How to amplify the voltage in(milli volts to volts )using opamp 741 with constant gain

Thread Starter

andhavarapu lokesh

Joined Aug 17, 2017
46
The circuit in #14 has issues. Any input offset voltage and/or bias current errors will be multiplied by the gain of the circuit.

To the TS:

What power supply voltages are available for the opamp?

What is the frequency range of the input signal?

What do you mean by "not able to get constant gain"? What gain does your circuit produce? In what way is the gain changing?

Please post your original schematic. While the 741 is not very good by today standards, there is no reason why its gain should vary in your application. Maybe we should solve the problem with your circuit before changing it to something else you don't understand.

ak
I am trying to amplify the I/P voltage of 0.001-0.133 using opamp 741
I am biasing with 12v power supply
ckt LM741.PNG ckt LM741.PNG ckt LM741.PNG
 

jayanthd

Joined Jul 4, 2015
904
Actually, there is nothing in the first 17 posts to indicate that that is true.

ak
I didn't check the datasheets of MCP6001 and LTC2053 recently but I guess LTC2053 will be fine. I will check its datasheet and reply.


Here is the circuit for low input offset voltage.

As you input signal can be as low as 1 mV this will be a better solution.

 

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AnalogKid

Joined Aug 1, 2013
8,815
I am trying to amplify the I/P voltage of 0.001-0.133 using opamp 741
I am biasing with 12v power supply.
The problem with using the 741 in this application is the input voltage range. This specification describes the acceptable range of input voltages. According to the 741 datasheet, it is +/-12 V (worst case) when the power supplies are +/-15 V. This means that if the negative power pin (pin 4) is at GND, the input must be greater than 3 V for the amplifier to work properly according to the spec. In fact, the input range is greater than this, but not enough for your application. You need a part with an input range that includes of goes below the negative power rail. An early example of this is the LM358, but it has a similar problem with its output stage - it cannot make an output all the way up to the positive power rail.

To do what you want, look for an opamp with *both* "rail-to-rail" inputs and output. Also, if this is for a DC signal application rather than something like audio, you eill need a part with low input offset voltage error.

ak
 
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