Friday, April 15, 2011

【 Weak current College 】 different LED lighting applications power solutions 】

Summary: high-brightness LED for lighting design, global energy saving, and innovative products is of great significance to the birth of solid state lighting revolution is critical. This revolution requires a holistic approach, which, LED and power conversion and control electronic devices and thermal management solutions and optical devices.
Compared to traditional light sources, light-emitting diode (LED) have many advantages, such as voltage low, energy–efficient, very compact and have a directional light. They can provide a very broad sense of color and white light, do not produce infrared (IR) or UV (UV) radiation, and because they are solid state devices, very strong on the machine, and does not contain mercury, in the proper design and use to have more than 5 million hours of work and life, far longer than standard incandescent 1 thousand hours of life. In addition, they are also fully adjustable light. These advantages make the application of LED more and more widely, and now has many applications in markets such as architecture and landscape lighting, traffic lights, screens, retail, small and medium-size LCD screen (LCD) backlight, cars and solar energy, and street lighting, home lighting, and even in large-size LCD backlight has more room for development.

High-brightness LED for lighting design, global energy saving, and innovative products is of great significance to the birth of solid state lighting revolution is critical. This revolution requires a holistic approach, which, LED and power conversion and control electronic devices and thermal management solutions and optical devices.

LED lighting power supply solution

As noted above, LED are essentially low-voltage devices; according to the color and the current, LED forward voltage is between less than 2V to 4.5V. In addition, the need for a constant-current LED to drive, to ensure that the desired brightness and color. This requires the appropriate power conversion and control solutions can adapt to different power, AC circuits, solar panels, 12V car battery, DC power or low-voltage AC system, or even the alkali and nickel-based batteries, or Li-ion battery.

As a global leader in high-efficiency power semiconductor suppliers, on semiconductor is focused on using its own low voltage and high voltage technology and power management solutions expertise to cope with LED lighting challenge: neither the portable display products, automotive interior lighting LED lights of ballast or. Below, we will combine a variety of LED lighting applications, such as construction, industrial, automotive and portable applications, discussion on semiconductor corresponding driver power solutions.

1) can be integrated 700V high pressure maximum FET off line SMPs solution AC-DC

On semiconductor in power from the AC power is converted to power levels in a few Watts up to several hundred watt range, suitable for many different applications of available energy resources has the experience. On semiconductor has developed a combination of high voltage switch transistor and medium voltage analog circuits in HV integrated circuits (VHVIC), the demand for broad power to provide integrated money solutions. On semiconductor offers a variety of fixed frequency controllers and converters, voltage high voltage high-700V MOSFET (FET) integration to simple, affordable, component count less solution.

This solution includes three aspects:

Single AC-DC (AC-DC) constant current drive, the power range between 5 and 15W, such as NCP1013, NCP1014 and NCP1028, etc.

NCP series offline controllers, both isolated and non-isolated DC-DC, up to 150W. On semiconductor provides for street lighting, with one stage power factor correction (PFC) reference design.
PFC solutions

For power lower than 25W (230Vac) of a lower power applications, the most commonly used is the integrated power switching regulator, because it can be component count is reduced to a minimum. Higher power range, you can use the controller, because the controller for the designer in selecting the most suitable high-voltage FET provides flexibility. The controller can be used to isolate applications, can also be used for non-isolated applications, on semiconductor offers a variety of different value-added features that allow designers for their specific design requirements optimization design.

Figure 2 shows on semiconductor NCP1351 off-line LED drive reference design. This reference design of the input power range 85-265Vac, has small size, low cost, good line voltage features, at 80% load with a 20W high power efficiency, and integrated overload protection and short-circuit protection and other safety features, the maximum size of only 125 × 37 × 35mm.

