Yep, from what I read, the trip current vs time to trip is a lot longer than for fuses, the advantage being only that they reset. From what I can see, they're best used in catastrophic failure cases where the battery (supply/circuit) can stand an overload for a bit of time, then the fuse trips.? They're not the kind of thing I'd think of using to protect an FET unless the trip current were substantially below the rating of the FET.? Just me, of course.
Harvey
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On 11/10/2019 1:27 PM, Dave wrote:
Hi Harvey,
? According to the LittleFuse datasheet, PTC fuses are used to protect:
USB peripherals
Disk drives? CD-ROMs
Plug and play protection for motherboards and peripherals
Mobile phones - battery and port protection
Disk drives
PDAs / digital cameras
Game console port protection
But in reality they may be used more in batteries. I just read about them in relation to protecting USB ports and in order to have an option other than a battery pack, I wanted to protect me from any liability. :) Probably never even gonna trip the PTC fuse except for when it is first soldered in. Just covering my you know what. I have thoroughly thought out my plan and everything will work fine. Just trying to learn as I go.
Thanks for the information,
Dave
On 11/8/2019 6:35 PM, Harvey White wrote:
I spent a little time looking at PTC fuses.
Made the following observations:
1) their resistance is higher than a regular fuse (and a fuse *must* have a resistance)
2) the best use of the fuses is to protect from a short circuit.? The more current through the fuse, the faster it blows. If you would expect a normal 1 amp fuse to blow at 2 amps, the PTC won't, not for a while
3) the normal use for a PTC fuse is to protect a high current battery.? It's generally installed inside the pack, not user replaceable.
4) the more you use them, slowly, the resistance creeps up.
5) if you're going to use them in a circuit where you're watching voltage drops, then very carefully think the voltages and currents.? They? have a higher resistance than you'd think.
Harvey
On 11/8/2019 5:43 PM, Dave wrote:
Brad,
? Thanks for the test procedure. The PTC's I am going to have to test are .100mA hold and .250mA trip. I should be able to figure it out but if not, I will ask for some more help. :)
Dave
