🚀 go-pugleaf

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.

-> --
-
-I'm with you John, "Load Dump" is my favourite automotive electrical term.
-Something like 40V transients?  Make that MOV a big one, preferably after
-the fuse &|| resistors..   ;-)

Crowbars are easy enough to do, but it wasn't a part of the discussion.

BAJ