Electronics > Beginners
First time laying out a PCB. Questions regarding power and ground planes.
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electrodoot:
Hey everyone. I've just joined the forum and have some questions about laying out power and ground planes the proper way on a PCB. This PCB is a power supply.

My first thought was to draw a large ground plane on the bottom layer of the PCB and use vias to connect all the ground pins to the plane, but then I realized that the LM2576HVS voltage regulator I was using has a large tab which must be connected to ground. Is it correct to connect that tab to the ground plane using a via as well?

And while I have your attention I'll ask about the power rails. This board needs 9VAC and 5VDC rails. I was just going to place these on opposite sides of the top layer of the board. Is this the right way of doing this?

EDIT: I forgot to mention, I am using surface mount components.

If it is relevant, I am using KiCAD.

Thanks in advance!
Jwillis:
Up to you but I don't see it necessary to use a double side board for such a simple design.Even most manufactured Switching supplies that size are single sided.But I suppose theirs no reason why you couldn't put your output rails on one side .Also your main variable output should have no less than 2mm wide traces.I could be wrong on that but I usually over build things anyway.
daubmaso:
Don't worry about the ground plane until after you've routed everything. And I wouldn't put vias everywhere, instead just have a ground plane on the top and bottom of the board. Definitely make sure the tab is directly connected to a ground plane, it will act as the heat sink for the regulator. A via will just add extra thermal resistance and your regulator might over heat.

You don't need the power rails to be separated across the board, just put them where it is most convenient.
electrodoot:
Thanks to both of you! I really wasn't sure what the best practice was.

Does it make sense to draw the ground plane to be the size of the board layer? When I draw the traces not connected to ground it should separate them from the ground, correct? At least that's what I saw KiCAD doing when I was playing around.
daubmaso:
I haven't used kicad before, but in eagle you make it larger than the board. Just make sure you name it gnd so that the software knows it's supposed to connect to the ground net. After that it should auto-fill everything and connect the ground nets together, while leaving clearance for other traces.

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