1. Application of PTC thermistors
1. Delayed start PTC thermistors
From the I-t characteristic curve of the PTC thermistor, it is known that after the voltage is applied, the PTC thermistor needs a period of time to reach the high resistance state. This delay characteristic is used for delayed start purposes.
Application principle
When the motor starts, it must overcome its own inertia and the reaction force of the load (such as the reaction force of the refrigerant must be overcome when the refrigerator compressor starts), so the motor needs a large current and torque when starting.
When the rotation is normal, in order to save energy, the required torque must be greatly reduced. Add a set of auxiliary coils to the motor, which only works at startup and is disconnected after normal operation.
Connecting the PTC thermistor in series with the starting auxiliary coil, the PTC thermistor enters a high resistance state after startup to cut off the auxiliary coil, which can achieve this effect.
2. Overload protection PTC thermistor
The overload protection PTC thermistor is a protective element that automatically protects and recovers from abnormal temperature and abnormal current, commonly known as "self-resetting fuse" and "ten thousand times fuse".
It replaces traditional fuses and can be widely used in overcurrent and overheat protection of motors, transformers, switching power supplies, electronic circuits, etc. The overload protection PTC thermistor reduces the residual current value by limiting the consumption in the entire circuit through its resistance mutation.
Traditional fuses cannot recover by themselves after the circuit is blown, while the overload protection PTC thermistor can recover to the pre-protection state after the fault is removed, and can realize its overcurrent and overheat protection function when the fault occurs again.
When selecting a PTC thermistor for overload protection as an overcurrent and overheat protection element, first confirm the maximum normal operating current of the circuit (that is, the non-operating current of the PTC thermistor for overload protection) and the maximum ambient temperature of the installation location of the PTC thermistor for overload protection (during normal operation), followed by the protection current (that is, the operating current of the PTC thermistor for overload protection), the maximum operating voltage, and the rated zero-power resistance. At the same time, factors such as the size of the component should also be considered.
Application principle
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 very small resistance value, which will not affect the normal operation of the protected circuit.
When a circuit fails and the current greatly exceeds the rated current, the PTC thermistor for overload protection suddenly heats up and becomes high-resistance, making the circuit relatively "disconnected" and thus 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.
3. Overheat protection PTC thermistor
The Curie temperature of the PTC thermistor sensor ranges from 40-300℃. On the R-T characteristic curve of the PTC thermistor sensor, the section where the resistance value rises sharply after entering the transition zone can be used for temperature, liquid level, and flow sensing.
According to the temperature-sensitive characteristics of the PTC thermistor, it is designed for overheat protection and temperature sensing, and is applied to switching power supplies, electrical equipment (motors, transformers), and power devices (transistors). It is characterized by small size, fast response time, and easy installation.
Wolong Nanyang Explosion Protection, three-phase asynchronous motor, high voltage explsion proof motor
