I am designing a single supply amplifier using Lm358. My input is a sine wave with a DC offset of 2V and an AC imposed on that with 0.2V peak.The gain of the amplifier is 11.

The expected output at the amplifier is 2.2V (4.4V peak to peak) . But I am getting only 323mV Peak to Peak.

My circuit is given below.


Please find the attached schematic and spice model of LM358.
Please let me know where I went wrong

 

hi hoy,
Note the Zimp of a 100R and a 3.2uF at 50Hz = 994R, so the gain is only 1*(1k/994) = ~ 2
This image is with a 47uF
E


E

 

Thank you.
Total impedance of R1 and C2 to be 100 Ohm for a gain of 11.
Need to fine tune the value of C2 and R1 such that the total impedance sholud be 100 Ohm.
Please correct me if I am wrong.

I choose C2 such that the filter formed by C2 and R1 needs to pass 50Hz

What can be done if the source frequency is changing

 

hi hoy,
Why have you chosen such a low value for R1= 100R & R2 = 1k ?

Using R1=4k7 and R2=47k will give you gain at 50Hz

E

 

Hi Eric,

My intention is to amplify only the AC content of the signal.I did not want to amplify the DC content.
Here the gain is 11.
The peak to peak amplitude of AC component is 0.4V .
The expected output voltage is 4.4V.(11*0.4).
But getting a value of 2.35V

 

But getting a value of 2.35V

The AC signal is reduced almost 50% by the voltage divider of R4-R5 in the simulation.

 

R4 and R5 provide a constant offset of 4V. It won't degrade the input signal

 

hi hoy,
You are losing ~267mV across Vs > Vi.
E

 

Need to fine tune the value of C2 and R1 such that the total impedance sholud be 100 Ohm.

Then C2 needs to be infinite since R1 is already 100 ohms.

 

hi hoy,
Your 3.5uF into 1k output load is also reducing the signal amplitude, to 2.33V
E

 

I figured the same losses but with the circuit below the gain was actually nine
I breadboarded that circuit using this configuration.
C2 has an impedance of 470 ohms at 100hz so the actual gain is 9+1 = 10.
There was a 0.2 volt loss across C1 on the output resulting in a total gain of 9

 

I changed the cut off frequency of HPF. I set it to 10Hz and redesigned R and C values.Now it is coming as expected.