Popularize of LED lamps must design method
2012/11/15
LED with its unparalleled energy-saving, environmental protection, long life, high controllability technology advantages, in recent years become the world's most promising high-tech one, officially opened the prelude to a comprehensive alternative to traditional lighting, semiconductor lighting technology innovation is changing centuries the history of traditional lighting. With the application of LED technology in the lighting field, LED lighting products in the world set off a storm of green energy saving, green lighting products industry as. Increasing energy consumption, and some even predicted: "in the next 10 years, LED lighting products will be the only product to replace the traditional high-pressure sodium lamps, incandescent lamps, fluorescent lamps, table lamps lighting LED lamps to be universal, not only need to substantially reduce costs, but also need to address the problem of energy efficiency and reliability, and how to solve these problems, share the design of high efficiency and high reliable LED lamps.

Do not use the bipolar power devices

Experts pointed out that the bipolar power devices are cheaper than the MOSFET, generally about 2 cents, so some designers use bipolar power devices in order to reduce the cost of LED driver, this will seriously affect the reliability of the circuit, because with LED drive circuit board temperature enhance effective working range of the bipolar device is rapidly shrinking, this will lead to device failure in the temperature rise which affects the reliability of the LED lamps, the correct approach is to choose MOSFET devices, the service life of the MOSFET devices much longer than bipolar devices.

Try not to use electrolytic capacitors

LED driver circuit Do not use electrolytic capacitors in the end? Supporters and opponents, supporters believe that the board temperature control, turn to reach the purpose to extend the life of electrolytic capacitors, for example, choose a life span of 105 degrees for a high temperature of 8000 hours electrolytic capacitor, electrolytic capacitor life estimation formula based on prevailing "temperature 10 degrees lower doubling of life expectancy, it is to work in an environment of 95 degrees life of 16,000 hours, 32,000 hours working life in an environment of 85 degrees in 75 Degree of working life of 64,000 hours, if the actual operating temperature is lower, then life will be longer! Seen in this light, as long as the selection of high-quality electrolytic capacitor drive power of life is not any impact.

Without electrolytic capacitors in the input section of the LED driver circuit can be considered, in fact, using PI's LinkSwitch-PH electrolytic capacitors can be omitted, PI single-stage PFC / constant current design allows designers to eliminating the need for large-capacity capacitor, the output circuit high voltage ceramic capacitors instead of electrolytic capacitors so as to enhance the reliability of some people in the design of two circuit output using a 400V electrolytic capacitor, which can seriously affect the reliability of the circuit, we recommend using the single the level circuit ceramic capacitors can. Design is not too concerned about the dimming function, high-temperature environment and the need for high-reliability industrial applications, it is strongly recommended to not use electrolytic capacitors.

Not to use voltage 600V MOSFET

The voltage 600V MOSFET cheaper, many believe that the input voltage of the LED lamps generally 220V, so enough voltage 600V, but many times the circuit voltage to 340V, 600V the MOSFET is easily surge breakdown LED lamps, thus affecting the life, in fact chosen 600VMOSFET may save some costs but pay is the cost of the entire board, therefore, the porcelain library experts recommend not to use the 600V breakdown voltage MOSFET best voltage over 700V of the MOSFET.

To make use of a single-level structure circuit

Doug said some LED circuit using a two-tier structure, 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's is 95%, while the efficiency of the DC / DC part is 88%, the efficiency of the circuit as a whole will be reduced to 83.6%! "PI's LinkSwitch-PH devices at the same time of the PFC / CC controller, a 725VMOSFET and MOSFET driver integrated into a single package, the efficiency of the drive circuit of the upgrade to the 87%! "Doug pointed out," this device can greatly simplify circuit board layout design up can eliminating the need for traditional isolated flyback design, the use of 25 elements ! the omitted elements include high voltage electrolytic bulk capacitor and the optocoupler. "Doug said the LED level two framework applicable to the PFC must use a second constant current drive circuit to drive old drive LED constant current. These design is outdated and no longer cost-effective, and in most cases are the best single-stage design.
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