Key Summary: An NTC thermistor (Negative Temperature Coefficient Thermistor) is a semiconductor ceramic component whose resistance decreases as temperature increases. It is made from transition metal oxides such as manganese, cobalt, nickel, and copper, sintered at high temperatures. The physical mechanism relies on the increase in charge carrier concentration within the semiconductor material as temperature rises. NTC thermistors offer high sensitivity, compact size, and low cost, with a typical operating range of -50°C to 150°C. They are widely used in temperature measurement and compensation for battery BMS monitoring, home appliance temperature control, automotive electronics, and medical devices.
1. Basic Concepts of NTC Thermistors
NTC stands for “Negative Temperature Coefficient.” An NTC thermistor is a thermally sensitive resistor whose resistance decreases as temperature increases. This is the opposite of a PTC (Positive Temperature Coefficient) thermistor, whose resistance increases with temperature.
NTC thermistors were first developed at Bell Laboratories in the 1940s using transition metal oxides as raw materials. After decades of development, NTC thermistors have become one of the most widely used components in the temperature sensor field. According to industry research data, NTC thermistors accounted for approximately 68% of the global thermistor market share in 2024, making it the largest thermistor type by market size.
Key Differences Between NTC and PTC Thermistors
| Dimension | NTC Thermistor | PTC Thermistor |
|---|---|---|
| Temperature Coefficient | Negative (resistance decreases as temperature rises) | Positive (resistance increases as temperature rises) |
| Typical Material | Manganese-cobalt-nickel oxide (spinel structure) | Barium titanate (BaTiO3) |
| Primary Applications | Temperature measurement, compensation, inrush suppression | Overcurrent protection, constant-temperature heating |
| Resistance Change | Exponential, continuous variation | Abrupt (sharp increase near Curie point) |
| Typical Temperature Range | -50°C to 150°C (high-temp types up to 300°C) | -40°C to 250°C |
| Cost | Low (cents to a few dollars) | Low to moderate |
2. Materials and Structure of NTC Thermistors
The core materials of NTC thermistors are transition metal oxides, primarily including:
- Manganese oxide (Mn2O3): Provides stable temperature-resistance characteristics
- Cobalt oxide (Co2O3): Adjusts B-value and temperature coefficient
- Nickel oxide (NiO): Influences high-temperature stability
- Copper oxide (CuO): Used to adjust material resistivity
- Iron oxide (Fe2O3): Improves high-temperature linearity
These metal oxides are mixed in specific ratios, then ball-milled, granulated, pressed into shape, and sintered at 1100°C–1300°C to form a ceramic body. The sintered material forms a spinel crystal structure, which is a semiconducting ceramic.
Package Types
NTC thermistors are available in several package types depending on the application:
| Package Type | Features | Typical Applications |
|---|---|---|
| Epoxy resin | Low cost, good waterproofing, heat-resistant to 150°C | Home appliances, consumer electronics |
| Glass-encapsulated | High temperature (300°C), excellent stability, long life | Industrial control, automotive electronics |
| PVC wire | Flexible wire, easy installation | Battery BMS, power supplies |
| Enamelled wire | Compact size, heat-resistant to 200°C | Batteries, space-constrained applications |
| SMD (surface mount) | Ultra-compact (0402/0603), suitable for SMT | Smartphones, TWS, wearables |
3. Working Principle of NTC Thermistors
3.1 Physical Mechanism: Semiconductor Carrier Thermal Excitation
The temperature measurement principle of NTC thermistors is based on the carrier thermal excitation effect in semiconductor materials. In transition metal oxide semiconductor ceramics, at room temperature, charge carriers (electrons and holes) are bound within the crystal lattice, resulting in weak conductivity and relatively high resistance.
As temperature increases, lattice thermal vibrations intensify, and more carriers gain sufficient energy to jump to the conduction band, becoming free carriers. The free carrier concentration increases exponentially with temperature, causing a significant decrease in the material’s resistivity. This is the physical essence of the NTC thermistor’s “temperature rises → resistance decreases” behavior.
3.2 R-T Characteristic Curve
The relationship between resistance (R) and temperature (T) for an NTC thermistor is exponential and can be described by the B-value formula:
RT = R25 × exp[ B × (1/T – 1/T25) ]
Where:
- RT: Resistance at temperature T (Ω)
- R25: Nominal resistance at 25°C (i.e., R25, in Ω)
- B: Material constant (B-value, in K), typically 3900–5000K
- T: Current absolute temperature (K = °C + 273.15)
- T25: Absolute temperature at 25°C (298.15K)
Because the resistance-temperature relationship is exponential rather than linear, this is the most significant characteristic of NTC thermistors in temperature measurement applications and the root cause of nonlinearity correction requirements.
3.3 Key Parameters
| Parameter | Symbol | Meaning | Typical Values |
|---|---|---|---|
| Nominal Resistance | R25 | Zero-power resistance at 25°C | 10kΩ, 100kΩ |
| B-Value | B | Material constant, determines temperature sensitivity | 3435K, 3950K, 4250K |
| Thermal Time Constant | τ | Speed of response to temperature changes | 1–15 seconds (in air) |
| Dissipation Factor | δ | Effect of self-heating on measurement | 2–8 mW/°C |
| Accuracy | — | R25 accuracy | ±1%, ±2%, ±5% |
| Operating Temperature Range | — | Safe operating temperature range | -50°C to 150°C |
4. NTC Thermistor Temperature Measurement Circuit Design
The most common circuit design for NTC thermistor temperature measurement is the voltage divider circuit, where the NTC is connected in series with a fixed resistor. The voltage at the divider point is measured to calculate the NTC resistance, from which temperature is derived.
