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).
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. Power ranges for low-power applications are typically between 1 and 12 W; medium power ranges from 8 to 40 W; for high-power applications, power is often higher than 40 W. Overall, the main challenge for LED lighting driver companies is that LED drivers should challenge higher conversion efficiencies, especially when driving high-power LEDs , because all power that is not used as a light output is dissipated as heat. 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 the 8W to 25W LED general lighting application requirements and solutions, it is divided into no PFC and PFC.
Typical applications for 8W to 25W AC-DC LED lighting such as PAR30, PAR38 and recessed lights for PFC-free applications. In such applications, the input voltage requirement is 85~135 Vac 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. Wait for different currents. Typical applications for PFC's 8W to 25W AC-DC LED lighting are also PAR30, PAR38 and recessed lights. These applications have an input voltage specification of 90 to 264 Vac, 80% performance, 350mA, 700 mA, and 1A constant current output, providing short-circuit and over-voltage protection with power factor requirements above 0.9. As for 50W to 200W LED general lighting is mostly used for street lighting and high-power area lighting, different LED solutions for 50W-150W or 100~200W power range can be used.
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 has also launched the LED lighting driver IC -RT84 series. Li said that it is different from the buck LED driver IC which uses hysteresis control in the market. The full range of products adopts fixed frequency control to maintain the reduction of inductance value as magnetic. One-third of the hysteresis control, the fixed-frequency control method also has less accuracy than the hysteresis control with the change of the input voltage and current. Li also offers different LED solutions for buck, boost and buck-boost for different LED lighting applications.
Li 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 limitations of the buck circuit, so that a large number of step-down ICs are needed. The use of a vertical boost driver IC can significantly reduce the usage 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.
Support for both isolated and non-isolated applications
When it comes to LED lighting driver power, of course, NXP Semiconductors, which introduced a new Led Controller SSL2103 in the first half of this year. NXP said the product further expands NXP's market-proven AC/DC LED driver portfolio (SSL2101/SSL2102), making it suitable for a wide range of lighting applications. Jacques Le Berre, director of marketing for NXP Semiconductors Lighting, said that SSL2101 not only meets the market demand for LEDs, but also leads the industry to provide more energy efficient lighting solutions. In fact, SSL2101 has sold more than 10 million units since its launch in the spring of 2009. The SSL2101 and SSL2102 products are well-established and can be used in a variety of dimmable LED drivers, making them ideal for highly integrated, low-power applications such as stand-alone rectifiers below 25 watts or LED bulbs below 15 watts.
The SSL2103 has the features and features of the similar product SSL2101 and can be used in higher power solutions. As a versatile AC/DC LED lighting Controller, the SSL2103 offers greater power range and better dimming compatibility, making it suitable for dimmable and non-dimmable LED illuminators. In addition, the SSL210x family of products integrates controllers with the same features to increase the versatility of the family in a variety of LED lighting applications. Designed for higher power LED lighting fixtures (PAR20, PAR30 and PAR38), the SSL2103 provides greater flexibility in power, form factor and dimming control for LED luminaire designs.
It is understood that in addition to the features and performance of SSL2101 and SSL2102, SSL2103 can also meet higher power applications. This feature is implemented through an external power switch and can simultaneously support dimmable or non-dimmable lighting drivers. Similar to the design of previous products, the SSL2103 can last more than 75,000 hours at normal operating temperatures. NXP's AC/DC LED driver product line offers a wide range of technical solutions and supports both isolated and non-isolated luminaire applications. In addition, the series can also be applied to AC power networks of 100V, 110V or 230V, and the board dimensions can be applied to E27, GU10 or PARx lamps. This product line also includes products that incorporate power switches and bleeder circuitry to make PCB boards smaller.
Ultra-high efficiency dimming solution
In addition, Infineon's dimmable LED driver solution ICL8001G, mainly used for 10W-60W, can support dimming function, high-efficiency LED bulb for residential lighting is enough to replace 40W/60W/100W incandescent bulb, and supports various Typical consumer lighting applications. Infineon said that the ICL8001G driver board is based on innovative master control technology to manage LED power consumption. 25 components are enough for a 10 watt LED lamp (60 watts equivalent), saving half of electricity and reducing cost by about 30% compared to other alternatives. The reference design printed circuit board area is only 20mm. The x 70mm can be easily embedded in a general screw-in bulb. All components are assembled on a single-sided board to help further reduce costs. It is understood that the ICL8001G can achieve up to 90% energy saving, support a variety of installed wall dimmers, and is the only master offline LED driver solution with integrated power factor correction (PFC) function. 98%.
