It is a special type of resistive component and the most commonly used type of sensitive component. For different environments such as temperature detection, overheating detection, circuit protection, suppression of inrush currents, and heating, users choose products with different specifications and installation types.
For temperature detection and temperature compensation applications, NTC thermistors are preferred, that is, Negative temperature coefficient thermistors. NTC thermistors are electronic components that decrease in resistance value as temperature increases. Their specific packaging types include soft lead, resin packaging, high reliability, and conductive adhesive compatibility, and are used in various products.
For applications such as overheat detection, circuit protection, suppression of inrush currents, and heating, positive temperature coefficient thermistors (PTCs) are generally used. Because PTC thermistors maintain a constant resistance value at room temperature, once a certain temperature is exceeded, the resistance value will sharply increase. PTC thermistor is obtained by adding trace rare earth elements to Barium titanate. The ceramic electrode with Barium titanate as the main component is widely used for its lead type and sheet type products.
Here are some commonly used technical terms for thermistors.
Before reaching a certain temperature, the resistance value is constant, and once it exceeds this temperature, the resistance value will also rise sharply. The change point of this resistance value is called "Curie temperature (also called Curie temperature)", which is specifically defined as the temperature at which the resistance value is twice the resistance value at 25 ℃.
It is caused by temperature changes that cause errors in instruments, measuring devices, etc., and is specially designed to compensate for auxiliary devices and electrical circuits. For components that change their characteristics due to temperature changes, they can work by suppressing temperature changes.
When starting the switching power supply of electronic devices, a large current exceeding the rated current value is flowing.
Using the resistance value at the specified ambient temperature of 2 points, calculate the constant representing the change in resistance according to the following formula.
R: Resistance value at ambient temperature T (K)
R0: Resistance value at ambient temperature T0 (K)
Extra high operating voltage
It refers to the extremely high voltage that can be applied to a thermistor within the working temperature range.
The voltage that can withstand even three minutes of application in still air at 25 ℃ is considered voltage resistance. The voltage is applied by slowly increasing from 0V to withstand voltage.
Heat dissipation coefficient (D)
It refers to the amount of heat lost per unit time when the temperature difference between the heating element and the surrounding temperature is 1 ℃.
W=I? V=D (T-T0)
Among them, T is the temperature of the heating element, T0 is the surrounding temperature, and D is the thermal divergence coefficient (W/° C), which is usually determined by the size, structure, and material of the heating element itself.
Thermal time constant（ γ Sec)
When the ambient temperature moves from T0 Teleportation to T1, 0.632 times the temperature difference is the time. It is generally expressed by heat dissipation coefficient (W/℃) and Heat capacity H (W? Sec/℃) γ＝ H/D.
Heating working point
The working point where there is a balance between self heating and external heating.
According to the characteristics of current and voltage, the maximum point of current is called current protection.
Current protection variation range
The current protection changes with the surrounding temperature, resistance value, temperature characteristics, shape, etc. The current field that exceeds the upper limit of current protection is the working field, the current field below the lower limit is the non working current field, and the current field between the upper and lower limits is called the current protection variation range.
The working time is the time required to reduce the inrush current flowing through the thermistor to half.
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