标签：LED lamp design

Solution for LED lamp design failure

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.

Solution for LED lamp design failure

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.

LED lamp design failure analysis

At present, although the theoretical life of the LED can be achieved 50kh, however, in actual use, due to various factors, LED lights often amounted to less than such a theory of life, premature failure phenomenon, which greatly hindered the LED as a new energy-saving the pace of the products. LED lamp design failure carry out systematic analysis, and proposed some improvement measures, and to expect to be able to improve the actual service life of the LED.

LED lamp design failure analysis

一、LED spot failure modes

LED failure modes: chip failure, the package fails, the thermal stress failure, electrical overstress failures and assembly failure, especially in chip failure and package failure is most common. The text will analyze these types of failure modes.

一、LED grow lights chip failure modes

Chip failure refers to the chip itself get failure or other causes chip failure. The reason of this failure are many: the die crack is due to improper bonding process condition, resulting in a larger stress, with the accumulation of heat generated by the thermo-mechanical stress, with the accumulation of heat generated by the term-mechanical stress also will strengthen, causing the chip to produce micro-cracks, work when injected into the current will be further exacerbated by the micro crack expanding until the device fails completely. Second, if the chip active are injured, it will lead to gradual degradation during power-up failure, the same can also cause the lamps in the use of a coherent state of serious decline until it does not shine. Furthermore, if the chip bonding technology is bad, chip bonding layer is completely out of the bonding surface and the sample will open to lapse. The same will cause the LED lamp design in the course of “dead light” phenomenon occurs. The bad chip bonding process may be due to the use of silver paste expired or the exposure time is too long, silver paste is too small, the curing time is too long, solid crystal base surface contaminated.

(2) package failure

Package failure is improper package design or production processes lead to device failure. Epoxy materials, packaging occur in the course of the degradation problem, resulting in reduced life of the LED.