Remote Living > Lighting

Voltage controlled LED drivers.

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TomW:


 Just my 2.2 cents worth and Admin's if your going to ban Bruce for fessing up what we all think that will be a dark day on feildlines.
Bryan


Never happen...
jeeze, it is always the young pups fresh from the mint who know it all.
I cannot condone profanity, but that word is common on the media here so that bit is a grey area unless it gets too prolific.
Call it as you see it, guys. but remember its a family type board.
Cheers,
TomW

Bruce S:
rembrant;

  I haven't had time to read what others are going to say and if Admin wants to kick me off for this so be it...

Go jump into traffic, I could careless what you think, come to St. Louis and I'll show you how to give respect where it's do. Amanda did this on her own time so go screw yourself.
Bruce S

finnsawyer:
Which came first, the chicken or the egg?  Which is more important for an Led, voltage or current?  SamoaPower gave us a set of representative curves.  It is clear from the linearity of the current versus voltage curve in the region of interest that the dependence of current on voltage may be represented by an exponential function from which I obtained the relationship I = 1x10^(-7)x 2.718^(3.22xV).  You are invited to try your hand at fitting the curve.  The importance here is that we may differentiate the current with respect to voltage and evaluate it at three volts.  This gives us dI/dV @ 3 volts = 1x10^(-7)x3.22X2.718^(9.66) mhos.  Or simply .005 amps per volt.  That is, 5 milliamps per volt.  It is quite feasible to build a voltage regulator that will keep the voltage stable down to the millivolt range, which would allow an Led string to happily perk along indefinitely.
Of course the regulator should also be capable of allowing for the change in Vf due to temperature, but there should be ways to do that as long as the 2 millivolt per degree drop is representative of all the Leds.  For a string of three we would only need to consider a total of six millivolts per degree even though the regulator may power several strings.  This brings us to the nub of the issue.  Is it better to build several current regulated supplies for several strings of Leds or one perhaps more complicated voltage regulated supply that can by itself power several Led strings, and which will continue to work adequately even after one or more 'normal' string failures.  I suspect that for a manufacturer looking to minimize his overall costs, the latter approach would look attractive.

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