Detailed data of PTC (thermistor)

PTC is the abbreviation of positive temperature coefficient, which means positive temperature coefficient, and generally refers to semiconductor materials or components with large temperature coefficient. Usually, the PTC we refer to is a thermistor used to correct the temperature coefficient, which is called PTC thermistor for short.

PTC thermistor is a typical semiconductor resistor with temperature sensitivity. When it exceeds a certain temperature (Curie temperature), its resistance value increases step by step with the increase of temperature.

Ceramic PTC is a semiconductor ceramic with barium titanate (or strontium and lead) as the main component and a small amount of rare earth (Y, Nb, Bi, Sb), acceptor (Mn, Fe), glass (silica, alumina) and other additives.

The resistance of ceramic PTC is very small below Curie temperature, and the resistance above Curie temperature increases by 1000 times, reaching one million times.

Chinese name: thermistor mbth: ptc composition: barium titanate, strontium, lead technology: sintering origin, classification, function, working principle, application of ptc, PTC terminology, selection, working characteristics of PTC, characteristics of high-temperature PTC materials, characteristic curve PTC (positive temperature coefficient) is a positive temperature coefficient thermistor with the characteristic that its resistivity increases with the increase of temperature. 1955, Hyman and others of Philips Company in the Netherlands found that the room temperature resistivity of BaTiO3 ceramics was greatly reduced after adding a small amount of rare earth elements, and its resistivity could be increased by more than three orders of magnitude in a very narrow temperature range. The characteristics of PTC materials were discovered for the first time [1]. Over the past 4 0 years, great breakthroughs have been made in the research of PTC materials, and the theory of PTC materials is becoming more and more mature, and its application scope is also expanding. Graded PTC resistor ">; Thermistors are divided into ceramic PTC resistors, organic polymer PTC resistors and PTC resistors. ; Thermistors are divided into PTC resistor for automatic degaussing, PTC resistor characteristic diagram for delayed starting, PTC resistor for constant temperature heating, PTC resistor for overcurrent protection and PTC resistor for sensor transmission. Generally speaking, organic polymer PTC resistors are suitable for products or circuits with occasional overcurrent protection, while ceramic PTC resistors are suitable for products or circuits with frequent overcurrent protection. The PTC effect of polymer still exists after 6000 times of PTC overcurrent, and the PTC effect of ceramic still exists after 654.38+ million times of PTC overcurrent. The function PPTC is the abbreviation of positive temperature coefficient of polymer. PPTC device is a polymer positive temperature coefficient device, which can protect the circuit when the current surge is too large and the temperature is too high. When in use, it is connected in series in the circuit. In general, its resistance is very small and its loss is very small, which does not affect the normal work of the circuit. However, if overcurrent (such as short circuit) occurs, its temperature will rise and its resistance will rise sharply, thus limiting the current and avoiding damaging the components in the circuit. When the fault is eliminated, the temperature of PPTC device automatically drops and returns to the low resistance state, so PPTC device is also called reversible fuse. Working Principle Self-healing fuse is made of polymer material with conductive particles. Its basic principle is an energy balance. When the current flows through the element, heat is generated, and part of the generated heat is radiated to the environment, and part of it increases the temperature of the polymer material. Under the working current, the generated heat and the emitted heat reach a balance, and the current can pass normally. When an excessive current passes, a large amount of heat generated by the element cannot be dissipated in time. It causes the temperature of the polymer material to rise. When the temperature reaches the crystallization and melting temperature of the material, polymer materials aggregate and expand, blocking the conductive path composed of conductive particles, resulting in a rapid rise in resistance and limiting the passage of large current, thus playing an over-current protection role. PTC adopts KT series polymer PTC thermistors (PPTC thermistors) for overcurrent protection, and a series of products such as optical sheet, TD, ribbon D/DL, lead package, lead unpacked, ring and surface mount. Among them, the annual output of thermistors exceeds 300 million. This series of products has the advantages of stable resistance, high safety, automatic recovery, good strong current resistance, short recovery time, small size and convenient installation. According to the rated working voltage (6V ~ 600V), working current (40mA ~ 14A) and different installation methods, the products are divided into more LAN IEEE categories. They are widely used for circuit protection in 6C industrial field, For example, computers, communications, consumer electronics, automobiles, channels, digital content, power supplies, small household appliances, IEEE 802.3 1394 iLINK, main distribution frame security unit, short-distance/internal protection requirements, user terminal equipment, analog line cards for protecting user terminal equipment with 2Pro modules, and T1/e/kloc. ADSL equipment, HDSL equipment, MDF module/wired telephone/power supply with primary and secondary protection 2. Application in battery industry: digital battery pack, mobile phone battery pack, wireless telephone battery pack, mobile wireless broadcasting battery pack, notebook computer battery pack, portable video recorder battery pack, walkman battery pack, power tool (charging cable) 3. Constant temperature heater applied to