introduction
This article refers to the address: http://
According to the statistics of Strategies Unlimited (see Figure 1), by 2012, the market size of high-brightness (HB) LEDs is expected to reach US$12 billion. By 2015, the market will grow to US$20.2 billion, with a compound annual growth rate of 30.6%. LEDs used to backlight displays are currently the main driver of this unprecedented growth. Applications include high-definition televisions (HDTVs), automotive displays, and a host of handheld devices. In order to maintain this amazing growth rate, LEDs must not only provide enhanced reliability, lower power consumption, and smaller/flatter form factors, but must also achieve significant improvements in contrast, picture clarity, and color accuracy. In addition, displays for automobiles, avionics, and marine electronics must maximize all of these improvements while accepting a variety of ambient lighting conditions, from bright sunlight to nights without moons. These display applications, implemented by Transistor Liquid Crystal Display (TFT-LCD), include infotainment systems, meters, and a wide variety of meter displays. Backlighting these displays with LEDs has created some unique LED IC driver design challenges because of the readability of the display under a variety of ambient lighting conditions. This requires LED drivers to provide a very wide dimming ratio and high efficiency conversion while being able to withstand the rigors of relatively harsh electrical and physical environments in automobiles. Finally, these solutions must provide a very flat, compact footprint while improving price/performance.
Figure 1: High Brightness LED Market Forecast (Source: Strategies Unlimited)
How can we support such an amazing growth potential in the automotive lighting market? First, in terms of producing light, LEDs are 10 times more efficient than incandescent lamps and almost twice as expensive as fluorescent lamps, including cold cathode fluorescent lamps (CCFLs), thus reducing the amount of light output (measured in lumens). Required electrical power. As LEDs evolve further, their effectiveness or ability to generate light lumens from electrical power will only continue to increase. Secondly, we are in a world that cares about the environment. When using LED lighting, there is no need to process, contact and remove the toxic mercury vapor that is common in CCFL/fluorescent lamps. Finally, incandescent lamps need to be replaced approximately every 1,000 hours, while fluorescent lamps can last for 10,000 hours, compared to LEDs with a lifetime of more than 100,000 hours. In most applications, this allows the LED to be permanently embedded in the final application. This is especially important in the case of backlighting for automotive instrumentation/navigation/infotainment system control panels that are embedded inside the car because they will never need to be replaced during the life of the car. In addition, LEDs are smaller and flatter than other lamps, so LCD flat panel displays can be very thin and require minimal automotive interior space. Also, by using red, green, and blue LED configurations, you can provide an unlimited variety of color lights. LEDs can also be dimmed and turned on/off at much faster than the human eye can detect, resulting in significant improvements in backlighting of LCD displays while allowing for extremely high contrast and high resolution.
One of the biggest challenges for automotive lighting system designers is how to optimize all the benefits of the latest generation of LEDs. Because LEDs typically require accurate and efficient DC current sources and dimming methods, LED driver ICs must be designed to meet these requirements under a variety of conditions. Power solutions must be efficient and reliable in terms of functionality and reliability, yet they are extremely compact and affordable. As a matter of fact, one of the most demanding applications for driving LEDs will be automotive infotainment systems and dashboard TFT-LCD backlighting applications, as they are in harsh automotive environments and must compensate for a wide range of ambient lighting. Conditions change and must be placed in a very confined space, all of which must be done while maintaining an attractive cost structure.
Automotive LED backlighting
Advantages such as small size, long life, low power consumption, and enhanced dimming capabilities have led to the widespread adoption of LED TFT-LCD backlights in today's cars, trucks, trains, airplanes and ships. LED backlighting is primarily from infotainment systems, which typically have an LCD display that is mounted in a central part of the dashboard so that drivers and passengers can easily see where they are and perform audio tuning. And various other tasks. Many newer car designs use a single dashboard to backlight all display instruments that are easy for the driver to control, as shown in Figure 2. LED backlighting for the dashboard is often shared with infotainment systems, making it easy to read the numbers on the control panel. Similarly, many vehicles, including cars and trains, as well as LCD displays mounted behind the aircraft seats, allow passengers to watch movies, play video games, and more. Historically, such displays have been using CCFL backlighting, but replacing relatively large CCFL lamps with very flat white LED arrays to provide more accurate and adjustable backlighting and a working life that exceeds the life of the vehicle or aircraft, which It has become more and more common.
