> However, the maximum currente at the '595 outputs are 6-8mA and I 
> need to power the LEDs with 20mA, to have more luminosity.

Can you add 8 transistors or one of the ULN2xxx family ?

eg http://www.ucapps.de/midio128/relay_example.pdf

Perhaps a ULN is a bit over-rated for this. Reliable though

If you intend using pulses with a short but known maximum width
then the value of the series resistor can be lowered, maybe you can
get your 20mA that way. The LEDs in moving signs often have as
low as 47R with 12V, but only because they are driven with short
pulses. Normally 12V + 47R would kill a LED stone dead

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist