# how to find the gain response of LM358

#### andhavarapu lokesh

Joined Aug 17, 2017
46
I want to amplify lower voltages from ranging from (0.3millivolts to 133millivolts ) using LM358P can anyone tell me how to find the gain response of the LM358

#### jayanthd

Joined Jul 4, 2015
904
I want to amplify lower voltages from ranging from (0.3millivolts to 133millivolts ) using LM358P can anyone tell me how to find the gain response of the LM358
What is the max input offset voltage of the OpAmp (LM358} ?

#### andhavarapu lokesh

Joined Aug 17, 2017
46
What is the max input offset voltage of the OpAmp (LM358} ?
In the datasheet it is given 2mv i don't know what does it mean

#### jayanthd

Joined Jul 4, 2015
904
In the datasheet it is given 2mv i don't know what does it mean
It means that device has max input offset of 2mV and you cannot input signals lower than 2mV to it and it is not a Rail-To-Rail output OpAmp.

#### andhavarapu lokesh

Joined Aug 17, 2017
46
It means that device has max input offset of 2mV and you cannot input signals lower than 2mV to it and it is not a Rail-To-Rail output OpAmp.
sir i am not getting the gain uniform if i vary from 3milli volt to 133mv whats happening means it is giving maximum gain around 31db at 3mv output voltage is also negative . But when it goes around 1.5 output voltage sign changes gain also reduced 17db and then onwards gain increases from 23-30.9

#### andhavarapu lokesh

Joined Aug 17, 2017
46
It means that device has max input offset of 2mV and you cannot input signals lower than 2mV to it and it is not a Rail-To-Rail output OpAmp.
sir i am not getting the gain uniform if i vary from 3milli volt to 133mv whats happening means it is giving maximum gain around 31db at 3mv output voltage is also negative . But when it goes around 1.5 output voltage sign changes gain also reduced 17db and then onwards gain increases from 23-30.9

#### andhavarapu lokesh

Joined Aug 17, 2017
46
is there any LTspice schematic for LM358

#### jayanthd

Joined Jul 4, 2015
904
sir i am not getting the gain uniform if i vary from 3milli volt to 133mv whats happening means it is giving maximum gain around 31db at 3mv output voltage is also negative . But when it goes around 1.5 output voltage sign changes gain also reduced 17db and then onwards gain increases from 23-30.9
Show your exact hardware circuit. What power supplies are you using ?

I have not use LTSpice. I use Proteus.

I checked the datasheet. It says Max input offset voltage is 5mV.

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#### andhavarapu lokesh

Joined Aug 17, 2017
46
Show your exact hardware circuit. What power supplies are you using ?

I have not use LTSpice. I use Proteus.
open source or licence proteus

#### jayanthd

Joined Jul 4, 2015
904
open source or licence proteus
I have both licenced version and cracked version and using both. I can show you my Proteus licence.

#### andhavarapu lokesh

Joined Aug 17, 2017
46
Show your exact hardware circuit. What power supplies are you using ?

I have not use LTSpice. I use Proteus.

I checked the datasheet. It says Max input offset voltage is 5mV.
ok if want to make gain constant how the circuite should be modified

#### jayanthd

Joined Jul 4, 2015
904
ok if want to make gain constant how the circuite should be modified
Show your circuit. What do you mean by output is not linear ? Are you testing in hardware ? If not, why don't you test it on hardware ?

#### andhavarapu lokesh

Joined Aug 17, 2017
46
Show your circuit. What do you mean by output is not linear ? Are you testing in hardware ? If not, why don't you test it on hardware ?

This LM308 just i have taken to show you acutally iam using LM358P

#### ericgibbs

Joined Jan 29, 2010
11,618
is there any LTspice schematic for LM358
hi,
Is this sim showing the non linearity, the circuit will be non linear, what is the frequency of your input signal.?

E

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#### andhavarapu lokesh

Joined Aug 17, 2017
46
hi,
Is this sim showing the non linearity, the circuit will be non linear, what is the frequency of your input signal.?

E
i am not giving any ac i am giving Input dc voltage to non inverting teriminal from 0.003 to 133 millivolts thats it

#### ericgibbs

Joined Jan 29, 2010
11,618
hi A,
Is like this sim.?
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#### andhavarapu lokesh

Joined Aug 17, 2017
46
hi A,
Is like this sim.?
E
yes it should be like this but now i am not getting gain constant

#### ericgibbs

Joined Jan 29, 2010
11,618
hi,
I assume you are talking about a real LM358 circuit.?
What is the source of the 3mV to 133mV signal.?
E
EDIT:
This is the LM358.mod, change the LM358mod.txt to LM358.mod

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#### andhavarapu lokesh

Joined Aug 17, 2017
46
hi,
I assume you are talking about a real LM358 circuit.?
What is the source of the 3mV to 133mV signal.?
E
this is the output of trimpot

#### jayanthd

Joined Jul 4, 2015
904
this is the output of trimpot
Show the full circuit. Are you measuring the voltage after amplification with a MCU ?