The future of the LED street light market depends on whether the reliability problem can be solved

Most of the world's governments are currently upgrading road lighting. The first step is to install LED street lights in newly developed areas. Next, LED street lights will replace existing old street lighting. According to estimates, most of today's street lights will be replaced by LED lighting in the next five years.

However, one of the major problems facing LED street lamps is their low reliability, because it is mainly used for outdoor lighting and faces a variety of extreme environmental conditions, such as long-term exposure to sun and rain, thunder and lightning, and large temperature changes. In order to be recognized by the market and used on a large scale, LED street lamps must first solve the reliability problem.

Liu Xuechao, Business Development Manager, TI Semiconductor Business Unit

Dr. Liu Xuechao, Business Development Manager of High Performance Analog Products, TI Semiconductor Division, said: "The LED street light market has broad prospects, but it must solve the reliability problem."

LED street light is a complex system consisting of optics, thermals and electronics. Although the LED itself has a long life, if the LED driver circuit is not properly designed, such as low-quality active or passive components, the overall drive circuit life is achieved. Failure to match the LED will affect the quality and life of the LED street light.

Furthermore, LED temperature management and heat dissipation are also very important. Once the operating temperature is higher than 100 °C, the reliability of the LED itself will be affected. Of course, factors such as early LED failure, assembly of local defects and transient phenomena also cause LEDs to occasionally fail. If proper shunt protection measures are not taken, the failure of a single LED will cause the entire string of LEDs to be off, affecting the overall street lighting effect. .

Liu Xuechao emphasized: "LED street light is a complex system design, involving light, electricity, heat, machinery and other fields. In terms of driving power, it is mainly the problem of efficiency and reliability. First, the operating temperature of the driving power supply is very high (generally At 70 degrees or so, in this way, it is desirable to drive the efficiency of the power supply (including constant voltage plus constant current) to a certain height (such as >90%), reduce the temperature of the driving power supply, improve reliability. Second, the tradition The drive topology is complex, including PFC, PWM isolation and constant current DC/DC three-level circuits (as shown below), with many components and low reliability, especially sensitive devices such as electrolytic capacitors and optocouplers."

Therefore, in the process of LED street lamp design, LED temperature management or heat dissipation must be well considered, so that the operating temperature of the LED is kept below its junction temperature (maximum junction temperature is 150 ° C). It is generally recommended that the LED operating temperature be lower than 100 ° C, to avoid the impact of LED reliability. In addition, LED driver circuit designers must carefully select active or passive components in the circuit to ensure they match the LED lifetime. For example, designers should avoid using electrolytic capacitors as much as possible, as such capacitors can leak during long-term use and result in reduced operating life.

Furthermore, in the overall LED lighting market, LED streetlights are the most powerful of all LED lighting applications, requiring multiple power levels and complex topologies to meet power factor correction (PFC) and total harmonic distortion (THD). , 85 PLUS efficiency and other standards and regulations, as well as multiple string LED current requirements.

Liu Xuechao also believes: "To solve the circuit reliability problem of LED street lamps, it is necessary to improve from the driving topology, improve efficiency, reduce the number of components, and further reduce costs."

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