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When trying to use the turns ratio to assist in the voltage conversion I found current transformers to have the greatest range in N, up to 1:500. Is a current transformer suitable for a flyback switching converter?

Otherwise, could someone please point to a transformer which would be appropriate for this purpose. Thank you!

Looking for one for a traditional isolated 5 V supply from mains.


marked as duplicate by Andy aka, Michel Keijzers, Finbarr, Voltage Spike, Sparky256 Mar 14 '18 at 1:40

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They're not the same.

An "ordinary" transformer never stores much energy in its magnetic field. Power entering its primary side is immediately delivered to the load on its secondary side.

A flyback transformer must build up a substantial magnetic field while current is applied to the primary, and only deliver the stored energy to the load after the primary current stops.

The requirement to store energy between the two parts of the cycle means a flyback transformer must be designed differently from an ordinary transformer. The core must be designed to store substantial energy without saturating. In the case of the application in a flyback switching converter, you'll often see them referred to as "coupled inductors" rather than "transformers" for this reason.

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    \$\begingroup\$ The core must be designed not to saturate when used with substantial stored energy. True, but unhelpful as it's coming at it from the wrong direction. Both flybacks and ordinary transformers mustn't saturate. The flyback core is designed to have a low permeability, so that it can store more energy than a high mu core, aka needs more magnetising current for the same field as a high mu core. \$\endgroup\$ – Neil_UK Mar 11 '18 at 6:17
  • \$\begingroup\$ Thank you both. I have looked at common vendors such as Mouser and have been unable to find flyback transformers. Is there another place you guys might be able to recommend from experience? Thanks again! \$\endgroup\$ – A.S. Mar 11 '18 at 6:20
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    \$\begingroup\$ @A.S., if you go to the major magnetics vendors websites, you will see they have parts recommended for flyback converter applications. If that's what you're doing, use those parts. (If you're making a CRT driver, you probably need a different part again) \$\endgroup\$ – The Photon Mar 11 '18 at 6:46
  • \$\begingroup\$ I believe these are also often custom designed for the application. It is not very challenging, TI has some good examples with some of there offline converters on flyback design. \$\endgroup\$ – MadHatter Mar 11 '18 at 16:05

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