Multisim and Ultiboard

cancel
Showing results for 
Search instead for 
Did you mean: 

DC integrator in multisim

Hi, I've been trying to get a very simple integrator circuit to work in multisim 10. I cannot get a DC response from the integrator, and I cannot get it to work at all as an exact (without a resistor parallel to the capacitor) integrator. If I use the parallel resistor with an AC signal, the results are fine. But with DC the result is totally wrong and as an exact integrator it gives me an impossible value (-150KV) on the output. What am I doing wrong? 

0 Kudos
Message 1 of 6
(5,009 Views)

- i should add I expect to see the output from the integrator ramp until it hits the supply rail and stay there

0 Kudos
Message 2 of 6
(5,008 Views)

Hello,

 

You are correct on the expected output value, and I went ahead and recreated your circuit on my computer and the output is as expected. I would like you to do two things if at all possible (since I can't recreate the problem here). Could you redo the circuit  and/or replace the opamp and run the simulation again (it could be a bug, but I have your last circuit saved to reference when we fix this)? Do you still get the same output?

 

Thanks,

Miguel V
National Instruments
0 Kudos
Message 3 of 6
(5,002 Views)

I installed a newer version of multisim - the problem was still there, but when I replaced the op-amp I get a realistic value for the output - the output sits on the the negative rail just below 15V. But there is no "ramping" to the negative rail, so this is still incorrect 

0 Kudos
Message 4 of 6
(4,994 Views)

Hi,

 

If you look at the SPICE models of the opamp you were using before you'll notice the difference in code. This was already fixed in the new multisim (opening your project on it kept the same model from before so it had the same effect, but replacing the opamp with the same model afterwards fixes this). As to the ramping part, this has to do with multiSIM's analysis methods. If you make a transient analysis and set the conditions to zero you should see ramping. Or to see this in the instruments (like the oscilloscope) simply click on interactive analysis settings under the menu Simulate and youll be able to find an option to set the circuit initial conditions to zero. This should show the ramping.

 

Best of Luck,

Miguel V
National Instruments
0 Kudos
Message 5 of 6
(4,988 Views)

great, thankyou that has sorted the problem. 🙂

0 Kudos
Message 6 of 6
(4,977 Views)