Small and wide input voltage LM2842 LED lighting

Most people believe that high brightness LED, HBLED) Will be a wise choice of lighting in the end. HBLED manufacturers greatly improve the product on the number of lumens per watt, continuously improve the product efficiency, it also makes the HBLED has become more and more popular. Believe that soon after, the LED on the number of lumens per watt will be much more than now level of fluorescent lamp.

LED lighting first replacement is mainly used in low voltage to shoot the light and track light these two areas. Including the standard size of replacing the original lamps and lanterns, such as: MR16, PAR20, PAR25, PAR30 PAR38. National semiconductor ( NS company) Has provided a variety of solutions used to beautify the LED, make it suitable for these occasions, including LM342X and LM340X series of LED driver. But no matter how the LED driver, they all face a common problem: how to heat dissipation. For these small size package, simply rely on the free flow of air to the role of heat sink is often not enough. This enables the designer must consider to add some to forced air flow fixtures. According to the size of the device, the most common way is to use dc fan, or adopt Synjet Nuventix company as a more delicate and durable solutions. Fans tend to save money, can be on the 5 v or 12 v dc voltage, but it is not easy to embed the lighting device, at the same time, the service life of the fan is tens of thousands of hours at most. Synjet, on the other hand, is designed specifically for these lighting installation, working voltage is 5 v dc, and the service life can be up to 100000 hours.

the standard input of these systems can be a dc or ac system. 12 v and 24 v ac system has been widely used in low voltage lighting system, at the same time 12 v and 24 v dc system is gradually promotion, and rising popularity. Due to the 12 v system is very common, so to design and drive a 5 v of the cooling system is not difficult. But it is precisely because there are so many systems, the distribution of the input voltage range will be very extensive, especially for ac input, the ideal situation is to be able to have a solution to a wide input voltage range for conversion, thus providing 5 v voltage, at the same time occupied space is small, can be easily embedded into the lighting device. Fortunately for small devices, LM2842 can well realize the above requirements, the similar models of LM2841 can also do it.

dc input system can be used as the input voltage transformer will be wider than directly into 5 v, which is the most easy and simple solution. Typical solution including the fan and the Synjet needed to drive current between 100 ~ 600 ma. LM2841 can provide current of 300 ma for small cooling system, LM2842 to power for the bigger, stronger cooling system to provide the current of 600 ma. Figure 1 shows the LM2842 design input voltage is dc 12 v or 24 v dc, can provide the required 5 v voltage. The whole scheme can provide up to 600 ma of current, to take up about a quarter of the PCB ( Printed circuit board) Area, so that it can be easily embedded into any improvement device. LM2841 based on exactly the same design, specifically for low current applications, and also allows the use of small physical inductance, which takes up less space.

however, as mentioned above, a number of 12 v and 24 v ac system is widely used, people are more hope they can continue to work after the improvement, rather than with more advanced dc system directly to replace it outright. This means that the design must be considered in a wider range of input voltage. To achieve this goal, you can simply use the bridge rectifier and a large number of AC - input capacitance of the original DC rectifier. Considering the line tolerance, 24 v ac system can provide the peak voltage will be 40 v. But if the minimizing input capacitance, the input voltage will be dropped to 10 ~ 12 v. LM2841 and LM2842 allow input voltage changes in a wide range, can provide enough power declined to ( 拒绝) And ensure the stable at 5 v output voltage accurately. Figure 2 and figure 3 respectively gives the ac 12 v and 24 v ac circuit diagram of the system.

here are a few things to note. Has the high RMS voltage 24 v ac input, make LM2842 current will be smaller. It also has a higher peak. For these reasons, LM2842 a smaller input capacitance can be used to maintain the operation of the reasonable input voltage. At the same time, it is important to note that the circuit in figure 2 and figure 3 is aimed at 600 ma the integrity of the output voltage is designed. Because of this, the obvious is that if the cooling system using low current, so the smaller input capacitance can be used in further circuit size. For example, if the LM2842 is replaced with LM2841, maximum output current is 300 ma, thus the input capacitance can be cut in half.

if you have the correct drive tools, LED thermal management will no longer be difficult problem.