Application of NTC Thermistor in Limiting Inrush Current

　　Various switching power supplies (SMPS), which are small in size, light in weight and high in performance, are often 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.

　　Limiting the magnetizing inrush current of an SMPS by inserting an NTC thermistor is widely used as a way to form a low-cost simple circuit for limiting magnetizing inrush current in a power supply. The same result can be obtained even if an NTC thermistor is connected after the rectifier circuit.

　　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.

　　Inrush Current Limiting in Industrial Inverters

　　Induction motors are often used in fans, pumps, air conditioners and other equipment in factories, large facilities, office buildings, etc. Induction motors are simple and stable in structure, but their speed depends on frequency. In order to control the rotational speed, an inverter is required. Motors equipped with inverters are called variable speed drives (VSDs) and can significantly reduce power consumption.

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