An NTC (Negative Temperature Coefficient) thermistor on a battery’s protection circuit is not designed to stop the battery from working. Instead, its purpose is to protect the battery by monitoring its temperature. Here’s how it works?


    1. Temperature Sensing: The resistance of an NTC thermistor decreases as the temperature increases. This characteristic allows it to sense the temperature of the battery.
    2. Overheat Protection: If the battery heats up (due to overcharging, high discharge rates, or a short circuit), the resistance of the NTC will drop. The protection circuit can then interpret this change in resistance.
    3. Safety Mechanism: If the temperature exceeds a certain threshold, the protection circuit can take action to prevent damage to the battery. This might involve disconnecting the battery to stop the charging or discharging process.

So, the NTC itself doesn’t stop the battery from working; it is part of a safety mechanism that intervenes only when the battery reaches unsafe temperatures. If the battery is not working and you suspect the NTC is at fault, it could be due to a malfunction in the NTC or the protection circuitry rather than the intended operation of the NTC.

The critical value of an NTC (Negative Temperature Coefficient) thermistor of a li-polymer battery is its temperature coefficient, which measures how much its resistance changes with temperature. The temperature coefficient is negative for NTC thermistors, meaning their resistance decreases as the temperature increases.

This characteristic is typically expressed as a percentage change in resistance per degree Celsius. For example, a standard value might be -4.5%/°C, indicating that the resistance decreases by 4.5% for every 1°C increase in temperature.

Other important values for an NTC thermistor include:

Nominal Resistance

This is the resistance at a specific reference temperature, often 25°C. It’s a primary identifier for the thermistor, such as a 10K thermistor having a resistance of 10,000 ohms at 25°C.

B-Constant: This parameter describes the relationship between temperature and resistance over a specified range. It’s used in the Steinhart-Hart equation, a mathematical model to convert the measured resistance of the thermistor to temperature.

Thermal Time Constant

This is the time the thermistor takes to change 63.2% of the total difference when the temperature changes rapidly.

Dissipation Constant

This indicates how much power the thermistor can dissipate (in watts) to maintain its temperature above the surrounding temperature.

Operating Temperature Range

This is the range of temperatures over which the thermistor can accurately and safely operate.

These values are crucial for selecting the suitable NTC thermistor for a particular application, especially in temperature sensing and control systems.

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