Help to select a high efficiency 220V/24V/12V 50-60HZ Transformer range between 10VA

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Pato2010

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Dear All,
I'm trying to use a transformer to step down 220V to 12V AC then pass the output to a rectifier to be an input to a DC-Dc converter.
So I'm looking for a high efficiency transformer larger than 85%.
I bought one from Digi-key (Part-Num.: 14A-10R-24) it's manufactured in china after testing it's efficiency it seems 60% efficiency so it's not good for me.
Can any one recommend a low cost and high efficient one please?
 

60% efficiency sounds very low. I'd expect much better from any half-decent transformer. I wonder if it isn't just defective - maybe a couple of shorted turns?

Something that can cause transformers to get hot (i.e. bad efficiency) is if the core is operated too close to saturation. That's not uncommon with small cheap transformers e.g. a 5VA transformer whose manufacturer doesn't care if an extra Watt is wasted as heat, so long as he can save a few pennies in material costs. I wouldn't expect that with larger transformers though.

Anyway, a transformer rated at 240V is less likely to suffer saturation than one rated at 220V. Bear in mind the output voltage will be a bit lower.
 

I don't know your application, but if you can't avoid the use of a mains transformer, you need an ECO mains transformer. These have better efficiency and less standby loss (compared to conventional transformers). Of course this comes with a higher price as they need to use better core material, or a larger core to enable lower flux density.

It is not uncommon that small transformers have very poor efficiency (and poor load regulation).
 

Use 14A-20R-24 if efficiency is major concern. It will ensure efficiency 80% or more. But size weight and price will be slightly higher.
 

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