0.01 ohm current sensor with LM358 problem?

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kamarn

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Hi,

I am having problem wiith the attach circuit. It is simple non-inverting dc amplifier with gain=11. But with 5mv Vin I get some -ve (3-4)mv at the output. What is the problem? thanks

 

I think LM358 isn't Rail to Rail Op Amp so you have to use instead of single supply symmetrical power supply with negative voltage as GND or use RtR Op Amp.
**broken link removed**
 

kamarn said:
But with 5mv Vin I get some -ve (3-4)mv at the output.
Click to expand...
It's impossible to get a negative output voltage from the circuit you showed. Either the circuit diagram is wrong or your measurement is wrong.
 

It looks the gain calculation is also not correct !
Both R1 and R2 are in series amounting to 110 K from output to the inverting input.
 

ark5230 said:
It looks the gain calculation is also not correct !
Both R1 and R2 are in series amounting to 110 K from output to the inverting input.
Click to expand...

Yes, I think your inverting input should be connected to a point between R2 and R1. You have it grounded.
 

Hello,

I think also, you have no connection between AGND and GND. In this case your input has no reference to the circuit.

I agree with gonespa. The negative input must be connected to the point with R1 and R2.

Regards

Rainer
 

I think that the OP doesn't care to get any replies because he has not posted a follow-up and it's been a month since his first post so maybe we can leave this thread fade away...
 

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