A PPTC is an overcurrent protection device having a positive temperature coefficient characteristic. It functions when connected in series in a circuit. When current in circuit is normal, the PPTC is in a low-resistance state. When the circuit is short circuited or overloaded, the PPTC transits to a high-resistance state. In this way, the circuit is rapidly and accurately limited and protected. When an out-of-order is eliminated, the PPTC is automatically restored to a low-resistance state.
With the development of the modern electronics industry, the requirements of PPTC components become increasingly high. PPTC components develop in a trend to have smaller sizes, lower resistance, and more stable performance. For low-resistance PPTC components, two types of PPTC materials presently dominate. The first type is a metal-based (for example, nickel or copper powder) PPTC material. The metal-based PPTC component has advantages such as low resistance and easy processability. However, the metal-based PPTC material is easily oxidized during production and processing and subsequent use. As a result, the resistance of a PPTC component rises to cause the PPTC component to fail (keeps decreasing current). A second type is a carbide-base (for example, titanium carbide or tungsten carbide) PPTC material. A carbide-base PPTC component has advantages of low resistance and being stable in air (is not easily oxidized in air). However, a carbide-base PPTC material has low processing performance. It is still a great challenge to use a carbide-base PPTC material to produce a PPTC device with stable quality and ultralow resistance (resistivity is less than 200 μΩ·cm).