Thermistor is a temperature sensitive resistor whose resistance value significantly changes with temperature. According to the temperature coefficient characteristics, thermistors are mainly divided into the following two categories:
1、 Negative Temperature Coefficient Thermistor (NTC)
characteristic
The resistance value decreases exponentially with increasing temperature.
Typical materials: metal oxides such as manganese, cobalt, nickel, etc.
Temperature range: -50 ℃~+300 ℃ (some models can reach+500 ℃).
Subdivision type
Power type NTC: used to suppress surge currents during power supply startup (such as switching power supplies, LED drivers).
Application: Computer power supply, charger, industrial equipment.
Parameters: Zero power resistance value (R25), maximum steady-state current (Imax).
Compensation type NTC: used for temperature compensation (such as transistors, integrated circuits).
Application: Communication equipment, precision instruments.
Parameter: B value (material constant, 2000K~5000K).
Temperature measuring NTC: high-precision temperature sensor (such as medical equipment, environmental monitoring).
Applications: thermometers, cold chain transportation, smart homes.
Parameters: accuracy (± 0.1 ℃~± 1 ℃), response time (<10s).
Typical packaging
Axial lead packaging (such as 3mm and 5mm glass packaging).
Surface mount packaging (such as 0402, 0603, 0805).
Epoxy resin encapsulation (waterproof and dustproof, suitable for outdoor scenes).
2、 Positive Temperature Coefficient Thermistor (PTC)
characteristic
The resistance value increases exponentially with temperature and sharply increases after reaching the critical temperature (abrupt PTC).
Typical material: doped ceramics (such as BaTiO3).
Temperature range: -40 ℃~+150 ℃ (some models can reach+300 ℃).
Subdivision type
Switch type PTC (mutation type):
Application: Motor start protection, self recovery fuse, electric blanket temperature control.
Parameters: action current (Ihold), maximum voltage (Vmax).
Slow type PTC (linear type):
Application: Temperature compensation, flow sensor, constant temperature heating.
Parameters: B value (500K~5000K), temperature coefficient (α=0.01~0.1/℃).
Typical packaging
Radial lead packaging (such as ceramic packaging with a diameter of 5mm or 10mm).
Surface mount packaging (such as 1812, 2920).
Metal electrode packaging (such as TO-220, suitable for high-power scenarios).
3、 Special type thermistor
Critical Temperature Resistors (CTR)
Characteristic: Near a specific temperature (Curie temperature), the resistance value drops sharply by 3-5 orders of magnitude.
Application: Temperature switch, fire alarm, motor overheating protection.
Parameters: Curie temperature (Tc=60 ℃~150 ℃), action time (<1s).
Silicon PTC Thermistor
Features: Linear positive temperature coefficient, high accuracy (± 0.1 ℃).
Applications: precision temperature measurement, medical equipment, aerospace.
Parameters: Temperature coefficient (α=0.7%/℃), long-term stability (<0.02 ℃/year).
4、 Key parameters for selection
Nominal resistance value (R25): The resistance value at 25 ℃ (such as 10k Ω, 100k Ω).
B value (NTC): Material constant that determines the slope of the temperature resistance curve (B=3000K~5000K).
Dissipation coefficient (δ): Power dissipation at unit temperature difference (mW/℃), affecting self heating effect.
Thermal time constant (τ): The rate of response to temperature changes (in seconds, such as τ=5s).
Rated power: maximum power during continuous operation (such as 0.1W, 1W).
5、 Typical application scenarios
Temperature measurement and control
Example: NTC thermistor is used for thermometers (accuracy ± 0.1 ℃), PTC is used for temperature control of electric water heaters.
Surge current suppression
Example: NTC power type resistors are connected in series at the power input end to suppress startup surges.
motor protection
Example: PTC thermistor embedded in motor winding, cuts off circuit when overheated.
battery management
Example: NTC monitors battery temperature to prevent overcharging/overdischarging.