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LM386 amplifier gain clarification

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Murugesh_89

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Hi,
I did analysis in lm386 opamp ic using proteus. I did it for three different gain values 20, 50, 200. In each of these case, the output of opamp is measured as 5.10783 V for the input at the non inverting amplifier of 0.00214857 V.

LM386 gain clarification.JPG

As per the gain definition i calculated the gain as Vout/Vin = 5.10783/0.00214857 = 2377. But in the datasheet they have stated that gain can be varied between 20 to 200. But for me it is coming as 2377. So i am wrong somewhere else!!!

Can anybody explain me why i am getting same output for same input with different gain values? and please let me know where i am messing?

Thanks,
Murugesh
 

I have never used that device but on the first page of the datasheet it says that the inputs are ground referenced but the output is biased at half supply rail. So,, measuring the DC output voltage tells you nothing unless you also sweep the input voltage (or apply a small AC input).

Also, you will only ever see a DC gain of 20 as the higher gains include a capacitor so only increase the AC gain.

Keith
 
Yes, the datasheet for the LM386 power amplifier (it is not an opamp) says that the AC voltage gain is 20, 50 and 200.
But your simulation shows DC voltages, not AC signal voltages.
 

Use a blocking capacitor at output and then check AC gain. It is an audio amplifier, not an ordinary operational amplifier.
 

using lm386, i am getting output biased about 2.7 rather than about Vcc/2(=2.5V)..I need output biased across exact 2.5V..what can be the possible problems or solutions
 

There's no datasheet specification about output bias voltage tolerance, expecting excatly Vcc/2 might be unduty. Did you modify the suggested circuit in a way that affects DC bias?
 

Mayank Jain said:
using lm386, i am getting output biased about 2.7 rather than about Vcc/2(=2.5V)..I need output biased across exact 2.5V..what can be the possible problems or solutions
Click to expand...

why?

you can bias a conventional op-amp at Vcc/2 in a number of ways
 

You can vary the DC output voltage of an LM386 amplifier a little by adding a high-value resistor (try 100k) from pin 7 to the positive supply or to ground.
 

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