Several common applications of PTC thermistors

PTC thermistor is a positive temperature coefficient thermistor that increases in resistance as the temperature increases. This kind of resistor is usually made of barium titanate, through different production processes, different applications need to be made into a special shape of the element, we often use its resistance-temperature, voltage-current and current-time characteristics of the three characteristics, different characteristics of the root cause of the different packages to be adapted to different occasions.

1.Over-voltage, over-current and overload protection

PTC over-voltage, over-current, overload protection is very widely used, PTC directly in series circuit, circuit short circuit or other reasons lead to the current, PTC thermistor can inhibit the current is too large, and even prevent the current protection required components or circuits. Mainly used in power transformers, a variety of chargers, a variety of instruments and meters, such as overcurrent and overheating protection occasions, this is the most widely used PTC thermistor application of a role, we also see more, especially in power equipment.

PTC thermistors are connected in series into the circuit as an overcurrent protection element, i.e. protection transformer. When the circuit due to a variety of reasons caused by a component or load short-circuit resulting in excessive current, at this time the PTC thermistor will play a role in inhibiting the circuit to produce excessive current. It should be noted that, in selecting the maximum reactive current and operating voltage, should also take into account the rated zero power resistance, operating temperature range and component packaging and other factors. Generally about 1.5 times the maximum operating current selected for normal operation of the circuit is appropriate.

2.Starting assistance for motors, motors, compressors, etc.

An electric motor must overcome its own inertia when starting. For example, single-phase starting, starting requires a larger torque. When the rotation is normal, the required torque is not very large, at this time, the auxiliary circuit can be added to the motor, which can be understood as an auxiliary source, equivalent to an electric car climbing a hill needs more power, the PTC thermistor series connection into the auxiliary circuit.

For example, in the case of a refrigerator compressor, the thermal resistance of the resistor becomes large at start-up, the starter winding of the compressor motor is energized, and the main winding of the compressor is run at the same time. When the resistance becomes very high, the start winding is equivalent to a disconnect and the compressor can run normally.

PTC thermistors are useful in many ways, not only for switching power supplies.

3.Color television sets, picture tubes and other demagnetization applications

The function of PTC thermistor is to eliminate the influence of color difference and stray magnetic field such as geomagnetism on color picture. The automatic degaussing circuit of an ordinary color TV generally consists of two parts: degaussing coil and degaussing resistor.PTC degaussing element works by using its current-time characteristic.

After connecting the demagnetizing circuit in series, due to the small initial resistance of the PTC element, the initial current through the demagnetizing coil is large, so that the coil produces a strong alternating magnetic field. the resistance of the PTC demagnetizing element will rise due to its own heat, and the current in the circuit will gradually decay, so that the alternating magnetic field in the coil will be weakened, so as to achieve the demagnetizing purpose. This series of products are used in the demagnetization circuits of color TVs, color TV monitors and other crt.

In addition to the above three functions, PTC thermistor also has various functions such as temperature detection and control, motor overheating protection, soldering iron constant temperature maintenance, filament preheating delay start, LED constant current compensation and so on.