I have an inductive load that I'm switching off, and when it's clamped I have flyback diodes in position to return the energy to the source. I'm trying to place another inductor (roughly 1/5 the size of the main load) in this path, essentially connecting 2 inductors in series with some diodes. I've tried varying this secondary winding in size and I'm not seeing any change to the inductor's discharge time. It's like LTspice is completely ignoring it. I have resistances for my switches and diodes, of course, so it's not like L/R is changing identically.

Anyone have any comments? I rarely use spice to simulate circuits, so I'm not well experienced here.

Thanks!

 

I have an inductive load that I'm switching off, and when it's clamped I have flyback diodes in position to return the energy to the source. I'm trying to place another inductor (roughly 1/5 the size of the main load) in this path, essentially connecting 2 inductors in series with some diodes. I've tried varying this secondary winding in size and I'm not seeing any change to the inductor's discharge time. It's like LTspice is completely ignoring it. I have resistances for my switches and diodes, of course, so it's not like L/R is changing identically.

Anyone have any comments? I rarely use spice to simulate circuits, so I'm not well experienced here.

Thanks!

It is more likely you are missing something. Post your .asc file so we can tell you what it is.

 

In the process of double-double checking before uploading the .asc, I found that the secondary inductor had a parallel resistance instead of a series one- guess I messed up setting it up and even while editing the value, never noticed.

I now see that any inductance there will cause such a massive voltage spike that it'll fry the diodes, which is what I expected to begin with- thanks for the help, still.

 

When the flyback diode us in place, the voltage does not spike. That is the whole point of it. The diode needs to withstand only the max voltage you place across the inductor.

 

In the process of double-double checking before uploading the .asc, I found that the secondary inductor had a parallel resistance instead of a series one- guess I messed up setting it up and even while editing the value, never noticed.

I now see that any inductance there will cause such a massive voltage spike that it'll fry the diodes, which is what I expected to begin with- thanks for the help, still.

You need to understand that the LTspice simulator is over two decades old and has gone through at least three major revisions since its inception. It also was based on an open-source simulation engine developed over 50 years ago. Based on that your claim of finding an error seemed dubious at best. I'm glad you were able to resolve your problem.

 

I didn't think I had found an error in LTspice, I knew I had something wrong- was hoping someone would give me feedback on what they expected would happen in that situation. Your offer to review the .asc was even more than I was expecting, which I appreciate.

Bob- the initial voltage spike is incredibly fast, on the order of several ns. The flyback diode might turn on fast enough, but I don't know if I want to count on that.

 

I didn't think I had found an error in LTspice, I knew I had something wrong- was hoping someone would give me feedback on what they expected would happen in that situation. Your offer to review the .asc was even more than I was expecting, which I appreciate.

Bob- the initial voltage spike is incredibly fast, on the order of several ns. The flyback diode might turn on fast enough, but I don't know if I want to count on that.

Because the .asc files are portable we can run the same simulation that you are running. It is common in the LTspice community to do this. Just so you know. In the presence of a fast spike the diode will turn on and conduct incredibly fast. No need to worry on that score. In your simulation you should compute the total power dissipated by the diode to make sure the package can handle it. You might be surprised at the values you come up with.

 

the initial voltage spike is incredibly fast, on the order of several ns.

it may be that fast in the sim with ideal components, but will likely not be that fast in the real circuit, due to stray capacitance.