[time-nuts] 100 watt & higher LED power supply...

[Bob Camp]

Hi

A LED is indeed a diode. It's current changes pretty fast as voltage
changes. It's voltage drop also highly temperature dependant. Driving one
with a constant voltage and no current limiting is a very tough proposition.
You would need to feedback the temperature of the device and adjust the
supply accordingly. 

It's much easier to do this some sort of current feedback. Compared to raw
rectified AC, current regulation will also keep you from blowing out the
entire array when there's a spike on the supply line. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chris Albertson
Sent: Tuesday, September 18, 2012 11:45 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 100 watt & higher LED power supply...

On Tue, Sep 18, 2012 at 5:56 AM, Michael Baker <mpb45 at clanbaker.org> wrote:
> Time-Nutters--
>
> OK-- So flicker would be objectionable running off a
> rectified 110VAC line.    My thinking was to find
> a way around needing a current limiter that would
> waste energy as heat.

Even if flicker were not a problem what happens if the AC line voltage
goes up?  How to prevent over driving the LEDS.  Or a voltage spike on
the AC mains.  I think you ned some kind of line regulation.     Andin
a 100W system you will have heat.  The LED's current draw depends on
temperature so you'd need some load regulation too.

Or another way around the need for regulation is to run the LEDS at
reduced power so there is a large safety margin for heat and line
voltage variation.   But then you need more LEDs for the same amount
of light.   A constant current DC power supply is not that hard nor
expensive but if LEDs are cheap enough just get 2X more of then and
run them at 1/2 rated current.
Chris Albertson
Redondo Beach, California

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