Simple and effective inrush-current limiter stops surges

摘要

Offline power supplies that drive loads of 200W and morernrequire inrush-current limiters. Unrestricted inrush currents can reach hundreds of amperes, which may damage the line rectifier, open the fuse and input-filter inductors, and damage the PFC (power-factor-correction) filter capacitors. A simple method of limiting the inrush current uses an NTC (negative-thermal-coefficient) thermistor that connects in series with the supply line. When cold, the thermistor presents a high resistance, but its resistance decreases significantly as its temperature increases, limiting the inrush current by virtue of its thermal inertia and inability to quickly decrease its resistance.