negative damping

[akunkeji]

Hello, everyone:
I use  pulse to drive a Air-core Coil, the resulting waveform makes me puzzled, negative damping or Self-excited oscillation? Please help me answer the causes of the waveform. Thanks!
Circuit diagram and waveform are as follows:
(Correction:Frequency of driving pulse is about 3.7Khz.)

[mscoffman]

Hello, everyone:
I use  pulse to drive a Air-core Coil, the resulting waveform makes me puzzled, negative damping or Self-excited oscillation? Please help me answer the causes of the waveform. Thanks!
Circuit diagram and waveform are as follows:

Self resonance in the coil - LC Between the L of the coil and the C in the coil.

Fourier Decomposition of the Pulse is a number of frequencies - that
is the exciter.

The transistor may play a role as amplifier, as it is not properly coupled/decoupled.
A real transistor has got to be considered caged by C's - interelectrode
capacitance. You gotta design your bipolar amplifiers better. 

:S:MarkSCoffman

[akunkeji]

@mscoffman

Thank you for your answers and suggestions, I will go to test in accordance with your suggestions. 

[Cherryman]

edit: wrong topic,my appologies.

[mscoffman]

I hope you see that the interelectrode capacitance of the
power transistor causes the ringing of the L/C from the coil to
begin increasing (it's really oscillating). The collector to base
internal capacitance couples the high power ringing into the base
of the transistor. (that's the oscillator). Then, when the trailing
edge of the input pulse "nors in" it causes these oscillations to be cut
off. So it's not damping at all. Those tall diffuse vertical bars at the
end of the oscillation is the actually the wire attached to the base
from the pulse source ringing, I believe. All these "ringings" are due
to lack of impedance matching and HF suppression.

Bedini circuit is simple to build but the lack of support components
which causes spurious waveforms to appear, confusing everyone.
Unfortunately, support components often make the circuit *less
efficient*. So there is design trade off between pretty waveforms
and extra components usually with lower net circuit efficiency to
boot. These semiconductor components are pretty good but they
are not perfect.

:S:MarkSCoffman