Re: [tlug] [OT] Any electricians / electrical engineers around?

["Daniel A. Ramaley" <daniel.ramaley@example.com>]

On Monday 31 December 2007 19:31, Dave M G wrote:
>Andrew mentioned that the LEDs would flicker if they were on AC
> current. Actually, I had noticed that when I was doing testing with
> my Christmas lights.

I have had some LED Christmas lights for a few years. They flicker at 
120 Hz (twice the 60 Hz power) which is not *consciously* noticeable to 
me, but if i am in the same room with them for a few hours i get a 
headache.

>It seems to me that it would be a good thing to convert the current to
>DC. 
>So, can (or should) this be built with an AC to DC converter?

AC to DC is quite easy. After stepping the AC down to whatever voltage 
you need, put a bridge rectifier on it (a ring of 4 diodes; electronics 
parts shops often sell the diodes already packaged). Coming out of the 
rectifier you'll have pulsed DC (in programming/mathematical terms, 
imagine abs(sin(X)) and that's what it looks like on an oscilloscope).

If you want the DC to be relatively flat rather than pulsed, you can 
then put a capacitor or two on the DC side of the rectifier to even it 
out. You'll end up with cheap DC (cheap in terms of cost of components, 
and in their size) that is clean enough for most applications, most 
likely including your LED lighting project.

AC -> transformer -> rectifier -> capacitors -> DC

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Dan Ramaley                            Dial Center 118, Drake University
Network Programmer/Analyst             2407 Carpenter Ave
+1 515 271-4540                        Des Moines IA 50311 USA