How to Apply Positive Temperature Coefficient (PTC) Thermistors

A PTC component refers to a thermistor whose resistance increases with rising temperature. Before reaching a specific temperature, the resistance of a PTC component changes very slowly with temperature. Once this temperature is exceeded, the resistance sharply increases, leading to a dramatic change. This critical temperature is called the Curie point temperature, which is one of the key indicators of a PTC component (typically ranging from 120°C to 165°C).

PTC components are widely used in applications such as temperature compensation, overheat protection, automatic temperature regulation and control, and constant temperature heaters. Currently, PTC components are also extensively employed as heating elements in household appliances, including electric foot warmers, electric slippers, and electronic mosquito repellents.diode

The following section primarily introduces the application methods of PTC thermistors in refrigerators and color televisions.

1) PTC thermistor controls the starting current of the refrigerator compressor  A PTC thermistor is connected in series with the starting winding of the refrigerator compressor (as shown in Figure 1). When the refrigerator starts, the full power supply voltage is applied to the starting winding. At this point, the PTC thermistor can reduce the current from approximately 7A to around 4A within 0.4 seconds, and then further decrease the starting winding current to about 15A in about 3 minutes. During this process, the running winding has already entered normal operating conditions.  Figure 1 Application of PTC in the refrigerator starting circuit

PTC thermistors used in refrigerator start-up circuits, with a rated voltage above 250V and a nominal resistance of 20~40nΩ, have a steady-state power consumption (4W2). The application of PTC thermistors in color TV demagnetization circuitsdiode

Figure 2 shows the application of PTC in the degaussing circuit of color TVs. When a color TV is powered on, the degaussing circuit generates a large current and a strong alternating magnetic field. The PTC thermistor connected in series in the degaussing circuit rapidly attenuates this strong alternating magnetic field to an extremely weak level within a short time. As the current in the degaussing circuit decreases from high to low, the magnetic field weakens correspondingly, automatically eliminating residual magnetism from iron components such as the cathode cover and explosion-proof band of the color picture tube.diode