PTC thermistor polycrystalline semiconductor material Introduction
PTCR Product Application Classification:
1. Transformer over-current overload protection using the common PTC thermistor;
2. Transformer over-current overload protection with a composite thermistor;
3. 485 communication interface protection with a thermistor;
4. The card table, bayonet attack prevention anti-attack protection module;
5. Relay contact protection PTC thermistor.
PTCR polycrystalline semiconductor material temperature:
PTC (Positive Temperature Coefficient of Resistance) is a very positive temperature characteristics of the thermistor. The main composition is BaTiO3, BaTiO3 ceramics is a typical ferroelectric material, Room temperature resistivity greater than 1012Ω/ cm, for the insulator. After semiconductor doping shows a strong PTC effect - room temperature resistivity is very low. With the increase of temperature, A mutation occurs near the Curie point, Resulting in several orders of magnitude change. This is because there is a barrier layer on the grain boundaries of the polycrystalline BaTiO3 semiconductor material caused by the surface states. At the Curie temperature, The grain boundary has ferroelectricity, A large dielectric constant, Barrier height is low, Electrons can easily cross the barrier, The corresponding material resistivity is small. However, when the temperature is higher than the Curie temperature, Grain boundary layer, Ferroelectric disappeared, The dielectric constant sharply decreases, According to Curie-Weiss law, So the potential barrier with the rise. With the rapid increase in barrier height, Electrons are difficult to cross the potential barrier, The resistivity of the corresponding material rises sharply, Macroscopically shows the PTC effect of the material. Due to this characteristic of the PTC thermistor, Whether in industrial electronic equipment or household appliances products, Thermal resistors have been widely used. Its application areas by PTC thermistor can be classified into three basic electrical properties, The basic parameters as shown.
PTCR Temperature Parameter Symbol:
The following figure:
Tc Curie temperature:
it is PTCR semi-conductive porcelain phase transition start point, generally PTCR components Rmin two times the corresponding resistance when the temperature point;
Tmax Maximum temperature:
the component reaches the highest resistance when the corresponding temperature;
Tp Maximum operating temperature:
the upper limit of the working temperature range;
Tmin minimum temperature: component (normal) showing the minimum resistance temperature; T25 standard room temperature 25 ℃;
Rc switch resistance: Curie temperature that corresponds to the resistance;
Rmax maximum resistance: the component can achieve the highest resistance;
Rp maximum working resistance: the maximum temperature corresponding to the resistance;
Rmin minimum resistance: the element (normal) can show the minimum resistance; R25 room temperature resistance: standard room temperature, the components of the corresponding resistance.