25 Aug
2014
25 Aug
'14
3:07 p.m.
On Sun, Aug 24, 2014 at 2:06 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Although to be fari, if yo get it to source more current (sensibly more
current, like the 10mA to light an LED), the IC will not be damaged but
the output voltage may well drop below the specification for a logic 1
output.
Plenty of (commercial) units drove LEDs form a TTL output to ground, even
though it is not good practice. (and here 'TTL' excludes the CMOS
families)
-tony
This is quite a nroaml way to do it. A TTL output
can sink a larger
current tahn it can source,
By which Tony means "can sink a **MUCH** larger current than it can source".
If you look at the spec for the TI SN7404, the difference is a factor of 40:
max -0.4 mA source (high), vs. max 16 mA sink (low). Generally speaking,