Hello,

I am building a flyback converter in LTspice and I am doing an experiment of disconnecting the input power source and the transformer if the input voltage source exceeds 500 V. When I try to simulate the circuit, I get an error saying, "Analysis: Time step too small; time = 1e-005, timestep = 1.25e-019; trouble with mysw2-instance s2." I have attached my schematic below for reference. I don't know if it has anything to do with the behavioral voltage source causing the switch to alternate positions too quickly where the simulation just can't handle or it what. Guidance would be greatly appreciated. All components besides S2 are non-ideal. Thanks!

 

I'm having no problem with your simulation.
Q: which version of LTspice are you using. I'm using Version 17.1.15

 

Version XV11 of LTS does have the problem. Changing the Vh parameter of SW2 from -.4 to -.2 overcomes it.

 

Wow, thanks! I don't know why Vh affected that, it always ends up being super simple.

 

Hello,

I am building a flyback converter in LTspice and I am doing an experiment of disconnecting the input power source and the transformer if the input voltage source exceeds 500 V. When I try to simulate the circuit, I get an error saying, "Analysis: Time step too small; time = 1e-005, timestep = 1.25e-019; trouble with mysw2-instance s2." I have attached my schematic below for reference. I don't know if it has anything to do with the behavioral voltage source causing the switch to alternate positions too quickly where the simulation just can't handle or it what. Guidance would be greatly appreciated. All components besides S2 are non-ideal. Thanks!

Three things:
1. B1 equation should be V = if (V(input) > 500,0,1) so the sim can converge at startup. This fixed the timestep problem.
2. Set the switches to reasonable values. SW2 Ron should be at least 1m or greater, assuming its a simulating a mosfet switch.
I set it to 20m ohms.
3. Add a reasonable serial resistance value to each voltage source.

I hope you realize that SW will turn off when the AC voltage crosses zero in the positive direction due to the 500vdc offset.

 

I've found that giving capacitors and inductors some small parasitic value can often get round the dreaded timestep issue too.