MOSFET gate driver quirk
The BS170 FET can switch 500 mA, with a maximum on-resistance of 5 Ω at 10 V Vgs. It also has a higher input threshold than a 2N3904 BJT which has high hFE as a emitter follower but reduce to 10% of hFE max as a common collector switch which can be as low as 7 Ohms u like the PN2222A which can be 4 Ohms.
But the resonance occurs due to the Ciss of the power FET and low gate resistance during transition which creates an unstable closed loop SCR effect with Q3:Q2 but which reduced current gain of the BJT in Q2 while the FET in Q3’s higher threshold offers some hysteresis and higher gm independent of the load so that Q3’s drain downing low is not bothered Q2’s bootstrapping pulling up the source for the FET in Q3’s source up to Vsup. Thus the FET’s Vgs is adequate for driving the power FET and no oscillation. Thus what I called a hysteresis effect ( of sorts).