Thoughts and remembered considerations missing from last post. Doc
About midway through that design cycle I changed to a P222 N Ch Mosfet because I had drive issues with the Bi-polar part due to beta changes that occur when the collector current increases. These changes require a big increase in base drive to the switch transistor. Mosfets don't have this issue. I also found early in the design that a "snubber" was required. I used a 4R7 ohm resistor in series with a .33uf cap and the combination worked well although the classical snubber design method didn't work very well. My final values were determined by experimentation. I hope this helps a litttle.
Doc