PTC Fuses for AC/DC Power Supplies

A Positive Thermal Coefficient fuse, or PTC thermistor, is a thermally sensitive semiconductor resistor that increases in resistance as temperature increases to limit current to a load. When the voltage input for a power supply is too far above or below what is specified, the excess current can damage components. Besides shutting down the power supply altogether, one can effectively limit the current by using the predictable resistive response of a PTC.