Maker Pro
Maker Pro

TTL Logic Output Voltage Not What Is Expected

JoshHyatt

Aug 21, 2014
1
Joined
Aug 21, 2014
Messages
1
I have a bunch of 74107 JK flip flop chips which require 5V vcc. I also use 5V for the logic inputs. The output, however, is 3-2 volts, so if I try to link one gate's output to another's input, the second gate doesn't register the input signal as a logic "1". The datasheet seems to claim that the output voltage can be 0 to vcc. Why isn't it outputting a high enough voltage? How do I fix it? Did I fry the chip a long time ago? Thanks!

EDIT:
Does this happen when not enough (or too much) current is applied?

--Josh
 
Last edited:

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
Joined
Jan 21, 2010
Messages
25,507
TTL only weakly pulls up and strongly pulls down.

the 2 to 3V should be sufficient for the gate to recognise a logic high input.

This page shows you.

A "high" TTL output should generate a 3.3V or higher voltage and an input should treat anything 2V or higher as "high".

If you're getting different values, or if the input isn't working, check that you actually have a TTL device and not something else.

Your part number seems like plain vanilla TTL.
 
Top