Zener wrote:You can get Pico fuses that are smaller than Polyswitches. I would use a fuse. Polyswitches seem like a neat idea, but in practice a fuse is usually a better choice. That's the short answer. Personally I would use a bigger fuse like an amp or 2. I think he most likely cause of a blown fuse in your circuit is from a voltage spike that causes the MOV to conduct. I would want a clamping voltage that is just a little lower than the Vin max of the regulator.
Zener, I am sorry but I can't figure out what you mean by clamping voltage. All the references I find talk about varistors and not fuses.
What I'm using is a buck converter sold here. The datasheet says it's short circuit protected, I am assuming that means on the Vout side. I went with this as it's a simple and compact way to get switching power into the project. http://www.adafruit.com/products/1065.
The max Vin of the buck is 36V. So am I looking for a fuse that is rated for (example) 32V 1A or 1.5A? And a plain old fast-acting glass fuse with the correct rating should be OK for the low power project, correct?
Originally I was going to use a board from a USB phone charger. The board from the phone charger has a surface mount fuse marked as "150". Since the charger is rated at 5V 1A I assumed the fuse was rated for 1.5A.
Semi-related, trying to identify fuses I found I have some scrap in my pile that appears to have SMD resettable fuses but cant find references (most of the stuff is old). A firewire card has green fuses marked "P" then 150 and 075. I recall that FireWire could have 30V unregulated provided on the bus. But the 150 and 075 doesn't mean a lot to me - milliamps? Amps? - and the part is old so searching yields no answers.