How to increase the reliability of LED lighting systems

An important reason for the low life of LED driver power supply is that the life of the aluminum electrolytic capacitor required by the driver power supply is insufficient. The main reason is that the ambient temperature inside the LED lamp is very high during long-term operation, which causes the electrolyte of the aluminum electrolytic capacitor to be quickly consumed and greatly shorten its life, generally only about 5,000 hours. The life of the LED light source is 50,000 hours, so the working life of the aluminum electrolytic capacitor becomes the shortcoming of the life of the LED driver power supply.

To solve this problem, some suppliers have invented LED driver solutions without aluminum electrolytic capacitors. However, not all LED driver suppliers agree with this approach. Chen Rong pointed out: "There is no LED driver currently in mass production that uses a driver solution without electrolytic capacitors, because without it, many test standards cannot be passed, such as EMI test and flicker-free test."

The LED driver power solution using aluminum electrolytic capacitors is easy to test above. What if it is replaced with film capacitors, ceramic capacitors or tantalum capacitors? To achieve the same capacitance (usually 100-220uF), the film capacitor will be very large and the cost is too high. The capacity of ceramic capacitors is generally too small. If multiple ceramic capacitors are used to achieve such a large capacity, the board area and cost are too large. Tantalum capacitors have such a large capacity. First, they are too expensive, and the withstand voltage is too low to meet the requirements. Therefore, if it is replaced with any other type of capacitor, it is basically either too large or too expensive. If it is replaced with a smaller capacitor for these shortcomings, the effect of eliminating ripples is not so good, and many export products cannot pass the strict certification test indicators. Therefore, high-quality LED driver power supplies still generally use aluminum electrolytic capacitors.

The electrolytic capacitor-free LED driver power supply solutions claimed by many suppliers may only remove the aluminum electrolytic capacitor at the AC input end. The aluminum electrolytic capacitor at the constant current output end should be difficult to remove or replace.

NXP has launched a 13W LED bulb with built-in driver power supply and TRIAC dimming. This driver power supply solution based on SSL2102 uses aluminum electrolytic capacitors. When the author asked about the working life of the bulb, the working life of the aluminum electrolytic capacitor will definitely affect the life of the entire LED bulb, but some physical methods can be used to alleviate this problem, such as placing the aluminum electrolytic capacitor close to the tail of the lamp on the PCB. Generally speaking, the temperature of the part closest to the LED light source is the highest, which can reach 100-200℃, and the heat dissipation metal shell part is second, generally around 100℃, and the tail of the lamp is the lowest, generally around 70℃. Therefore, as long as you pay attention to placing the aluminum electrolytic capacitor close to the tail of the lamp, its life will not decay too much. Our experiments show that its life can reach about 10,000 hours, which is equivalent to 10 years of use. For ordinary household users, it is basically acceptable to replace LED bulbs once every ten years.

In terms of the architecture of LED driver power supply, Chen Rong said that Japan and the United States will adopt non-isolated solutions as the mainstream because their grid input voltage is only 110V. China and Europe will adopt isolated solutions as the mainstream because their grid input voltage is as high as 220V. The safety of isolation solutions is guaranteed, although the cost may be higher.