Help! Circuit output not right

Thread Starter

peaac

Joined Sep 17, 2011
11
So I have this chip... SN74LS47N which I found the datasheet for and it is a TI BCD to 7-Segment driver.

I have two of these and I have checked the circuit about 10 times and this is what I am getting:

I have VCC = 5v
and connected the H to the same VCC for high and to ground for L.

What I see is that the chip "almost" works but the H and L outputs are at 0.11v and 0.07v!!! And I cannot figure out why!
 

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SgtWookie

Joined Jul 17, 2007
22,210
Here is a link to the datasheet:
http://www.ti.com/lit/ds/symlink/sn7447a.pdf

Note that the very first thing on page 1 of the datasheet after the part numbers, description and revision date, is a bullet that says:

"Open-Collector Outputs Drive Indicators Directly"

Open collector means that the outputs can sink current, but cannot source current.
If you wish to see if they are working as expected, use a ~270 Ohm resistor from +5v to the output; the resistor will source current so that you will then see the voltage on the output pin change.
 
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