Lighting designers' efforts to illuminate light-emitting diodes ( LEDs ) are due to the many potential benefits that are lacking in incandescent, halogen, fluorescent and aerated/arc lamps. Although the business opportunities of today's LED lighting systems are large, what really illuminates lighting designers is the basic design of Solid State Lighting.
To succeed in LED lighting design , three factors must be closely monitored: electronic drive, thermal management, and optical efficiency. Only by successfully balancing these three factors can you enjoy the advantages of long life, high electronic efficiency, high brightness and solid color (or color temperature strictly controlled by white LED) brought by solid state lighting. This article will provide designers with valuable references on how to choose high-power LEDs (1 watt and above) and design circuit drivers.
LED series configuration to achieve ideal lighting standards
LED dies for solid state lighting are typically made of semiconductor materials. Red, orange, and amber LEDs are almost always made of InAlGaP, while green and blue LEDs are mostly made of InGaN; while white LEDs use blue LEDs with conversion phosphors, from an electronic drive point of view. It is the same as the blue LED. As with standard PN junction diodes, when the LEDs are forward biased, they begin to conduct current; unlike standard PN junction diodes, the LEDs in forward biasing illuminate. The current is driven by the LED (the LED and the extremely low DC forward voltage of the LED, which makes the LED different from other light sources. The typical forward voltage VF of the InAlGaP LED is 2 to 3 volts, while the forward voltage of the InGaN LED is It is 3 to 4 volts, but the luminous flux of the LED is proportional to the forward current IF. The first problem in the electronic drive design is the fixed drive current, and the second problem is to determine the voltage range of each LED. Look carefully at the manufacturer's The product data sheet will find the recommended drive current and corresponding standard values ​​of VF, dominant wavelength and luminous flux, minimum and maximum values. The typical VF vs. IF comparison chart (Figure 1) should note that the current is independent. The amount of current indicates that current control is the key to LED drivers .
Figure 1 Comparison of VF and IF of red InAlGap LED and white InGaN LED
In recent years, although high-power LEDs have undergone significant development, single devices are still unable to meet general lighting needs. The flagship product produced by the industry is a 1-watt white LED (standard color temperature of 6,500K) that produces 100 lumens of luminous flux. However, compared to a typical 60-watt incandescent bulb, the LED illumination angle is relatively narrow. The typical luminous efficiency of incandescent bulbs is 15 lm/W, which produces 900 lumens of light, which is distributed almost evenly in all directions. If the goal is to illuminate the space previously used with incandescent bulbs, multiple LEDs are required. Connecting the LEDs in series ensures that the current flowing through each device is equal and that each component emits a uniform light. In summary, connect as many LEDs as possible and then add serial circuits further until the total light output reaches the desired standard. The number of LEDs that can be placed in series depends on several factors, but is primarily determined by input voltage, electronic specifications and safety standards, and LED drivers . Figures 2, 3, and 4 show three methods of driving an illumination system consisting of nine 1 watt LEDs, respectively.
The advantage of the LED configuration is that a single LED driver can be used (Figure 2) and the current through each LED is equal. The disadvantage is that it results in the highest output voltage, which requires larger, more expensive circuit components and meets safety requirements. In addition, if any of the LEDs has an "open circuit" problem, all of the LEDs will not be illuminated.
Figure 2 Nine LEDs in a single serial circuit
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