The ER, EC, and ETD ferrite cores are presented in a datasheet but visually I don't see any difference between them. The search results also say the same thing.
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1\$\begingroup\$ Compare price, mean length of turn, minimum core area and total core volume for them. Also, notice the straight legs on the ER. \$\endgroup\$– winnyJun 15 at 12:26
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\$\begingroup\$ See also the central leg gap if one. \$\endgroup\$– Antonio51Jun 15 at 14:26
1 Answer
EC and ETD are almost identical. ER is slightly different.
EC and ETD (ETD means economic transformer design) have both circular centre leg and circular winding window. ER's winding window is not perfect circular. Look at the outer legs closely and you'll get what I mean.
EC and ETD can generally be used interchangeably (e.g. EC34 or ETD34).