Inrush Current Limiter - Thermistor


An NTC thermistor's resistance is high at low temperatures. When the circuit is closed, the thermistor's resistance limits the initial current. After some time current flow heats the thermistor, and its resistance changes to a lower value, allowing current to flow uninterrupted. It is inherently impossible for 100% of supply voltage to appear on the protected circuit, as the thermistor must continue to dissipate power (producing heat) in order to maintain a low resistance. The resulting voltage drop from the operating resistance, and the power consumption of the thermistor must be taken into account.

  • Inrush current limiting thermistors are usually disk-shaped, with a radial lead on each side.
  • NTC resistor power handling is proportional to its size.
  • NTC resistors are rated according to their resistance at room temperature.

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