Design methods necessary for popularization of LED lamps

LED has become one of the high and new technologies with development prospects in recent years due to its technical advantages of energy saving, environmental protection, long service life and high controllability, officially opening the prelude to comprehensively replacing traditional lighting, semiconductor Lighting Technology innovation is changing the history of traditional lighting for 100 years. With the application of LED technology in the field of lighting, LED lamp products have set off a green storm of energy conservation and environmental protection, and have been praised as green lighting products by the industry. In today's increasingly high energy consumption, some even predict that in the next 10 years, LED lamp products will replace traditional lighting products such as high-pressure sodium lamps, incandescent lamps, fluorescent lamps, desk lamps, etc. To popularize LED lamps, not only the cost needs to be greatly reduced, but also the problems of energy efficiency and reliability need to be solved. How to solve these problems and share the design methods of high-efficiency and high-reliability LED lamps together. Do not use bipolar power devices experts point out that because bipolar power devices are cheaper than MOSFET, usually about 2 cents, some designers use bipolar power devices in order to reduce LED driving costs, this 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 the bipolar device will be rapidly reduced, this will cause the device to fail 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. Try not to use electrolytic capacitor. Do you want to use electrolytic capacitor in the LED drive circuit? At present, there are supporters and opponents. Supporters think that if the temperature of the circuit board can be controlled well, the purpose of prolonging the life of the electrolytic capacitor can be achieved in turn, for example, a high-temperature electrolytic capacitor with a life of 105 degrees and a life of 8000 hours is selected, according to the prevailing electrolytic capacitor life estimation formula, when the temperature decreases by 10 degrees, the life will double, then its working life in 95 degrees environment is 16000 hours, the working life is 32000 hours at 85 degrees and 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 effect on the service life of the driving power supply. In the input part of the LED drive circuit, it can be considered not to use electrolytic capacitor, actually using PI LinkSwitch- PH can save electrolytic capacitor, PI's single-stage PFC/constant current design can let designers save large capacity capacitor, in the output circuit, high voltage ceramic capacitor can be used instead of electrolytic capacitor to improve reliability, some people use a 400V electrolytic capacitor in the output when designing a two-stage circuit, which will seriously affect the reliability of the circuit. It is recommended to use a ceramic capacitor for a single-stage circuit. For industrial applications that do not pay much attention to dimming function, high temperature environment and need high reliability, it is strongly recommended not to use electrolytic capacitor for design. Don't choose a MOSFET with a withstand voltage of 600 V. a mosfet with a withstand voltage of 600V is cheaper. Many people think that the input voltage of LED lamps is generally 220 V, so a withstand voltage of 600V is enough, however, most of the time the circuit voltage will reach 340 V. When there is surge, the MOSFET of 600V is easy to breakdown, thus affecting the life of LED lamps, in fact, the selection of 600VMOSFET may save some costs, but the cost is the price of the entire circuit board. Therefore, porcelain library Chinese experts recommend not to use 600V withstand voltage MOSFET, it is good to choose MOSFET with withstand voltage exceeding 700 V. Try to use a single-stage architecture circuit Doug means that some LED circuits adopt a two-stage architecture, namely PFC (Power factor correction) The architecture of isolated DC/DC converter will reduce the efficiency of the circuit. For example, if the efficiency of PFC is 95 and the efficiency of DC/DC is 88, the efficiency of the whole circuit will be reduced to 83. 6! LinkSwitch of PI- The PH device integrates PFC/CC controller, a 725VMOSFET and MOSFET driver into a single package at the same time, improving the efficiency of the drive circuit to 87! Doug pointed out that such devices can greatly simplify the layout design of circuit boards, and can save 25 components used in traditional isolated flyback design! The omitted components include high-voltage large-capacity electrolytic capacitors and Optocouplers. Doug said that the LED level two-stage architecture is suitable for old drivers that must use a second constant current drive circuit to enable PFC to drive LED constant current. These designs are outdated and no longer cost-effective, so single-stage designs are preferred in most cases.