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I have a 10W AC/DC converter that works in the range of 80~265Vac and I was using it with an input of 220Vac, but now I need to supply with 220Vac or 380Vac.

I was thinking about using a step down transformer to divide by two the input voltage and use the same AC/DC converter. I am looking forward a transformer to do this but I am newbie and I don't know where to start. Could you give me some advice?

Thanks

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    \$\begingroup\$ Where is your 380V coming from? Is that a three-phase supply? \$\endgroup\$ – Finbarr Apr 21 '17 at 10:19
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    \$\begingroup\$ The 220Vac comes from Phase-Neutral and the 380Vac from Phase-Phase. \$\endgroup\$ – JMP Apr 21 '17 at 10:46
  • \$\begingroup\$ Unless your converter is designed to run directly from a three phase supply, you would just power it between one of the phases and neutral, which would give you 220V. You would never connect a piece of equipment between two phases and an individual wall outlet would never be wired that way. \$\endgroup\$ – Finbarr Apr 21 '17 at 10:52
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    \$\begingroup\$ @Finbarr Lots of industrial equipment (big motors etc.) is only fed with Delta-connected 3 phase - there is no need for a neutral with a balanced load. Contactors are readily available with coils rated for 380-415VAC, and there are transformers for 380>220 available if one finds themselves in this position. \$\endgroup\$ – Someone Somewhere Jul 8 '17 at 10:50
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Off the shelf small power supplies are very cheap and common for normal single phase mains voltages .Their internal voltage clearances are rated for single phase mains .Most small SMPS are flyback which gives a simple low cost design.The efficiency and power factor of these units is generally poor .If they do not specify these important parameters then assume the worst and specify your 480 to 220 VAC mains transformer to have a VA rating of at least twice the output rating of the supply .This means for you 20VA or better .Do not go crazy on the VA rating because you will be wasting lots of money and power if you used say 200VA .Remember that the proposed power transformer under no load will waste more power than the SMPS .This is relevant for meeting energy efficiency specifications in some countries .You will find that this safe bulky mains transformer approach is cheaper and easier than getting a small 380VAC SMPS .Do fuse the primary of your transformer and get your wiring checked by a registered person .

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