🚀 go-pugleaf

JoeBloe wrote:
> On 4 Oct 2002 12:48:17 -0400, byron@cc.gatech.edu (Byron A Jeff) Gave
> us:


>>In article <Qrhn9.27982$kd3.80464@news-server.bigpond.net.au>,
>>Grog <shem_an_na@SPAM_ME_NOThotmail.com> wrote:

>>-"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
>>-news:B7hloTAPDZn9EwGz@jmwa.demon.co.uk...
>>-> I read in sci.electronics.design that Uwe Zimmermann <uwezi@kth.se>
>>-> 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
>>LEDs.

>>And frankly an extra 2N2222 and base resistor per string isn't exactly rocket
>>science.



>   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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