PW,
you are right, the scope shot i directed you to was still taken with the 3.3K R17 resistor while the recent ones are with 8.2K.
Below screenshots ares with the 8.2K R17, 1st normal, 2nd expanded:
green: collector signal
purple: base signal
yellow: pin 7 IR2113 (LO)
blue: pin 1 IR213 (HO)
Trigger is on rising edge of LO.
12V on the collector
Let me know if you want additional screenshots.
Itsu
Itsu,
Thanks for the scope shots. Next time you post an expanded view, slow the horizontal down just a bit more so as to include the turn waveforms as well.
Regarding the older scope shot you referenced, have you adjusted RV7 differently (lengthened the pulse) between the old scope shot and your recent posts?
Observations:
Q6 turns on rather slowly due to R15's value and Q5's gate capacitace. Q6 turns on even slower due to R17 having to charge Q4's drain capacitance. As Q6 turns on, an oscillation in the collector coil is initiated, the frequency of which, I assume, is determined by the collector coils LC resonance and feedback from the antenna. Q6 is turned on only very briefly, around a half cycle in the recent scope shots, and perhaps a cycle or two (of collector oscillations) in the older scope shot. The setting of the pulse width using RV7 determines the number of collector oscillation cycles Q6 is allowed to be on before Q6 is turned off.
The ring down in the older scope shot looks much cleaner than your newer captures. The newer captures show a clipped signal on the negative going portion of the ringing. Perhaps RV7 needs to be adjusted so that Q6 is on just a tad longer (for another cycle or two). Perhaps it is related to R17 having been increased to 8.2K.
I would, however, check for leakage on D1, Q4, and Q5 to ensure they were not damaged in your recent 100V excursion and perhaps the cause of the observed clipping.
I would also consider returning R17 to 3.3K. For no longer than Q6 is turned on, dissipation at the higher current level should not be an issue.
As Vasik suggested, diodes can be used to protect the Q6 base from overvoltage. A single diode, cathode to base, anode to ground, and an additional two diodes in a series string, anode to base and cathode to ground, will clamp the base between -.7 and +1.4.
Suggestions:
See if you can get the cleaner ringdown of the older scope shot before considering the use of clamping diodes. First, check components for leakage/damage. Second, increase the pulse width slightly using RV7. Third, return R17 to 3.3K.
The ringdown is much cleaner in the older scope shot, I'd aim for that.
PW