Skin effect in fuses.

[cupoftea]

Hi,
We have the attached 10.9A RMS current flowing in a 15A fuse.
Its at 450kHz.
The fuse is 2.16mm thick and surface mount.

Fuse part number is AF2-15.0V065TM

AF2-15.0V065TM Fuse

https://www.farnell.com/datasheets/3200536.pdf

We calculated that the RAC/RDC is 5.1

Therefore the AC resistance of the fuse is 19.3mR (DC is 0.0038R)

As such, the power dissipation in it will be 2.9W.

Do you agree, this is way excessive. Do you agree, We must filter the current before it goes through
this fuse?

 

[KlausST]

Hi,

we assume the full 2.16mm thickness is carrying the fuse current

I´m sure this is not the case.

Such a huge volume would result in huge thermal capacitoy, needing a rather high resistance, and rather high power dissipation, and very lagging timing.

****
With a fuse you want
* the "fusing element" hot spot facing away from the PCB, not to (over-) heat the PCB. Also the PCB (copper or not) to have low influence on tripping characteristic
* you want the fusing energy to be small, not to cause high temperature to the PCB, not to cause explosion or fire
* you want the fusing element cross section minimal for safe, fast and wide opening.

Klaus

 

[Easy peasy]

The fuse will be largely un-affected by the 450kHz current ( as reasoned and shown above ) - not several times the DC resistance as you posited,

putting the fuse right by the fet drain allows a high speed fuse to be used - as the peak current in the fuse will only be that determined by the power circuit and control,

thus, if the rms and/or peak is 10A, a 15A fast blow fuse would be ideal - it would likely save the semis in the event of: - sustained shoot thru, other semi failure, choke failure, sustained short ckt on the output along with control failure in the current limit.

Easy Peasy