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[SOLVED] PTC resettable fuses in parallel

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ArticCynda

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Hi everyone,

I'm designing a power supply circuit that can take inputs from USB (max. 500mA) and a DC jack (max. 1A). I'd prefer to protect both with a PTC resettable fuse.

Can I wire 2 PTCs with a trip current of 500mA in parallel to act as a 1A PTC for the DC jack? Is this a good practice? If not, why?

Thanks in advance!
 

Its better to have jumper selection whenever you are switching between these two supplies.

Mainly when you are using fuses in parallel how come current will get divide?
 

The trip current of these fuses will not be exact. If any one fuse opens less at than 500mA, the remaining one will open soon after since it tries to pass all the current. I think you will find that the circuit will always trip at a much lower current than you expect. It is not a good idea to parallel them up.
 
Thanks for the response, I suspected it might behave that way, similarly to why you can't parallel diodes to get the effect of a higher current diode, but wanted to check to be sure.
 

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