Anyone who has seen one of my PCB designs knows how much I love polymeric resettable fuses. When placed where the power lands on the board, they allow narrower power traces, enabling increased density without increased risk of trace failures and fires, but like any device they are not ideal and their characteristics must be considered when the board is designed.
- They effectively limit current flow, allowing narrower traces downstream.
- They are inexpensive.
- They consume little board space.
replacement fuses are needed in the field.
- A fuse cannot be replaced with one of a larger value.
- They have a wide trip current range, between 100 and 200% of the given value. Traditional thermal devices are not much better, 100
- 150% is typical.
- They can cause confusion when troubleshooting a system. When an overload is present, a voltage reading at the
nonworking device will be nearly zero, but if the device is removed the voltage returns to normal. I have seen a technician repeatedly
unplug the cable from an inoperative device (no lights, no activity), measure the voltage (hmmm...seems OK), plug it back in, still
- Slower when compared to a fast-blow type fuse.
- There is a small amount of resistance in the ON state, and some leakage
in the TRIPPED state.
Well, no worse than a "pico fuse" or similar device, but the fact is there is no way to tell when a trip has occurred without measuring
the voltage across the leads (sometimes difficult and always risky), or my preferred method, the old finger probe. Feel all of the
poly fuses with your fingers, I guarantee the tripped one(s) will be readily identified. Don't worry, they do not get hot enough to
cause injury. I am pleased to announce that the Ideas and Inventions Department here at Artco Engineering has solved this problem,
and the result can be seen below for your viewing pleasure. Unfortunately, I have not found any fuse manufacturers to be theleast bit interested, but if anyone has any promotional ideas let me know!
© 2012 www.artcoengineering.com
About Reference Designators
Resettable Polymeric Fuses