The five recommendations of high energy efficiency and reliability design of LED lighting
In 2011, Australia has been the first to ban the use of incandescent, which led to the large-scale popularization of LED lamps. In addition, with the EU countries, Japan, Canada and other countries in 2012 will prohibit the use of incandescent. The popularity rate of LED lighting will be further enhanced, which makes thousands of LED lighting manufacturers in the Nuggets green lighting revolution in China rejoice - because a huge market will open, and this is the protagonist of the Chinese manufacturers. However, it should be noted that LED lamps to be universal, not only need to significantly reduce costs, but also need to solve the energy efficiency and reliability of the problem. How to solve these problems, PowerIntegrations vice president of marketing DougBailey shared five advice of the high efficiency of LED lighting design.
First, do not use bipolar power devices
Doug Bailey pointed out that because the bipolar power devices is cheaper than the MOSFET, usually about 2 cents a, so some designers in order to reduce the cost of LED drive bipolar power devices, which will seriously affect the reliability of the circuit, because with the LED Drive board temperature rise, the effective working range of the bipolar device will quickly shrink. This will lead to the device in the temperature rise when the failure and thus affect the reliability of LED lamps. The correct way is to use MOSFET devices. MOSFET device life is much longer than bipolar devices.
Second, the MOSFET voltage is not less than 700V
Voltage 600V MOSFET is relatively cheap, many believe that the LED lamp input voltage is generally 220V, so the pressure 600V enough, but many times the circuit voltage will be 340V, in a surge when the 600V MOSFET is easy to be punctured. Which affected the life of LED lamps, in fact, the choice of 600VMOSFET may save some cost but pay the whole circuit board is the price, so "do not use 600V pressure MOSFET, the best choice of more than 700V voltage MOSFET." He stressed.
Third, try not to use electrolytic capacitors
LED drive circuit in the end do not use electrolytic capacitors? There are also supporters who have opponents, supporters believe that if you can control the circuit board temperature, in order to achieve the purpose of extending the life of electrolytic capacitors, such as the use of 105 degrees of life of 8000 hours of high-temperature electrolytic capacitors, according to the popular electrolytic capacitor life estimation formula "The temperature is reduced by 10 degrees, life doubled," then it is 95 degrees in the working life of 16,000 hours, 85 degrees in the working life of 32,000 hours, 75 degrees in the working life of 64,000 hours, if the actual working temperature is lower, then the life will be longer! From this, as long as the choice of high-quality electrolytic capacitors on the life of the drive is no impact!
Some supporters believe that the low-frequency flicker caused by the high ripple current caused by the electrolytic capacitor can cause physical discomfort to some human eyes, and the low frequency ripple of large amplitude can cause some digital camera equipment to appear poor stroboscopic bright and dark grid. Therefore, high-quality light source lamps still need electrolytic capacitors. But the opponents believe that the electrolytic capacitor will naturally aging, in addition, LED lamps are extremely difficult to control the temperature, so the life of electrolytic capacitors will inevitably be reduced, thus affecting the life of LED lamps.
In this regard, DougBailey that the input part of the LED driver circuit can be considered without electrolytic capacitors, in fact, the use of PI's LinkSwitch-PH can save electrolytic capacitors, PI single-stage PFC / constant current design allows designers to save large capacity Capacitor, in the output circuit, you can use high-voltage ceramic capacitors to replace the electrolytic capacitor to enhance reliability, "Some people in the design of two-stage circuit, the output uses a 400V electrolytic capacitor, which will seriously affect the circuit reliability, it is recommended to use a single-stage circuit with a ceramic capacitor on it. "He stressed. "For industrial applications that do not focus on dimming, high temperature environments and require high reliability, I strongly recommend that you do not use electrolytic capacitors for design."
Fourth, try to use MOSFET devices
If the design of the LED lamp power is not very high, Doug recommends the use of integrated MOSFET LED driver products, because the benefits of this is the integrated MOSFET conduction resistance less heat generated less than the discrete, in addition, the integrated MOSFET is the controller and the FET together, generally have overheat shutdown function, the MOSFET will automatically turn off the circuit when the power protect the purpose of LED lamps, which is very important for LED lighting. LED lighting is generally very small and difficult to air cooling the "Sometimes the LED will be overheated because of the burning of the situation, but our program will never be the case." He said.
Fifth, try to use single-stage architecture circuit
Doug said that some LED circuits use a two-stage architecture, the "PFC (power factor correction) + isolation 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 part is 88%, the overall circuit efficiency will be reduced to 83.6%! "The PI's LinkSwitch-PH device also combines the PFC / CC controller, a 725VMOSFET MOSFET drivers are integrated into a single package, boosting the efficiency of the drive circuit to 87%! "Doug noted." This device greatly simplifies board layout design and eliminates up to 25 components used in traditional isolated flyback designs "The missing components include high-voltage, high-capacity electrolytic capacitors and optocouplers." Doug said the LED two-stage architecture is suitable for legacy drives that must use a second constant-current drive circuit to enable the PFC to drive the 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.