Application of NTC Thermistor in Limiting Inrush Current

　　NTC thermistor is a negative temperature coefficient resistance (power thermistor), its resistance value decreases with the increase of temperature, widely used in switching power supply, module power supply, temperature sensor, UPS power supply, electronic ballast , Automatic adjustment of heating and other places.

　　NTC thermistor is small in size and high in power. It is mainly used in the power supply circuit to suppress inrush current, and is generally connected in series with the mains input. It has a rated zero-power resistance value, and when connected in series in the power loop, it can effectively suppress power-on inrush current and consume almost negligible power.

　　The resistance value decreases as the temperature rises and is often used as anti-surge protection. In the rectifier filter circuit, in order to avoid the instantaneous surge current caused by the capacitive load charging when the electronic circuit is turned on, it is usually used in the power supply circuit. Connect a power NVT thermistor in series. This can effectively reduce the inrush current at startup, and after the inrush current reduction is completed, due to the continuous action of the passing current, the resistance of the NTC thermistor will drop to a very small value, and the power consumption is very small. It can be ignored and will not affect the normal operation of the circuit.

　　Application of NTC Thermistor in Limiting Inrush Current

　　Magnetizing Inrush Current Limiting in Switch Mode Power Supplies (SMPS)

　　Various switch mode power supplies (SMPS) - which are small, lightweight and high performance - are commonly used as power supplies for electronic devices. When the SMPS is energized, the magnetizing inrush current with a high peak charges the smoothing capacitors, thereby charging the device. Since this inrush current can have a detrimental effect on the life of the capacitor, damage the contacts of the power switch or destroy the rectifier diode, it is necessary to take corresponding countermeasures.

　　Inrush Current Limiting in AC-DC Power Modules

　　A built-in power supply in which various power supply circuits and peripheral circuits are compactly integrated is called a power supply module. The AC-DC power module is a power supply composed of an AC-DC rectifier circuit, a DC-DC converter and a small number of external components, which can form a space-saving optimized power system. Inserting an NTC thermistor (power thermistor) can effectively limit the magnetizing inrush current applied to the input and output capacitors at power-up.

　　Magnetizing Inrush Current Limiting in DC-DC Converters

　　In DC power supply circuits such as DC-DC converters, etc., NTC thermistors are used as power supply thermistors to effectively limit the magnetizing inrush current, and the input and output capacitors are charged when the power is turned on. The resistance of an NTC thermistor becomes very low after power-up, achieving lower power losses than when using a fixed resistor.

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