NTCInrushLimiter

NTCInrushLimiter, or NTC inrush limiter, is a passive electronic component that uses a negative temperature coefficient (NTC) thermistor to limit inrush current in AC power circuits. It is typically placed in series with the mains input or with a large capacitive load to control the initial surge when power is applied.

Operation is based on the temperature dependence of the thermistor. When power is first applied, the thermistor is cold and presents a relatively high resistance, which reduces the peak current drawn by charging input capacitors or energizing transformers. As current flows, the thermistor heats up, causing its resistance to fall rapidly toward a low steady-state value. When warmed, the device allows normal operation with minimal voltage drop and heat generation.

Construction and ratings: NTC inrush limiters are usually disc-shaped ceramic thermistors with radial leads, often encapsulated in epoxy. The resistance at 25°C (R25) typically ranges from fractions of an ohm to several ohms up to tens of ohms, chosen to achieve the desired inrush reduction for a given supply voltage and load. Manufacturer specifications include the maximum ambient temperature, continuous operating temperature, and an inrush current rating or I²t rating. They dissipate heat during startup and require appropriate derating in high-temperature environments.

Applications and considerations: They are widely used in power supplies, AC adapters, battery chargers, and lighting ballasts to reduce peak currents and voltage dips, protect components, and smooth power-up. Limitations include added resistance and heat during startup, potential voltage drop under load, and sensitivity to ambient temperature. Proper selection depends on input voltage, expected inrush, and total load capacitance or transformer size. Related devices include PTC thermistors, which serve different protection roles.