Ic stops working

Thread Starter

Humor

Joined Oct 28, 2019
6
My adder including the 74HC series xor and or ic stops working when I connect the 7447 decoder ic to bcc and ground. I am a newbie please help
 

Thread Starter

Humor

Joined Oct 28, 2019
6
Hi Humor,
Welcome to AAC.
Do you have a sketch of the circuit you could post.?
E
It is a simple full adder one that everybody makes simple design with one xor gate , one and , one or gate. I don’t have the sketch at this moment but will try to provide one
 

MrChips

Joined Oct 2, 2009
21,877
In general, do not mix logic families unless you are certain that they are compatible.
7447 is made from BJT (bipolar junction transistor) technology.
74HC is made from CMOS FET (field effect transistor) technology.
 

dl324

Joined Mar 30, 2015
11,543
You're probably okay with 74HC driving standard TTL, as long as you pay attention to HC fanout limitations, but not the other way around.
1572306071367.png
 

Thread Starter

Humor

Joined Oct 28, 2019
6
Thank you guys for all your help and advice. I changed the power source from my battery to a 5 volt phone charger which outputs 1 amp current and it works just fine. Maybe the battery was not able to provide adequate current.
 

MrSoftware

Joined Oct 29, 2013
1,914
Just for the learning experience, if you can put it back on your battery and attach a scope then you will be able to see the voltage drop on the scope if that was the problem. If the battery is at 5V, set the trigger point as falling edge around 4.5V, put the scope in normal mode then turn the circuit on and watch. If you have a storage scope (digital) set it to record multiple frames, because if you have multiple dips they may go by so fast that you only see the last dip, and it might not be the worst dip. If you set it to record frames then it will record basically a screen shot every time it triggers. If you don't have a storage scope, then just keep moving your trigger point lower until it doesn't trigger anymore, then you'll know what the lowest dip is.

One more side note; those phone chargers are often not regulated very well and the voltage can get really high when there's little or no load. Measure its output with no load attached and compare that against the "absolute maximum ratings" in the data sheets for each of the parts you're using. If the voltage is higher than the absolute max for any of your parts, then you can add a zener diode between your V+ input and ground and that will spare your parts from being cooked by over voltage. This is not always ideal as a big power supply can just smoke the diode, but for a learning project with a small power supply, a sufficiently large zener is likely fine.
 

Thread Starter

Humor

Joined Oct 28, 2019
6
Just for the learning experience, if you can put it back on your battery and attach a scope then you will be able to see the voltage drop on the scope if that was the problem. If the battery is at 5V, set the trigger point as falling edge around 4.5V, put the scope in normal mode then turn the circuit on and watch. If you have a storage scope (digital) set it to record multiple frames, because if you have multiple dips they may go by so fast that you only see the last dip, and it might not be the worst dip. If you set it to record frames then it will record basically a screen shot every time it triggers. If you don't have a storage scope, then just keep moving your trigger point lower until it doesn't trigger anymore, then you'll know what the lowest dip is.

One more side note; those phone chargers are often not regulated very well and the voltage can get really high when there's little or no load. Measure its output with no load attached and compare that against the "absolute maximum ratings" in the data sheets for each of the parts you're using. If the voltage is higher than the absolute max for any of your parts, then you can add a zener diode between your V+ input and ground and that will spare your parts from being cooked by over voltage. This is not always ideal as a big power supply can just smoke the diode, but for a learning project with a small power supply, a sufficiently large zener is likely fine.
Thanks for the information will surely try.
 
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