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For DC to DC application, I see these charts often for inductors, but I don't understand what they actually mean. What does this chart mean, and how does it relate Volt-uS, Irms, & Freq?

enter image description here

Edit:

This image was taken from this inductor's datasheet. Full Datasheet Here.

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The chart gives guidance on how much to reduce applied Irms compared to the typical Irms value given in the specification table. It's usual for the specified Irms, really this basically a DC current, to cause a 40C temperature rise. As ripple current is added on top of the DC, core loss and also winding loss contribute to heating. Core loss is a function of drive level, meaning B-H loop size, and frequency, which V-uS is related to also and much easier to measure than the B-H loop path. Winding loss is a function of frequency and rms current level. The Chart says Core Loss, but also will include winding loss.

Let's say you decided to operate the 22uH part at 32V-uS and 500kHz. According to note 5 that would mean an Ipk-pk of about 1.7A. To keep the temperature rise to 40C, the total Irms including the 1.7A of ripple would have to be less than 58% of the rated typical Irms of 6.3A.

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  • \$\begingroup\$ what is "drive level"? mmf? \$\endgroup\$
    – hassan789
    Commented Apr 17, 2015 at 13:42
  • \$\begingroup\$ Yes, @hassan789 mmf. V-uS is effectively equivalent to NI or mmf in the core because V = L di/dt. For a given inductor, it will set the extent of the B-H loop, which is the main component of core loss. \$\endgroup\$
    – user16497
    Commented Apr 17, 2015 at 20:44

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