Multisim Circuit Design

[Wolfgang.Black]

Hello, 

I've got a couple of questions on using mutlisim to design a circuit and was wondering if any one could help shed some light. First off, I'm a mechanical engineer dabbling in Electrical so if my questions seem simple, please excuse them- I appreciate the help. 

I'm currently using multisim 14.1 to try to design a circuit, but I have a strange challenge. First off, my circuit starts with a really simple DC power supply with resistors in series and parallel. I'm able to calculate the load current and everything agrees between theory and multisim. The problem I run into, is that I need to inject a short burst of AC current into my circuit. I'm not sure how to calculate this by hand so instead i'm trying to use Multisim to reproduce what I'm seeing in experiments- and then design around it. 

For ease of discussion I've attached 2 figures, the circuit diagram I'm using and the simulated current at point 1 (shown in the diagram)

Multisim issues:
1) When I use a switch to inject a 1/2 Hz 1 Amp AC current into my circuit for 1 second, after the switch turns off the AC signal stays in the rest of the circuit (See Figure 2, which is the current at point 1 on Figure 1). This doesn't make sense to me, it should die out as the current goes through the circuit to ground right? 

2) Is there a way to set a threshold on the DC supply. For instance, if the max current in my circuit goes above 1 Amp, is there a way to force the powersupply to drop its voltage- essentially operating in a constant current mode?

Engineering Issues: 
1) What I see in experiments is that the current goes above 1 in the circuit due to the injection of the AC source and drops the voltage supplied to the circuit. This is an issue as the current source is dependent upon the DC voltage. I want to prevent the surge of current from the AC source from reaching the DC supply. Does anyone have any suggestions for this? 

I'm playing around with a Capacitor now, but I'm afraid that problem 1 I mentioned above is preventing me from seeing reliable simulated effects. 

Thank you for your help, if there are any clarifying questions please let me know,

[JKarma]

Hello Wolfgang.Black:

Can you please explain me the objective of the circuit and the conditions that you want to fulfill? 

Please take in consideration that you already have the switch names, please use those or more screenshots.