What is the working principle of PTC thermistor

时间:2019-06-11 丨 预览:157 人次

PTC thermistor is a sensitive element. The resistance value of the thermistor changes with temperature. Unlike general-purpose fixed resistors, it is a type of variable resistor widely used in various electronic components. Unlike resistance thermometers that use pure metals, the materials used in ptc thermistors are usually ceramics or polymers. Positive temperature coefficient thermistors have higher resistance values at higher temperatures, and negative temperature coefficient thermistors have lower resistance values at higher temperatures. They belong to semiconductor devices. Thermistors usually achieve high accuracy within a limited temperature range, usually -90 ° C to 130 ° C.


Early development of ptc thermistors variety developed more mature sensitive components. The ptc thermistor is composed of semiconductor ceramic materials. PTC thermistors are made of semiconductor materials, and most have a negative temperature coefficient, that is, the resistance decreases with increasing temperature. Temperature changes will cause large resistance changes, so it is the most sensitive temperature sensor.


The main features of ptc thermistor are:


1) High sensitivity, the temperature coefficient of resistance is 10 to 100 times that of metal, and the temperature change of 10-6 ℃ can be detected;


2) Wide operating temperature range, room temperature device is suitable for -55 ° C ~ 315 ° C, high temperature device is suitable for temperatures higher than 315 ° C, low temperature device is suitable for -273 ° C ~ 55 ° C;


3) Small size, able to measure the gap that other thermometers cannot measure the temperature of the cavity and the blood vessels in the living body;


4) Easy to use, the resistance value can be arbitrarily selected between 0.1 and 100kΩ;


5) It is easy to process into complex shapes and can be mass produced;


6) Good stability powerful overload capacity.


PTC thermistor is a sensor resistance. The resistance value of ptc thermistor changes with the change of temperature, which is different from the general fixed resistance. The resistance value of the metal increases with the increase of the planting degree, but the semiconductor reverses, and its resistance value drops sharply with the increase of temperature, showing a nonlinear.


When the temperature changes are the same, the resistance change of the ptc thermistor is about 10 times the thermal resistance of the lead, so it can be said that the thermistor is particularly sensitive to temperature changes. This temperature characteristic of semiconductors is because the conduction mode of semiconductors is that carriers (electrons holes) are conductive. Since the number of carriers in a semiconductor is much smaller than the number of free electrons in a metal, its resistivity is very large. As the temperature increases, the number of carriers participating in conduction increases in the semiconductor, so the conductivity of the semiconductor increases and its resistivity decreases. The ptc thermistor is a thermistor made with the characteristic that the resistance value of the semiconductor changes significantly with temperature. It is made of certain metal oxides with different formulations. Within a certain temperature range, according to the measured thermistor resistance change, you can know the temperature change of the measured medium.


When the ptc thermistor is installed in the circuit, at the same ambient temperature, as the current increases, the working time will be sharply shortened; the working time of the thermistor is shorter, when the ambient temperature is higher, the thermistor is more small. Holding current and working current. When the circuit works normally, the thermistor temperature is close to room temperature. The resistance is very small. The series connection in the circuit does not hinder the passage of current. When an overcurrent occurs due to a fault in the circuit, the temperature of the ptc thermistor will increase due to the increase in heating power. When the temperature exceeds the switch temperature, the resistance will increase sharply, and the current in the loop will quickly drop to a safe value.