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: Tue, 08 Oct 2002 08:01:49 GMT
NNTP-Posting-Date: Tue, 08 Oct 2002 04:01:49 EDT
On Mon, 07 Oct 2002 17:53:11 -0700, Lizard Blizzard
>> On 4 Oct 2002 12:48:17 -0400, email@example.com (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...
>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.
Not true (about the availability and maker). We buy and use them by
the thousands. I think we get them from ST. I don't know what we get
them for, but we get the to-18 package as well as the epoxy body job.
The canned jobs are about 37 cents each in small quantities, new,
just as you said. Much less in larger batches.
Neat stuff. I like the 900 volt, high wattage FETs myself. :-]