Teensy 4.1 500 ma Fuse
- Thread starter mcharlesmorrison
- Start date
PaulStoffregen
Well-known member
The part you circled in the schematic is F1. It's 0603 size.
The part you circled in the photo is Q1. It's SOT-23 size.
If F1 broke off the circuit board, you can get the board running by just soldering a wire in its place.
The part you circled in the photo is Q1. It's SOT-23 size.
If F1 broke off the circuit board, you can get the board running by just soldering a wire in its place.
Curt Welch
Member
The F1 PTC fuse I suspect, is this part: https://www.digikey.com/short/5t5fjzj3
Bel Fuse Inc.
0ZCK0050FF2E
PTC RESET FUSE 6V 500MA 0805
But as Paul already said two years ago, you have Q1 circled in your picture.
I had to hunt this down for myself, and thought it would be helpful to have in this thread.
The F1 fuse causes reboot loops on heavily loaded Teensy 4.1 projects.
A more robust polyfuse that's 0603 might be 0603L075SLYR which has a 750mA hold current at 20C. It has a much lower max resistance after tripping too.
https://www.digikey.co.uk/en/products/detail/littelfuse-inc/0603L075SLYR/3661955
https://www.digikey.co.uk/en/products/detail/littelfuse-inc/0603L075SLYR/3661955
PaulStoffregen
Well-known member
PTC fuses limit current by increasing their resistance. They don't stop the current from flowing like a traditional fuse. Instead the current stabilizes at some high but hopefully not too destructively high amount. How high the steady current ends up being depends on the fuse's resistance, the nature of the fault attempting to draw too much current, and the capability of the power supply.
A much lower max resistance will mean the steady fault condition current will (probably) end up much higher. You could imagine the word "robust" to mean different things, but at the very least you shouldn't expect "robust protection" from a part which much lower max resistance.
A much lower max resistance will mean the steady fault condition current will (probably) end up much higher. You could imagine the word "robust" to mean different things, but at the very least you shouldn't expect "robust protection" from a part which much lower max resistance.
Fuses generally protect against fire or wiring (or battery) damage caused by hard short circuits. Don't expect semiconductors to be protected adequately by a fuse.
Polyfuses have the characteristic that once triggered they have a permanent increase in resistance, making them more likely to trigger again - and also they trigger more readily at even modestly higher temperatures. Under-sizing them is probably a common pitfall. I have been hit by this when using one to protect a tungsten light bulb - the startup current surge of the bulb triggered it despite the hold current being well above the steady state current of the bulb.
Or put another way they are less than ideal components whose key feature is the convenient self-resetting ability.
"Robust" protection usually requires more sophisticated protection circuitry than any kind of fuse.
Polyfuses have the characteristic that once triggered they have a permanent increase in resistance, making them more likely to trigger again - and also they trigger more readily at even modestly higher temperatures. Under-sizing them is probably a common pitfall. I have been hit by this when using one to protect a tungsten light bulb - the startup current surge of the bulb triggered it despite the hold current being well above the steady state current of the bulb.
Or put another way they are less than ideal components whose key feature is the convenient self-resetting ability.
"Robust" protection usually requires more sophisticated protection circuitry than any kind of fuse.