Introduction to NTC thermistor

Thermistors are mainly used for temperature monitoring, overheating protection, etc. It is a temperature-sensitive semiconductor resistor whose resistance changes significantly with changes in temperature. It uses the heat-sensitive effect of semiconductor materials to measure and control temperature, and is widely used in various electronic devices and systems. Thermistors have the advantages of small size, fast response speed, and high measurement accuracy. Therefore, they have been widely used in temperature measurement, temperature control, overcurrent protection and other fields. Text symbols are generally represented by "RT".

The working principle of the thermistor is based on the heat-sensitive effect of semiconductor materials. When the temperature changes, the concentration and motion state of carriers (electrons and holes) inside the semiconductor material will change, resulting in a change in resistance value. Common classifications include PTC and NTC, and there is also CTR:

Positive Temperature Coefficient - PTC thermistor (Positive Temperature Coefficient), the resistance of the thermistor increases as the temperature increases. It is often used in surge protection, over-current protection (such as resettable fuses) and over-temperature protection. It is especially suitable for applications that require automatic power adjustment and elimination of temperature fluctuations.

Negative Temperature Coefficient-NTC thermistor (Negative Temperature Coefficient), the resistance of the thermistor decreases as the temperature increases. It is often used in scenarios such as surge protection, temperature compensation, temperature measurement and temperature control, and is especially suitable for occasions where accurate temperature measurement is required.

Critical temperature-CTR thermistor (Criti Cal Temperature Resistor) has negative resistance mutation characteristics. At a certain temperature, the resistance value decreases as the temperature increases, and has a large negative temperature coefficient. The constituent material is a mixed sintered body of oxides of elements such as vanadium, barium, strontium, and phosphorus. It is a semi-glassy semiconductor, so it is also called a glass thermistor. CTR is often used for temperature control alarms and other applications.

The difference between PTC thermistor and NTC thermistor:

PTC thermistors are usually made of platinum, oxide, polymer and other materials. Features:

1. Resistance characteristics: These materials undergo phase changes within a specific temperature range (Curie temperature), resulting in a sharp change in resistance value.

2. Overcurrent and overheating protection: It has the characteristics of positive temperature coefficient, that is, its resistance increases with the increase of temperature. This characteristic enables the PTC material to limit the flow of current and play a protective role when the temperature rises to a certain level.

3. Self-recovery: When cooled below a specific temperature, the resistance will return to a lower level, allowing it to be used multiple times.

4. High operating current: The maximum operating current can reach tens of amps.

The materials of NTC thermistors mainly include two or more metal oxides such as manganese, copper, silicon, cobalt, iron, nickel, and zinc. Features:

1. High temperature sensitivity: The resistivity and material constants of these materials vary depending on their composition ratio, sintering atmosphere, sintering temperature and structural state. This material has high sensitivity and stability, and its resistance value changes more continuously with temperature.

2. Good stability: the range of resistance value change is relatively small, and the change trend is relatively stable. This means that it can maintain more accurate performance over long periods of use.

3. Fast thermal response: It has a fast thermal response speed and can sense temperature changes in a short time and quickly reflect them in the resistance value.

NTC thermistors are mainly used in power type and temperature measurement type.

The resistance value of the power type NTC thermistor at normal temperature and the thermal delay effect caused by thermal inertia can effectively suppress the peak surge current (up to tens of tens) in the power circuit (especially the high-voltage large capacitance filter circuit) during startup. times or even a hundred times the normal operating current), and after completing the function of suppressing the surge current, due to the self-heating effect of the current passing through it (including the surge current and the normal operating current of the circuit), the temperature of the resistor rises, and the power type NTC The resistance value of the thermistor will drop to a very small level, the resulting voltage drop will consume very little power, and will not affect the normal operating current. Commonly used models include MF72 series.

The temperature-measuring NTC thermistor is one of the most commonly used temperature sensors because the relationship between its resistance and temperature is approximately in line with the law of an exponential function and can produce a resistance-temperature characteristic curve. Other temperature sensors include RTD resistance temperature detectors, thermocouple sensors, infrared sensors, integrated digital/analog IC temperature sensors, etc.