• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Two SMPS simulations are essentially the same but one malfunctions...why?

Not open for further replies.


Well-Known Member
Here are two like-for-like LTspice simulations…one works well but the other doesn’t. Why is this?
Each simulation has two offline buck converter LED drivers.
In one simulation there is one mains source supplying both bucks. But in the other simulation each buck has its own mains source. That is the only difference between the two simulations.
So why does the one with a single mains source show a disturbance in its inductor current i(L3) from the 2ms point onwards? The other simulation doesn’t malfunction like this. Why? They are both essentially the same.

LTspice sims and pdf schematics attached



Well-Known Member
Most Helpful Member
Strange indeed. I suspected the AC source impedance, or the maximum timestep setting, might account for the difference; but playing with those didn't resolve the issue.


Well-Known Member
Would both circuits really be connected to a single AC source that way?
Or would there be separate AC windings feeding each circuit?
Not open for further replies.

Latest threads

EE World Online Articles