Electrolytic vs. Ceramic Caps

Questions about the Really Bare Bones Board
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bullet308
Posts: 1
Joined: Fri Aug 12, 2011 12:40 am

Electrolytic vs. Ceramic Caps

Post by bullet308 » Fri Aug 12, 2011 12:46 am

Hi:

I am working on an application for the RBBB where it might be exposed to rather high temperatures. Having just replaced a BUNCH of bad caps in a pile of Dell PCs, I am not that fond of electrolytics as used in the power supply on the RBBB. They are also some of the bulkier components on the board and I am trying to get it into a very small space. Is there any particular reason I cannot substitute ceramics, tantalums, or any of the other more reliable capacitor technologies on an RBBB?

Thanks, and loving all things Arduino so far. :-)

-Tom

scott-42
Posts: 12
Joined: Tue May 17, 2011 5:28 pm

Re: Electrolytic vs. Ceramic Caps

Post by scott-42 » Fri Aug 12, 2011 1:23 pm

My guess as to why the electrolytics are there is because the VRs specified ask for them in their typical application circuit diagrams (check the spec sheets for L4931 and LM2940). And I would further speculate that with the current design of the board to allow for multiple substitutions of the VR to suit your needs he went with a slightly over-sized cap to accommodate any popular VR choice (three are listed in the build instructions).

For a space constrained build (short of making your own board), I would change out the VR out to a surface mount part with surface mount ceramic caps. I like the MCP1702 which calls for ceramic caps. If you get a SOT-23A version, a couple of 0805 caps, and a little surfboard 6103 (http://capitaladvanced.com/6100.htm), you can mount all three chips on the tiny board and it will end up in the same pinout as the L4931, namely GND in the middle. It will actually plug directly into the VR holes on the board that way. You can bend the pins at 90 degree angles and it mounts flatter than the IC socket.

If you want to keep the same VR I'm not sure what changes you can make to the caps, that would probably be in the relevant datasheet for the one you are using on your build.

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