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Definition of NTC thermistor: a negative temperature coefficient resistance and its resistance value decrease with the increase of temperature. NTC thermistor is widely used in switching power supply, module power supply, temperature sensor, UPS power supply, electronic ballast, automatic adjustment heating and so on.
NTC thermistor is small in size and large in power. Its main function is to suppress the surge current in the power supply circuit, and it is generally connected in series to the mains input. It has a rated zero power resistance value, and when connected in series in the power loop, it can effectively suppress startup inrush current and consume almost negligible power.
1. Temperature compensation in instrument circuits
In meter circuits, there are many elements made of wire like wire wound resistors. Metal wire generally has a positive temperature coefficient, and the compensation of NTC thermistor with a negative temperature coefficient can offset the temperature changes caused by the error.
2. Stabilize operating points in transistor circuits
When the ambient temperature changes, the line output current will also change. NTC probe meaning electronics can automatically adjust the collector DC current of the transistor, and stable transistor output gain.
3. NTC thermistor for temperature measurement
As the resistance of the thermistor changes with temperature, the microammeter indication connected to the bridge diagonal changes accordingly. The accuracy of the thermistor thermometer can reach 0.1℃ with less than 10s temperature sensitivity.
Working principle of positive temperature coefficient NTC thermistor
This thermistor is sintered at high temperature with barium titanate as the basic material and some rare earth elements added. When the temperature is low, due to the electric field in barium titanate semiconductor, conductive electrons can easily cross the barrier, so the resistance value is small; when the temperature rises to the Curie point temperature, the internal electric field is destroyed and cannot help conductive electrons cross the barrier, so it shows a sharp increase in resistance.
Working principle of negative temperature coefficient NTC thermistor
Negative temperature coefficient thermistor is made of manganese oxide, cobalt oxide, nickel oxide, copper oxide, alumina and other metal oxides. These metal oxide materials have semiconductor properties, similar to germanium and silicon crystal materials, with a small number of carriers (electrons and holes) in the body and high resistance. As the temperature increases, the number of carriers in the body increases and the resistance decreases naturally.
In practical application, power type NTC thermistors should work in the rated operating temperature range as far as possible. Beyond the specified upper and lower temperature, there may be the failure or damage of power type NTC thermistor.
Because the power type NTC thermistor is greatly affected by the ambient temperature, the maximum steady-state current is generally given in the product specification at normal temperature (0 ~ 25℃). Some foreign brands of power NTC thermistors give the maximum steady-state current 0~65℃, which will be more in line with the actual use of the product.
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