Electronics > Projects, Designs, and Technical Stuff

Polyfuse 8MILLI-ohms post-trip? am I missing something?

<< < (3/4) > >>

SiliconWizard:

--- Quote from: james_s on September 28, 2019, 10:36:09 pm ---That's interesting, I never realized that. Why don't they pre-trip them prior to shipment so that they're consistent throughout their useful life?

--- End quote ---

Because that's how they are supposed to be used. Don't you prefer a component that has minimal series resistance in normal conditions, and degrade a bit when shit happens (which should be a rare occurence unless your design is fucked up).

Besides, they will not really stabilize to a given ESR. Every time they trip, they will tend to degrade a bit more.

Siwastaja:

--- Quote from: SiliconWizard on September 29, 2019, 04:09:47 pm ---Besides, they will not really stabilize to a given ESR. Every time they trip, they will tend to degrade a bit more.

--- End quote ---

This. If they did stabilize after one or two trips, pre-conditioning them would make sense.


Use polyfuses only if you expect handful (tens, not thousands) of trips, and design for a large leeway in resistance (much more than R1). If you can't make it work, then don't use a polyfuse; design an active electronic efuse circuit (ICs do exist), protected by a classical single blow fuse (which only blows if the efuse circuit fails).

T3sl4co1l:
Yeah, that's the other thing about polyfuses: the self-resetting is a convenience, not a guarantee.  They are good for ~hundreds of cycles and are supposed to fail (permanently) open.

Tim

ejeffrey:
One more thing: surface mount ones are considerably worse than through hole in most parameters. I haven't paid much attention to the R R1 spread, but the hold to trip ratio in particular is much worse for surface mount devices.

T3sl4co1l:
THT also more consistent on current rating, since less dependence on trace/plane heatsinking.  But way slower, since they're usually much bigger (and amps+).

Tim

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod