Five tips for designing efficient and reliable LED lamps
in 2011, 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, with the EU countries, Japan, Canada and other countries will ban the use of incandescent lamps in 2012, the lighting penetration rate of LED lamps will further improve, This makes thousands of LED lamp manufacturers in China who have made the Nuggets green lighting revolution rejoice - because a huge market is about to open, and this time the Chinese manufacturers are playing the leading role. However, it should be noted that in order to popularize LED lamps and lanterns, we not only need to significantly reduce costs, but also need to solve the problems of energy efficiency and reliability. How to solve these problems, Doug Bailey, vice president of marketing of power integrations, shared five tips for the design of efficient and reliable LED lamps and lanterns
first, don't use bipolar power devices
doug Bailey pointed out that because bipolar power devices are cheaper than MOSFETs, usually about 2 cents. In order not to affect our experimental results and prolong the service life of experimental equipment, some designers use bipolar power devices in order to reduce the LED drive cost, which will seriously affect the reliability of the circuit, because with the increase of the temperature of the LED drive circuit board, The effective working range of bipolar devices will be rapidly reduced, which will lead to device failure when the temperature rises, thus affecting the reliability of LED lamps. The correct way is to choose MOSFET devices, whose service life is much longer than that of bipolar devices
second, do not choose 600V MOSFETs. 600V MOSFETs are relatively cheap. Many people think that the input voltage of LED lamps is generally 220V, so 600V is enough, but many times the circuit voltage will reach 340v. When there is a surge, 600V MOSFETs are easy to be broken down, which affects the life of LED lamps. In fact, choosing 600V MOSFETs may save some costs, but it pays the price of the whole circuit board, Therefore, "do not choose a 600V withstand voltage MOSFET, and it is best to choose a MOSFET with a withstand voltage of more than 700V." He emphasized
third, try not to use electrolytic capacitors
? At present, there are supporters and opponents. Supporters believe that if the temperature of the circuit board can be controlled well, and the purpose of prolonging the service life of electrolytic capacitors can be achieved in turn. For example, a high-temperature electrolytic capacitor with a service life of 8000 hours at 105 degrees can be selected. According to the current electrolytic capacitor service life estimation formula "the service life will be doubled for every 10 degrees of temperature reduction", then its service life will be 16000 hours at 95 degrees and 32000 hours at 85 degrees, The working life is 64000 hours at 75 degrees. If the actual working temperature is lower, the service life will be longer! From this point of view, as long as the selection of high-quality electrolytic capacitors has no impact on the service life of the driving power supply
some supporters believe that the low-frequency flicker caused by the high ripple current brought by the non electrolytic capacitor will cause physiological discomfort to some human eyes, and the large low-frequency ripple will also cause some digital camera equipment to appear the bright and dark grids of differential 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, thereby affecting the life of LED lamps
in this regard, Doug Bailey believes that electrolytic capacitors can be considered not to be used in the input part of the LED drive circuit. In fact, electrolytic capacitors can be omitted by using PI's linkswitch pH. Pi's single-stage pfc/constant current design allows designers to omit large capacity capacitors. In the output circuit, high voltage withstand ceramic capacitors can be used to replace electrolytic capacitors to improve reliability, "When designing a two-stage circuit, some people use a 400V electrolytic capacitor at the output, which will seriously affect the reliability of the circuit. It is recommended to use a ceramic capacitor for a single-stage circuit." He emphasized. "For industrial applications that do not pay much attention to the dimming function, high temperature environment and need high reliability, I strongly recommend not to use electrolytic capacitors for design."
use the 5 W A19 drive circuit scheme (rdk-251) designed by linkswitch pl.
fourth, try to use integrated mo. while implementing the national and provincial inclusive policies, SFET
if the designed LED lamp power is not very high, Doug suggests that the future growth trend of smart energy should be worth waiting for the LED driver products with integrated MOSFETs, because the advantage of doing so is that the on resistance of integrated MOSFETs is less, and the heat generated is less than that of discrete ones, In addition, the integrated MOSFET is the controller graphene biological device: because graphene has the characteristics of modifiable chemical function, large contact area, atomic size thickness, molecular gate structure and so on, it generally has the function of overheating shutdown. When the MOSFET overheats, it will automatically turn off the circuit to protect the LED lamps. This is very important for LED lamps, because LED lamps are generally small and difficult to heat the air. "Sometimes, people will be injured by overheated led combustion, but our scheme has never been like this." He said
v. try to use a single-stage architecture circuit
doug indicates that some led circuits adopt a two-stage architecture, that is, "PFC (power factor correction) + isolated dc/dc converter", such a design will reduce the efficiency of the circuit. For example, if the efficiency of PFC is 95% and the efficiency of dc/dc part is 88%, the efficiency of the whole circuit will be reduced to 83.6%! "Pi's linkswitch pH device integrates pfc/cc controller, a 725 V MOSFET and MOSFET Driver into a single package at the same time, improving the efficiency of the drive circuit to 87%!" Doug pointed out, "such devices can greatly simplify the layout design of the circuit board, and at most 25 components used in the traditional isolation flyback design can be omitted! The omitted components include high-voltage large capacity electrolytic capacitors and optocouplers." Doug said that the LED two-level architecture is suitable for old drivers that must use the second constant current drive circuit to make PFC drive LED constant current. These designs are outdated and no longer cost-effective, so in most cases, it is best to use a single-stage design
a 14W LED drive circuit scheme with a power factor greater than 0.9 designed by PI linkswitch pH
doug revealed that Pi ranked first in the world in terms of its market share based on LED driver shipments in 2010! The use of a large number of customers enables pi to deeply understand the application trend of LED and continuously launch new products to meet the needs of customers. Looking forward to the future, he said that China's indoor LED lighting, LED fluorescent lamps and LED street lamps will be well applied in 2011