Figure 2: LED Backlighting Dashboard
There are several positive implications for using LEDs in such environments. First, LEDs never need to be replaced because their reliable life span exceeds 100,000 hours (11.5 years of service life) and has exceeded vehicle life. This allows automakers to permanently embed LEDs into the interior backlighting system without having to leave room for replacement. Because the LED lighting system does not require as much depth or area as the CCFL lamp, the style can change significantly. In addition, LEDs are generally more efficient than incandescent lamps in providing light output (in lumens) from input electrical power. This has two positive effects. First, LEDs leak less electrical power from the car bus, and just as importantly, LEDs reduce the amount of heat that needs to be dissipated in the display, eliminating the need for bulky, expensive heat sinks.
Another important benefit of LED backlighting is the wide dimming ratio capability offered by high performance LED driver ICs. Since the interior of the car is subject to a wide range of ambient lighting conditions, including every change from direct sunlight to complete darkness, the human eye is very sensitive to small disturbances in the light output, and the display needs to be adjusted accordingly. Dark or bright, so first and foremost, LED backlighting systems offer very wide dimming ratios from 1,000:1 up to 30,000:1. With a suitable LED driver IC, this wide dimming ratio is relatively easy to achieve, while CCFL backlighting is not possible. Figure 3 shows an LED backlighting dashboard and an infotainment system display with shared LED backlighting.
Figure 3: LED Backlighting Dashboard and Navigation Display
Automotive LED lighting design parameters
To ensure optimum performance and long operating life, LEDs require efficient drive circuitry. This type of driver IC must be able to operate on a very demanding automotive power bus, and is economical and space efficient. To maintain a long working life, first and foremost, do not exceed the LED current and temperature limits.
One of the major challenges in the automotive industry is to overcome the harsh electrical environment on the automotive power bus. These main challenges are called transients of load dump and cold car launch. Load dumping refers to the situation where the battery cable is disconnected while the alternator is still charging the battery. This can happen when the battery cable is not securely connected and the car is running, or when the battery cable is disconnected and the car is driving. This sudden disconnection of the battery cable can produce transient voltage spikes of up to 40V because the alternator is trying to fully charge a battery that is no longer present. Transient voltage suppressors on alternators typically clamp the bus voltage to approximately 36V and absorb most of the current surges; however, the DC/DC converter downstream of the alternator is subject to this 36V to 40V transient voltage spike. These converters are required to be uncorrupted and regulate the output voltage when such transient events occur. There are a variety of different protection circuits to choose from, usually transient voltage suppressors. Transient voltage suppressors can be used externally, but add cost and weight and take up space.
"Cold car launch" refers to what happens when a car engine is subjected to cold or freezing temperatures for a period of time. The engine oil becomes extremely viscous and requires an engine starter to provide more torque, which in turn draws more current from the battery. This high current load can pull the battery/main bus voltage down to 6V when ignited, after which the load typically returns to the nominal 12V.
Fortunately, there is already a solution to these problems, that is, Linear Technology's LT3760, which can be damaged in both cases and adjusts to a fixed output voltage. The LT3760's 6V to 40V input voltage range makes it ideal for automotive environments. Even when VIN is greater than VOUT (which may occur at 40V transients), the LT3760 will still regulate the required LED current.
Since most automotive LCD backlighting applications require 20W to 35W of LED power, the LT3760 is designed to meet these needs. The device boosts the automotive bus voltage (6V to 18V / nominal 12V) to 44V to drive eight parallel LED strings (each with 10 80mA series LEDs). Figure 4 shows a schematic of the LT3760 driving eight parallel LED strings, each consisting of 10 80mA LEDs with a total power of 28W.
Figure 4: 28W LED backlight circuit with LT3760 and 90% efficiency
The LT3760 uses an adaptive feedback loop design that adjusts the output voltage to be slightly higher than the highest voltage of the LED string. This minimizes the power lost through the ballast circuit and helps optimize efficiency. The circuit in Figure 2 provides greater than 90% efficiency. This is important because it eliminates any heat dissipation requirements and results in a flat solution with a very compact footprint. As far as driving an LED array, it is equally important to provide accurate current matching to ensure consistent backlight brightness across the entire panel. The LT3760 guarantees less than ±2% change in LED current over the -40 to 125 degree temperature range, and as can be seen in Figure 5, it is typically close to ±0.5%.
