LED driver power factor will soon reach more than 95%

With the advancement of technology, lighting tools and methods are constantly changing, users are increasingly demanding the illuminance, uniformity, color rendering and energy efficiency of lighting fixtures. At this stage, the most eye-catching lighting rising star When non- LED lighting is none other than. For example, in the general lighting market, such as bulbs and fluorescent tubes, recessed lights, street lights and parking lights, work lights (table lamps, cabinet lighting), landscape lighting, billboard text circuits, building lighting, etc., it is expected that by 2012, LED The lighting market will grow to 1.308 billion US dollars, with a compound annual growth rate of 17.4%. Therefore, LED general lighting has become a hot market.

However, LED still has some problems in the lighting market application, including LED consistency, life testing, especially power supply and drive system specifications and other issues remain to be solved. Requirements for LED drive power include high efficiency, high power factor, high current control accuracy, high reliability, safe isolation, compliance with EMI standards, small size, and low cost. It is worth noting that the latest ENERGY STAR standard proposes that for LED lighting products larger than 5W, the required power factor index (PFC) must be greater than 0.7 in order to further achieve energy saving.

Power input system requirements vary

Analysis of the cost structure of LED lamps, cooling components accounted for about 30%, power supply systems accounted for 20%, assembly parts accounted for 5%, LED components accounted for the largest proportion, up to 45%. In each part of the LED luminaire, the power module shoulders the burden of energy saving. At present, the LED lighting power input system on the market can be divided into two categories. One type of front end is an AC power input system plus a back end constant current control module. Such products include freezer light strips, indoor lamps, street lamps, table lamps, MR16. , AR111, etc. The other is an AC power direct input system that integrates AC/DC converters and constant current lines. These products include bulb-type LED lamps such as E27 and GU10, PAR lamps, T5 and T8 LED tubes.

According to He Shaojia, senior manager of Cathy Technology, the first type of power supply design should select a constant voltage power supply with better front-end efficiency, and the power supply module with back-end constant power control adopts a more efficient power supply according to its product characteristics. design. The advantage is that the front-end AC/DC power supply, such as a switching power supply, a DC adapter and other constant voltage power supplies, can be highly selective and have a safety certification scheme, thereby reducing the design threshold.

The second type of power supply design, due to the integration of AC / DC circuits and constant current circuits, the main difficulty lies in the power factor, power efficiency and safety considerations, the design also has some difficulties. In response, the industry has indicated that power supply topologies for AC-DC LED lighting applications of different powers are different. In applications with power below 80 W, the flyback topology is the standard choice; in high-performance applications, the resonant half-bridge dual inductor plus single capacitor (HB LLC) is preferred.

High power conversion efficiency is the goal

It is understood that ultra-high performance LED lighting topology has been popular in recent years, and the industry is mainly looking to provide more than 90% performance at relatively low power levels (<50W), and such high performance requirements This is achieved with a new topology, such as replacing the flyback topology with a resonant half-bridge topology, which gives full play to the advantages of zero-voltage switching (ZVS).

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