The latest breakthrough in LED technology has enabled people to produce LEDs that can output a wide spectrum of light, rather than just traditional red and green derivatives. Therefore, the absolute number of LEDs used in products (lighting and other aspects) is increasing exponentially.
From flashlights to car headlights to backlighting of LCD TV displays, LED applications are expanding into new areas. In short, the most important driving force behind the rapid growth of LED applications is the efficiency gain brought by LED technology (that is, the energy consumption per watt can provide higher lumen lighting output).
Power requirement
LEDs have different power requirements than previous incandescent lamps. In addition, depending on the power level and overall system requirements, the best solution for driving LEDs is different.
In traditional lighting solutions (such as incandescent lighting), the load is resistive. The power consumption and the corresponding brightness of the lamp are a function of the voltage applied to the lamp and the resistance of the lamp (according to Ohm's law).
The light intensity increases or decreases as the input voltage changes. Taking the car headlight as an example, when the engine is started, the battery voltage is low, so the headlights will be darkened; once the engine starts running, the battery voltage will recover and the headlights will return to the standard brightness.
LEDs are fundamentally different from traditional incandescent lamps. The brightness of the LED is controlled by adjusting the LED current, and the resistance of the LED load varies with the applied load. LEDs require a constant current instead of constant brightness and resistance to maintain a constant brightness. The method of achieving the above effects differs depending on the power level of the LED.
For very low power LEDs, a very simple circuit as shown in Figure 1 is basically sufficient. Compared to R, the effective resistance of the LED is very small, so the current flowing through the LED is determined by V/R. Its disadvantages are as follows:
Figure 1 Simple Power Solution for Resistor-Limited LEDs
â— Brightness is a function of voltage. The change in V essentially changes the current, which in turn changes the brightness of the LED. Back to the original example of a car headlight, the light will still be weak when the engine first starts.
â— This solution cannot take advantage of the efficiency of LEDs. Because R is very large compared to the resistance of the LED, most of the power is consumed on R.
High power LED
For high-power LEDs, in order to maximize the efficiency advantages of LEDs, a current-controlled solution is needed. Figure 2 shows an example of such a solution.
Figure 2 Current controlled LED power supply solution
V
There are several advantages to using PRM and VTM to provide a constant current compared to conventional methods. The use of VTM in the system enables current multiplication at the point of load. According to the following formula, the output current of VTM is proportional to its input current, and the ratio is a fixed turns ratio K, IOUT = IIN/K.
Therefore, in current controlled applications, the output current of the VTM can be controlled by detecting and controlling its input current. Detecting lower currents requires smaller sensors that consume less power and improve overall efficiency. Similarly, high efficiency and high power density make the entire LED system low in temperature and maximize the lumen output per watt of energy consumed.
An important additional advantage is that the current flowing through the LED (IOUT) is not a function of the input voltage. Therefore, in our example of a car headlight, as long as the current flowing through the LED remains constant, the brightness of the LED will remain constant regardless of the battery voltage. This is because the PRM is a variable negative resistance that can change with V, providing a way to keep the current constant.
More importantly, the resistance of the PRM is the effective resistance, not the real resistance, which means that the power loss is very small and not a function of the effective resistance value. Therefore, most of the power is consumed on the LEDs, making this solution as efficient and efficient as the LEDs it uses.
Some of the shortcomings of this solution include its complexity significantly higher than the solution shown in Figure 1, so its proper implementation requires more attention and control. The increased complexity also brings cost increases, so this solution is more suitable for high-power LEDs, and the power saved in high-power LEDs (and the cost of electricity in LED operation) can more easily compensate for the increased cost and the complexity.
Finally, there are different solutions ranging from simple to complex for different power requirements of LEDs. The resistive current limiter shown in Figure 1 is simple and low cost, but it is inefficient for high power LEDs and is not suitable.
The adjustable current source shown in Figure 2 optimizes efficiency and size, but they require higher cost and increase complexity. Adjustable current sources offer additional advantages, such as being unaffected by input voltage fluctuations, which may or may not be important for overall system goals. Designers of LED power supplies should be aware of the different options available to power LEDs and the goals of the entire system.
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Newly renovated landscape lighting in Shanghai Waibaidu Bridge
Light effect diagram
The Waibaidu Bridge is old and old, and its appearance is the biggest change in the past. It may be a new installation of landscape lighting. The new landscape lighting is divided into two modes: normal and festive. The main color is warm yellow. On the front side, the bridge with the north and south lights is like a seagull's wings, flying lightly on the water. In the festival, the lights can be changed into blue, silver, purple and other colors. The reporter learned from the scene yesterday that the installation of landscape lighting is about to begin.
Various colors can be changed during festivals
As the designer of this landscape lighting, Zhang Ajing, deputy general manager of Shanghai City Light Lighting Design Co., Ltd. told reporters yesterday: The construction of the Bund is classical and solemn, and the Lujiazui on the other side is modern and fashionable. The architectural characteristics of Waibaidu Bridge can be summarized as a combination of historical complexity and modern simplicity. Therefore, our lighting design is to express the simple and heavy historical sense of architecture and the modern sense of industrial civilization. Classical and modern coincide on a bridge.
According to reports, the new landscape lighting is divided into two modes: normal and holiday. The usual mode has the choice of bright and non-bright outer frame. The main color is warm yellow, and the front side looks like the bridge between the north and the south is like a seagull's wings, flying lightly on the water. In the festival, the lights can be changed into blue, silver, purple and other colors.
The company's director lighting designer Ying Jinsong revealed that the warm yellow is mainly considering that the Waibaidu Bridge should be the continuation of the entire Bund landscape lighting. In some important festivals or in order to cope with important activities, the landscape lighting of the Waibaidu Bridge is gradually changed to other colors through the intelligent control system. It can be coordinated with the night scene lighting of Lujiazui. Of course, it depends on the actual needs. At the same time, the lighting control can have two modes, automatic and manual, to ensure the control of landscape lighting.
Best observation point river interchange
In the future, on the Huangpu Road, Wusong Road, Zhapu Road, Changzhi Road and South Suzhou Road around Waibaidu Bridge, motorists can watch at night in the middle and near distance. For those who walk, the south side of Huangpu Park and Huangpu Road is suitable for medium and short distance static viewing. The Pudong Riverside Avenue side of Pudong can be viewed from a panoramic perspective. The best observation area is at the intersection of Suzhou Creek and Huangpu River. You can have a good night's sleep in Pujiang.
The installation of this luminaire is also different from the past. See no light. Zhang Ajing told reporters that this is to avoid possible glare pollution, but also to not affect the architectural landscape during the day. It is reported that the bracket and outer casing of the luminaire are painted with the same appearance color as the Waibaidu Bridge. The installation of the luminaire is fixed with a special material in the groove where the steel beam and the steel beam meet, which is difficult to find and does not hit a bridge. eye. In addition, it is equipped with anti-leakage, anti-shock and anti-theft monitoring equipment.
It is understood that the new landscape lighting uses LED light source instead of the original metal halide lamp. The total number of lamps is 2,000, originally only 490, but the energy consumption has dropped from 73 kW to about 42 kW, which is reduced. More than 30%.
By next month, the Waibaidu Bridge will be reopened and the lights at night will be of interest to visitors. The reporter learned that some bridges on the Suzhou River to the east of the North and South elevated, the design of the landscape lighting will also enter the agenda.
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