HCT vs LS..

[Lord-Data]

I've got a circuit specifying a "74HCT138" and can find a 74LS138 at Jaycar,
is this a compatible component?

Thanks in advance!

 

[Mark Harriss]

I've got a circuit specifying a "74HCT138" and can find a 74LS138 at Jaycar,
is this a compatible component?

Thanks in advance!

The HCT is CMOS and the LS isn't, there are differences
in speed, voltage levels and power consumption. You can
try it but it maybe erratic

 

[Trevor Wilson]

I've got a circuit specifying a "74HCT138" and can find a 74LS138 at
Jaycar, is this a compatible component?

**Same basic function, but fundamental differences in performance. Best not
to substitute, unless the circuit is uncritical.

 

[Lord-Data]

Thanks to both who replied

I'd guess timing probably ISNT too criticial, but for the sake of a day or
2, i'll order the correct parts from farnell

Thanks again!

 

[David L. Jones]

I've got a circuit specifying a "74HCT138" and can find a 74LS138 at Jaycar,
is this a compatible component?

Thanks in advance!

For all but the most critial aplication they should be compatible,
although usually it's the other way around. The HCT series is designed
to be a low power high speed CMOS replacement for the 74LS series, as
it has TTL compatible voltage levels, that's what the "T" stands for.
Best to get the same part if you can though, substituting parts may
work at first try, but unless you try it over the full performance
envelope you won't really know.

Dave