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PTC Thermistor Working Principle

PTC Thermistor Working Principle

1. What is PTC thermistor?

PTC thermistor (Positive Temperature Coefficient Thermistor) is a temperature-sensitive semiconductor resistor. Once it exceeds a certain temperature (Curie temperature), its resistance value increases almost stepwise with the increase of temperature. The temperature change of the PTC thermistor can be obtained by the current flowing through the PTC thermistor, or by the external heat input or the combination of the two.


Ceramic materials are usually used as excellent insulators with high resistance. Ceramic PTC is made of barium titanate and doped with other polycrystalline ceramic materials, which has low resistance and semiconductivity. It is achieved by purposefully doping a material with higher chemical valence as the lattice element of the crystal: a part of barium ions or titanate ions in the crystal lattice is replaced by higher valence ions. Therefore, a certain number of free electrons are obtained.


2. PTC thermistor effect

Then, let's look at the reason for PTC thermistor effect, in other words, the reason for the step increase in resistance value. The material structure is composed of many small crystallites, and the potential is formed on the grain boundary, which prevents the electrons from crossing the boundary into the adjacent area, thus resulting in high resistance. This effect is offset at low temperatures: the high dielectric constant and spontaneous polarization at the grain boundary hinder the formation of barriers and allow electrons to flow freely at low temperatures. At high temperatures, this effect greatly reduces the dielectric constant and polarization, leading to a substantial increase in the barrier and resistance, showing a strong PTC effect.


PTC is a kind of semiconductor heating ceramic. When the external temperature decreases, the resistance value of PTC decreases, and the calorific value increases correspondingly. PTC thermistor working principle is as follows: once it exceeds a certain temperature (Curie temperature), its resistance increases with the increase of temperature almost in a step-by-step manner. The temperature change of PTC thermistor body can be obtained by the current flowing through it, or by the external input heat or the combination of the two. Ceramic materials are usually used as excellent insulators with high resistance, PTC ceramics are based on barium titanate and doped with other polycrystalline ceramic materials, which have low resistance and semiconductivity. It is achieved by purposely doping a kind of material with higher chemical value as the lattice element of the crystal: in the lattice, part of barium ions or titanate ions are replaced by higher valence ions. Therefore, a certain number of free electrons are obtained.

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