Thanks,
Page 4 of the MC33063 datasheet states that the hfe of the transistor is 50 (min).
Page 13 of the AN920-D application note shows an example where they are forcing the gain to be 20, by simply driving too much base current into the switching transistor.
This seems pointless, since there is an available gain of 50.....so why use 20, -it just means youre running too much current in the drive circuit?
(I wonder if the hfe of 50 at 25 deg C alters for other temperatures?)