What are the considerations when selecting a negative temperature coefficient thermistor?
Categories: Industry News
2025-01-02
To purchase a product, you must first consider what product it is suitable for, what temperature range it can operate in, and what current and voltage it can 'work' under. If there is any slight misselection in the above, any product will quickly be damaged. Today, let's take a look at the factors to consider when selecting a negative temperature coefficient thermistor!
1. Consider the working environment:
Negative temperature coefficient thermistors are greatly affected by environmental temperature. Generally, the product specification only provides resistance at room temperature (25°C). If the product application conditions are not at room temperature, or if the product design itself leads to...Or, if due to structural reasons, the NTC thermistor's environmental temperature is not at room temperature, then before selecting in the above steps, the resistance must be calculated in the initial state of the NTC. When the environmental temperature is too high or too low, the power reduction curve provided by the manufacturer should be used to design the reduction amount. The power consumption curve generally has two forms.
2. Consider the maximum rated voltage and filter capacitor value
The size of the filter capacitor determines the size of the NTC that needs to be selected. For a specific size of NTC thermistor, the allowable filter capacity size is strictly necessary, and this value is also related to the maximum rated voltage. In power applications, surge currents are caused by capacitor charging, so the ability of the NTC thermistor to withstand surge currents is usually evaluated based on the amount allowed at the specified voltage value. The maximum energy that a specific NTC thermistor can withstand is determined. According to the energy consumption formula E=1/2 × CV² for the first circuit resistance, it can be seen that the allowable access capacity value is inversely proportional to the square of the rated voltage. In short, the higher the input voltage, the smaller the maximum allowable capacity value, and vice versa.
The specifications of negative temperature coefficient thermistor products usually define the maximum capacity value allowed at 220Vac. Assuming the maximum rated voltage for applicable conditions is 420Vac and the filter capacity value is 200F, then according to the above energy formula, the equivalent capacity value at 220Vac can be converted to 200 × 420²/220²=729F. Therefore, when selecting, a capacity value greater than 220Vac to 729F should be chosen.
3. Final summary:
In product selection, the product series must be chosen based on the maximum rated voltage and filter capacity value. Select the resistance value of the negative temperature coefficient thermistor according to the maximum allowable starting current value of the product and the working current for long-term loading, and consider the temperature of the working environment for appropriate liquid reduction design.
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2025/01/02
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