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 to this, the industry has indicated that power supply topologies suitable for AC-DC LED lighting applications of different powers are different. For applications with power below 80W, the flyback topology is the standard choice; in high-performance applications, resonant half-bridge dual inductor plus single capacitor (HBLLC) 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).

From the power level of the application, AC-DC powered LED general lighting applications include different types of low power, medium power and high power. Low power applications typically range from 1 to 12W; medium power covers 8 to 40W; high power applications often have powers above 40W. Overall, the main challenge for LED lighting driver companies is LED drivers. Challenge higher conversion efficiency, especially when driving high-power LEDs, because all power that is not used as light output is dissipated as heat, and the power conversion efficiency is too low, which will affect the LED energy-saving effect.

First, typical applications such as G13, GU10, PAR16, PAR20, and recessed lights in low-power LED general illumination from 1W to 8W. The input voltage range for this type of application is between 90 and 264V AC. The constant current output current includes 350mA and 700mA. The performance requirement is 80%. It is required to provide protection functions such as short circuit protection and over voltage protection. In terms of 8W to 25W LED general lighting application requirements and solutions, it is divided into no PFC and PFC.

Typical applications for 8W to 25WAC-DCLED lighting such as PAR30, PAR38 and recessed lights for PFC-free applications. In such applications, the input voltage requirement is 85~135Vac or 185~264Vac (or universal input), the performance requirement is greater than 80%, and the protection functions such as short circuit protection and open circuit protection are provided. The constant current output current is 350mA, 700mA and 1A. Different currents. Typical applications for PW's 8W to 25WAC-DCLED lighting are also PAR30, PAR38 and recessed lights. This type of application has an input voltage specification of 90 to 264Vac, 80% performance requirement, 350mA, 700mA and 1A constant current output, short circuit and overvoltage protection, power factor requirement higher than 0.9. As for 50W to 200W LED general lighting is mostly used in streets. Lighting and high-power area lighting can be used for different LED solutions for 50W-150W or 100~200W power range.

Active power factor adjustment reaches over 95%

In response to LED lighting power supply requirements, in terms of constant current drivers, Kay Technology is the main push T6316, which is a constant current LED driver with 4 channels. The output current can be determined according to the external resistor. Kathy Technology's T6322 is a step-down constant current LED driver whose current is determined by external resistors. It can support up to 1.5A output current, providing ±5% precision current and high power performance (low power consumption) and high line adjustment capability. The T6316 has ±6% accuracy current and ±3% matching accuracy between channels, and can be used for lighting equipment such as street lamps and lamps.

He Shaojia further stated that in terms of power factor, the current passive power factor adjustment can reach 0.8, its structure is simple, the price is low, the working frequency is the same as the power source, but the passive components are bulky, heavy, and need to be specific to the input voltage and Load conditions to design. In response to this, Cathy can provide a corresponding passive valley filter to correct the overall power factor, so that the power factor of the LED driver is more than 85%. It is understood that the driver will be developed with the active power factor. Adjustment, the overall power factor of more than 95%, will be able to further achieve energy-saving goals.

Li Wei has also launched the LED lighting driver IC-RT84 series. Li Wei said that it is different from the buck LED driver IC which adopts hysteresis control in the market. The full range of products adopts fixed frequency control to reduce the inductance value. Maintaining one-third of hysteresis control, its fixed-frequency control method also has less accuracy than hysteresis control with changes in input voltage and current. Lixin also offers different LED solutions for buck, boost and buck-boost for different LED lighting applications.

Li Wei said that most of the current product applications on the market are designed with buck LED driver ICs. The advantage of this method is that the design concept is simple, but the number of LED drivers is limited by the limitation of the buck circuit, so that a large amount of buck is needed. IC, the use of the vertical boost driver IC can significantly reduce the use and cost of more than half of the LED step-down driver IC. The current LED driver power supply products can meet the customer's application of buck, boost and buck-boost, and provide corresponding products from 1W to 400W. And provide solutions for standard luminaires such as MR16, AR111, GU10, E27, PAR30, PAR38 and other specifications.