🚀 go-pugleaf

In article <h6hvpu8hnhuag56b3rr5sqlompgmj984dm@4ax.com>,
JoeBloe  <theguyattheendofthebar__nicepingeh?> 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...
-
-  DC/DC converter from surplus store for five bucks, drop to five
-volts, clean instead of 12, dirty.

It really doesn't matter too very much since it'll be the same amount of
current regardless of the voltage...

-  Two copper rails.

Why?

-  A series resistor in each leg of each LED that gets BUSSED in parallel onto 
- the copper rails.

Again why when you can string multiple LEDs per string this saving both 
components (resistors) and power loss (due to the lower voltage drop.

-
-  Ten bucks total... maybe.  On a bad day.

I never heard price being an issue.

Any you still haven't dealt with the most important issue, brightness! Here
are the simple facts:

* The LEDs at continuous max current probably won't be bright enough.
* More current can be delivered only at a lower than 100 percent duty cycle.
* This requires that the power to the LEDs to be switched.
* Ergo you need a transistor. The current limiting is simply a bonus.

LEDs are not about voltage. They don't care about voltage. I've run them at
2.5V. I've run them at 120V AC. LEDs are current devices and have a brighter
response to more current. So any LED supply is about current management.

BAJ