From: firstname.lastname@example.org (N. Thornton)
Subject: Re: Wrestlemania Royale: Tantalum vs. Electrolytic Vs. Polys, etc.
Date: 27 Oct 2002 16:39:12 -0800
References: <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: 28 Oct 2002 00:39:12 GMT
email@example.com (The little lost angel) wrote in message news:<firstname.lastname@example.org>...
> On Fri, 25 Oct 2002 20:17:40 +0100, John Woodgate
> >>Say for a low voltage 10~20v, low current 0.2A, what would be the best
> >>type of capacitor with smallest physical size?
> >Frequency? And where is this current going? Through the capacitor or
> >past it?
> Past it, I noticed that while fixing the LED widget for those PC SMPS
> that on some low quality PSU, the voltage appears to spike/dip enough
> to notice momentarily flickers.
Does it even matter?
> Though I'm quite confused about the capacitor rating to use
> The thing was going to shop revealed that I either made a serious
> maths error or they aren't stocking the type of caps I need, hence the
> question for smallest physical size.
> C= I* Dt/Dv
> The nominal input is 12V, I'll think a momentarily drop to 9v
> shouldn't cause a noticeable flicker.
Your LED can go off altogether and you wont notice it. Fluorescent
lights do, 100 times every second. (120 if you're American.)
If you look directly at a fl light and dart your eyes across real
fast, you'll see a retinal image of bright and dark lines. And what's
curious, you tend to get blue and yellow lines rather than just white.
> And if I can see a flicker, it's
> got to be quite a long dip, say 0.04 sec (since the eye perceives
> smooth motion, thus no flicker at 24 to 30fps)
> C= 0.2 * 0.04 / 3 = 0.00266
> That's about 2660 uF... and the caps are quite large relative to the
> LED... the small round ones barely hit 1 uF. That's why I'm kinda
> confused since I didn't expect to need a too big a cap for just a few
Try a smaller one then. See how it works. And try it with the PSU
normally loaded, then you'll get a real world result.
BTW dont put the cap acros the supply, it may object to that,
depending how its configured. Put it across the LED itself, or better
still half way thru the series R chain... you using a regulator? if
so, more complications...
I wouldnt bother about it. At some point you got to ask yourself what
life is all about, and what you want to do with your time, one LEd
project or 10 projects that flicker occasionally.
And to think you're doing all this for 3 USD! Good luck.