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

[Steve Ward <steve.ward@xxxxxxxxx>]

It acted like a very out of tune class E setup.  Essentially, the
capacitor was a voltage snubber, used to avoid very large voltage
transients due to the fast turn off of the mosfet with the inductance
of the primary.  It was basically not designed right ;-).

Steve

On Sun, Aug 26, 2012 at 7:53 PM, Andreas Hahn <andreas.hahn@xxxxxxxxxxx> wrote:
> Hi Steve,
> Thanks, that clarifies things. What's the function of the capacitor across
> drain and source in the non-Class-E original MicroSSTC? It's obviously not
> capable of blocking DC across the HEXFET.
>
> Andreas
>
>
>
> On Sun, 26 Aug 2012, Steve Ward wrote:
>
>> 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
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>>>>> http://www.pupman.com/mailman/listinfo/tesla
>>>>
>>>>
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