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Lighting LED drive solutions - (AddTime - 2013-03-14)

As a solid state light emitting diode (LED) emerge in a large amount, make incandescent lamp increasingly lonely. In the past few years, LED technology has had great progress, in the heat dissipation, packaging and technology progress make LED a higher brightness, higher efficiency and longer life and lower cost.

However, in the energy conversion efficiency, heat management and production costs, LED still have further promotion space. For example, LED efficiency already has obtained great improve. LED many to improve from now on a chip can better play in real estate, and there is a better way from the chips encapsulation for light source. Likewise, and the price of white LED ma has been greatly reduced, the LED's just come out, batch purchase price for $1. And there are possible to less than 30 cents around the group to buy twenty ma white light LED.

200W led Flood light applications demand analysis

Of course, all these advances will not only promote LED in different application as the use of lighting source, but also stimulate the 200W led Flood light IC needs. To understand the design and manufacture of 200W led Flood light IC face what obstacles, we must understand the white light LED to luminous need what conditions. The white light LED must use a constant current source drive, so that white spot won't change (i.e. brightness must agree). In addition, since the white LED is a diode, then must overcome it internal positive pressure drop (Vf). Vf with white light LED current value different and different, also with the temperature changes. Usually, in the whole working temperature range, and white LED ma the Vf in 2.5 V to 3.9 V range change. Most applications are using multiple white light LED, but also could these LED configured to parallel, serial or parallel hybrid form. This means that the white light 200W led Flood light IC must be able to for a particular configuration of multiple LED provide enough electric current and voltage, and the IC the voltage switching topology must at the same time satisfy the input voltage range and output voltage and current requirements.

LED the common applications include automobile and aircraft panel display and instructions, traffic light, mobile phones, flat panel display QiBei light source, miner's lamp, building and outdoor stadium lighting, etc., and the current and future within a few years, LED the market the biggest driving force growth from the flat panel display backlighting demand. The display USES a LCD screen, used for television, navigation system, portable media players, digital billboard and computer monitor. However, using LED heat management facing technical challenges. Although LED is not like other light source that radiation so much heat, but according to the output power is different, some LED may need appropriate radiator, so that light output won't reduce, life will not shorten. For example, light output is 25 lm high brightness LED by general consumption of power more than 1 w. This means that the white light 200W led Flood light IC must be in the conversion of high efficiency, so that it can not be ReWenTi main causes. In addition, in many cases there is the problem of limited space, LED drive solutions must be accounted for plate area is small, small in size and shape.

Use of mobile phones as an example, today most mobile phones have built-in digital camera, to take high resolution photos and video. The camera also lead to the improvement of the performance of the high power white light source demand, camera indoors or in dark environment need to use this source, the white light LED has become a mobile phone camera the main light source. For white LED has a variety of modern mobile phone designers want features: small size, specular output, to provide "flash" and "video" object continuous lighting. Has been designed for integrated type camera lighting developed high output power LED.

Portable product lighting solutions

Although with high power LED produce visible light is very simple, but if not for design improvement, to form a high performance power and current control solution is very difficult. LingLiEr special company LTC3454 is a kind of new products, special used in large current camera lighting application in improving the power conversion efficiency and accuracy, and optimize the LED current control.

Graph: the power LTC3783 based on PWM LED drive circuit

LTC3454 is a kind of synchronous decompression - boost DC/DC converter type, single day for lithium ion battery input up to 1 a current drive a single high power LED and optimization. This device apparent VIN and LED forward voltage of the relationship between different, automatic in synchronous buck, synchronous booster and four switch decompression - booster mode conversion between. Can be used in the lithium ion battery voltage range (2.7 ~ 4.2 V) can achieve higher than 90% PLED/PIN efficiency.

Almost all the battery powered portable products using color active matrix LCD to display the user the information and data. However, manufacturers are faced with a challenge, which need to ensure that the user in any environment all can see from this display information. In order to achieve this goal, manufacturers must provide backlighting strength suitable color LCD. The backlighting is usually provided by white light LED. Therefore, produce compact, high efficiency and low noise LED power supply solution needs.

