# Not gate troubleshooting 74LS06N

Discussion in 'General Electronics Chat' started by holz1100, May 8, 2016.

1. ### holz1100 Thread Starter New Member

Apr 27, 2016
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0
I am having troubles with the 74LS06N not gate.
An input of 5v gives an output of 0.05v (correct).
However, an input of 0.128v gives an output of 1.350v (not high enough)
I am powering the gate with 5v. Any advice on troubleshooting?

Apr 5, 2008
15,799
2,386
Hello,

Are you using pull-up resistors on the outputs?
The 7406 is an open collector device:

Bertus

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3. ### dl324 Distinguished Member

Mar 30, 2015
3,377
651
As @bertus mentioned, that device needs a pull-up resistor. The value depends on what the output is driving.

4. ### holz1100 Thread Starter New Member

Apr 27, 2016
14
0
The output is just fed into another logic gate (an AND gate). Any help in the way of how to calculate the pull up resistance value if i'm feeding into another and gate?

The switch by the not gate represents the input being either high or low

5. ### dl324 Distinguished Member

Mar 30, 2015
3,377
651

Assuming the AND gate is 74LS08, the maximum high level input current is 0.1mA and the minimum high level input voltage is 2V. The largest pull-up you can use is R = V/I = 3V/0.1mA = 30KΩ, but you could only drive 1 LS TTL load. LS gates have a fanout of 20, so I'd use nothing larger than 1.5KΩ.

6. ### hp1729 Well-Known Member

Nov 23, 2015
2,097
232
You need a pullup resistor on the output of the NOT gate to +V. 1K to 10K. The voltage you are reporting (1.35 or whatever it was) is the floating input of the next gate.