A look at the practical System Design with LEDs

By Scott Watson

Lighting designs are made up of various components such as LEDs, ballasts, drivers, thermal performance and a lot more.  In most cases, these components have to be integrated to make a complete design.  The LEDs in particular have vital roles to play.  A look at the practical system design with LEDs is therefore very important.

A printed circuit board can be made for the LEDs. There’s also the need to design optics in order to get the light from the LEDs to go to the appropriate direction and also have the right characteristics desired.  The LEDs ought to be designed to meet the needs of the customers.  This will surely enhance their efficacy even as new versions of the devices are being manufactured.  There’s also the need to make the design very flexible in order to accommodate the next generation of components that are fast coming out.  Discussed below are some aspects of the practical system designs meant for LEDs.

PCB design
PCB refers to “printed circuit board” design. Some LED specialists use the design a great deal.  Many of them also focus on power supply layouts as they carry out the design.  The details of the PCB design are very voluminous. However, some pointers will be given here.

In the first place, making a good schematic is very vital for creating quality PCB.  This is because; such a schematic will be easy to follow.  The specialists need to make it as simple as possible.   The good schematic also helps in providing a simple layout   for the PCB design.  If you spend quality time in preparing a good schematic, it can easily turn out to be the best guide that tells you where each component should go as you work on the PCB design.  You’ll be able to arrange some components together in order to come out with a nice design.

Basically, the best way of drawing a good schematic is to begin by numbering all the components from the upper left and then proceeding towards to the lower right.  Some of the components may not have clear sequential numbering system but you can still get them arranged neatly.  This helps you to locate them   on the schematic whenever you want to carry out any design.  You can also enhance the schematic in diverse ways.  You can use the ground for all the power components. You can also separate the bigger components from the smaller ones.  You can use special alphabets and characters to mark components on the schematic board.  You may also use nice color code to mark components on the schematic.  You can use yellow to indicate high current traces while you can also use red to indicate high voltage traces.  By so doing, the PCB design layout can easily be followed.

Meanwhile, there’s a checklist of design elements you need to include in your PCB design outline. Here are some points to note:

•    Use  real pin-outs to  draw the schematic

•    Make sure you place the reference designators in order. You have to start from 1 till you reach the end. You shouldn’t skip any number.

•    You have to assign reference designators beginning from the upper left hand side and move down towards the lower right hand side.

•    Make sure you have separate symbols for the power and signal grounds

•    Use color code to represent high current, high frequency and high voltage traces.

•    Try and make notes about each component in order to get the right attention for it.


The Grounding

It’s important that your PCB should also have a unique ground system.  You don’t just go ahead to connect all the grounded components together with possible traces.  You have to connect all the power grounds together with strong traces.  You need to   distinguish all the available grounds. The power grounds usually carry substantial currents which may reach up to 100mA.  You can use enough copper as the space allows separating them.  You’ll then go ahead to connect all the grounds together.   They should also connect back to the input capacitor’s ground.

You have to avoid making unnecessary loops on the power ground.  By loops, we mean two ways for the current to get back to the input. If you create such loops, there’s bound to be an EMI problem.   There’s a need to create via in the middle of the ground plane instead of creating it at the edge of the plane. It’s also necessary to retract the place a little bit away   to avoid giving room for small traces.  It’s also important to allow each ground to link directly back to the input via the plane rather than trying to connect one trace to the other in a chain.

You need to make sure that all the power grounds are directed to the ground plane through   one via or more.  The small grounds should be combined together using traces or separate tiny plane.  You don’t need to hook them directly onto the power ground.  The separate small plane is simply called an island. It has the sole purpose of keeping the high currents on power grounds from causing voltages on sensitive nodes.

Other Necessary Connections
There are other necessary connections that must be made to make the entire design feasible.  Power connections   should be well arranged. Wide traces can be made on the design but they should only be wide enough to fit into the design.  Extra spaces should be created between some traces or high and low voltages. This is necessary in order to avoid arcing problems.  High current traces together with the power traces should be wider enough.  This helps in reducing voltage dissipation and lowering of efficiency.

Again, high frequency traces must not cross over other traces.  They should be short enough.  This helps in reducing the loop area of radiation.

Getting the Light Out
The end purpose of designing LEDs is to generate light.  The LEDs actually produce light but there are more to that.  The light produced should have a certain unique distribution. It has to be bright in some conditions and dark in orders.  The light should also have specific colors.  All these must be put into consideration when looking at the practical design systems for LEDs.

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