Re: [TCML] Tuning SSTC to avoid losing oscillation when I try and draw discharge

[Steve Ward <steve.ward@xxxxxxxxx>]

Hi Andreas,

The class E design, such as my old one here:

http://stevehv.4hv.org/classEsstc.htm

does exploit resonance on the primary side.  The tuning of the
primary, however, does not strictly have to match the tuning on the
secondary side.  If the primary tuning is "off" then the voltage
waveform across the mosfet/IGBT will be non-ideal (there will be some
energy left in the tank capacitor at turn ON for each cycle).  The
frequency that the system oscillates at is determined by the secondary
coil's frequency, which does depend on the primary tuning to some
extent.

For a "typical" SSTC driven by a half or full bridge, the capacitor on
the primary side is only for blocking DC, which would not contribute
to the tesla coils power output (but would contribute to heating the
silicon in the bridge!).  This capacitor is often ~10X bigger than a
resonantly sized capacitor so that its AC reactance is insignificant.

Steve


On Sat, Aug 25, 2012 at 8:55 PM, Andreas Hahn <andreas.hahn@xxxxxxxxxxx> wrote:
> Steve,
> Thanks, I'll give it a try.
>
> Also, I didn't realize the primary wasn't intended to be resonant in an
> SSTC. How does Class-E work if not for the primary LC resonant frequency
> matching the secondary LC...?
>
> Andreas
>
>
>
> On Sat, 25 Aug 2012, Steve Ward wrote:
>
>> Andreas,
>>
>> You may want to experiment with the placement of the antenna,
>> bringing it closer to the tesla coil should help.  Ultimately this
>> design does suffer from loss of good feedback during ground arc
>> conditions.  If nothing else, the ground arc produces high frequency
>> "junk" that goes right into the antenna input and causes undesired
>> switching of the mosfets.  The fets seem to tolerate it OK, since the
>> switching is often far above resonance and so the current that can be
>> delivered to the inductive load stays pretty small.
>>
>> This is why DRSSTCs evolved to use feedback from the primary circuit,
>> where ground arcs cannot give junk feedback signals.  Sadly, this
>> cannot really be applied to a SSTC, you cannot simply take primary
>> feedback because the primary itself is not resonant.
>>
>> Steve
>>
>> On Sat, Aug 25, 2012 at 12:05 PM, Andreas Hahn <andreas.hahn@xxxxxxxxxxx>
>> wrote:
>>>
>>> I have sitting in front of me a lovingly wound Tesla coil adapted from
>>> Steve
>>> Ward's MicroSSTC plans, so young it hasn't even blown its first HEXFET.
>>>
>>> Sadly it's a bit shy. When I approach the breakout point with a metal
>>> object
>>> held in my hand, the breakout retreats back into the comfort of the metal
>>> from which it sprang (i.e. it stops).
>>>
>>> Thoughts on how to best give it the courage to keep oscillating and
>>> making
>>> high voltage despite the menacing approach of a big pair of pliers?
>>>
>>> This doesn't happen if I try and draw an arc with a small piece of metal
>>> mounted to an insulating rod.
>>>
>>>
>>> _______________________________________________
>>> Tesla mailing list
>>> Tesla@xxxxxxxxxx
>>> http://www.pupman.com/mailman/listinfo/tesla
>>
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