Compared to many current dimmable LED dimming solutions, dimming can cause a 30% reduction in energy efficiency. The Infineon driver solution uses a number of phase-cut dimmers. Ultra high efficiency (>80%) is maintained in the light range. Other features of ICL8001G include: independent driver output, which can effectively prevent overheating; digital soft start function, built-in startup unit, on and off; cycle-by-cycle current limit; short circuit protection, over voltage protection and over temperature detection.
Electroless capacitor LED drive power solution
Moreover, in the current market, LED lighting driver power solutions that do not require electrolytic capacitors are also worth mentioning. For example, Murata Manufacturing Co., Ltd. exhibited digital power circuits for LED lighting at TECHNO FRONTIER 2010 in July this year. Its input and output capacitors replace the electrolytic capacitors with the company's multilayer ceramic capacitors (MLCC), which can be built into straight tubes. In the tube of a type of LED lighting fixture. In addition to reducing the size of the product, this solution can extend the life of the product compared to the use of aluminum electrolytic capacitors. In order to obtain a constant current, this solution uses a DSP microcontroller with a switching frequency of approximately 200 kHz. The output capacitor uses two MLCCs of approximately 5μF. The input voltage supports AC100V and 200V. It is understood that under normal circumstances, the capacity of the MLCC can not fully absorb the ripple current, but by improving the control of the DSP side, it will not feel the flicker of the lighting fixture. The main circuit uses a non-insulated buck-boost type, and no PFC (power factor improvement) circuit is provided. The external dimensions are 180 mm x 19.4 mm x 6.5 mm.
Basically, the reason why it is to replace the electrolytic capacitor is mainly because the working life of the conventional LED lighting driving power supply depends on the electrolytic capacitor that the smoothing circuit must use when the AC is turned to DC. The working life of LEDs is up to 40,000 hours, and the life of electrolytic capacitors is only a few thousand hours. Since the life of the system is determined by the life of electrolytic capacitors used in power supply components, if you do not want to remove electrolytic capacitors, then LED lighting The life of the driving power supply cannot match the life of the LED, and the long working life of the LED lighting is bound to be affected. Therefore, the industry has been actively developing the LED lighting driving power solution of the electroless capacitor.
Directly driven by AC can bring more application space
In order to solve the problem that the life of the AC/DC converter is shorter than the life of the LED, in addition to the above solutions, the development of the AC LED is also attracting attention. For example, Acriche developed by Seoul Semiconductor does not need an AC/DC converter and can be directly connected to the AC power supply. drive. In addition, the on-chip AC LED lighting technology developed by Taiwan Industrial Technology Research Institute also uses AC power to directly drive the LED chip . The director of the Institute of Electro-optics, Optoelectronics and System Application of the Institute of Technology, Zhu Mudao pointed out that this technology does not require a rectifier transformer. LED saves 15~30% power, with stereo heat conduction, pluggable packaging technology, small size and other characteristics, it is easier to carry out multi-change lighting design. ITRI said that this technology not only saves energy and reduces carbon, but also improves the overall LED. The luminous efficiency, and the LED lighting application, bring more space and market opportunities. It is believed that this technology will become the most promising lighting technology in the next five years.
The PV Charge Controller works as a voltage regulator, its primary function is to prevent the Battery from being overcharged by the P.V array, being overly discharged by the load, or both.
Controller types:
• Single Stage controllers:
This type of controllers prevents battery overcharging by switching the PV array off when the battery voltage reaches the state of charge set point. The array and battery are automatically reconnected when the battery voltage reaches a lower value called the charge resumption.
• Pulse Width Modulation (PWM) controllers:
PWM controllers are the most common controller on the market today. These charge the battery by rapidly switching the full charging current on and off when the battery reaches a fully charged state. The length of the charging current pulse gradually decreases as battery voltage rises, reducing the average current into the battery.
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