Coils temperature ratings

[iliya24]

Hello i need to choose a coil or high current application and i read some articles about it and i saw 2 importan things 1)HEAT RATING CURRENT DC AMPS

2)SATURATION CURRENT DC AMPS can u help me to understand the meaning and the difference.

Thx.

 

[ZekeR]

These are two different ratings, and they have very different implications.

HEAT RATING CURRENT DC AMPS:
The inductor has a certain amount of thermal conductivity to the PCB, and therefore when heat is generated in the inductor, the PCB keeps it cool. However, if you run too much current through the inductor, it can still reach a point where it still becomes hotter than its hottest specified operation. (The reason heat is generated is because of the inductor's internal DC resistance). So, to stay within specified temperature limits, never run more DC current than this specification.

SATURATION CURRENT DC AMPS:
This one is interesting. Even if the inductor isn't hot, exceeding this specification can cause serious problems. When you try to increase the current through an inductor by applying a voltage across it, any increase in current is impeded by the inductance (and the inductance depends on the permeability of the core material). This is because a change in inductor current requires a change in magnetic flux, and as we remember from physics class, changing magnetic flux induces an electromotive force in a coil around it which tends to oppose the change.

Magnetic cores are made of high permeability materials. Unfortunately, once you exceed a certain magnetic field strength, the permeability suddenly drops (the magnetic domains are already aligned, and the core is "saturated"). This means the inductance drops, and suddenly the inductor current is able to increase rapidly—see this image.


When this happens, the inductor current can increase to very large values very quickly, potentially burning out the power switches in your circuit. Basically, the inductor becomes a short-circuit. And even if it doesn't break anything, it is still highly undesirable.

So, when designing a power converter, ensure that the AVERAGE inductor current is less than the "HEAT RATING CURRENT DC AMPS." In addition, ensure that the PEAK inductor current never exceeds the "SATURATION CURRENT DC AMPS." As always, build in an additional 20% or 30% margin for safety.

Hope this helps!

 

[iliya24]

Thank you for help