The development of high-power LED lighting solutions manufacturer currently experiencing the biggest design challenge is the thermal design and thermal overload protection, they must overcome ‘s LED lights source is sensitive to heat problems, and will cause excessive heat or improper application of the performance of the LED light source be discounted.
Theory and practice has proven that LED performance and life expectancy is closely related to the PN junction temperature of the LED. When the LED chip junction temperature rise of 10 ° C, the luminous flux will decay to 1%, 50% reduction in the life of the LED, overcurrent, overvoltage and overheating will significantly reduce the performance and service life of the LED street light. Therefore, in addition to good thermal design, safe and reliable overheating protection must be considered.
Usually on the LED, about 20% of the input power is converted to light, 80% is converted to heat. This depends on many factors, fever may be related to the underlying irregular and phonon emission, seal materials. 90% of the total heat generated by the LED, by conduction transmission. Dissipation of heat from the LED junction, conduction is the thermal conductivity of the main channel, convection and radiation is only about 10% of all heat transfer.
Obviously, LED light source requires accurate power and thermal management systems, as compared with other light sources to provide electricity to the LED most of the conversion to heat. Without proper thermal management, heat will affect the LED life and color output. The same time, due to the LED driver devices are silicon devices, they will soon fail. This must be equipped with fail-safe backup overcurrent protection devices.
So why the success of high-power LED lighting design can not be separated from PPTC? Many people think that the LED driver can provide overcurrent and overtemperature protection is not necessary to add a PPTC device in the external, because it would add additional cost. But this is wrong, many of the LED driver is easy to be damaged due to DC voltage and polarity errors. LED driver outputs will damaged or destroyed due to short circuit. Although most LED drivers contain built-in security features include thermal shutdown, open LED and short circuit detection. However, to protect the integrated circuit (IC) and other sensitive electronic components, and may require additional overcurrent protective device. Therefore, only the PPTC (especially resettable PolySwitch PPTC) is to prevent overheating damage to the most appropriate solutions in the high-power LED down lights.
To illustrate this problem, we first look at a typical LED driver to provide what protection function. The most high-power LED constant current drive to provide the typical protection features include: thermal shutdown protection, overvoltage / overcurrent comparator, high-current MOSFET, the current size of the adjustment, a certain level of ESD protection. However, the thermal shutdown feature is just a self-protection function, it is difficult to be applied to the LED overheat designed to protect. Overvoltage / overcurrent protection characteristics of the need for external overvoltage protection circuit, turn off the power may cause other problems. High-current MOSFET failure modes are usually short-circuit, which is potentially unsafe factors. LED dimming with the current regulation characteristics may cause the LED over-temperature.
But the concept of the the PPTC the protection of high-power LED is different, it has the following four unique advantages:
1) failure mode is a high-impedance, even in the fault state, LED is safe.
2) PPTC can directly measure the temperature of the LED, so you can close protection.
3) PPTC can be achieved over temperature, overcurrent and overvoltage protection. Very easy to use, does not require an external circuit. LED, even in protected state can work.
4) allows designers to lower cost, dimming design, without worrying about security issues. Therefore outside of the LED driver with a PPTC device can achieve stronger security, and meet the most stringent safety standards and to achieve cost reduction.