Re: A double resonance solid state Tesla coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi Jimmy and All,

Merry Christmas!

(all snips from Jimmy)
 > None of the solid state tesla coils I've seen use a resonant
 > primary.

Normal continuous-wave SSTC's drive a resonant load, which is the
resonator. The resonant characteristics of the load are reflected
(inductively coupled) back to the drive circuit, therefore,
primary-side resonance is unecessary.

In other words, the primary is resonant without there being physical
components.

 > One of the downsides of the SSTC is the large magnetizing current,
 > especially when you try to get a fast voltage rise. This leads to
 > high losses in the power switches and makes it impractical to
 > generate 'normal' rise times and streamers.

There are very very little losses in the power switches in a properly
designed SSTC. The power switches change state (ON to OFF or vice
versa) when there is zero current flow...and since it takes voltage
AND current to dissipate power, there is no power loss. The vast
majority of SSTC's run about 90 percent efficient if not more.

 > Pspice simulation shows that the energy transfer is much more
 > efficient.

In switch-mode power supply lingo, SSTC's are resonant mode,
zero-current-switching forward converters. This type is one of the
most, if not THE most efficient topology known.

 > At this point, the switches are held closed emulate a spark
 > gap before it quenches. This prevents the diodes from sucking power

 > back from the secondary. After one or two beats, the switches are
 > left open as the secondary decays.

Keeping the power switches on as the secondary rings would not work.
Energy would be coupled out of the resonator through the primary, and
dissipated in resistance in series with filter capacitors.

In the above snip, if you're referring to the freewheeling, or
"catch" diodes, they do not conduct when the SSTC is in tune. They
only conduct when there is current flowing through the power switches
when they switch (out of tune). The fast change in current (di/dt)
generates a voltage spike, which forward-biases the catch diodes,
finally resulting in a current spike through the diode(s).

 > Compared to a SSTC
 >  1) The fast rise allows real streamers instead of 'brush
discharge'
 >  2) There is no magnetizing current

I don't fully understand your idea, do you mean to turn the power
switches ON, let current flow, then turn them hard OFF in a
non-resonant fashion? Like a normal spark-gap type coil, just
replacing a spark gap with a big power device (solid-state spark
gap)?

Take care, have a good Christmas.

Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com

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