Hi folks
PLease refer to the two schematics below. I am trying to simulate them in Multisim. The circuits are simply to to show the working of AD736 RMS to DC converter chip. The schematic/circuit 2 uses a dual power source one for +5V and another for -5V and this works fine and the output gives me the RMS value as expected. But the schematic/circuit 1 fails miserably. Here all i have done compared to the circuit 2 is to replace the individual DC sources with a single battery source and use that for getting both the +5V and the -ve 5V. Am i missing something in circuit 1 ? Please advice

 

R4 and R5 @ 100kΩ are way too high to form a pseudo ground reference.
Try changing R4 and R5 to 100Ω.

 

Thanks Mr Chips I tried changing it 100Ω, but makes no difference, the output keeps jumping all over the place before it finally gives the convergance error.

 

Folks any advice on this. Is the circuit design wrong or is it an issue with the simulation software. I wanted to avoid using two power sources to get +5v and -5V and this seemed like a good solution as it was mentioned on the data sheet of AD736 also.

 

Things almost never work well using a resistive divider to create a virtual ground.
The impedance of the ground will always be too high, lowering the resistor values just wastes more power.

Here is a chip designed to address this:
http://www.ti.com/product/TLE2426

Better to keep your ground where it belongs and generate a negative supply:
https://www.intersil.com/en/products/power-management/isolated-power/charge-pumps/ICL7660S.html

 

I see no ground connection in Circuit 1
The simulation will give flaky results without a ground reference.
You had U1's common connected to ground in Circuit 2, why did you remove it in Circuit 1?

 

Thanks folks. My problem is that multisim does not have any of the Charge Pump Chips so I cannot continue with the simulation. Any idea where i can get the component details for ICL7660?

Crutschow i did not remove the ground i simply moved it to virtual. Since in the first ciruit there is no external ground i had to use the virtual ground or common point where the voltage will be zero.

 

Crutschow i did not remove the ground i simply moved it to virtual.

That's not the point.
I see no ground symbol on Circuit 1.
You must have a ground symbol connected somewhere to the circuit (the IC com is the logical place for that) for the simulator to operate properly.
And in the real world the circuit will also need to be connected to some ground point.

 

I tried putting the ground at the common point, but the simulation still goes hay wire. I also tried using the TLE2426, but that also did not help and though the convergence error went away the readings were all wrong. the below is the circuit using the TLE2426