NTC Thermistor Limiting Magnetizing Inrush Current

Apr. 18, 2022

NTC thermistor is a temperature-dependent resistor using special semiconductor ceramics with a negative temperature coefficient (NTC). They have a high electrical resistance at room temperature. When they are energized, they generate heat by themselves. As the temperature rises, the electrical resistance decreases. Because of this feature, they are used as current protection devices for electrical and electronic equipment, conveniently and effectively limiting abnormal currents, including magnetizing inrush currents when energized. NTC thermistors used as current protection devices are also called power supply thermistors.

Fixed resistors or NTC thermistors can be used to limit the magnetizing inrush current. However, fixed resistors always lead to power loss and performance degradation. NTC thermistor limits the magnetizing inrush current with its higher initial resistance, and then the temperature rises due to energization, and the resistance drops to a few percent of the room temperature level, thereby achieving lower power loss than using fixed resistors. In other words, using an NTC thermistor to limit the inrush current is more effective than using a fixed resistor with the same initial power loss.

NTC Thermistor Limiting Magnetizing Inrush Current

Application examples of NTC thermistor in limiting the magnetizing inrush current:

1) Excitation inrush current limitation in switched-mode power supply (SMPS)

Switched-mode power supplies (SMPS) are small, light, and of good performance - they are often used as power supplies for electronic devices. When the SMPS are energized, the high-peak magnetizing inrush current charges the smoothing capacitor, thereby charging the device. Since this inrush current will have a harmful effect on the life of the capacitor, damaging the contacts of the power switch or destroy the rectifier diode, corresponding countermeasures must be taken.

For this reason, we found through experiments that by inserting an NTC thermistor to form a low-cost simple circuit, the inrush current in the power supply can be limited. Even if the NTC thermistor is connected after the rectifier circuit, the same result can be obtained.

2) Excitation inrush current limitation in AC-DC power supply module

The 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 supply 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 supply system. Inserting an NTC thermistor (power supply thermistor) can effectively limit the inrush current applied to the input and output capacitors when power is applied.

The above content is the application of NTC thermistor in limiting the inrush current. Hopefully the article is helpful. Dongguan Zhixu Electronic Co., Ltd. (also JYH HSU(JEC)) has a full range of varistor and capacitor models with guaranteed quality. JEC has passed ISO9001:2015 quality management system certification; JEC safety capacitors (X capacitors and Y capacitors) and varistors have passed national certifications of the main industrial powers across the world; JEC ceramic capacitors, film capacitors and super capacitors are in compliance with environmental protection indicators. Welcome to contact us for free samples and any questions.

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