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Comparator switching voltage levels

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Murugesh_89

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Comparator.jpg

Hi,

In the above comparator circuit, i am only getting 4V at the output instead of 5V.

When Vin+ > Vin-, then Vout = Vcc.

Why i am not getting 5V at the output?
 

You are operating LM358 with +5v only.
Proper biasing is necessary for this configuration.
 

Hi,

My recommendation: when you want a comparator, then use a comparator. Many Opamps are not suited to operate as a comparator.

And - read datasheets:
Vout = Vcc.
Click to expand...
No datasheet will tell you this. Instead they give informations about "output voltage swing". In your case V_OH.

Klaus
 
If you look at the data sheet for the LM358 (gasp) you will see that the output does not go to the positive supply rail.

To get 5V output with a 5V supply you either need to use a comparator, such as the LM339 which uses an output pull-up resistor to the supply rail, or use a rail-rail output type op amp.
 

srizbf said:
You are operating LM358 with +5v only.
Proper biasing is necessary for this configuration.
Click to expand...
The LM358 can work fine with a supply as low as 3.0V. The circuit here is biased properly.

Murugesh_89 said:
In the above comparator circuit, i am only getting 4V at the output instead of 5V.
Why i am not getting 5V at the output?
Click to expand...
Don't you know that the datasheet for the LM358 and for every other opamp tells you everything about it?
Here is a graph from the datasheet showing that with a very low output current feeding a resistor to ground then its output high is about 1.15V LESS than the supply:
 

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