Hi guys

Where in this circuit should I put a fuse..and what should the value be? The MOSFET switches 40V from a 10A PSU.
I guess the 40V line is a good bet!
(see attached file)

Thanks!

 

A fuse is current related not voltage. However, high voltages should avoid fuse sparking so they are larger.

In your case inrush current and supply will define fuse.
than what do you want to protect PSU or device?
for PSU use a fuse smaller than the max current to be delivered by PSU.
for protecting your circuit take the max current x 1.3 .
Picbuster

 

Fuses come in all different categories from fast blow to slow blow, there are also Rectifier or Semiconductor fuses which have extra fast sweep through, if using a slow blow fuse to protect semiconductors, the device will blow way before the fuse in the presence of a heave fault current.
Max.

 

A fuse is current related not voltage. However, high voltages should avoid fuse sparking so they are larger.

In your case inrush current and supply will define fuse.
than what do you want to protect PSU or device?
for PSU use a fuse smaller than the max current to be delivered by PSU.
for protecting your circuit take the max current x 1.3 .
Picbuster

So, for protecting the PSU something like a 250V 9A (or other value lower than 10A) fuse?

 

No, if you want to limit current to 10Amps 24V your fuse is 5mm long but is you want 10amps @ 1000V your fuse is >10mm long but still 10 Amps
This an example to indicate difference in length. ( see fuse spec's related to this subject)
If your PSU can not deliver more than 10 Amps your fuse should be =< than 10Amps.
A fuse > 10 Amp could be seen as a PSU shortcut and could produce smoke depending on PSU.

Picbuster