Electronics > Projects, Designs, and Technical Stuff
PCB design practise
silvestron:
Hey folks! I've recently found that I absolutely love doing PCB design since it's like a video game puzzle but in the end I can actually make something that does something!
For poops and gigs and since I don't have any active projects on my mind, I decided to take a stab at making a drop-in 7805 replacement switch-mode regulator using the cheapest appropriate buck converter I could find in a few minutes of searching, the AP65211A.
I don't really have much experience with buck converters, so decided to just start with their typical application circuit and component values, and then enjoying the challenge of shoehorning all that onto one side of a 10x16mm board.
Anyway, now that I've got it down on paper, just wondering if anyone had any thoughts on my design and layout? I'll post the schematic and screenshot from kicad here, and will have them in a github repo that I can share if anyone wants to take a full look. Happy to answer any questions and take any feedback, even negative!
Cheers!
doktor pyta:
Welcome silvestron!
Just some thoughts:
1. I'd suggest to remove the hole for the heat sink. It will give You more space for optimal layout.
U1 does not have thermal pad and has relatively high thermal resistance to PCB. So I think the heat sink won't help a lot.
2. I'd start with laying out group [C1, U1, L1, C4] optimized for possibly shortest tracks and smallest current loops.
silvestron:
You're definitely right re: point 1, this wouldn't need a heatsink and it really is just getting in the way - esp since I realised after posting that I hadn't updated the track width to match the current rating and trying to squeeze everything in with .78mm tracks is TIGHT!
Thanks for the tip on the group to start with. I tried to keep them as close as possible to where their power was used, ie C1 is input cap, so closest to U1 and C4 is output so closest to OUT pin, but I can definitely see that L1 is facing the wrong way. Back to the drawing board!
doktor pyta:
3. please take some time to consider how the three pins will be attached to the PCB.
Metalized holes + wires ? SMT pad + extra vias to prevent delamination + wires ?
silvestron:
I had originally used 2.54mm right angle pin headers, but much like the mounting hole I kinda wanted to keep full compatibility with the OG 7805 and have the back flush mountable to whatever, even if it doesn't really need to be, hence the SMT pads which I would plan on soldering standards straight pin headers to.
Good point about delamination though! How do extra vias help prevent that? That's a new concept for me.
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