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Selecting power supplies for LED lighting apps

Posted: 21 Oct 2014     Print Version  Bookmark and Share

Keywords:LEDs  luminaire  power supply  series  parallel 

Matrix configuration
In a matrix layout, the LEDs can be arranged in a similar manner to that of parallel configuration but there are links between each LED form string to string. The big advantage of this configuration is that if a single LED becomes open circuit, there is still a path for current to flow through all the other LEDs in that string and so light output is hardly diminished. The main disadvantage is that it is more difficult to control the current in each string as a current balancing device cannot be used. This means that the LEDs used must have a closely match forward voltage which could add to the cost.

Figure 3: LEDs connected in a matrix configuration.

Figure 4: LEDs connect by the multiple channel method.

Multiple channel configuration
Using this approach, the LEDs are arranged in series in multiple strings arrangements similar to the parallel and matrix configurations. This has the benefit that the total string voltage can be reduced for any given brightness required and as each string is fed from an individual power source the failure of any one string will not affect the other strings in any way. A disadvantage is that the power source will be more costly as each string has an individual output however it does allow for more flexibility in applications where the brightness of one string needs to differ from the others or where individual string dimming is required.

References
1) IEC61347 Part 1 – an overview of the standard is available at this link http://www.iecee.org/ctl/equipment/pdf/lite/IEC%2061347_1%202007%202007_06_04.PDF
2) IEC61347 Part 2, section 13 – an overview of the standard is available at this link http://www.iecee.org/ctl/equipment/pdf/lite/LITE_61347-2-13_%202006%202009_05_18.PDF
3) UL 8750 safety standard for LED lighting.—A presentation on UL8750 may be downloaded from this link http://www.americanlightingassoc.com/Downloads/Conference/2009-and-earlier/MichaelShulman_LEDFireElectricalSafety.aspx
4) IEC 61000-3-2 "Electromagnetic compatibility (EMC)—Part 3-2"—an overview of the standard is available at these links—http://epsma.org/pdf/PFC%20Guide_November%202010.pdf , http://en.wikipedia.org/wiki/IEC_EN_61000-3-2

About the author
Andrew Bryars is Technical Manager at XP Power.

To download the PDF version of this article, click here.


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