 PTC fuses are used to protect a circuit by stopping the flow of current when it exceeds a certain amount. But unlike classic filament fuses, PTC fuses don't need to be replaced every time they stop the flow of current. They automatically reset. PTC stands for Positive Temperature Coefficient. As more current passes through, the fuse heats up, and the internal resistance increases exponentially. Once they reach a certain temperature, the fuse's resistance gets so high that it effectively stops conducting. But instead of a permanently blown fuse, a PTC fuse can cool down and essentially reset, so it's ready to be used again. That's why when your microcontroller, computer, laptop, or USB port stops working, you can sometimes turn off the power, wait a bit, and it'll work when you restart.