IEC1000-3-2 standard set limit implantation to AC line harmonics specifications. The lighting applications, if you enter more than 25W (C class), this specification will apply. In addition, even if in some regions are not required to comply with the IEC specification, may also be requested by the lowest power factor. As a result, these applications need front-end PFC controllers. Added a paragraph leads to comply with energy efficiency and space and other system requirements difficult, unless you make a wise choice.

Fortunately, on semiconductor understands these challenges with innovative PFC controller portfolio meet the designers on simple, compact and strong solution of expectations. On semiconductor has not only supported the traditional application of 2-stage, have also introduced a number of sections to further simplify the design of unique solutions, such as NCP1651 one stage Flyback controller.

NCP1651 in single-chip solution with integrated power factor correction and converters with external FET, allow for the required powerAchieve a scalable solution. NCP1651 have isolated buck features that support continuous or discontinuous mode operation, and support the average current-mode control (ACMC) and fixed frequency control, high precision multiplier can be used to reduce total harmonic distortion (THD). It also has an over-temperature shutdown and external features such as closed. This one stage PFC controllers suitable for electronic ballast, street lights, traffic lights and lighting applications.

For input power between 25W and 60W between led lighting applications, you can use NCP1351 such PWM controller for input power range in 60W-150W, PWM controllers can use NCP1271; input power 150W-300W range, you can use NCP1396 such PWM controller. For 25W to 300W input power range, can be critical conduction mode (CRM), PFC controller NCP1606.

2) wide input range of medium-voltage led application DC solutions

In addition to the portable power supply applications, there are a range of high brightness LED applications work in 8-40VDC range of power, the power supply including lead-acid battery, 12-36VDC adapter, solar cells and low voltage of 12 and 24VAC AC system. This type of lighting applications, such as adjustable lighting, landscape and street lighting, automobile and traffic lighting, solar-powered lighting, as well as showcase lighting etc.

Even if the target is the use of constant-current LED driver, it is first necessary to understand the event is the application's input and output voltage change. LED forward voltage from the material characteristics, the junction temperature range, driving current and manufacturing tolerances. With this information, you can select the appropriate linear or switching power supply topologies, such as linear, Buck, boost or buck-boost, etc.

40V input voltage is less than the LED applications, if the output voltage is less than the input voltage, choose buck topology. On this basis, the output current to be selected. If the output current is greater than you can use 1.2A designed for high-brightness LED constant current powersupply of 1.5A switching regulator NCP3065. This device has a rating of very low 235mV feedback voltage, suitable for the average current LED strings for steady flow. It has high-40V's wide input voltage range, enabling it to work in 12Vac or 12Vdc power source. NCP3065 also offers suitable for automotive grade application version — NCV3065. Just a few external components (such as low VCEsat switch MOSFET or), NCP3065 switching regulators can be configured to step-up or step-down SEPIC, topology, etc. This makes it also be used for the application of electric current is less than 1.2A. For the application of electric current is less than 1.2A, NCP1215 + can be used to form the buck converters MOSFET. For current less than 500mA and input voltage near output voltage applications, you can use this constant current NUD4001 linear drives.

If the output voltage is greater than the input voltage, choose boost topology. On this basis, if it is a low-battery-powered applications, you can choose NCP5005, NCP5604, NCP5608 and NCP5050 such low voltage led driver; if it is not a low-battery-powered applications, and then look at its output voltage values, if greater than 40V, similarly you can use NCP3065 switching regulators, this time in conjunction with external NMOSMOSFET NCP3065 configured to boost controller structure; otherwise, also switched-current. If you switch currents greater than 1.3A, combined with low VCEsat switch MOSFET or, configured to boost controller NCP3065; if less than 1.3A, uses the configuration of the boost converter NCP3065.

In addition to mere buck or boost topology, in certain circumstances, also need to buck-boost topology, as from a standard power input-driven LED strings; in addition, the input voltage and LED load voltage overlap occasions using this topology is also very common. But also be able to configure NCP3065 buck-boost controller. This architecture requires 2 power switch. Although NCP3065 itself also contains 1 power switch, but we can use 1 low VCEsatPNP/NPN on the tube to achieve higher conversion efficiency. This is an Extensible scheme, Rectifier and power switch are depending on the input and output voltage and the current level to adjust. It is worth mentioning that such as low VCEsat NSS40500UW3 so adopt compact transistor 2 × 2mm package that provides excellent performance.

