I am trying to do simulation for differential amplifier by using P Spice ,but the output is not right ,can please someone check what is the problem
the output should be 10 Vdc

 

What output are you getting? The differential gain of the amp is 100k/3010k = 0.0332 and thus the output for the 600V at the input should be 19.93V, not 10V.

 

thanks ,I got 14.4 Vdc,i attach the p spice

 

thanks ,I got 14.4 Vdc,i attach the p spice

Of course. Your amp is saturated. It's trying to get to 20V but can only get to 14.4V with a 15V supply.

 

Takymounir, your circuit cannot work as a diff. amplifier because the input signals have no ground reference.

 

the gain is 100k/6010 =.0166 so vo= 600 * .0166=9.983 is this right or no
I get 14.4 not 9.98

 

the gain is 100k/6010 =.0166 so vo= 600 * .0166=9.983 is this right or no
I get 14.4 not 9.98

Kilo-Volts, Milli-Volts, Volts or Amperes or something else?

Question: Did you correct the circuit (input ground reference)?

 

Takymounir, your circuit cannot work as a diff. amplifier because the input signals have no ground reference.

The input doesn't need a separate ground reference for this circuit. That's provided through R5, R6, and R7.

TAKYMOUNIR, the differential gain is 100k/3010K (look here under Differential Amplifier). Don't know how you arrived at your value.

 

The resistor values in the second circuit are different than the first circuit. 6 Meg vs 3 Meg for R3 & 6.

 

The input doesn't need a separate ground reference for this circuit. That's provided through R5, R6, and R7.

Crutschow, thank you. You are right. There was something like an obstacle in my head. Perhaps, because the circuit looks rather uncommon?

 

OK, I missed the resistor values being changed in the second circuit. For that the calculated output should be 9.98V, and that's what my simulation also showed, so don't know why your simulation is different. What op amp is that?

 

The input doesn't need a separate ground reference for this circuit. That's provided through R5, R6, and R7.

TAKYMOUNIR, the differential gain is 100k/3010K (look here under Differential Amplifier). Don't know how you arrived at your value.

sorry I change it it is 6 mega instead of 3 mega

 

OK, I missed the resistor values being changed in the second circuit. For that the calculated output should be 9.98V, and that's what my simulation also showed, so don't know why your simulation is different. What op amp is that?

I use LF411,I WAS USING LETTER M AS MEGA AND THAT IS WHY MY SIMULATION WAS WRONG,SO SORRY FOR THIS