Look at the 74F245 an 8 output transceiver, the B side can drive some
SERIOUS currents!
I drive lots of LEDs with the HC version.

  *
  |  __O    Thomas C. Sefranek   WA1RHP@ARRL.NET
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> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jinx
> Sent: Monday, January 27, 2003 8:56 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: DIP alternative to transistors for driving LEDs??
>
>
> > >as well, eg 4050
>
> > think of just using a logic buffer...makes a lot of sense I think.
>
> If you do decide to go that way, the 4049/4050 like most common
> gate ICs can sink more current than they can source. With only one
> LED probably doesn't make much difference either way. Putting
> 3 LEDs in series on 5V without R could be marginal depending
> on their Vf
>
> Connect the LEDs  V+ -- R --- >|--  pin. If you use the 4049 you
> can keep the PIC s/w logic positive. ie BSF --> PIC o/p goes
> high, 4049 (an inverter) o/p goes low and the LED comes on.
> Obviously if you use a 4050 then BCF for LED on unless you
> put the LED from 4050 o/p to 0V
>
> In displays such as scrolling signs where strobing / PWM is on
> permanently and there's no chance of static DC across the LED
> the current limiting resistor can be reduced, depending on the
> MS ratio of the drive. For example perhaps 47R or 56R with a
> 12V supply and a few percent duty cycle. And also IR LEDs that
> may pass 10's of amps in microsecond bursts with only 1R to
> limit the current. LEDs in such situations do get warm and you'd
> need to read up on the tolerances to get the best out of them. For
> an experimental circuit it would be wise to keep a couple of 100
> ohms in series
>
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