Five suggestions for solving LED lighting design problems

In 2011, Australia has taken the lead in prohibiting the use of incandescent lamps, which opened the curtain for the large-scale popularity of LED lamps. In addition, with the countries of the European Union, Japan, Canada and other countries will prohibit the use of incandescent lamps in 2012, LED lighting lighting The penetration rate will further increase, which will please the thousands of LED lighting manufacturers in the Nuggets green lighting revolution in China - because a huge market is about to start, and this time the main players are Chinese manufacturers. However, it should be noted that the popularity of LED luminaires not only requires significant cost reductions, but also solves the problems of energy efficiency and reliability. How to solve these problems? Doug Bailey, vice president of marketing for Power Integrations, shared the design of highly efficient and reliable LED luminaires. Five advices.

Do not use bipolar power devices

Doug Bailey pointed out that since bipolar power devices are less expensive than MOSFETs, typically around 2 cents or so, some designers use bipolar power devices in order to reduce LED drive costs, which can seriously affect the reliability of the circuit because As the temperature of the LED driver circuit board increases, the effective operating range of the bipolar device will rapidly shrink. This will cause the device to malfunction when the temperature rises, thus affecting the reliability of the LED lamp. The correct method is to use the MOSFET device and use the MOSFET device. Lifespan is much longer than bipolar devices.

Second, do not choose to withstand 600V MOSFET

Voltage-tolerant 600V MOSFET is cheaper, many believe that the LED lamp input voltage is generally 220V, so 600V voltage enough, but many times the circuit voltage will reach 340V, in the event of a surge, 600V MOSFET is easily broken down , Which affects the life of LED luminaires. Actually using a 600V MOSFET may save some cost but it will cost the entire circuit board. Therefore, "Don't use a 600V MOSFET, and it's better to use a MOSFET that can withstand more than 700V. He stressed.

Third, try not to use electrolytic capacitors

Do you need to use electrolytic capacitors in the LED driver circuit? At present, there are supporters and opponents, and supporters believe that if you can control the temperature of the circuit board in order to achieve the purpose of extending the life of electrolytic capacitors, such as the use of high-temperature electrolytic capacitors with 105-degree life of 8000 hours, according to the prevailing electrolytic capacitor life estimation formula "For every 10 degrees lowering temperature, life expectancy doubles," then it has a working life of 16,000 hours at 95 degrees, a working life of 32,000 hours at 85 degrees, and a 64,000 hours working life at 75 degrees. The lower the operating temperature, the longer the life expectancy! From this point of view, as long as the use of high quality electrolytic capacitors has no effect on the life of the drive power supply!

Other proponents believe that the low-frequency flicker caused by the high ripple current caused by the non-electrolytic capacitor may cause physiological discomfort to some human eyes, and the large-scale low-frequency ripple may also cause some digital camera equipment to appear poor. Flashing light and dark grid. Therefore, high-quality light fixtures still require electrolytic capacitors. However, opponents believe that electrolytic capacitors will naturally age. In addition, the temperature of LED lamps is extremely difficult to control, so the life of electrolytic capacitors will inevitably decrease, which will affect the life of LED lamps.

In this regard, Doug Bailey believes that in the LED driver circuit input part can be considered without electrolytic capacitors, in fact using PI LinkSwitch-PH can eliminate electrolytic capacitors, PI's single-stage PFC / constant current design allows designers to save large Capacity capacitance, in the output circuit, can use high-voltage ceramic capacitors instead of electrolytic capacitors to improve reliability, "Some people in the design of two-stage circuit, the output uses a 400V electrolytic capacitor, which will seriously affect The reliability of the circuit, it is recommended to use a single-stage circuit with ceramic capacitors on it.” He stressed. "For industrial applications that do not care much about dimming capabilities, high temperature environments, and require high reliability, I strongly recommend that no electrolytic capacitors be used for design."

Fourth, try to use integrated MOSFET

If the designed LED lamp power is not very high, Doug recommends the use of integrated MOSFET LED driver products, because the advantage of this is that the integrated MOSFET has less on-resistance, generates less heat, and in addition, is an integrated MOSFET. It is the controller and FET together, there is generally a thermal shutdown function, when the MOSFET is overheated, it will automatically turn off the circuit to protect the purpose of LED lamps, which is very important for LED lamps, because LED lamps are generally small and difficult to air cooling . "Sometimes, it will happen that the LED burns because of overheating, but our plan will never be like this," he said.

Fifth, try to use a single-level architecture circuit

Doug said that some LED circuits use a two-stage architecture, the "PFC (power factor correction) + isolated DC / DC converter" architecture, this design will reduce the efficiency of the circuit. For example, if the efficiency of the PFC is 95% and the efficiency of the DC/DC section is 88%, the overall circuit efficiency will be reduced to 83.6%! "PI's LinkSwitch-PH device integrates the PFC/CC controller, a 725 V MOSFET, and the MOSFET driver into a single package, increasing the efficiency of the drive circuit to 87%!" Doug noted, "This device can greatly simplify the circuit The board layout design can save up to 25 components used in the traditional isolation flyback design! The omitted components include high-voltage large-capacity electrolytic capacitors and optocouplers.” Doug said that the LED two-stage architecture is suitable for the use of the second constant The flow drive circuit enables the PFC to drive the old driver of the LED constant current. These designs are outdated and no longer cost-effective, so single-stage designs are best used in most cases.

Doug revealed that PI's market share in terms of LED driver shipments in 2010 accounted for the world's largest! The use of a large number of customers allows PI to deeply understand the application trends of LEDs and can continuously launch new products that meet the needs of customers. Looking ahead, he said that in 2011 China's indoor LED lighting, LED fluorescent lamps and LED street lamps will have a very good application.