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Need to design an isolated 230Vac to 24VDC with I < 300mA

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Junior Member level 2
Jan 4, 2005
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Dear all,

I need to design the above cc to power my board. I have on hand an old TNY278 circuit, but the datasheet has not been too helpful in assisting inexperience ppl like to to select the components (specifically the transformer).

My questions -
1. Is the TNY278 still being used nowadays? Are they other similar components like these with better documentation?
2. What kind of transformer should I used? Must I use pulse transformer?
3. Should the transformer be 1:1 or according to the voltage output we need? for example 1:0.1?

Thank you.

Best rgds,

There's a huge offer of application notes and design guides at, in so far I can't agree to your comment. Transformer selection is almost a common problem of flyback converter design and not too specific to TNY278. You should consider however, that the design support documents are primarly addressing professional designers and aren't written as DIY guidelines or power supply tutorials.

TNY278 is a previous generation product, but still a good decision for a small power supply.

The transformer is a dedicated flyback transformer, voltage ratio rather 5:1 than 10:1.
Dear FvM,

You are right, just checked the website and they have extensive application notes which we can use according to the power consumption.

I believe with the application note, a power supply can be designed. The question now is where to obtain the required transformer according to the application note? Are there any off shelf transformer which one can easily obtained from Element14 (farnell) or RS components that fits the purpose?

Custom design transformer is possible but with MOQ. Is this the usual setback for designers that wish to incorporate the power supply board into the main logic board but with low volume? Do you have any other recommendations?


Happy New Year.


Manufacturers like Wuerth or Coilcraft have a number of standard flyback transformers in their catalogs, some of them are also available from catalog distributors. I'm under the impression, that the catalog distributors have difficulties to present this product category appropriately, you'll find it under misleading names etc. So searching their web sites without knowing a specific transformer type is probably useless.
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