Three important roles of negative temperature coefficient thermistor NTC.SMD PIR IC manufacture

　　NTC (Negative Temperature Coefficient) refers to the thermistor phenomenon and material whose resistance decreases exponentially with increasing temperature and has a negative temperature coefficient. The material is a semiconductor ceramic made of two or more metal oxides, such as manganese, copper, silicon, cobalt, iron, nickel, zinc, etc., which are fully mixed, formed, and sintered. It can be made into a negative temperature coefficient. (NTC) thermistor. Its resistivity and material constant vary with the proportion of material composition, sintering atmosphere, sintering temperature and structural state. Now there are also non-oxide NTC thermistor materials represented by silicon carbide, tin selenide, tantalum nitride, etc.

　　NTC thermistor is a thermistor with a negative temperature coefficient. This resistance value is realized to decrease with the increase of temperature. The material it uses is a semiconductor material with a large negative temperature coefficient. This kind of resistance is widely used in switching power supply, UPS power supply, electronic ballast, temperature sensor, automatic adjustment heater and other occasions. The following describes the three functions of the thermistor in surge absorption, temperature measurement, and temperature compensation.

　　1. Suppress surge current

　　This type of thermistor belongs to the power type. Although the size is small, the power is very large. Generally, it is connected in series with the mains input line. It has a rated zero-power resistance value. Generally, this resistance value is very small. The most basic parameters of resistors are generally given by manufacturers. When connected in series in the power loop, the power-on inrush current can be effectively suppressed, and the power it consumes is almost negligible. Generally connected in series with the main power circuit, the electronic circuit will generate a large surge current at the moment of starting up. The NTC element can effectively suppress the surge current when starting up and protect the electrical equipment from damage. A new type of device used. At the moment of startup, a large current flows through the NTC element, and the resistance value of the NTC element increases. After the current is suppressed, the resistance value gradually decreases to a minimum, which will not affect the circuit and protect the electronic circuit from the impact of the startup current. NTC (full name: negative temperature coefficient thermistor, the higher the temperature, the lower the resistance value) thermistor, as its name suggests, is a resistor that controls the resistance value through the temperature. When the temperature of the thermistor is low, the resistance value of the resistor is usually about 6-12 ohms. When the power is turned on, the temperature of the resistor rises, and the resistance value is about 0.5-1 ohm.

　　2. Use a temperature sensor to measure the temperature

　　As a thermistor for measuring temperature, it uses the change of the resistance value of the external temperature change, because the NTC resistance always passes a certain amount of current when it is connected to the circuit, this current will cause the NTC itself to generate heat, and the resistance value of the NTC will decrease. It has a great influence on the measurement, so it is necessary to control the self-heating to avoid the measurement error caused by the excessive current flowing through the thermistor and the self-heating of the component. Write all or part of the resistance value corresponding to the temperature into the CPU, so that when the external temperature changes, the resistance value changes, which is realized as a voltage change. This package includes chip type, epoxy head type, glass sealing type, straw hat type and so on.

　　3. Temperature compensation

　　Electronic components usually have a certain temperature coefficient, and their output signals will drift with temperature changes, which is called "temperature drift". In order to reduce the temperature drift, compensation measures are used to offset or reduce the temperature drift of its output to a certain extent, which is temperature compensation. Sensors are widely used in various industrial and agricultural production. In the production process, information needs to be converted into electrical signals that are easy to transmit and process. However, most sensors use metal or semiconductor materials for their sensitive components. Temperature is closely related. In actual work, due to the large temperature change of the working environment of the sensor, the thermal output caused by the temperature change will bring a large measurement error; at the same time, the temperature change also affects the size of the zero point and the sensitivity value, which in turn affects the static characteristics of the sensor. Therefore, measures must be taken to reduce or eliminate the influence of temperature changes, which requires temperature compensation of the sensor through an NTC thermistor.

　　In some electrical appliances, the accuracy requirements are very high, especially instruments and meters. Many components are made of metal wires, such as wirewound resistors. Metals generally have a positive temperature coefficient, and a negative temperature coefficient thermal sensor can be used. The resistance is compensated, one positive and one negative, which can offset the error caused by temperature change and improve the accuracy.

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