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LED driver: lighting applications heat dissipation is still bullish technical problems 2

The first two levels are usually designed and manufactured by the power company, is a relatively independent power supply, providing a stable DC voltage to the lamps, while the third level by the LED system manufacturers own design, with light to form a whole. As the third-stage circuit and the heat of the LED with a serious, demanding conversion efficiency. Indoor lighting is usually single-level structure, although the need for PFC has not yet conclusive, but the industry has generally agreed that if we changed all the traditional incandescent LED, harmonic pollution on power quite a lot, it is necessary PFC; have incandescent and fluorescent lamps and dimmers are installed is complete, and dress up the LED lamps must be dimmer and the original matching; In addition, depending on the application, the drive circuit can be isolated or may not isolation. "
    To be done to extend the life of
    - solve the heat problem is the key to extend the LED life
    - LED device protection thermistor bear responsibility
    LED service life of the product is of great concern to consumers, and even view a short piece of driving circuit boards for LED products have become "short-lived." Zheng Zhaoxiong told reporters: "LED product itself has a long service life, if the reliability of the lower drive circuit will affect their life, thereby affecting the life of the entire lighting system. Provide high reliability of the drive circuit itself is not difficult The hard part is maintaining the high reliability while lowering costs. Therefore, the designer select the appropriate LED drive and external components is particularly important to ensure that the drive circuit and LED reliability and life of the reliability and life match. "appears in Lee Peng to solve life problems is subject to the power according to the different devices to be selected, he said, according to the power from low to high, respectively non-isolated step-down, isolated flyback PSR, single stage flyback, quasi-resonant, and LLC half-bridge topology to achieve higher efficiency, constant current control to achieve precise. "In the lighting field, the drive circuit of the greatest difficulty is how to solve the heat problem." Remote office, said, "If the poor heat dissipation, the circuit electrolytic capacitor life will be greatly reduced, will seriously affect the life span of LED products. Solutions include improve the driving circuit efficiency and cooling capacity, in the circuit through a number of unique design can even remove the electrolytic capacitor. "Jian-Xing Wu believes that, LED lighting is a system, the LED, electronic systems, cooling systems etc., these three are inseparable; LED life requires a stable input voltage, constant output current, less than 60 ,, of ambient temperature can be reflected.
    In addition to improving system efficiency, the industry has to consider the use of special devices for protection of the LED to enhance the system's life. Tyco Electronics Circuit Protection Division Director Senior Application Manager? In the "China Electronics News" interview, said: "LED performance and lifetime of the PN junction LED is closely related to temperature, on the effective control of LED junction temperature is protection of the fundamental requirements of LED. Although the technology is constantly popular, but LED lighting LED lighting manufacturers continued to overcome the strong thermal sensitivity problem. excessive or improper application of heat will cause the LED light source performance greatly reduced. When the LED chip junction temperature of 10 degrees Celsius, the flux will decay 1%, LED life to reduce by 50%. over-current, over voltage and over temperature will significantly reduce the LED's light performance and reduced service life. So, in addition to good thermal design, the safe and reliable thermal protection and must be taken into account. "According to Dong? introduction, Tyco Electronics, the first time in 1980, PPTC (polymeric positive temperature coefficient) material used to protect the thermistor circuit. This single-device options can be due to damage caused by improper use of power to provide protection, and have transient suppression, reverse bias capability to protect, but also prevent damage due to over-current events can be reset LED PPTC device can prevent lighting applications in the over-current and over-temperature fault damage.

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