The thermistor is usually a nonlinear resistance made by burning the oxides of manganese, cobalt and nickel into semiconductor ceramic materials which are extremely sensitive to temperature and have very little thermal inertness, and its resistance value changes with the change of temperature. Thermistors are divided into negative temperature coefficient (NTC), positive temperature coefficient (PTC) and critical temperature coefficient. The resistance value of the positive temperature coefficient resistor increases with the increase of temperature, the resistance value of the negative temperature coefficient resistor decreases with the increase of temperature, and the resistance value of the critical temperature resistor is basically zero near the critical temperature.
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Most thermistors are directly heated, that is, the heat source is obtained by heating the resistor itself through the current. In addition, there is a side heat type, which requires an additional heat source. Common thermistors are round, gasket shape, tube shape, etc. At present, the most widely used is negative temperature coefficient thermistor (NTC), which can be divided into temperature measurement type, voltage regulator type, ordinary type. There are many kinds and shapes of it, the common tubular, disc shape and so on.
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In addition to temperature control and temperature measurement circuit, PTC is widely used in color TV deagnetization circuit, refrigerator, electric mosquito repellent, electric iron and other household electrical circuits.