Subject: Re: Best way to power array of LEDs?
Summary: What do you think of these ping times eh?
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <3D9D5939.CD795C11@kth.se>
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Date: Sun, 06 Oct 2002 04:57:44 GMT
NNTP-Posting-Date: Sun, 06 Oct 2002 00:57:44 EDT
On 4 Oct 2002 12:48:17 -0400, firstname.lastname@example.org (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...
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
Ten bucks total... maybe. On a bad day.