2017-04-12 09:49:38
SARA Series

Applications
2012-06-18 10:55:47
Less means more, why should you pay more attention to LED datasheets

Light designers have a continuously growing choice of elements they can use in their projects, as well as companies that are manufacturing those elements. This is directly connected to the necessity of correct analysis of datasheets and parameter comparison.

 

Current, voltage and power

 

In the last few years the priorities of LED purchasing have shifted, the flux of one diode becomes less important than the efficacy and cost of the whole system. Mid-power products became more popular, because of their lm (lumen) to $ ratio. 5630 casing diodes have appeared in the portfolio of many manufacturers, and their use in lighting projects allowed to build systems with better – more uniform – light distribution. Provided that the overall power and brightness are enough for the project. Reliable comparison of these LEDs requests, in the contrary of also popular 3535 package, checking more than only certificates, prices and tables in the datasheets. Unfortunately every manufacturer decided to use a different nominal current (ranging from 60mA to 120mA), so the first step is to decide one value and recalculate the other values according to the provided characteristics – flux in relationship to current and voltage, the power of one diode and finally the efficacy.

Seoul Semiconductor is using 100mA as the nominal driving current, which in case of STW8Q14BE diode, in cool white, gives 38lm of brightness and a efficacy of 119lm/W. These parameters allow to design a light source with a 4000lm brightness on a FR4 board with a 10x10cm area (with the necessary space for heat management). If the desired area should be smaller, the need of using 1W (or higher) power LEDs occurs, and a MCPCB is a necessity. Predicting these problems, Seoul Semiconductor has released the 3020 diodes, enclosed in a smaller package, but with brightness and efficiency equal to (STW8B12D) or higher (STW9B12D) than the 5630 series – allowing the reduction of the FR4 PCB area by appx. 40% to have the same effect, which leads also to overall price reduction.

 

When it gets hot

 

In many cases the desired brightness of the lamp forces the use of more powerful light sources. Currently the most popular are 3535 package diodes or similar. In this case comparison and choice seems relatively easy, all parameters are shown in relation to a 350mA driving current. Lower voltage, higher flux and we seem to know, which component has a better efficiency. Unfortunately, all of the datasheets contain parameters for a Junction Temperature of 25°C, and every experienced engineer knows that even with a very good heat management the Tj will be at least a few times higher (90-100°C are quite normal values). And again a characteristic analysis comes handy. This time – flux degradation in relation of junction temperature, which usually is more than 20%.

In the datasheets of Z5P and Z5M Seoul Semiconductor has added one row to the flux values (measured at 100°C), with anamazing small difference – only a few percent. This result allows to use the “best hot lumen maintenance” description for these LEDs.

Next generation 

 

All thanks to the next generation of chips used in the improved Z5 series. Besides the great results they allow also to increase the driving current to 1A (Z5P) and 1.2A (Z5M), because their sizes have been increased. These new LEDs are perfect for interior lighting as well as for more demanding exterior lighting systems.

Light degradation characteristic in relation to Tj - Z5 series (5%, 3%) and the competition (over 21%) at 120°C

Conclusion


Help regarding component choice and explanation of all the hidden parameters is only one of the benefits of choosing the right, authorized  distributor. Years of experience, current knowledge and direct contact with the manufacturer can result in a quicker time to market for your products.

In case of technical or application questions, our international team of application engineers will be pleased to support You under the following e-mail address:

marketing@microdis.net

 

Broad range of services offered by Microdis are available by our sales offices across Eastern Europe.