What is an Inrush Current Limiter?

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Editorial Team - everything PE

Jan 9, 2023

An Inrush Current Limiter is an electronic component that limits the flow of surge current or switch-on surge current. Surge current is the maximum current that flows into a device or instrument when it’s first turned ON. Usually, the surge current is high and if not regulated can damage the electronic circuit.

For a better understanding, we can relate this to a tap that prevents the sudden rush of water flowing out of it when first turned ON. You need to rotate the valve of the tap to control the flow of water. Similar is the function of an Inrush current limiter. It controls the instantaneous flow of current, prevents the components from getting damaged, and avoids the tripping of breakers and fuses.

Inrush current limiters are most commonly used in power circuits devices like AC-DC Converters and SMPS (Switch Mode Power Supply) circuits, which are connected directly to the AC mains and hence are prone to overvoltage, overloading, voltage spikes, and fluctuations. For protecting these systems, Inrush Current Limiters like temperature coefficient thermistors (thermal resistors) and fixed resistors (resistors that have fixed-resistance and are not adjustable) are directly connected to the systems.

Temperature Coefficient thermistors are the most widely used inrush current limiters. These are of two types: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC) thermistors. The difference between the two is that, in NTC, the temperature is inversely proportional to the resistance of the thermistors while in PTC, the temperature is directly proportional to the resistance of the thermistors. This means that in NTC thermistors, resistance increases with a decrease in temperature while in PTC thermistors, resistance increases with an increase in temperature.

NTC thermistors are widely used for the measurement, control, and protection of thermal devices and applications while PTC thermistors are used for the protection of circuits from high temperatures.

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