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Why can't ferrite cores be used at lower frequencies like 50Hz? To my knowledge, they can only operate at high frequencies.

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It is possible to make a ferrite transformer for response down to 50Hz .However there is a penalty .Garden variety ferrites are only good for around 300mT where the more orthodox laminated iron core is good for at least 1 Tesla .Your proposed 50Hz ferrite transformer would have to have about 3 times as many turns if it was to be wound on a core of the same area as the standard laminated iron cored transformer.So copper losses would be up and power rating would be down and voltage regulation would be worse .If you want to keep the winding DCR the same and hence not lose anything the proposed ferrite cored transformer would be much larger .Ferrite cores were used for telco Audio where I had to get down to 300Hz in a Napier branch of a Swedish Telco company .The power was very low like I think +6dBm so the size was not in the day an issue .RM8 cores were used as a mainstay and I sometimes used high pearmeability RM6 .The upper frequency response of these was superb but we limited things to 3.4 KHz .It would be interesting to try a ferrite output transformer in a valve amp where size does not matter .

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Why can't ferrite cores be used at lower frequencies like 50Hz? To my knowledge, they can only operate at high frequencies.

Core saturation is the issue. Ferrite cores saturate in a lower H-field than (say) silicon steel core laminates. Ferrite cores are used in high power buck converters up to many amps - they are passing DC - that's a lot lower frequency than 50 Hz!

There is nothing intrinsic about ferrites that make them a bad choice at very low frequencies. On the other hand, there are plenty of things you need to take care of when choosing a ferrite for a 2 MHz application.

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  • \$\begingroup\$ Please explain it in simple words...what will happen if i use ferrite core transformer at 50 hz? why should i only use it at high frequency? \$\endgroup\$ – Afra Syab Apr 22 '17 at 11:08
  • \$\begingroup\$ Providing you don't saturate the core with too much current, nothing particularly problematic will happen. You can use ferrite cores from dc to a frequency where the core losses make it unsuitable. Ferrite cores can be used at dc as I said in my answer. Please also note that an extended comment trail will attract moderator attention. This is a question and answer site and not a blow by blow learning experience. Not my rules! \$\endgroup\$ – Andy aka Apr 22 '17 at 11:13

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