Newsgroups: rec.arts.theatre.stagecraft
Subject: Re: Polarity Behringer Eurolight LC2412 BNC-Socket
References:      
Christian Marg  writes:

> Tomi Holger Engdahl wrote:
> > When building LED replacements for goosenect lights, I think based
> > on the discussion gone here is to build them in such way that they
> > work with DC on both polarities and AC, so they will work with every
> > device you plug them in that has right voltage for your circuit. You
> > can easily make a LED lamp to work on DC at both polarities and also
> > with AC by adding a small full wave rectifier to your LED lamp
> > circuit. THis kidn of rectifiers are available as a small four wire
> > component or you can build your own from four diodes.
> 
> I already thought about that, but it would decrease the total voltage
> about 1,4V and need more parts/place to put them... In general this of
> course is right, but for my case its just overkill I think...

Anohter idea is to use two LEDs in parallel in different directions. 
They work so that when voltage is in one direction, one of  them 
makes light and protects the other one against too much wring 
polarity voltage. And on other voltage dirction the things work 
in opposite. Both LEDs have one common current limiting resistor,
So with DC one LED lights (depends on polarity which one), 
and with AC you see both LEDs makign light. This could be a 
construction that could be built to a very small space. 

> One might also add some kind of regulator to the led-supply so that
> they also can work correctly if attached to an unloaded
> AC-Transformer... 

A suitably seleced current limiting resistor is in many LED 
applications a suitable for this. In case you jsut use few LEDs 
in series, most voltage drop is always on the resistor.  
Keep the resisance value such that you get maximum allowed LED current 
(or less) when voltage is at maximum. At normal conditions the LED 
is then somewhat lower current, meaning a little bit less brigth, 
but usually bright enough for all uses. This is the simplest approach. 

> Do regulators work useful if the input voltage isn't
> filtered by $big condensator ? Of course the output voltage will have
> ripple in it, but how much? Does that ripple need special
> consideration or could I just feed it to the LEDs?

Most reulator ICs and circuits are designed to work with 
filtered input power. And expct that certain capacitors 
The performance without the filtering capacitors can vary greatly 
and might not be useful.

The LEDs do not be bothered by soem voltage ripple, as long 
as their maximum ratings are not exceeded.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/