References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <3D9D32DE.firstname.lastname@example.org> <3D9D5939.CD795C11@kth.se>
Subject: Re: Best way to power array of LEDs?
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Date: Fri, 04 Oct 2002 14:19:28 GMT
NNTP-Posting-Date: Sat, 05 Oct 2002 00:19:28 EST
Organization: BigPond Internet Services (http://www.bigpond.net.au)
"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.
> 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!
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.. ;-)
Greg the Grog