How the thermistor works

What is a thermistor? How does it work? When it comes to the thermistor, everyone will know that it is one of the sensitive components. According to different temperature coefficients, they are divided into positive temperature coefficient thermistors and negative temperature coefficient thermistors. Everyone knows a little bit about these superficial knowledge, but what other thermistor technologies are we are not familiar with? Let’s learn together with the editor!

1. Introduction to thermistor technology

Since 1950, when Heimann and others from the Dutch Philips Company discovered that BaTIO3 series ceramics can obtain positive temperature coefficient (PTC) characteristics after semiconductorization, people have become more and more knowledgeable about it. At the same time, its applications are becoming increasingly widespread, penetrating into various fields such as daily life, industrial and agricultural technology, military science, communications, and aerospace. The reason for this situation is that the PTC thermistor has its unique electrical-thermal-physical properties. It is currently at a stage where the performance of PTC ceramic materials is further optimized and the application of PTC ceramic components is further promoted, and the three are mutually reinforcing. The application of PTC thermistor is the most popular new application technology with broad prospects today.

Thermistors are divided into positive temperature coefficient (PTC) and negative temperature coefficient (NTC) thermistors according to the temperature coefficient of resistance. PTC is the abbreviation of Positive Temperature Coefficient, which actually means positive temperature coefficient. It is customarily used for bulk semiconductor materials or components with large positive resistance temperature coefficient. The practical use of PTC components began in the early 1960s. The earliest commercial products were temperature compensation components used in transistor circuits. Subsequently, a series of products used for motor overheat protection, color TV degaussing current limiting and constant temperature heating were commercialized one after another, and soon formed a large-scale production scale.

The application range of PTC components is very wide, and the application products to be developed are extremely rich. This has become the consensus of more and more experts.

2. Introduction to PTC thermistor

PTC thermistor heating element is a high-tech and cutting-edge product in modern and future times. It is widely used in light industry, housing, transportation, aerospace, agriculture, medical care, environmental protection, mining, civil equipment, etc. It has excellent advantages compared with heating elements such as nickel, chromium wire or far infrared.

1. It has special functions of constant temperature, temperature regulation and automatic temperature control. When AC or DC voltage is applied to the PTC element to heat up, the resistivity is very low below the Curie point temperature; when the Curie point temperature is exceeded, the resistivity suddenly increases. large, causing the current to drop to a stable value to achieve the purpose of automatic temperature control and constant temperature.

2. Non-flammable, safe and reliable

The PTC element does not turn red when heated and has no open flame (the resistance wire turns red and has an open flame), and is not easy to burn. When the temperature around the PTC component exceeds the limit value, its power automatically drops to the equilibrium value, and there is no danger of burning.

3. Save electricity

The energy input of the PTC element adopts a proportional type and has a current limiting effect, which saves electricity compared with the switching energy input of heating elements such as nickel-chromium wires.

4. Long life

The PTC element itself is an oxide, without the disadvantages of high-temperature oxidation of nickel-chromium wires, and without the fragility of infrared tubes, and has a long service life. And the porous type has a longer life than the non-porous type.

5. Simple structure

The PTC element itself automatically controls the temperature, and no additional automatic temperature control circuit device is required.

6. Wide operating voltage range

PTC components work well with both low voltage (6-36 volts) and high voltage (110-240 volts).

Application of PTC thermistor

Low-voltage PTC components are suitable for various types of low-voltage heaters, low-temperature compensation of instruments, heaters on automobiles and computer peripheral equipment.

High-voltage PTC elements are suitable for heating the following electrical equipment: electric heating plates, shoe dryers, hot melt glue guns, rice cookers, electric heating boots, electric mosquito repellents, intravenous injection heating, lightweight plastic sealing machines, steam hair combs, steam generators , humidifier, curling iron, video recorder, copy machine, vending machine, hot air curtain, hand warmer, tea dryer, water pipe heater, travel clothes dryer, car paint room, liquefied gas bottle heater, shower , beauty appliances, electric heating tables, baby bottle thermostats, electric thermal massagers, electric hot water bottles, electric blankets, etc.

Technical requirements for PTC thermistor

3. Application of thermistor

Applications of PTC thermistors in circuit controls and sensors: transistor temperature compensation circuits, temperature measurement and temperature control circuits, overheating protection circuits, incubators, electric fans, color scroll washing, kettles, electric water heaters, electric blankets, fluorescent lamps, energy-saving lamps , battery charging, transformer winding, heater, delayer, compressor, color TV, color display, over-current security, liquid level control, electronic ballast, program-controlled switch, electronic component aging station.

Applications of PTC thermistors in electric heating appliances: heaters, room heaters, dryers (cabinets), tumble dryers, hand dryers, hair dryers, hair curlers, steam beauty devices, rice cookers, mosquito repellents, hand warmers , shoe dryer, pressure cooker, disinfection cabinet, kerosene gasifier, electric iron, electric soldering iron, plastic welding gun, sealing machine.

Applications of PTC thermistors in automobiles: electrical overload protection devices, hybrid heaters, low-temperature starting heaters, fuel heaters, honeycomb heaters, fuel level indicators, engine cooling water temperature detection tables.

How to select a PTC thermistor: Each thermistor has parameters such as "voltage resistance", "current resistance", "maintenance current" and "action time". You can make a selection based on specific circuit requirements and product parameters. The specific methods are as follows:

1. First determine the maximum ambient temperature when the protected circuit is working normally, the operating current in the circuit, the maximum voltage that the thermistor needs to withstand after action, and the required action time and other parameters;

2. Select thermistors of different shapes such as "chip type", "radial lead type", "axial lead type" or "surface mount type" according to the characteristics of the protected circuit or product;

3. Based on the maximum working voltage, select a product series with a "withstand voltage" level greater than or equal to the maximum working voltage;

4. Based on the maximum ambient temperature and the operating current in the circuit, select a product specification with a "maintenance current" greater than the operating current;

5. Confirm that the action time of the thermistor of this specification is less than the time required by the protection circuit;

6. Compare the data provided in the specification book to confirm that the size of the thermistor of this specification meets the requirements. The above is the relevant technical knowledge of thermistor, I hope it can help you.