Transformer design for SMPS


I'm sorry if I make silly questions about transformers.

I use 230V ac rms @ 50Hz. I took 210V as min and 250V as max input. I need to get 5V@2A as output and using TNY266 as offline switcher for SMPS regulation. 

Ihave made my design by using this references

And I have calculated all the values so itt seems I need to wind transformer myself. I calculated primary and secondary turns, and used this table for the wire selection

So, primary is 144 turns of AWG 27 wire based on switching frequency and current and secondary is 4 turns of AWG 15 based on current but the switching frequency of that AWG is very low compared to the switching frequency of TNY266 i.e. 132 kHz. Did I select the correct AWG of wire for primary and secondary? And as per Infineon-Mouser design guide, I have decided to use EE16/8/5 core, is this the correct selection?

Am I doing correct calculations? If not, what are the corrections? Any recommended readings on subject to help design power supply and transformer design?



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Hello Andrea,

You should just check that core does not saturate with peak primary current.
Core losses are not too high and you need to be sure you are not reflecting too much voltage to the primary. And also beware to the same at the secondary.
Maybe you must have a gap for the flyback. Did you think about using ome isolation?
Remeber that if you have a too high NS/NP ratio, then your duty cycle will get too small, and your on time will go below the controllers minimum on time.


Published: 6 months ago