Figure 4 shows the power of up to 12W NCP3065 buck-boost circuit. This circuit is designed to work with currents up to 0.7A applications, input voltage range of up to 8 to 26Vdc. Output voltage Vout-16Vdc @ 700mA and input voltage Vin is 13-26Vdc, the energy efficiency of up to 72% to 80%.

LED portable backlight application power solutions

White led and RGB led is widely used in small-size LCD Panel and keyboard backlight, led applications. Application in mobile phones and digital cameras, high brightness LED power can also be used as a flashlight. These applications require optimized solutions, not only to maximize battery life, but also maximum decrease PCB footprint and height.

In this class, LED backlight application, you can use linear regulator, or switching regulator, has its advantages. Linear regulators-structure is relatively simple, simple, low cost, low noise, small size, low quiescent current. And switching regulator of energy efficiency is high, up to 70~ 85%. On semiconductor application based on the user's needs, providing multiple types of solutions. In switching regulator solution, while providing inductive type and a charge pump type both types. Specifically, the inductor boost drive NCP5005, NCP5050 has efficient and high-output voltage advantages, its energy–efficient 90%, but most of them can be driven for up to five-line LED (output voltage up to 21V). In addition, because of the LED-line connection, this type of diodes is also ideal for lighting/current matching characteristics. No inductors, charge pump type drive NCP5602, NCP5612, NCP5623 help createcompact solution, which application for small and medium-size LCD portable products is still as important. This type of drive is equipped with low-cost capacitance and resistance, the ability to create more cost-effective solution. This drive can drive 1 to 3 LEDs, for smaller devices with backlit applications.

In addition to LCD, organic light-emitting diode (OLED) this emerging display technologies in recent years have begun to use in portable devices, and even in a large flat-panel TV. Originally appeared on the market is passive matrix OLED (PMOLED), due to its driving topology, its display size limitations in 1.8 and following, commonly used for MP3 players and mobile phones slave. Update of active matrix OLED (AMOLED) technology is not display size constraints, it is better than LCD with a number of important advantages, such as a broad viewing angle, high-contrast, extremely fast response time and slim thickness, which benefited from it eliminates the backlight. AMOLED panels are used in the phone's main screen, MP3 player, etc.

On semiconductor market pioneered specialized active matrix (AMOLED) Panel power supply IC — NCP5810D. NCP5810D dual-output DC-DC converters in 1.75MHz oscillator frequencies for the entire power energy–efficient 83%. It has excellent line transient suppression capability, when the current 25mA line transient voltage 5mV. In order to adapt to the AMOLED display slim shape, the converter can convert to high frequency 1.75MHz, use the smaller of inductors and ceramic output capacitors. Its thin package 0.55mm thick, making NCP5810D applies to the thinnest portable product design. In addition, it is in shutdown mode power off function will display a current limitation in the leakage of 1 µA, saving off battery power. NCP5810D also has a peak-by-cycle current limit and thermal shutdown protection. The use of ultra-thin NCP5810D 3.0mm×3.0mm×0.55mmLLGA-12 package.

Apart from the LCD backlight and AMOLED power application, on semiconductor also Unveils camera Flash application of led driver IC, such as NCP5680, etc. For example, this NCP5680 is a band super capacitor (supercap) dual-LED Flash drives to 2.5A or higher current drive 2 high-brightness LED. It takes the I2C control, with built-in Flash sequences. It's the PC functionality in bright environments can limit the Flash time, saving energy. This device uses super capacitor to support audio and other large peak current circuit, also has short circuit protection and other protective functions. This device to begin July 2008 volume production.

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