Larry wrote about changed behavior between LTspice IV and LTspice XVII, when a sine wave voltage or current source has Ncycles.
? ? "I assume this was done intentionally or is this possibly an error."
Looking at LTspice's Help, I think it was an old bug that has finally been found and fixed.? The way it behaves now, is the way it was always SUPPOSED to be.
The LTspice IV Help page says that the output before Td or after Ncycles have completed, should be:
? ? V(time) = Voffset?+ Vamp * sin(PI*Phi/180)
? ? I(time) = Ioffset?+ Iamp * sin(PI*Phi/180)
Therefore its steady starting AND ending values should have been the value at that point along the sine wave where it starts and ends, determined by Phi.? Thus the sine wave should be continuous at both ends.? (But even that description is in error, because Ncycles doesn't need to be an integer, and because it doesn't take Theta into account.? That's been fixed in the Help page for LTspice XVII.)
However, LTspice IV's actual behavior differed from this.? Instead of being the steady value given on the Help page (adjusted if necessary if Ncycles is not an integer), it actually shot straight to zero at the end of Ncycles, as you saw.
I would call that a bug in LTspice IV because it clearly doesn't do what the Help says it should have done (for integer Ncycles).
LTspice XVII fixes the bug.
The LTspice XVII Help pages now say, "For times after Ncycles have completed, the voltage (current) is the last voltage (current) when Ncycles have completed.? Note Ncycles does not have to be an integer."? I think that was the intention all along, but LTspice IV was (and is) wrong.
It might be interesting to go back several versions and see if this big appeared at some point or if it was always there.? But I am not currently set up to easily do that.
Regards,
Andy