Figure 5: LED current matching in Figure 4
The LT3760 uses a fixed frequency, constant current boost controller topology. The device uses a single 60V external N-channel MOSFET that can drive up to 8 strings of LED strings consisting of up to 10 100mA series-connected LEDs. Its switching frequency is programmable and can be synchronized from 100kHz to 1MHz, allowing it to provide optimum efficiency while minimizing external component size. The design also allows the device to run four strings of 200mA LED strings or even two strings of 400mA LED strings. Each LED string can use the same number of LEDs or can operate asymmetrically with a different number of LEDs per string.
The LT3760 provides direct PWM with a dimming ratio of up to 3,000:1 and analog dimming through the control pins (providing a dimming ratio of up to 25:1). In applications that require up to 30,000:1 dimming ratio, these two dimming functions can be combined to achieve the desired dimming ratio. It seems that with the improvement of automotive display technology, most manufacturers prefer to use higher LED current (50mA to 100mA) to make the display more readable under bright ambient lighting conditions, and prefer to use larger dimming. Than to compensate for changing ambient lighting conditions.
In addition, the LT3760 has integrated protection features including open and short circuit protection and a /FAULT diagnostic pin. For example, if one or more LED strings are open, the LT3760 will adjust the remaining LED strings and set the /FAULT pin high. If all LED strings are open, the device will still regulate the output voltage, and in both cases, the /FAULT pin will be set high. Similarly, if a short circuit occurs between VOUT and any of the LED pins, the LT3760 immediately disconnects the channel and continues to regulate the remaining channels. Deactivating this channel protects the LT3760 from high power heat dissipation and ensures reliable operation. For additional LED protection, the LT3760's CTRL pin allows the LED current derating curve to be set by the ambient temperature of the LED string. An NTC resistor placed close to the LED reduces the CTRL pin voltage as the temperature rises, reducing the LED current. Other features that optimize readability include output disconnect during shutdown, programmable undervoltage lockout, micropower shutdown, and internal soft start.
in conclusion
The unmet need for higher performance and affordability drives the continued acceleration of LED backlighting applications in automotive displays. These requirements must be met by the new LED driver IC. As a result, these LED drivers must provide a constant current to maintain consistent brightness regardless of the input voltage or LED forward voltage, must operate at high efficiency, must provide a very wide dimming ratio, and must have various protection features to Improve system reliability. Of course, these LED driver circuits must also provide a very compact, flat and thermally efficient solution footprint. Fortunately, Linear Technology is constantly redefined the LED driver family to meet these demanding challenges with high-brightness LED driver ICs such as the LT3760 for display applications. In addition, Linear Technology has developed a complete line of high current LED driver ICs specifically for automotive applications ranging from LCD backlighting to turn signal lights and advanced forward lighting headlights. As automotive lighting systems continue to demand higher performance LED drivers, designers will also have IC solutions that meet their needs.
Like to play games for the computer configuration,Gaming Keyboard have certain requirements,mouse as one of the most important accessories,is also very important.While Wireless Gaming Mouse is fine,there are still friends who find the delay and charging a hassle and prefer a wired mouse.Compared with the wireless mouse in business office portability. Wired mouse is more suitable for esports games,whether in terms of transmission delay or anti-interference ability convenient wired mouse is stronger than wireless mouse. Therefore, it is essential to choose a suitable wired mouse for those who often play esports games.
Playing games are generally selected cable mouse, cable mouse data transmission is stable,perfect,playing games do not have to worry about losing frames.The Wired Gaming Mouse has a huge advantage in stability because it is directly connected to the computer with a wire, so it has little interference from the outside world.More suitable for the mouse operation requirements of the game and design use. Wired mouse also has some disadvantages,such as can not operate too far, can only be used in the vicinity of the chassis (mouse wire length is limited).In addition,due to the cable, it will be a little messy feeling, and its disadvantages are summarized as follows. It drags and drags and feels uncomfortable to use, which is inevitable unless you have to use a wireless mouse.Use distance is short.This also can't be done.But if you don't think the mouse cable is troublesome, now there is a USB extension cord to sell, as long as you want.
Wired Gaming Mouse,Led Wired Gaming Mouse,Wired Optical Gaming Mouse,Both Wired And Wireless Mouse
Henan Yijiao Trading Co., Ltd , https://www.yjusbcable.com