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I am designing a 5V, 5A buck converter, and I am trying to spec my output inductor.

The datasheet specifically mentions that my inductor should have an appropriate current rating, but

I also wonder about the saturation current rating.

Wouldn't it be important for my inductor to have the same inductance over the entire range of the

output load?

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  • \$\begingroup\$ You're going to want an inductor that has a saturation current > 5A for this application. The inductance is relatively constant until you reach saturation in the magnetic material. \$\endgroup\$
    – jwh20
    Commented Jul 1, 2021 at 13:40
  • \$\begingroup\$ Try to think of it this way: rated current related to thermals with very long time constant and saturation current relates to your peak current ripple in the worst case scenario and microsecond time scale. You can cheat a little but with rated current for example inrush or something very short whereas you should threat saturation current as a hard limit unless you really know what you are doing. \$\endgroup\$
    – winny
    Commented Jul 1, 2021 at 13:54

1 Answer 1

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The two current values are distinct.

The rated current is used mainly for average DC current due to heating.

But as it is used in a buck converter, there will be by design about 30% of ripple current on top of the average DC.

So under maximum load, the inductor needs to handle the peak ripple current without saturating, so that the switching current does not go off the safe limits for the buck converter, and it does not shut down due to overcurrent.

The datasheet of your buck converter will usually indicate what kind of inductor ratings you typically need.

So for a 5A buck converter, you need at least 5A rated current, and maybe 6.5A or 7A saturation current, depending on how much ripple current the buck converter is intended to have.

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