LingLiEr, the company has provided a lot of white light 200W led Flood light IC solutions. These solutions or use low noise no inductor DC/DC converter (more common way is charge pump), or use DC/DC converter, the two converter main difference is whether to need to inductor (magnetic element). No inductor DC/DC converter is very suitable for space limited application, in this application, must provide low to medium sized load current. In addition, the converter using small package, need very little external components, usually need only three ceramic capacitor. Most of the booster type DC/DC converter were specifically designed for white LED backlighting to provide high efficiency and constant current drive.

LTC3208 is a no inductor, large current, software configurable many display LED controller, can drive and a LED. The device contains a 1 a high efficiency, low noise charge pump, give priority to, vice, RGB, camera and auxiliary power supply LED display. LTC3208 has as much as 95% of efficiency and the I2C serial interface, give the user the benefits of a longer battery life, simple 2 line micro controller interface, etc. LT3486 is A kind of double channel, 1.3 A white light LED booster type converter, with wide dimming range, specifically for lithium ion batteries with single section with constant current drive up to 16 LED (each converter drive eight series LED) and design.

High brightness LED drive solutions

High-end TV, industrial lighting applications, car navigation screen and projector LCD TFT backlighting may adopt high brightness (HB) and ultra bright LED. This kind of LED common application fields are panel backlighting, interior lighting, and a lot of cars and trucks brake light. Luxury car makers are increasingly using the latest solid state 200W led Flood light technology to improve the future models aesthetic feeling, with these lighter, smaller and more durable components to achieve internal and external lighting. Obviously, and, compared with incandescent lamp lighting LED has a lot of advantages, such as LED is expected to reduce the long-term costs and has a long life.

However, with the current drive LED for DC/DC converter accurate control current, to ensure that the same intensity of light and color consistency and the protection of LED. In addition, there is a big challenge, which may be less than, equal to or higher than the load voltage of the battery voltage for one or several LED string of power supply. Another concern is the major problem than efficient light of these LED dimming, and at the same time also in low light and high brightness while maintaining these LED color characteristics unchanged. Finally, one of the most important requirement is that the DC/DC drive to work efficiency, especially in the drive HB LED is such, because all not into light power is converted into heat consumed.

Use the car battery drive LED for DC/DC converter accurate control LED current, to ensure that the same intensity of light and color consistency, and the protection of LED. In addition, depending on the use of LED is different, DC/DC voltage regulator should also be for a specific power requirement and optimization. The major challenge is to use may be less than, equal to or higher than the load voltage of the battery voltage for one or several LED string of power supply. Need to concern is with major efficient than light to LED dimming, and at the same time in low light and high brightness while maintaining these LED color characteristics unchanged. DC/DC drives to work with high efficiency is also very important requirement, especially drive HB LED, reason and the same, not into the light power is converted into heat wasted.

LTC3783 is a current mode, a variety of topological converter, with constant current PWM dimming ability, it is fit to drive high power LED string and LED group. This device using proprietary technology, which has a very fast speed, and PWM load switch without transient under voltage or over voltage problem. LTC3783 to digital means to realize 3000:1 dimmer than (in 100 hz), because True Color PWM dimming can guarantee white and RGB LED Color consistency. Using analog control mode, LTC3783 still can achieve 100:1 additional dimmer than. The dimming ability is very important, because the human eye to ambient light small change extremely sensitive. The general controller can be used as a booster, decompression, step-down - booster, SEPIC or flyback type converter, and used as a constant current/constant voltage regulator. No RSENSE work mode using the MOSFET on resistance, no current detection resistance and improve the efficiency. The typical application of LTC3873 as below.

LT3475 is A dual channel 36 v, 2 MHZ of decompression type DC/DC converter, used as A constant current 200W led Flood light , each channel to provide up to 1.5 A LED current. The internal testing resistance and the dimming control so that the device is very suitable for driving large current LED. In LT3475 fifty ma to 1.5 A wide current range to maintain the high output current accuracy, and at the same time, the unique True Color PWM circuit can realize 3000:1 dimming range.

LT3475 has 4 v to 36 v of wide input voltage range, adjustable from section 4 basic/nickel cadmium/nimh metal battery and 5 v logic voltage rail to uncontrolled wall transformer and automobile power system of power supply. The switch frequency can be in 200 KHZ to 2 MHZ range Settings, thereby allowing the use of slender inductor and ceramic capacitor, and also can avoid some key band (such as AM radio band). LT3475 for drive two or four large current LED very compact solution.