foot bath heater 4. Rated zero power resistor R25. The term PTC is applied to the carbon rod hot rail electric floor heating material, which means that when measuring the PTC thermistor value at a certain temperature, the power consumption added to the PTC thermistor is very low, so that the resistance change of the PTC thermistor caused by its power consumption can be ignored. The rated zero-power resistance refers to the zero-power resistance measured when the ambient temperature is 25℃. The minimum resistance Rmin refers to the minimum zero power resistance that PTC thermistors can have. Curie temperature Tc is very important for the application of PTC thermistor, and the temperature at which the resistance value begins to increase sharply is defined as Curie temperature. The resistance RTC of PTC thermistor corresponding to Curie temperature is 2 * rmin. Temperature coefficient The temperature coefficient of PTC thermistor is defined as the relative change of resistance caused by temperature change. If the temperature coefficient is larger, the PTC thermistor is more sensitive to temperature change. Surface temperature Tsurf surface temperature Tsurf refers to the surface temperature of PTC thermistor when it is in thermal balance with the surrounding environment for a long time at a specified voltage. Action current Ik The current flowing through PTC thermistor is enough to make the temperature rise of PTC thermistor exceed Curie temperature, which is called action current. The minimum action current is called the minimum action current. Action time ts Under the condition of 25℃, an initial current (guaranteed to be the action current) is applied to the PTC thermistor, and the action time is reduced to 50% of the initial current. No-action current The current that ink flows through PTC thermistor is not enough to make the temperature rise of PTC thermistor exceed Curie temperature since heating. Such current is called no-action current. The maximum value of no-action current is called maximum no-action current. Maximum current Imax Maximum current refers to the maximum current bearing capacity of PTC thermistor. When the maximum current is exceeded, the PTC thermistor will fail. Residual current Ir Residual current is the current at thermal equilibrium at maximum working voltage Vmax. Maximum working voltage Vmax maximum working voltage refers to the highest voltage that PTC thermistors are allowed to maintain continuously at the specified ambient temperature. For the same product, the higher the ambient temperature, the lower the maximum working voltage value. Rated Voltage VN The rated voltage is the power supply voltage lower than Vmax at maximum working voltage. Generally speaking, Vmax = VN+ 15%. Breakdown voltage VD Breakdown voltage refers to the highest withstand voltage of PTC thermistor. When the breakdown voltage is above, PTC thermistor will be broken down, leading to failure. Select 1 to list the actual average working current I and V (regardless of instantaneous current) 2 on the equipment line. Select PTC series components according to I value, V value, product category and installation method. 3. If the internal ambient temperature of the equipment is greater than 25 degrees, the self-resetting fuse will reduce the current flowing with the increase of the temperature. In order to maintain the normal current through the load, IH can be calculated according to the reduction rate of the relevant formula. 4. According to the fuse series components selected in step 2 and the IH value calculated in step 3, select the components that meet the requirements in the following specification table. It is particularly important to emphasize that the IH value of the selected component must be greater than or equal to the IH value calculated in step 3. IH= maximum working current (I)÷ reduction ratio 5. According to the selected component, the running time when abnormal current value is generated can be viewed in the corresponding running time curve table. 6. Choose the appropriate PTC according to the characteristics of equipment failure. The sizes of normal overcurrent and short-circuit current are different, so the sizes of PTC models should also be different. The working characteristics of ptc are extremely low impedance and small volume at room temperature, which can be widely used for overcurrent protection of various circuits and electrical appliances, and can be installed in different lines to protect the safe use of each line to the greatest extent, making up for the defects of previous centralized protection circuits. Compared with traditional over-current protection devices such as fuses, ceramic PTC materials and metal sheets, this device has the following characteristics: 1, rapid response to overload current, stable and reliable performance; 2. Strong impact resistance and long service life; 3, non-polarity, both AC and DC; 4, it can be automatically restored; 5, the maximum working current can reach tens of amperes; 6. Small in size, and can process and produce products with different shapes and specifications according to customer requirements; 7, a wide range of uses, can be used for micro-motors, motor vehicle circuits, audio equipment, communication equipment, instrumentation, battery components, industrial control systems, computer peripherals and so on. Characteristics of high-temperature PTC materials PTC materials are semiconductor ceramic materials based on BaTiO3. The resistivity of this material rises sharply with the increase of temperature in a certain area, and the temperature at which the resistivity rises suddenly is called Curie temperature. The Curie temperature of barium titanate is 65438 0 20℃. When a part of Pb2+ is used instead of Ba2+, it becomes Ba( 1-X)PbX? The Curie temperature of TiO3 _ 3 material increases with the increase of Pb2+ content. The highest temperature of PTC heating materials that have been put into practical use is 300℃. The following figure is the curve of PTC thermosensitive material. PTC characteristic curve