# How does a 74LS47 works basically?

Discussion in 'Homework Help' started by zener_16, Feb 8, 2010.

1. ### zener_16 Thread Starter New Member

Feb 1, 2010
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i read the datasheet of the 74LS47 but cant really understand how it works..
i just know that it is a BCD to 7 Segment decoder..
anyone can tell me more about 74LS47 function?
Ty.

2. ### t06afre AAC Fanatic!

May 11, 2009
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Which part of the function do you not understand?

3. ### zener_16 Thread Starter New Member

Feb 1, 2010
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how does it works basically? A very general one.
like why is it active-low at the outputs?

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
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7447 is is a simple IC that "converts" BCD code to LED 7-SEGMENT display.
And 7447 is design to driving command anode LED displays. And that is why we have active-low at the outputs.
http://en.wikipedia.org/wiki/Binary-coded_decimal
http://en.wikipedia.org/wiki/Seven-segment_display
And see the TRUTH TABLE
http://maven.smith.edu/~thiebaut/270/datasheets/sn74ls47rev5.pdf

Last edited: Feb 8, 2010
5. ### Papabravo Expert

Feb 24, 2006
11,063
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Each segemnt of the display has associated with it a Boolean equation that determines weather the segment is on or off. For a single digit there will be seven equations, with each equation using four inputs. The equations can be written as a Sum of Products (SOP) or as a Product of Sums (POS) depending on which is easier to implement.

Here is the important point. A decoder is a combinatorial circuit with NO memory elements.

Feb 28, 2009
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7. ### nodoubtman New Member

Oct 21, 2011
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Hi! What's the difference between 74ls47 and 7447 ic??

thank you!
good evening!
marC

8. ### BillB3857 AAC Fanatic!

Feb 28, 2009
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Have you looked at the spec sheets of each? No better way to learn!

9. ### tshuck Well-Known Member

Oct 18, 2012
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No doubt that this is a resurrection!

Post a new thread if you need a question answered, not highjack a two year old one

10. ### Papabravo Expert

Feb 24, 2006
11,063
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The LS device has less drive capability and the inputs represent a smaller load. It's all in the datasheet. Get them, read them, and appreciate them!