Sep. 03, 2021
Thermistors can be divided into NTC thermistors and PTC thermistors. Thermistors are typically sensitive to temperature and show different temperature resistance values at different temperatures. The thermistor can protect the circuit, so what should we pay attention to when NTC thermistor is used in the switching power supply? Read this article to find out.
Precautions for NTC thermistor in switching power supply:
1) From the analysis of the working principle of the circuit, we can see that under normal working conditions, a certain current flows through the power NTC thermistor. This working current often causes the surface temperature of the power NTC to reach above 100℃. When the product is turned off, the power NTC thermistor must be restored from a high-temperature low-resistance state to a normal-temperature high-resistance state in order to achieve the same surge suppression purpose as the previous time.
The recovery time is related to the dissipation coefficient and heat capacity of the power NTC thermistor. Generally, the cooling heat time constant is used as a reference. The cooling heat time constant is not the time required for the power NTC thermistor to return to the normal state, but the larger the cooling time constant, the longer the recovery time required, and vice versa. Therefore, the power NTC thermistor cannot provide good protection in the case of frequent switching.
2)In practical applications, try to make the power NTC thermistor work within the rated operating temperature range. If it exceeds the specified upper and lower temperature limits, it may cause the power NTC product to fail or be damaged. Since the power NTC thermistor is greatly affected by the ambient temperature, the large steady-state current at room temperature (0～25℃) is generally given in the product specification.
Under high or low operating temperature conditions, the rated current will be linearly derated to zero. When the application conditions of power NTC thermistor products are not at room temperature (0～25℃), or due to the design or structure of the product itself, such as the power supply with some devices that generate more heat. When the ambient temperature is too high or too low, it must be derated according to the current reduction curve.
The above are the things we need to pay attention to when using NTC thermistors. If you want to purchase high quality thermistors, Dongguan Zhixu Electronic Co., Ltd. (also JYH HSU(JEC)) is a trustworthy choice for you. JEC has a full range of varistor and capacitor models. 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.