In the design of LED lighting power supply, there are several design challenges: the common life of electrolytic capacitors and LEDs are not matched, the common causes and treatments of LED flashing, the effect of PWM dimming on the life of LEDs, and the use of TRIAC dimming to control LEDs.
A potential problem with brightness. Zheng Zongqian, senior application engineering manager of ON Semiconductor, discussed the causes and solutions of these problems in the article.
The problem that the life of the electrolytic capacitor does not match the LED
An important consideration for LED lighting is that the LED driver circuit and the LED itself should have a comparable working life. Although there are many factors that affect the reliability of the drive circuit, electrolytic capacitors have a crucial impact on overall reliability. In order to extend the operating life of the system, it is necessary to analyze the capacitance in the application in a targeted manner and select the appropriate electrolytic capacitor.
In fact, the effective operating life of an electrolytic capacitor is largely affected by the ambient temperature and the internal temperature rise caused by the ripple current acting on the internal impedance.
Electrolytic capacitor manufacturers offer electrolytic capacitors rated for life based on exposure to the highest rated temperature environment and application of maximum rated ripple current. The typical capacitor rating life at 105 ° C may be 5,000 hours, the actual operating stress experienced by the capacitor is lower than the rated level, and the effective working life is longer.
Therefore, on the one hand, selecting an electrolytic capacitor with a long rated working life and capable of withstanding a high rated operating temperature can of course prolong the working life. On the other hand, depending on the actual stress and operating temperature, capacitors with lower rated operating temperature and rated life can still be selected to provide a lower cost solution; in other words, proper stress and operating temperature are considered in the design. It can effectively extend the working life of the electrolytic capacitor, making it more compatible with the LED life.
For example, ON Semiconductor’s off-line LED driver GreenPoint® reference design meets the ENERGY STAR solid-state lighting standard. Panasonic’s ECA-1EM102 aluminum electrolytic capacitor is rated at 1,000μF, 25V, 850 mA, 2,000. Hours and 85 ° C. The available life of this capacitor exceeds 120,000 hours under the assumption of an ambient temperature of 50 °C.
Therefore, the best way to make the LED driver circuit work under suitable temperature conditions and properly handle the heat dissipation problem can achieve the matching problem between the LED driver circuit and the LED working life.
In general, if an electrolytic capacitor must be used in the LED driver circuit, efforts must be made to control the applied force and operating temperature of the capacitor to maximize the capacitor operating life in order to match the LED lifetime.