Reading Diodes / Capacitor question

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Kurt_
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Reading Diodes / Capacitor question

Post by Kurt_ » Sat Sep 02, 2006 12:58 pm

I need a diode for my DC/DC converter, and I found an old board with a lot of them. This post pertains to one (is pertains a word?)

But these diodes aren't like normal ones with bands and such. Yes, it does have a band on one end to identify the current flow direction, however, it has some writing on it instead of coloured bands. It says (in no particular order, due to the fact that it goes all the way around)

18 on one side
3 on the other

What do you think these mean? Here's the readings off of some other ones like the other one:

02
9

and a third simply has a yellow band.

Any help identifying the Amperage and Voltage of these would be great.


Also, about the capacitor...

http://focus.ti.com/lit/ds/symlink/uc2577-adj.pdf

The calculated value for Cc is a minimum of 1080. Would using a 1000 ohm capacitor hurt? They're much more readily available in my parts bin.
Hey, sup?

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codeman
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Post by codeman » Sat Sep 02, 2006 8:12 pm

I think for the first diode it's just telling you that it's a DO-18 package and a current rating of 3 amps...that's just a guess though.

As for the capacitor, always use more than the recommended minimum amount...never less. Also switching regulators are picky. Every capacitor isn't really just a capacitor. It has a parasitic inductance and resistance along with it. The resistance needs to be as small as possible to keep the switching regulator feedback loop stable. I'm sure all you have are electrolytic capacitors which tend to have a very high ESR (equivalent series resistance). I would suggest using the 1000 micro-farad (not ohm!!!) electrolytic capacitor, a few 100 micro-farad capacitors...and A LOT of small ceramic disc capacitors. The ceramic caps have a very low ESR, and these in parallel with the other capacitors should lower the total ESR to something acceptable. Hopefully my ramblings help...good luck!
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Post by Kurt_ » Sun Sep 03, 2006 1:52 pm

Tim has a bunch of surfacemount parts. I might steal a ceramic cap and put it in parallel with the one I have. That would work, right?
Hey, sup?

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