When the motor starts, it needs to overcome its own inertia and the reaction force of the load (for example, the reaction force of the refrigerant must be overcome when the refrigerator compressor is started), so the motor needs a large current and torque when starting. When the rotation is normal, in order to save energy, the required torque will be greatly reduced. Add a set of auxiliary coils to the motor, it only works when it starts, and it disconnects when it is normal. Connect the PTC thermistor in series with the starting auxiliary coil. After starting, the PTC thermistor enters the high resistance state to cut off the auxiliary coil, which can achieve this effect.

When the circuit is in a normal state, the current passing through the PTC thermistor for overload protection is less than the rated current, and the PTC thermistor for overload protection is in a normal state, with a small resistance value, which will not affect the normal operation of the protected circuit.

When the circuit fails and the current greatly exceeds the rated current, the PTC thermistor for overload protection suddenly heats up and is in a high resistance state, making the circuit in a relatively "off" state, thereby protecting the circuit from damage. When the fault is eliminated, the PTC thermistor for overload protection also automatically returns to a low resistance state, and the circuit resumes normal operation.

The Curie temperature of the PTC thermistor sensor is from 40 to 300°C. On the RT characteristic curve of the PTC thermistor sensor, the steep rise of the resistance value after entering the transition zone can be used as a temperature, liquid level, and flow sensing. application. According to the temperature-sensitive characteristics of PTC thermistors, it is designed to be used in overheat protection and temperature sensing occasions, and is used in switching power supplies, electrical equipment (motors, transformers), power devices (transistors). It is characterized by small size and fast response time. , Easy to install.