Inductors - current rating for large transient currents

#1

Hi,

I want to apply a single brief pulse of a large sinusoidal current (300 microsecond pulse with a peak Imax = 100 A (say)) to a fixed inductor as a part of an LC circuit. If the DC current rating of the 15 uH fixed inductor is stated as 850 mA, what is the overshoot that it will allow?

Thanks.

#2

I don’t believe there’s a rule of thumb for transient surge current for inductors; that sort of thing would be specified on a part-by-part basis by the manufacturer. May I ask which specific inductor you’re looking at?

#3

This is an example – CBC3225T150MR

The DC current rating is stated to be 850 mA.

#4

If there are fixed inductors for which the manufacturers specify transient surge current, I could use those as well. I am looking for L in the 10-20 uH range.

#5

I’m following up with one of our product experts on this question and will be in touch here when I have new information to share.

1 Like
#6

I’ve just received word from our Taiyo specialist on this issue. Taiyo Yuden is willing to investigate this for you but would require me to get you a form you need to fill out and get sent their way. Otherwise our specialist informed me that no manufacturer he works with or is aware of rates their inductors for surge; that’s something you would have to either test yourself or speak to a manufacturer directly about to see if they’re willing to do the testing for you. Apologies, Tottochan. Let me know how I can be of further assistance on this issue.

#7

Thank you for the followup. I can fill the form and tell the manufacturer exactly what I would like to do. I know the specs pretty well so I can outline them in the form. Thanks again for your help.

#8

The initial question could be understood in at least two different ways:

  1. “Will inductor X physically tolerate a single sinusoidal current pulse of 100A peak amplitude and 300us duration?”

  2. “Will inductor X physically tolerate such a pulse AND behave like an inductor in the process?”

The answer in case # 2 is usually quite straightforward; the listed saturation current is the current flow magnitude at which the inductor “stops” behaving like an inductor, reckoned as the point where observed inductance has fallen by some manufacuturer-defined percentage (30% in case of the CBC3225T150MR). That value is given as 730 mA for the part mentioned, so if you want your inductor to behave like an inductor while you’re applying a 100A pulse, that part won’t come anywhere even close to doing so; I’d suggest using 3-6 of P/N 732-5623-ND or similar in series if maintenance of inductive behavior is desired.

Case # 1 is a different; if you don’t care about the inductor behaving like an inductor and just want to gauge the probability that your current pulse will convert part X into to a cloud of expanding gasses and shrapnel, that’s not readily answered conclusively from the datasheet info. One could guesstimate things by finding the energy content in the pulse (I^2*R), assuming the device is a solid block of some material, and calculating the resulting temperature rise of that chunk of material when the calculated amount of energy is dumped in. I get a figure of around 5°C assuming a solid copper mass of equivalent size to the CBC3225T150MR.

Problem is, that inductor isn’t solid copper; the conductors that are carrying the current within the part are actually rather thin and a fraction of the part’s mass, so if the energy in an applied pulse would be sufficient to raise the temperature of an equivalent-size chunk of copper by 5°C in a third of a millisecond, chances are pretty good that the internal conductors in the part number mentioned would end up getting a -lot- warmer than suggested by the above guesstimation.