Electric iron（4）

PTC element refers to the thermistor with positive temperature coefficient, which is made of barium titanate as the main raw material, and adding trace rare earth elements, using semiconductor ceramic technology. The resistance-temperature characteristic of the PTC element, as the temperature increases, its resistance has a minimum value (the corresponding temperature point is the Curie point) and a maximum value. In the positive temperature coefficient range, the current flowing through the element increases, the electric power increases, and the temperature of the element increases, which increases the resistance value, which causes the current to decrease and the electric power to decrease. When the temperature rise caused by the electric power is balanced with the heat dissipation, the temperature and resistance will no longer change.

This automatic control function of PTC components is often used for current control and temperature control of electronic equipment, and is also used to manufacture constant temperature heaters, such as electronic soldering irons, dryers, and mosquito killers. The volt-ampere characteristics of PTC components can be inferred from the resistance-temperature characteristics. If the current flowing through the PTC element suddenly increases for some reason, the sudden increase in electric power will quickly make the element high resistance, and the current will drop to close to zero, which will play a "self-limiting" effect on current and temperature. Therefore, PTC components can be used for over-current protection and over-heat protection of electronic equipment, such as over-heat protection of motors. The current-time characteristic of the PTC element shows that the current has a delay from large to small. This delay function is often used for starting motors and refrigerator compressors. Connect the PTC element in series in the start winding. When the power is turned on, the PTC element is in a low resistance state, so a large current flows through the start winding group. After starting, the PTC element is in a high-impedance state, so the current is very small, and there is only a large current in the running winding. In short, the structure and parameters of PTC components are different and can be applied to different occasions.