Australia has taken the lead in banning the use of incandescent lamps, which has opened the prelude to the large-scale popularization of LED lamps. In addition, as EU countries, Japan, Canada and other countries will ban the use of incandescent lamps in 2012, the popularity of LED lamps will further increase, which makes thousands of Chinese LED lamp manufacturers who are digging for gold in the green lighting revolution excited - because a huge market is about to open up, and this time it is Chinese manufacturers who play the leading role. However, it should be noted that in order to popularize LED lamps, it is necessary not only to significantly reduce costs, but also to solve the problems of energy efficiency and reliability. How to solve these problems, Doug Bailey, vice president of marketing at Power Integrations, shared five tips on the design of efficient and reliable LED lamps.

1. Do not use bipolar power devices

DougBailey指出由於双极型功率器件比MOSFET便宜，一般是2美分左右一个，所以一些设计师为了降低LED驱动成本而使用双极型功率器件，这样会严重影响电路的可靠性，因为随着LED驱动电路板温度的提升，双极型器件的有效工作范围会迅速缩小，这样会导致器件在温度上升时故障从而影响LED灯具的可靠性，正确的做法是要选用MOSFET器件，MOSFET器件的使用寿命要远远长於双极型器件。

二、MOSFET的耐压不要低於700V

MOSFET with a withstand voltage of 600V is relatively cheap. Many people think that the input voltage of LED lamps is generally 220V, so a withstand voltage of 600V is sufficient. However, in many cases, the circuit voltage can reach 340V. When there is a surge, a 600V MOSFET can easily be broken down, thus affecting the life of the LED lamp. In fact, choosing a 600V MOSFET may save some costs, but the price paid is the entire circuit board. Therefore, "do not choose a 600V MOSFET. It is best to choose a MOSFET with a withstand voltage of more than 700V." He emphasized.

 

3. Try not to use electrolytic capacitors

LED驱动电路中到底要不要使用电解电容？目前有支持者也有反对者，支持者认为如果可以将电路板温度控制好，依次达成延长电解电容寿命的目的，例如选用105度寿命为8000小时的高温电解电容，根据通行的电解电容寿命估算公式“温度每降低10度，寿命增加一倍”,那麽它在95度环境下工作寿命为16000小时，在85度环境下工作寿命为32000小时，在75度环境下工作寿命为64000小时，假如实际工作温度更低，那麽寿命会更长！由此看来，只要选用高品质的电解电容对驱动电源的寿命是没有什麽影响的！

Some supporters believe that the low-frequency flicker caused by the high ripple current without electrolytic capacitors will cause physiological discomfort to some people's eyes, and the large amplitude low-frequency ripple will also cause some digital camera equipment to have light and dark grids with difference frequency flicker. Therefore, high-quality light source lamps still need electrolytic capacitors. However, opponents believe that electrolytic capacitors will age naturally. In addition, the temperature of LED lamps is extremely difficult to control, so the life of electrolytic capacitors will inevitably be reduced, thus affecting the life of LED lamps.

对此，DougBailey认为，在LED驱动电路输入部分可以考虑不用电解电容，实际上使用PI的LinkSwitch-PH就可以省去电解电容，PI的单级PFC/恒流设计可以让设计师省去大容量电容，在输出电路中，可以用高耐压陶瓷电容来代替电解电容从而提升可靠性，“有的人在设计两级电路的时候，在输出采用了一个400V的电解电容，这会严重影响电路的可靠性，建议采用单级电路用陶瓷电容就可以了。”他强调。“对於不太关注调光功能、高温环境及需要高可靠性的工业应用来说，我强烈建议不采用电解电容进行设计。”

4. Use MOSFET devices as much as possible

If the power of the designed LED lamp is not very high, Doug recommends using LED driver products with integrated MOSFET, because the advantage of doing so is that the on-resistance of the integrated MOSFET is small, and the heat generated is less than that of the discrete one. In addition, the integrated MOSFET is the controller and FET together, and generally has an overheat shutdown function. When the MOSFET is overheated, it will automatically shut down the circuit to protect the LED lamp, which is very important for LED lamps, because LED lamps are generally very small and difficult to dissipate air. "Sometimes LEDs may burn and injure people due to overheating, but our solution will never be like this." He said.

5. Try to use single-stage architecture circuit

Doug表示有些LED电路采用了两级架构，即“PFC（功率因数校正）+隔离DC/DC变换器”的架构，这样的设计会降低电路的效率。例如，如果PFC的效率是95%,而DC/DC部分的效率是88%,则整个电路的效率会降低到83.6%!“PI的LinkSwitch-PH器件同时将PFC/CC控制器、一个725VMOSFET和MOSFET驱动器集成到单个封装中，将驱动电路的效率提升到87%!”Doug指出，“这样的器件可大大简化电路板布局设计，最多能省去传统隔离反激式设计中所用的25个元件！省去的元件包括高压大容量电解电容和光耦器。”Doug表示LED两级架构适用於必须使用第二个恒流驱动电路才能使PFC驱动LED恒流的旧式驱动器。这些设计已经过时，不再具有成本效益，因此在大多数情况下都最好采用单级设计。