PPTC overcurrent protection and thermal protection in the LED lighting
Although many high-end LED lights driver components are gradually integrated over-current, over temperature protection function, but on many occasions, especially overheating protection, we still need discrete components of the program as a collaborative protection program, so that the lamps have a higher reliable and longer life.
The PPTC refers to the polymer positive temperature thermistor, which is of the polymer and conductive particles. After special processing, the conductive particles in the polymer chain conductive path. When the normal operating cuurrent through(or components in a normal ambient temperature), PPTC was the low resistance state; abnormal over-current through the large current(or environmental temperature (or ambient temperature), when the circuit). heat polymer rapid expansion cut off the conductive particles form a conductive path, PPTC was a high impedance state; over-current circuit (over-temperature condition) is removed, the polymer cooling. The volume is back to normal again, in which conductive particles constitute a conductive path, PPTC showing initial low resistance state. The PPTC the small size, low cost, reusable, and thus to achieve the protection function automatically starts and automatic recovery.
In LED lighting, led lamp design fixtures and led down lights to the different applications have different thermal protection requirements, usually divided into two, respectively, reaching the required temperature, such protection is usually applied to road traffic signs; Another is starting protection, which has reached a certain temperature to drop current drive, such protection is usually used in indoor lighting and road lighting.
On the mutual balance of cost and protection programs of Overcurrent and overtemperature protection in the series combination of a giant array of lighting, or landscape lights, there are usually two kinds of protection schemes are available:
1. A shut protection. For multiple strings of led lamp design systems, we can protect in every branch. The benefits of this approach can achieve accurate protection, not a slip of the fault result in the lamps failure.
2. Main road protection. This protection is in the main loop of the lamps in series a PPTC, to protect the entire lamp. The benefits of this aproach is low cost, small footprint.