Why Use NTC Thermistors to Suppress Inrush Current

An NTC (Negative Temperature Coefficient) thermistor is a simple temperature sensor commonly found in consumer electronics. It is a type of semiconductor resistor whose resistance decreases as the temperature increases.

Applications of NTC Thermistors

Inrush Current Suppression
Temperature Measurement
Temperature Compensation
Liquid Level Measurement
Overheat Protection
In addition to these common uses, NTC thermistors are cost-effective, come in various packaging forms, and are simple to use. They are widely used in household appliances, the power industry, communications, military science, and aerospace.

Returning to the Main Topic: Why Suppress Inrush Current

Upon startup, a large current can flow through the diodes, potentially damaging them. Rectifier diodes have a parameter called IFSM, which is the maximum allowable inrush current.

Why Use NTC Thermistors to Suppress Inrush Current

As shown in the diagram below, without an NTC thermistor, the current is very high. Adding an NTC thermistor in series with the circuit limits the inrush current at startup. Before powering on, the thermistor is at a low temperature, so its resistance is high, effectively limiting the inrush current. After startup, the thermistor heats up, its resistance drops, and it does not cause significant losses.

For small power supplies, an NTC thermistor alone is sufficient. For larger power supplies, a relay may be needed.

In addition to the benefits mentioned, NTC thermistors have several advantages in suppressing inrush current, including low cost, easy design, reduced PCB space, and self-protection.