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Design of SMPS - Not sure what these spikes are being caused by.

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Zog:
Something is still bugging me.
All the datasheets mention Irms for their current ratings and not peak to peak.
Surely I should be following that advice and not be using peak to peak for inductor selection ? Right ?

T3sl4co1l:
Irms is a thermal rating only.

You're looking for saturation current, which should be greater or equal to the peak current used in circuit.

Tim

Zog:
Ok. That's two of you now telling me. I will listen. Thank you. :-+

edit: one more quick question.
A 10uH to 1000uH is a 1:10 ratio right. I just need you guys to tell me that I am not a complete idiot.

MagicSmoker:

--- Quote from: Zog on September 21, 2019, 10:34:02 am ---Ok. That's two of you now telling me. I will listen. Thank you. :-+

edit: one more quick question.
A 10uH to 1000uH is a 1:10 ratio right. I just need you guys to tell me that I am not a complete idiot.

--- End quote ---

And you better pay close attention to the inductance at "rated saturation current" as it has typically fallen to 50% of the unbiased value, which is way lower than the usual definition of when "saturation" occurs (that is, by anyone besides commercial choke manufacturers), or a decline of 20% to, at most, 30%. Hence why I said you might want to limit peak current in a commercial choke to 50% of the saturation rating.

And yes, if one winding is 10uH and the other winding is 1000uH (1mH) then the turns ratio is 10 (either 1:10 or 10:1, depending on the direction).

EDIT - and no, not all the datasheets only mention RMS current; the part number I suggested before has Isat ratings, too.

Zog:
Great.
I realise that most mention Isat, but was a little confused.

Should I also include that huge inrush when it first starts up and getting to voltage as part of the selection process ? I am guessing yes. ie: I should take the peak to peak of the whole simulation and not just when it has settled down.

I am guessing yes because it's not working if it's saturated of course. But then again it's only for a few ms so is it that mission critical ?

edit:

--- Quote ---as it has typically fallen to 50% of the unbiased value
--- End quote ---
better look up what that means.

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