LED has become one of the most promising high-tech in the world in recent years due to its unparalleled energy-saving, environmental protection, long life, high controllability and other technological advantages. It has officially opened the prelude to a comprehensive replacement of traditional lighting. History of traditional lighting. With the application of LED technology in the field of lighting, LED lighting products have set off a green storm of energy saving and environmental protection in the world, and are known as green lighting products in the industry. Today, with higher and higher energy consumption, some people even predict: "In the next 10 years, LED lamp products will become the only products to replace traditional lighting lamps such as high-pressure sodium lamps, incandescent lamps, fluorescent lamps, table lamps and so on." Need to significantly reduce costs, but also need to solve the problems of energy efficiency and reliability, how to solve these problems, now let us share the efficient and reliable LED lighting design method.
Do not use bipolar power devices
Experts pointed out that because bipolar power devices are cheaper than MOSFETs, generally about 2 cents each, so some designers use bipolar power devices in order to reduce LED driving costs, which will seriously affect the reliability of the circuit, because with the LED As the temperature of the driving circuit board increases, the effective working range of the bipolar device will rapidly shrink, which will cause the device to malfunction when the temperature rises and affect the reliability of the LED lamp. The correct approach is to select the MOSFET device and the service life of the MOSFET device. It is much longer than bipolar devices.
Try not to use electrolytic capacitors
Should electrolytic capacitors be used in LED drive circuits? At present, there are supporters and opponents. The supporters believe that if the temperature of the circuit board can be controlled well, the purpose of extending the life of the electrolytic capacitor can be achieved in turn. For example, a high-temperature electrolytic capacitor with a 105-degree life of 8000 hours is selected. According to the commonly used electrolytic capacitor life estimation formula "Every temperature decreases by 10 degrees, the life expectancy doubles", then it has a working life of 16000 hours in a 95-degree environment, 32,000 hours in an 85-degree environment, and 64,000 hours in a 75-degree environment. The lower the working temperature, the longer the life! From this point of view, as long as the use of high-quality electrolytic capacitors has no effect on the life of the driving power supply.
In the input part of the LED drive circuit, it is possible to consider not using electrolytic capacitors. In fact, PI LinkSwitch-PH can save electrolytic capacitors. PI's single-stage PFC / constant current design allows designers to save large-capacity capacitors in the output circuit. , You can use high voltage ceramic capacitors instead of electrolytic capacitors 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 single Ceramic capacitors for class circuits are sufficient. For industrial applications that do not pay much attention to the dimming function, high temperature environment and require high reliability, it is strongly recommended not to use electrolytic capacitors for design.
Do not choose MOSFET withstand voltage of 600V
600V withstand voltage MOSFET is cheaper, many think that the input voltage of LED lamps is generally 220V, so 600V withstand voltage is enough, but many times the circuit voltage will reach 340V, 600V MOSFET is easily broken down when there is a surge , Which affects the life of LED lamps. In fact, the selection of 600VMOSFET may save some costs but pay the price of the entire circuit board. Therefore, porcelain experts in China recommend that you do not choose 600V voltage-resistant MOSFETs. 700V MOSFET.
Try to use single-stage architecture circuits
Doug said that some LED circuits use a two-stage architecture, that is, a "PFC (power factor correction) + isolated DC / DC converter" architecture, such a 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 efficiency of the entire circuit will be reduced to 83.6%! "PI's LinkSwitch-PH device simultaneously integrates a PFC / CC controller, a 725VMOSFET and MOSFET driver into a single package, increasing the efficiency of the drive circuit to 87%!" Doug pointed out, "such a device can greatly simplify the circuit board layout The design can save up to 25 components used in the traditional isolated flyback design! The omitted components include high-voltage large-capacity electrolytic capacitors and optocouplers. "Doug said that the LED-level two-level architecture is suitable for the use of a second constant current The driving circuit can make the PFC drive the old-style driver of 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.
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