Precautions for using NTC thermistors

NTC thermistors are similar to variable resistors. They are important electronic components for circuit protection. There are some details to pay attention to when using them, otherwise, it is easy to damage the NTC thermistor.

1. Consider the working environment:

NTC thermistors are greatly affected by environmental temperature, and the resistance value is generally only provided at room temperature (25°C) in the product manual. If the product's operating conditions are not at room temperature, or due to the design or structure of the product itself, the surrounding environmental temperature is not at room temperature, the initial resistance value of the NTC must be calculated first before selecting the above steps.

2. Consider the maximum rated voltage and filter capacitor.

The size of the filter capacitor determineshow large the NTC should be selected. For a thermistor of a certain size, there are strict requirements on the allowable size of the connected filter capacitor, which is also related to the maximum rated voltage. In power applications, the startup surge is caused by the charging of the capacitor, so the allowable capacitance at a given voltage is usually used to evaluate the NTC thermistor's ability to withstand surge current. For a specific NTC thermistor, the maximum energy it can withstand has been determined.

The specifications of the NTC generally stipulate that the maximum allowable capacitance is 220Vac. Assuming the maximum rated voltage condition of the application is 420 volts AC, and the filter capacitor value is 200 F, the equivalent capacitance value that can be converted based on the energy formula above is 220 years off 200×4202/2202 = 729 F, so when selecting, it is necessary to choose a capacitor value that exceeds 729 F at 220 volts.

3. Pay attention to the operating temperature.

It is prohibited to use theNTC thermistor outside its working temperature range. The working temperature range for the series products is -40 ~ +150°C; the working temperature for the series products is -40 ~ +200°C.

4. Precautions for use in high temperature and high humidity environments.

If it is necessary to use the thermistor in high temperature and high humidity environments,a sheath thermistor should be used, and the protected sheath should close part of the exposure to the environment (water and moisture), and the open part of the sheath should not directly contact water and steam.

5. NTC thermistors must not be used in environments with harmful gases and liquids.

Do not use in environments with corrosive gases or in contact with electrolyte solutions, saltwater, acids, bases, and organic solvents.

6. Keep away from heated electronic components.

Easily heated electronic components should be avoided around the power supplyof the NTC thermistor. It is recommended to use products with higher leads at the top of the bent legs and to use NTC thermistors that are higher than other components on the circuit board to prevent heat from affecting the normal operation of other components.

For applications that require frequent switching, a relay optical fiber channel must be added to the circuit to ensure thatthe NTC thermistor can completely cool down and return to its initial resistance. When selecting products, the product series should be chosen based on the maximum rated voltage and filter capacitor, and the resistance value of the NTC thermistor should be selected based on the maximum allowable startup current and the working current loaded on the NTC thermistor for a long time.