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

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

However, a big problem LED street is currently facing low reliability, because it is mainly used for outdoor lighting, facing extreme environmental conditions, such as long-term exposure to the sun rain, thunder and lightning, temperature change may be larger. LED street lamps to be recognized by the market and large-scale use, we must first solve the reliability problem.

TI semiconductor business development manager Liu Xuechao

TI semiconductor business performance simulation products business development manager Dr. Liu Xuechao said: LED street market prospects, but we must solve the problem of reliability. "

LED street is a complex system composed of optical, thermal and electronics, although the longer life of LED itself, but if the improper design of LED driving circuit, such as the use of the low quality of the active or passive device, make the whole life can not match with the LED drive circuit, it will affect the quality and service life of LED lamp.

Furthermore, LED temperature management and heat dissipation is also very important, once the operating temperature is higher than 100 DEG C, the reliability of the LED itself will be affected. Of course, LED early failure, assembling partial defects and transient phenomena and other factors, also may occasionally cause LED failure, if you do not take appropriate measures of protection of shunt, LED will lead to the failure of a single whole string of LED is not bright, affect the overall lighting effect.

Liu Xuechao stressed: LED street lamp is a complex system design, involving light, electricity, heat, machinery and other fields. In terms of efficiency and reliability of the power supply is concerned. First of all, the driving power working environment temperature is very high (generally at 70 degrees up and down), so I hope the efficiency of power supply (including constant voltage and constant current) efficiency reaches a certain height (such as >90%), to reduce the temperature and improve the reliability of power supply. Secondly, the traditional drive topology is more complex, including PFC, PWM isolation and constant current DC/DC three circuit (pictured below), many components, low reliability, especially electrolytic capacitors and optocoupler and other sensitive devices. "

Circuit topology of traditional LED street lamp driver

Therefore, in the process of LED lamp design, must be well taken into account LED temperature or heat management, so that the work of LED keep the temperature below its junction temperature (maximum junction temperature is 150 DEG C), the general recommendations of LED working temperature is below 100 DEG C, avoid the reliability of LED affected. In addition, LED driver circuit designers must carefully select the active or passive devices in the circuit, to ensure that the life of the LED match. For example, the designer should avoid the use of electrolytic capacitors as much as possible, because the capacity of the capacitor in the long-term use conditions may cause leakage and shorten the working life.

Moreover, in the overall market for LED lighting, LED street lamp is the highest power of all LED lighting applications, so we need more power level and complex topology, in order to meet the power factor correction (PFC), total harmonic distortion (THD), 85 PLUS efficiency standards and regulations, and the requirements of multi string LED constant current the.

Liu Xuechao also said: "to solve the problem of LED street lamp circuit reliability, we must improve the drive topology, improve efficiency, reduce the number of components, in addition to further reduce costs. "

LED street lamp driver proposal

Aiming at the above problems, related to the semiconductor industry to the development of low complexity and high power level integration solutions, on one hand can meet the requirements of high efficiency and low cost of BOM, on the other hand can meet the world's energy efficiency standards and regulatory requirements. Korean vice president Zhao Donghui pointed out that the flying Fairchild Semiconductor, LED lamp demand, Fairchild has recently released a four channel current control IC (FAN7346), with its simple LED series positive voltage feedback function, can replace the complicated secondary DC-DC module, and the product is compatible with the flyback converter and the half bridge or derivative the topology, can provide simulation and PWM dimming function.

Zhao Donghui, vice president of Korea Fairchild Semiconductor

In addition, Fairchild also provides a highly integrated power switch solution (FLS1600-2100XS), through the integration of two single high voltage MOSFET in a single package, and the use of LLC resonant half bridge controller to reduce the cost of BOM. Fairchild's CRM PFC controller IC products FL7390B/C can provide low power solutions for high power factor and low THD applications. The controller can eliminate the overshoot of Vout by soft start function and second OVP function, thus improving the reliability of the system.

At present, several European and China customers have begun using Fairchild Semiconductor for high power and high power street lighting outdoor lighting application solutions, PFC control and IC control of LLC resonant half bridge IC is the main product delivery.

The Fairchild Zhao Donghui pointed out that if only pay attention to the cost, will again lead to low quality and low reliability, which is the Fairchild to avoid new products, so the Fairchild rather focus on simplifying the system, improve the efficiency and reduce the development trend of THD.

He said that the system efficiency and cost related to specific power topology, if you choose a higher level of components, can easily improve efficiency. Therefore, the first step is to select the best topology for the system. The second step is to find support