AC voltage-triggered flyback transformer - This simulates now, after the diode that was directly across the 60 Hz source was removed, and the op-amp was replaced with a comparator of similar performance. Since there was no feedback around the op-amp in the original version of this design, it simulates more robustly with a comparator.
This comparator model does not have a direct power supply connection, but it does use a 0V to 12V swing, corresponding to the simulation results that show the approximately 12V rail available in this circuit (net8).
This design uses the "More Speed" and the "Convergence Assist" options in the Advanced Options for simulation. This improves speed and robustness, of course!