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From: Lizard Blizzard
Subject: Re: Best way to power array of LEDs?
Date: Mon, 07 Oct 2002 17:53:11 -0700
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <3D9D5939.CD795C11@kth.se>
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> On 4 Oct 2002 12:48:17 -0400, email@example.com (Byron A Jeff) Gave
>>In article ,
>>-"John Woodgate" wrote in message
>>-> I read in sci.electronics.design that Uwe Zimmermann
>>-> wrote (in <3D9D5939.CD795C11@kth.se>) about 'Best way to power array of
>>-> LEDs?', on Fri, 4 Oct 2002:
>>-> >You then connect the drain of the transistor to the positive supply and
>>-> >the gate/source to the anode of the first LED in each chain. The cathode
>>-> >of the last LED is connected to the negative supply.
>>-> This is an *extremely* unreliable circuit, because it has no protection
>>-> against the large transients, of both polarities, that occur on vehicle
>>-> electrical supplies.
>>That's an apples and gorillas discussion. Transient and spike surppression
>>is a completely different issue from powering the LEDs. I didn't even attempt
>>to address it.
>>-> Don't bother with adding transistors just to get rid of a few resistors
>>-> (or maybe add a few more, and MOVs and capacitors and fuses ...). KISS!
>>But it isn't simple if the array isn't bright enough to do the job. It's
>>quite likely that the LEDs will need to be pulsed with higher current in
>>order to give brighter perceptual intensity. Once you start down that road
>>you're going to have to have transistors to modulate/switch power to the
>>And frankly an extra 2N2222 and base resistor per string isn't exactly rocket
> Yeah... they're all of what 10 cents a piece? Hehehe...
The PN2222 in the plastic package is less than a dime, but the true
2N2222A in the metal package is more like $.25 to $.40 each if you can
find them. And the ones that you find are made by some off-the-wall
company in Hong Kong.
> DC/DC converter from surplus store for five bucks, drop to five
> volts, clean instead of 12, dirty. Two copper rails. A series
> resistor in each leg of each LED that gets BUSSED in parallel onto the
> copper rails.
This weekend I was reading about an AC or DC to DC converter that would
accept any input from 10VDC on up to 400V. There should be no problems
with spikes, then!
> Ten bucks total... maybe. On a bad day.
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