Ferrite Core Power Capacity Table for Flyback SMPS

Designing flyback transformers for custom SMPS power supply units can usually be the bulk of the design process. Determining the core size for an SMPS flyback transformer is the first step towards figuring out the winding diagram. Here is a ferrite core power capacity table that we often use as a quick reference table for picking ferrite cores.

The recommendation here is based on common materials and uses broad assumptions. Though the ferrite core power handling capacity will differ widely across manufacturers based on material and physical dimensions, this table acts as a good starting point.

Some assumptions:

  • 5kHz – 200kHz switching frequency
  • Double E shaped, wire wound transformer
  • No or very small air gaps

Core Model vs Power

EE and EI Cores
EE and EI type ferrite core structures (Source: MMG Ferrite)
Core ModelMaximum PowerSwitching Frequency
EE103 W5kHz – 200 kHz
EE135 W5kHz – 200 kHz
EE16 or EI166 W5kHz – 200 kHz
EE19 or EI198 W5kHz – 200 kHz
EE22 or EI2210 W5kHz – 200 kHz
EE25 or EI2516 W5kHz – 200 kHz
EE28 or EI2822 W5kHz – 200 kHz
EE3040 W5kHz – 200 kHz
EE40100 W5kHz – 200 kHz

The above power capacity table should cover your requirements for isolated flyback SMPS design in the range of 1 to 100W. For power output higher than 50W, PQ series cores are recommended over EE series cores. We will update this page soon with those cores listed as well.

EFD Cores
EFD type ferrite core structure (Source: MMG Ferrite)
Core ModelMaximum PowerSwitching Frequency
EFD2011 W5kHz – 200 kHz
EFD2518 W5kHz – 200 kHz
EFD3028 W5kHz – 200 kHz

EFD cores are gaining popularity in low profile designs these days. If your application is not very high power and needs a low profile design, you may find the above table very useful.

Need help with low power SMPS design?

You can always reach out to us for help!


Reference 1: BetterFuse Cores
Reference 2: MMG Canada
Reference 3: CEC Coils

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