What is an Inrush Current Limiting Thermistor (Surge Limiter)?
Inrush Current Limiters are among the most common design options used in switching power supplies to prevent damage caused by inrush current surges. A thermistor is a thermally-sensitive resistor with a resistance that changes significantly and predictably as a result of temperature changes. The resistance of a Surge Limiting thermistor decreases as its temperature increases. As the inrush current limiter self-heats, the current begins to flow through it. Its resistance begins to drop and a relatively small current flow charges the capacitors in the power supply. After the capacitors in the power supply become charged, the self heated inrush current limiter offers little resistance in the circuit. So low that the voltage drop is an insignificant factor with respect to the total voltage drop of the circuit.
