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lm339

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shubhra14

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hey can anyone please help me with the circuit diagram for lm339 for voltage comparison with proper value of resistor. i have tried all online circuits but it is giving very low output as for 5v input its giving only 300-400 mv . and also led is not glowing.
can anyone help please.
thank a lot in advance.
 

ronsimpson

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Many circuits are like this: Problem is that it will not work.
1554226085793.png
Note on this one there is a pull up resistor on the output. The LM339 only pulls down. The resistor is needed to make the output go up.
1554226144728.png
 

alec_t

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shortbus=

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Can I join in? What is the best resistance level to use on the inputs? Or would that be impedance instead of resistance? What value is commonly used?
 

crutschow

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What is the best resistance level to use on the inputs?
The maximum resistance is generally limited by the offset you can tolerate due to the input bias currents.
 

ronsimpson

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best resistance
I chose 10k & 10k on the (-) input. But 2.2k through 2.2 meg will be fine.
On the output I chose 10K to be simple but 1k through 100k is OK.
I added a 10K pot to the (+) input. But almost any pot will work. (2k through 2 meg)
1554246497233.png
Many people will put a LED and 2k resister in series for the output.
 

shortbus=

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Thanks for the answers, the reason I asked was you see all kinds of values used in web posted circuits. And reading the data sheet doesn't give any help or I don't know the correct term to look for in the DS.
 
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