If I wanted to use my PC's USB port for a 5V source of power, what is the formula or best way to size a PTC fuse? It seems they come in various forms but they leave some questions as the specs vary enough to leave room for confusion. At least for me. So lets say I have a 300mA circuit connected and want to protect the USB port from damage. I can find PTC fuse that have a hold current of 300mA and a cutoff current of 600mA. That seems like a big gap to me. I found one with 100mA hold and 200mA trip. I would think I would want a 300mA hold with a 340 or 350mA trip but I can't find any. What is the best option?
Thanks

 

hi bert,
Look thru this PDF for information on PTC fusing selection.
E

 

hi bert,
Look thru this PDF for information on PTC fusing selection.
E

Thanks. I will check it out.