Inrush current limiter

src: powersolve.co.uk

A surge current limiter is a component used to limit current inrush to avoid gradual damage to the component and avoid fusing of fuses or tripping circuit breakers. The negative temperature coefficient (NTC) of thermistors and fixed resistors is often used to limit current inrush. NTC thermistors can be used as inrush limiting devices in power supply circuits when added in series with protected circuits. They present a higher resistance at first, which prevents large currents from flowing in turn. As the current continues to flow, the NTC thermistor heats up, allowing higher current flows during normal operation. NTC thermistors are usually much larger than thermistor-type measurements, and are deliberately designed for power applications.

Video Inrush current limiter

Thermistor

NTC thermistor resistor is LOW at HIGH temperature. When the circuit is closed, the thermistor resistance limits the initial current. After some time the current flow heats the thermistor, and its resistance changes to a lower value, allowing the current to flow uninterrupted. It is inherently impossible for a 100% supply voltage to appear in a protected circuit, since the thermistor must continue to discharge (generate heat) to maintain low resistance. The voltage drop resulting from the operating resistance, and the power consumption of the thermistor must be taken into account.

• Incoming currents that limit the thermistor are usually disk-shaped, with radial leads on each side.
• The power handling of NTC resistors is proportional to its size.
• NTC resistors are ranked according to their resistance to room temperature.

Maps Inrush current limiter

Fixed resistance

Resistors are also widely used to limit current inflow. This is inherently less efficient, since the resistance never falls from the value required to limit the current inflow. Consequently they are generally selected for lower electrical circuits, where the ongoing additional power waste is small. Inrush limiting resistor is much cheaper than thermistor. They are found in most compact fluorescent lamps (light bulbs).

They can be routed from the circuit using a relay or MOSFET though, after the inrush is complete.

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Apps

A typical application of the current boundary current is at the input stage of the switching non-power factor corrected supply, to reduce the initial spikes of current from the line input to the reservoir capacitor. The most popular application is the protection of AC current inflows in the switching power supply (SPS). The main reason for having a current surge suppression in SPS is to protect the diode bridge rectifier as input or charging the initially charged capacitor. This capacitor draws significant current during the first half AC cycle and can subdue the component according to the capacitor to the excess current. The initial equivalent series resistance (ESR) of the capacitor provides very little protection for the diode bridge rectifier.

src: www.atlhifi.com

References

• EPCOS AN2 Application Note on Current Inflow Capping

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See also

• Gently start

Source of the article : Wikipedia