.com tutorial. Clem

kkazem · Answer

Peter, Unless you need that evaluation kit for the electronic converter, I'd say away from it as It looks like it has a ready-made transformer in it. If you want to design and build your own transformer, that's not too hard. I'd Google transformer design. I've seen several DIY articles on transformer design. I design and manufacture transformers and DC-DC and DC-AC converters/inverters and I can help you a little here. Do look at the TI/Unitrode seminars in pdf form on the TI website. Look for article on magnetics or transformer design by LLoyd DIxon. These are very good, but are at a moderately high level engineering wise. If you want to get a kit, try the CoilCraft C-356 planar transformer design kit. They even replace the materials in the kit as you use them if you ask. It's about $ 120 for 1 kit. The power level is up to 120 watts per transformer. Go to the Coilcraft website and search for the C356 kit if you're interested. This is a planar kit, so the windings are circuit boards and copper stampings and it has only one size core. You can design your own transformer from scratch by using a manufacturer's core datasheets. I have no ides what power level you want and what frequency you're thinking of, or else I could help you with an initial core selection. Once you have that, it's easy to calculate whether or not the wire will fit or not. If not, something has to give. Before you can compute the "build" as we call it, which is percent build or percent of the available window area, you must compute the number of primary turns required and this depends on a lot of factors, but here is a general equation: Np= Ein*10^8/(4*Fo*Ac*Bmax) where Np = primary turns, Ein = primary voltage, Fo = frequency, Ac=Core cross-sectional area in cm^2, and Bmax= maximum applied flux density in Gauss, which is your choice to keep the core from saturating, based on the manufacturer's core material datasheets. The factor of 4 is only for bipolar square wave form applied and it would be 4.44 for a sine wave. For a unipolar pulse, the equation would change to: Np=(E*10^8)*Ts/(Fo*Ac*Bmax) where Ts is the on time per pulse for a unipolar pulse. This assumes that the off-time and/or circuit for transformer core reset is such that the core will be reset under all conditions. For if it is not, it will saturate, often blowing up your power converter.

What is the best way to learn how to design and make SMPS transformers?

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