Fuse options - want to minimise thickness

Thread Starter


Joined Sep 25, 2021
I'm working on my first real PCB and wondering what fuse I ought to use because I want it to be as thin as I can reasonably make it. I was going to use THT resettable fuses bent over but I think they will be thicker than necessary. Each MOSFET shouldn't switch more than 2 A and the total circuit not more than ~5 A. I think I can replace the smaller fuses with SMD ones without issue but for the main fuse I was thinking about using two 3 A fuses in parallel. The main problem I think is the heat that will come from the dual diode which at 5 A will be 6.25-8.75 W (250-350 milliohm on the diode) depending how hot the diode gets and the heat will go straight through the tracks into the fuses. I will use thermal vias on the diode's pad and the enclosure will be made of aluminium core PCB with a corresponding exposed copper area to get the heat off the the diode but might it still melt the fuses? I know there's usually some amps between I(hold) and I(trip). I was also thinking of using a glass fuse or an SMD chip fuse? Hopefully I won't be blowing fuses too frequently.

The thickest part will be the terminals but I will have cutouts in the top part of the enclosure anyway because they need screwdriver access so it would be nice to keep the rest no higher than the top of the terminals including the thickness of the top part of the enclosure.

You can see the schematic/PCB in better detail IF YOU SCROLL TO THE BOTTOM here (the top two have a bug and are out-of-date): https://oshwlab.com/THX1138/arduino-nano-thermostat

The fuse areas on the PCB right now look a mess because there's multile components on the schematic fighting to be chosen.

PCB_v2_PCB_Arduino Nano Thermostat_fixed_FPC_moved_GND5A_D1_footprint_2021-09-25.png