Detailed PTC thermistor

Parallel thermistor / NTC thermistor / product complete / Sunlord first-class agent

NCP18XH103F03RB MURATA Murata thermistor original spot

We know that the abnormal increase of current often occurs in the circuit, which is generally caused by abnormal power supply or reduced load impedance in the line. For example, if the power supply voltage in the circuit is too high or too low, the line is connected to other power sources, the load short circuit connection error has occurred, and lightning, external transient current, etc. may cause abnormal current increase in the circuit. This overcurrent is very likely to cause damage to the electronic components in the circuit, making the circuit not working properly.

Polymer PTC thermistors (self-recovery fuses, hereinafter referred to as thermistors) are extremely suitable for use as overcurrent protection devices due to their unique positive temperature coefficient resistance characteristics (ie, PTC characteristics, as shown in Figure 1). The thermistor is used in the same way as a normal fuse, as shown in Figure 2.

When the circuit works normally, the thermistor temperature is close to room temperature and the resistance is very small. The series connection in the circuit does not hinder the current from passing through; and when the circuit has an overcurrent due to the fault, the thermistor increases the temperature due to the increase of the heating power. When the temperature exceeds the switching temperature (Ts, see Figure 1), the resistance becomes very large instantaneously, limiting the current in the circuit to a very low level. At this time, almost all of the voltage in the circuit is applied to both ends of the thermistor, so that it can protect other components. When the human is cut off the circuit to eliminate the fault, the resistance of the thermistor will quickly return to the original level. After the circuit is removed, the thermistor can be used without replacement. Figure 3 is a schematic diagram showing the change of current during the protection of the thermistor to the AC circuit. After the thermistor is activated, the current in the circuit is greatly reduced.

In the figure, T is the operating time of the thermistor. Because the polymer PTC thermistor has good designability, it can adjust its sensitivity to temperature by changing its switching temperature (Ts), so it can play both over-temperature protection and over-current protection, such as HY16. The -1700DL specification thermistor is suitable for overcurrent and overtemperature protection of Li-Ion and NiMH batteries due to its low operating temperature.

The polymer PTC thermistor is a conductive polymer material with positive temperature coefficient characteristics. The most significant difference between it and the conventional fuse is that the former can be reused many times. Both products provide overcurrent protection, but the same polymer PTC thermistor provides this protection multiple times, and the fuse must be replaced with another one after providing overcurrent protection.

The main difference between a polymer PTC thermistor and a bimetal circuit breaker is that the former does not reset until the accident is not eliminated, but the bimetal circuit breaker can reset itself when the accident still exists. This can result in electromagnetic waves and sparks at reset. At the same time, reconnecting the circuit in the event of a fault in the circuit can damage the device and is therefore unsafe. The polymer PTC thermistor can maintain a high resistance state until troubleshooting.

The difference between a polymer PTC thermistor and a ceramic PTC thermistor lies in the initial resistance of the component, the operating time (reaction time to an accident event), and the difference in size. Polymer PTC thermistors with the same holding current Compared with ceramic PTC thermistors, polymer PTC thermistors are smaller in size, lower in resistance, and faster in response.