What Is a PTC Fuse?
PTC is the abbreviation of Positive Temperature Coefficient, which means a positive temperature coefficient, and generally refers to a semiconductor material or component with a large positive temperature coefficient. Generally, we refer to PTC as a positive temperature coefficient thermistor, or PTC thermistor for short.
- PTC resistance ">; Thermistors are divided into: Ceramic PTC resistance Organic polymer PTC resistance
- PTC resistors>; Thermistors are divided into:
- PTC resistor for automatic demagnetization
- PPTC is the abbreviation of Polymeric Positive Temperature Coefficient. PPTC devices are
- KT series polymer PTC thermistor for overcurrent protection (
- Rated zero power resistance R25
- Zero power resistance means that when the PTC thermistor value is measured at a certain temperature, the power consumption added to the PTC thermistor is extremely low, so low that the resistance change of the PTC thermistor caused by its power consumption can be ignored. Excluded. Rated zero power resistance refers to the zero power resistance value measured at an ambient temperature of 25 ° C. The minimum resistance Rmin refers to the minimum zero power resistance value that a PTC thermistor can have.
- Curie temperature Tc
- For PTC thermistor applications, the temperature at which the resistance value starts to increase steeply is important. We define it as the Curie temperature. The resistance of the PTC thermistor corresponding to the Curie temperature is RTc = 2 * Rmin.
- Temperature coefficient
- The temperature coefficient of a PTC thermistor is defined as the relative change in resistance caused by temperature changes. If the temperature coefficient is larger, the PTC thermistor responds more sensitively to temperature changes.
- Surface temperature Tsurf
- The surface temperature Tsurf refers to the temperature of the surface of the PTC thermistor when the PTC thermistor is at a specified voltage and has been in thermal equilibrium with the surrounding environment for a long time.
- Action current Ik
- The current flowing through the PTC thermistor is sufficient to cause the PTC thermistor to increase its self-heating temperature above the Curie temperature. Such a current is called the operating current. The minimum value of the operating current is called the minimum operating current.
- Action time ts
- Under the environment of 25 ° C, add a starting current to the PTC thermistor (guaranteed as the operating current). The time elapsed when the current through the PTC thermistor is reduced to 50% of the starting current is the operating time.
- Non-operating current INk
- The current flowing through the PTC thermistor is not enough to cause the PTC thermistor to increase its self-heating temperature above the Curie temperature. Such a current is called a non-operating current. The maximum non-operating current is called the maximum non-operating current.
- Maximum current Imax
- The maximum current refers to the highest current carrying capacity of the PTC thermistor. When the maximum current is exceeded, the PTC thermistor will fail.
- Residual current Ir
- Residual current is the current under thermal equilibrium at the maximum operating voltage Vmax.
- Maximum working voltage Vmax
- The maximum operating voltage refers to the maximum voltage allowed to be continuously maintained on the PTC thermistor under the specified ambient temperature. For the same product, the higher the ambient temperature, the lower the maximum operating voltage value.
- Rated voltage VN
- The rated voltage is the supply voltage below the maximum working voltage Vmax. Usually Vmax = VN + 15%.
- Breakdown voltage VD
- The breakdown voltage refers to the highest voltage withstanding capacity of the PTC thermistor. When the PTC thermistor is above the breakdown voltage, it will be broken down and cause failure [2]
- 1. List the actual average working current I and V values on the equipment line (without considering instantaneous current)
- 2. Select a PTC series component according to I value, V value, product category and installation method.
- 3. If the internal ambient temperature of the device is greater than 25 degrees, the reset current fuse will reduce the passing current as the temperature increases. In order to maintain the normal current of the load, IH can be calculated based on the reduction rate of the relevant formula.
- 4. According to the Fengfu fuse series components selected in step 2 and the IH value calculated in step 3, select the matching components in the subsequent specification table. It is 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 operating current (I) ÷ reduction ratio
- 5. According to the selected components, the operation time when abnormal current value is detected can be compared in the corresponding operation time curve table.
- 6. Choose a suitable PTC according to the characteristics of the equipment failure. The normal overcurrent and the current generated by the short circuit are different, so the size of the PTC model must also be different.
- At low temperature, the impedance is extremely low and the volume is small. It can be widely used for overcurrent protection of various circuits and electrical appliances, and can be installed separately. Compared with traditional overcurrent protection devices such as fuses, ceramic PTC materials, and metal sheets, the characteristics of this device are as follows:
- 1. Quick response to overload current, stable and reliable performance;
- 2. Strong impact resistance and long service life;
- 3. No polarity, AC and DC are available;
- 4, can be automatically restored;
- 5. The maximum working current can reach tens of amps;
- 6, small size, can be processed to produce various shapes and specifications of products according to customer needs;
- 7, widely used, can be used for micro-motors, motor vehicle circuits, audio equipment, communication equipment, instruments, battery components, industrial control systems, computer peripherals, etc. [3]
- PTC materials are semiconductor ceramic materials based on BaTiO3. The resistivity of this material rises sharply with increasing temperature in a certain area. The temperature at which the resistivity rises abruptly is called the Curie temperature. The Curie temperature of BaTiO3 is 120 ° C. When Ba2 + is replaced with a part of Pb2 +, it becomes a Ba (1-X) PbX TiO3 material, and its Curie temperature rises with the increase of the content of Pb2 +. The maximum temperature of a PTC heating material that has been put into practical use is 300 ° C.
- The figure below shows the PTC thermosensitive material curve.