I have a mains-rated transformer that is a leftover part from my previous project. Now since I am experimenting with the idea of SMPS, I am wondering how it would behave when handling the higher frequency of a SMPS. Does this spells a higher capacity?

The transformer in question is rated for input of 220V 50Hz, outputs 12V and have a rated capacity of 3VA. What happens if I try to put it in a SMPS with an operating frequency of 150kHz? Will it catch fire?

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    \$\begingroup\$ The core material in a normal 50Hz/60Hz transformer doesn't usually behave all that well at SMPS frequencies. Lots of losses. \$\endgroup\$ – brhans Jan 30 '15 at 18:54
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    \$\begingroup\$ It'll probably work at switching frequencies up to 1kHz or a bit higher, maybe 5 kHz if you're lucky. But people who designed transformers using the same materials, to cover the audio high frequency range (for vacuum tube amp output transformers) really had to work for it. So you probably won't get success at 20kHz let alone 150kHz. \$\endgroup\$ – Brian Drummond Jan 30 '15 at 19:18
  • \$\begingroup\$ For one thing, the inductance would be so high that you would get hardly any power into and out of it. \$\endgroup\$ – rioraxe Jan 30 '15 at 22:30

If this is a ferrite core transformer, maybe you could get comething out of it, but if you have a laminated core transformer, the eddy currents will cause too much trouble. Would not be a practical design.

There is a paper detailing high frequency bahaviour of laminated core inductors.

You could probably get some useful info out of it.

  • \$\begingroup\$ It's a laminated core transformer. So if I kick 150kHz into it it may catch fire then? \$\endgroup\$ – Maxthon Chan Jan 31 '15 at 6:40
  • \$\begingroup\$ If you give it enough power and leave it on long enough. But I would expect the copper winding to give in faster than the core itself. One of the risks would be exceedeng the curie point of the core. From then on you only have some wire connected to mains. It's not a transformer anymore in that case. \$\endgroup\$ – iggy Jan 31 '15 at 9:18

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