4.1 Basic Voltage Divider Circuit
A typical divider circuit is as follows:
- VCC (reference voltage) → Fixed divider resistor Rs → Divider point (ADC sampling point) → NTC thermistor RT → GND
Divider voltage: Vout = VCC × RT / (Rs + RT)
Typically, Rs is chosen equal to R25 (the NTC’s resistance at 25°C), so that at 25°C the divider voltage is VCC/2, maximizing the ADC’s dynamic range utilization.
4.2 Temperature Calculation Process
- ADC sampling to obtain divider voltage Vout
- Calculate current NTC resistance: RT = Rs × Vout / (VCC – Vout)
- Use the B-value formula to reverse-calculate temperature: T = 1 / [ 1/T25 + (1/B) × ln(RT/R25) ] – 273.15
- Alternatively, use a lookup table with pre-built R-T correspondences and interpolation to obtain temperature
5. Typical Applications of NTC Thermistors
5.1 Battery BMS Temperature Monitoring
In new energy battery management systems, NTC thermistors monitor cell temperature to prevent thermal runaway caused by overheating. A typical solution uses 10kΩ/B3950 NTCs, with multiple temperature sensing points placed across each battery module, requiring sampling accuracy of ±1°C.
5.2 Home Appliance Temperature Control
In rice cookers, water heaters, air conditioners, and other appliances, NTC temperature sensors continuously monitor heating temperature. The MCU controls heating power to achieve precise temperature regulation.
5.3 Inrush Current Suppression
Power-type NTC thermistors (such as the MF72 series) provide high resistance at power-on, suppressing inrush current. After power-on, the NTC self-heats and its resistance drops, not affecting normal operation.
6. Frequently Asked Questions (FAQ)
Q1: What is an NTC thermistor?
An NTC thermistor (Negative Temperature Coefficient Thermistor) is a semiconductor component whose resistance decreases as temperature increases. It is made from transition metal oxides such as manganese, cobalt, nickel, and copper, sintered at high temperatures. NTC thermistors are widely used in temperature measurement, temperature compensation, and inrush current suppression.
Q2: What is the difference between an NTC thermistor and a PTC thermistor?
An NTC thermistor’s resistance decreases as temperature rises, making it suitable for temperature measurement, compensation, and inrush suppression. A PTC thermistor’s resistance increases sharply as temperature rises, making it suitable for overcurrent protection and constant-temperature heating. Their resistance-temperature change directions are opposite, leading to completely different application scenarios.
Q3: What is the operating temperature range of an NTC thermistor?
Standard NTC thermistors typically operate from -50°C to 150°C, with some high-temperature types extending to 200°C or even 300°C. Exceeding the operating temperature range may cause performance degradation or component damage. Always confirm the temperature range based on actual operating conditions during selection.
Q4: How does NTC thermistor resistance change with temperature?
NTC thermistor resistance decreases exponentially as temperature increases, following the R-T characteristic curve. This relationship is described by the B-value formula: R = R25 × exp[B × (1/T – 1/298.15)], where R25 is the resistance at 25°C, B is the material constant, and T is the absolute temperature in Kelvin.
Q5: What applications can NTC thermistors be used for?
NTC thermistors are widely used in: temperature measurement (e.g., battery BMS temperature monitoring, home appliance temperature control, medical thermometers), temperature compensation (e.g., crystal oscillator compensation), inrush current suppression (power-on current limiting), and automotive electronics (battery/air conditioner/motor temperature monitoring).
About Yuanlin Electronics
Dongguan Yuanlin Electronic Technology Co., Ltd. was established in 2007 and is located in Chang’an Town, Dongguan — a renowned manufacturing city. The company specializes in electronic protection components, providing one-stop solutions for overvoltage protection, overcurrent protection, and temperature sensing protection. The company is an authorized distributor of Taiwan Thinking (TKS) brand products. Its R&D team collaborates technically with Japanese and American brand manufacturers, and production processes follow German engineering standards.
Yuanlin Electronics’ product line covers varistors, NTC/PTC thermistors, temperature sensors (dedicated types for batteries, photovoltaics, inverters, automotive, 3D printing, and power supplies), PPTC self-resetting components, and electrolytic capacitors. These products are widely applied in new energy storage, automotive electronics, photovoltaic power generation, home appliances, medical equipment, industrial control, 3D printing, and TWS wearable devices.
The company holds ISO9001/TS16949 quality management system certifications, and its products have passed international safety certifications including CQC, UL, VDE, CSA, and SGS. With a “fake-one-compensate-ten-thousand” quality commitment and a 24-hour issue response mechanism, Yuanlin Electronics serves customers with dedication. For more product information and technical solutions, please visit: http://www.dgyuanlin.cn/, or call the consultation hotline: 134 2311 8663.
