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NTC Thermistors: Overview and Applications
NTC thermistors are temperature-sensitive resistor elements made from semiconductor ceramics with a negative temperature coefficient (NTC). This property means that their resistance value decreases exponentially as the temperature rises. The steeper the resistance-temperature (RT) curve, the more pronounced the change in resistance within a given temperature range.
Working Principle of NTC Thermistors
This exponential decrease in resistance makes NTC thermistors highly effective for applications requiring precise temperature sensing and control. As temperature increases, the thermistor’s resistance decreases significantly, allowing circuits to measure or respond to temperature fluctuations accurately.
Temperature Compensation in Electronic Circuits
Temperature compensation is vital for maintaining circuit stability in environments with fluctuating temperatures. For example:
Transistor-Based Circuits: Transistors in amplifiers or power circuits can become unstable as temperatures vary. NTC thermistors effectively mitigate this instability by dynamically adjusting the circuit’s response.
Crystal Resonators: The oscillation frequency of crystal resonators may drift with temperature changes, impacting timing precision. NTC thermistors help counteract this effect, maintaining consistent performance.
Some prominent use cases for temperature compensation include:
Operating Point Stabilization: Power electronics systems integrate NTC thermistors to ensure stable performance by adjusting the circuit’s operating point as temperatures fluctuate.
LCD Brightness Control: NTC thermistors regulate brightness levels in LCD displays by compensating for temperature-induced changes in screen output.
How NTC Thermistor Works On Detecting Temperature In Battery
All rechargeable batteries, especially lithium-ion batteries, must be monitored and protected by intelligent charging circuits because mobile communication devices that draw power from the batteries must operate in a variety of environments, including low and high temperature operation. NTC Thermistors are the preferred temperature sensing device in protection circuits. NTC thermistors can detect ambient temperature for different purposes, depending on the battery system. Especially for fast charging, the ambient temperature must be measured because not all batteries allow charging in high and low temperature ranges. Typically, battery pack manufacturers recommend slow charging temperatures of 0°C to 45°C and fast charging temperatures of 5°C, 10°C to 45°C depending on the battery chemistry.
NTC Thermistors are part of the intelligent charging control unit (see circuit below) and ensure that the ambient temperature is within the range that allows fast charging. During the charging process, the NTC thermistor repeatedly measures the temperature for 5 to 10 seconds each time and can detect the increase in battery cell temperature at the end of the charging cycle or caused by abnormal charging conditions.
During the discharge process, the NTC thermistor also performs temperature compensation on the voltage measurement, which helps to measure the remaining charge in the battery.
What Are RTD Sensors?
RTD sensors (Resistance Temperature Detectors) operate on the principle that the resistance of certain metals changes predictably with temperature. This characteristic makes them well-suited for high-precision applications.
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