Diode Simulation Error

[MyamigoSH]

I've been having problems with a more complex circuit that I've been playing with and I've narrowed the problem down to Multisim's handling of diodes during simulation.

The circuit below shows two branches that have identical resistors but one has a diode in series with it so it only conducts every other half cycle. This is a half-wave rectifier and the theory tells us to expect the RMS current through the resistor to be 70.7% of the current flowing through a resistor that doesn't have the series diode (for an ideal diode). For R2 below I(R2) = 12/2.88 = 4.16A and this is correctly determined by multimeter XMM2. The current through the diode branch should then be 4.16*0.707 = 2.94A but as you can see multimeter XMM1 is way off. I changed the diode to a virtual model and the current dropped to 2.14A..

I checked this using LTSpice with the same model diode and resistor values and I get the correct results with that program (allowing fior diode charactersists)...

I've attached both of the simulaiton files (Multisim 14 & LTSpice) for reference.

So what's going on here?

[Rairiki · Accepted solution]

Hi Myamigo

Thanks for that information, I think the issue here is with the multimeter and not with the circuit. I used a current probe and I got 2.8 A on that line. I am attaching an image showing this.

I think this could be caused for a configuration on this device or it also can be a CAR but I need to do further research on this to see if this is a wrong behavior of the multimeter on Multisim.

[MyamigoSH]

Hi Rairiki,

Thank you very much for pointing me to the use of probes. They're easier to work with than multimeter's... and they work! I am seeing the right numbers now 

I would like to know if this was a configuration issue or if it would be addressed by a CAR. My earlier related post may also warrant a closer look if you are able. In this case the 4-channel oscilloscope is not operating properly. This may also be a configuration issue or needing a CAR.

Cheers!