Understanding NTC Thermistors: The Hidden Guardians of Power Supply Circuits

Thermistors may be small, but their role in electronic circuits, especially power supply boards, is massive. Among them, NTC (Negative Temperature Coefficient) thermistors are frequently used as inrush current limiters. This post walks you through how NTC thermistors work, why they’re wired in series with hotlines, and how to test or diagnose them.     What Is an NTC Thermistor? An NTC thermistor is a temperature-sensitive resistor that decreases its resistance as temperature increases. When cold, it provides high resistance; as it heats up (due to current flow), its resistance drops, allowing higher current to flow safely into the circuit. This makes it perfect for power-up scenarios where large capacitors or switching components could otherwise cause a surge. Why Is It Wired in Series on the Hot Line? The primary role of an NTC thermistor in a power circuit is inrush current suppression. It is always installed in series with the AC input "hotline." On s...