Analysis: The Importance of PPTC Devices in LED Lighting Products

Under the background that LED lighting is more and more widely used, PPTC will once again show its strength in LED technology. Although many drive devices have gradually integrated protection functions such as overcurrent and overvoltage, in many cases, especially overheat protection, discrete component solutions are still needed.

PPTC full polymer positive temperature coefficient device, its working condition is similar to a switch, when the fault occurs, PPTC heat, resistance increases, thereby protecting the device from damage; troubleshooting, PPTC reset, return to ground resistance state. Not strictly speaking, the PPTC is a "self-healing fuse." Sounds like a fuse? The difference is that after the fuse is disconnected, there is almost no current in the circuit, and after the PPTC is actuated, there is a small holding current in the circuit, and the current size is determined by the typical power consumption of the PPTC. For LED lighting applications, the threat of overvoltage comes from many aspects, such as voltage fluctuations, instant switching noise, and induced lightning strikes and ground potential kickbacks. Overvoltages can cause overheating, PN junction damage, reverse breakdown, and even burnout.

Overflow will also bring a series of problems. High current does not represent high brightness, and sometimes the operating current is reduced, bringing about an increase in performance and lifetime. The thermal effect is also an issue that cannot be avoided in LED lighting. When the junction temperature in the LED chip rises by 10 degrees Celsius, the luminous flux will be reduced by 1%, and the LED life will be reduced by 50%. In addition to the thermal design, overheat protection is a factor that must be taken into account.

For PPTC devices, its failure mode is high-impedance, good security; it can directly measure the temperature of the LED, to achieve closed-loop protection. PPTC can achieve overheating, overcurrent or even overvoltage protection, no external circuit, easy to use. Even in the protected state, the LED lights are not all extinguished, and for engineers, the current dimming design can be more safely achieved. The PPTC itself is hotter, and with the closeness of the LED heat, the protection speed is relatively faster. In addition, the PPTC product has more package forms and can be packaged according to customer requirements. Therefore, the flexibility is very strong. However, PPTC is not a standard product. It is necessary to study the implementation and layout strategies according to the different conditions of the system. So after-sales service has become a key.