Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!hpda!hpcupt1!dclaar
From: dclaar@hpcupt1.HP.COM (Doug Claar)
Newsgroups: sci.electronics
Subject: powering 50ma LED from TTL logic?
Message-ID: <6220013@hpcupt1.HP.COM>
Date: 20 Mar 90 19:49:39 GMT
Organization: Hewlett Packard, Cupertino
Lines: 15

I'd like some ideas on a circuit to drive a high power infra-red LED from
TTL. I know that standard LEDs can be driven straight from TTL, but this
little beastie wants a maximum of 1.5V forward at 50ma. (3V reverse if it
matters). For proof of concept for my mostly digital hack, I used an AS640
buffer driver (sinks 64ma) and a resistor, but it sure is ugly when that's
all I use the chip for, and all I think that I really need is a transitor
and some resistors. Any hints would be appreciated. Also, any hints on
practical transistor fundamentals book(s) would be appreciated. (At my
school, they taught us how IC wafers were made, which is MUCH more useful
than how to use transistors...of course, I WAS CS :-()

Doug "closet hardware hacker (and do I mean hack)" Claar
HP Computer Systems Division
UUCP: mcvax!decvax!hplabs!hpda!dclaar -or- ucbvax!hpda!dclaar
ARPA: dclaar%hpda@hplabs.HP.COM