adjustable bimetal thermostat switch

　　The difference between polymer PPTC and ceramic CPTC

　　Positive temperature coefficient thermistor PTC (also known as self recovering fuse) is an overcurrent and over temperature protection component, which can be divided into two categories according to manufacturing materials: organic polymer PPTC and ceramic PTC (CPTC).

　　Polymer PPTC is formed by extruding high molecular weight polymer into carbon powder. Carbon powder forms carbon chains for conductivity, and when heated, the polymer expands, causing the carbon chains to break and form high resistance. Ceramic CPTC is made by high-temperature sintering of barium titanate powder with positive temperature coefficient characteristics through electronic ceramic technology. Their commonality lies in their recoverability, which can be reused more than 6000 times.

　　The main advantages of polymer PPTC are: zero power resistors at room temperature can be made very small, high current products only have a few milliohms, low power consumption in the circuit can be ignored, and the volume is relatively small. It can be connected in series in vulnerable circuits for overcurrent protection and temperature fuse use. The resistance changes quickly, in the order of a few milliseconds, with small heat capacity, short recovery time, shock resistance, and can be protected up to 8000 times in a cyclic manner. PPTC can be used as a temperature fuse, which to some extent reflects the performance and function of temperature fuses in circuits. Realize dual protection functions of overcurrent protection and over temperature protection in the circuit.

　　The main advantages of ceramic CPTC are: easy manufacturing, relatively low price, but high resistance, large volume, and high road loss, with a range of tens to thousands of Ω, suitable for small current overcurrent protection. When overheated at high temperatures, negative resistance effect is prone to occur (resistance decreases), protection speed is slow, in the order of hundreds of ms, large heat capacity, and long recovery time. The application scope is relatively narrow, such as not suitable for fast protection circuits, automotive wiring harness protection, PCB trace protection, etc. It is mostly used for heating devices and can be selected in some small signal circuits where loss does not need to be considered.

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