In the past few years, the improved efficacy of modern LEDs has allowed engineers to use fewer chips in their lighting fixtures to achieve the same light output as the old design. The key benefits are reduced cost and simple design. Today's chips, strong anti-jamming capabilities have allowed engineers to further enhance the brightness of individual LEDs by increasing the forward current and reducing their number even further in a phase of the approach taken in a given design (see the technical section of the article " Maximize LED brightness to drive down system cost "). However, although the LED light is brighter, the higher the drive current is brighter, increasing the brightness positive value and reducing the cost (the chip has the highest efficiency at relatively low current, please refer to the technical pavilion article "Determining the cause of LED efficiency sag" ). This increases power consumption and negates the cost of reducing the gain of the component over the life of the lighting device. The increased power consumption also makes the chip run hotter and shortens its life. This article describes the trade-off between cost, design simplicity, power consumption and longevity, running a given LED application at high drive currents. Looking for limits In the early days of LEDs, the fledgling technology provided less light and was more fragile than today, and engineers suggested limiting the LED drive current to maximize efficacy and extend the life of the device. However, the development of the past two decades (Fig. 1) has seen a dramatic increase in LED light efficiency and resistance to high junction temperatures, resulting in a significant increase in drive current. Many engineers question why low drive currents are still necessary when such current limits the chip's output to a fraction of the capacity. Osram high power LED image Figure 1: Today's high-power LEDs allow fewer chips for a given output of a lighting fixture. In addition, evidence from industry-standard tests such as the LM-79, LM-80 and TM-21 is increasingly showing that modern LEDs can quickly kill thousands of hours of work in previous generations of equipment. Manufacturers are encouraged to use higher drive currents by offering chips that can push more than 350 mAh equipment at the beginning of the year. Cree's XLamp MK-R, for example, is a 120 lm/W, 1000 lumens (at 1.4 / 6 V) LED that can be driven up to 2.5 A. Similarly, Philips Lumileds' LUXEON M is 134 lm/W , 1000 lumens (2.8 A / 2.8 V) chip, the chip can drive up to 4.8 A. However, due to the strong modern LEDs, there is no limit to the extent to which this strategy can be adopted. Increasing the drive current increases the luminosity, which also doubles the power consumption and pushes up the temperature. In particular - lighting applications from mains power supply have increased power consumption to a certain extent, when trading offsets other benefits of reducing LED count, but engineers still need to make a sensible decision about the working point of the luminaire that is acceptable for low power A key advantage over other light sources that consume touted LEDs. In addition, with modern thermal management technology and products, while higher junction temperatures can now be tolerated in solid-state lighting, the technology used in limited spaces, for example, how much heat can be used to get a safety ceiling Computing power consumption How do a design engineer know the best working point in his or her application for LEDs? This depends a lot on the application of course, but there is actually no clear answer. The key is to identify key design parameters. For example, the purchase cost of the final product may exceed the life of the product at the expense of greater energy consumption, dictating fewer LEDs. Or limiting chromatic drift (increasing with temperature - see the technical section of the article "About white LED chrominance thermal effects") may be important, high-quality lighting fixtures that require more LEDs to drive at a lower current to Keep the temperature down. However, a good starting point is to check the effects of forward current on power consumption and effectiveness. Forward current and efficacy are rarely detailed in the LED data sheet. Table efficacy data is also often difficult to track down. However, it is relatively simple to use forward current (IF) and forward voltage (VF), and to calculate this key indicator for forward current and relative photometric data. Another useful number is the typical lumen output at a given IF. This data is usually available from the manufacturer's data sheet. LED brightness (ΦV), power consumption, and power efficiency (η) can then be calculated with the mid-frequency. As mentioned earlier, the peak power is used for LEDs to occur at relatively low IF and tail destabilization steps as the current approaches the maximum level [1]. Figures 2 and 3 show the forward current (IF) vs. forward voltage (VF) and forward current vs. white LEDs with relative brightness of OSRAM OSLON SSL 150, a popular device for lighting applications. According to the manufacturer's data sheet, this LED produces 147 lumens of 142 lumens per watt at 350 mA and 2.95 V. But at VF IF, the LED can drive up to 1 A, so let's consider a 1100 lumen Two design solutions for lighting fixtures. (For ease of calculation, the LED driver has been assumed to be 100% efficient). Picture of forward current forward voltage Figure 2: Forward voltage of the OSLON SSL 150 white LED for forward current. The forward current to the relative brightness is a picture of the OSLON SSL 150 white LED Figure 3: OSLON SSL 150 white LED for relative brightness forward current. In the first hypothetical example, the designer chose to drive the LED at 350mA (hence - as shown in Figure 2 - at 2.95V forward voltage). The manufacturer's data sheet shows that each LED produces 147 lumens under these operating conditions. The power consumption is 1.03W ̄, so the effect is 142 lumens / watt. Designers who need to get the output from the fixture will need 1100 lumens / 147 lumens = 8 LEDs. Therefore, the total power consumption of the fixture will be 8.24 W. A fellow designer has decided to take another route and choose to push up the drive current, allowing her to reduce the number of LEDs in the fixture and simplify the bill of materials for design and cutting. At this point the designer chose a drive current of 800 mA (the ability of the inner LED as well). The forward voltage shown in Figure 2 will climb to 3.18 V. Figure 3 shows that the relative luminosity of the LEDs at this drive current has climbed to 1.9, so now each device produces 1.9 & TImes; 147 lumens, or around 279 lumens . However, the power consumption of each device has now increased to 2.54 W and the efficiency has dropped to 110 lm/W. In order to achieve a specified output of 1100 lumens, this alternative design of lighting fixtures would require four LEDs so the designer has achieved certain design goals. However, total power consumption has climbed to 10.2 W (more than 20% for the original design). Beware of shortcomings Increasing the drive current boost LED brightness is a good way to reduce the number of LEDs in the lighting design with the specified output. Fewer LEDs reduce design complexity and simplify the product; but designers should be aware of the shortcomings. First, the LEDs are less efficient at higher drive currents, and the increased (given output) power consumption luminaires use fewer devices. Second, higher drive currents increase LED junction temperature and shorten equipment life. Third, both high drive current and higher temperature have been shown to cause the chromatic drift to drift away from the intended color point. Such drift is difficult to control and will result in the same design, different light projections, which can lead to consumer disappointment.
Electronic Burglary Safes
Electronic burglary Safes are safes that have passed Chinese 3C certification and use digital password lock systems.
Details:
They are convenient, safe and easy to use;
The safes provide high levels of security;
The Passwords can be changed easily to prevent theft and they`re also quite convenient for official usage because the personnel turnover in the office is normal, hence changing passwords is necessary;
3 times wrong passwords will cause alarm;
The emergency supply can be used when the electricity is off or in case of a black out or EMP Surge;
They possess elegant designs hence they not only provide protection but also serve as decoration pieces.
Electronic Mini Safe,Electronic Safe Box,Electronic Security Safe,Electronic Lock YONGFA INTELLIGENT TECHNOLOGY SECURITY CO., LTD. , http://www.yongfa-safe.com
