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Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
If the idea is to give the secondary of the tesla coil a push when it crosses zero voltage then it must mean that the pulse of RF, that triggers the antenna input to the UCC373321/22 must be emitted when the magnetic field in the secondary is collapsing.
Registered Member #46164
Joined: Wed May 07 2014, 08:16AM
Location: California, USA
Posts: 89
Gregary Boyles wrote ...
If the idea is to give the secondary of the tesla coil a push when it crosses zero voltage then it must mean that the pulse of RF, that triggers the antenna input to the UCC373321/22 must be emitted when the magnetic field in the secondary is collapsing.
Is that correct?
From his website.
"I made another change to the circuit that improves some things. It seems the coil will work fine without U1 (the 555) even installed! Basically, when the driver chips are enabled, the inverting chip will send a short pulse to the MOSFETs causing the oscillation to start without any problem. The fact that there is only 1 signal going to the 74hc14 means there is no room for conflict here. This ALSO means that the feedback is stronger... shorter antenna! Now the coil will happily run WITH the toroid and produce up to 8" sparks now. Here is the revised schematic:"
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
The only way it could work without the 555 would be to connect the 'ENB' inputs of the UCC37322/21 chips to Vcc so that only the 'IN' pins control the gate drivers.
But that was not precisely the question I was asking - it was actually at what point in the cycle on the secondary coil is the pulse of RF produced?
While the current and magnetic field in the secondary is building?
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
I think the dominant effect is the capacitive coupling. The electric field from the secondary intersects the antenna, it's basically the same as taking feedback from a transformer with a capacitive divider.
The signal from a CT over the secondary's ground wire depends on the current flowing in the coil and the magnetic coupling.
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
GrantX wrote ...
I think the dominant effect is the capacitive coupling. The electric field from the secondary intersects the antenna, it's basically the same as taking feedback from a transformer with a capacitive divider.
The signal from a CT over the secondary's ground wire depends on the current flowing in the coil and the magnetic coupling.
But for this to work it surely must mean that the peak of the RF occurs when the current through the secondary is almost zero so that the small delays introduced by the two consecutive hex inverting Schmidt trigger gates allows the fet gate drivers to trigger another pulse through the primary coil when the secondary current is close to zero amps?
Think of the SSTC as sort of amplifier, the input being, where you feed in the antenna signal and the output the secondary top. If you input a sine wave, you'll get out a sine wave, which is somewhat phase shifted against the input. Usually the phase shift will increase for higher frequencies, the output being "later". A late output will cause a late input in the feedback loop, which means, the the frequency will drop, as the next cycle is "late" respective to the previous one. The lower frequency implies less lateness due to less phase shift. So basically the whole system corrects itself by changing the frequency and will run at just the frequency for the feedback to be at the right time.
The resulting frequency might not be the best one for max voltage, though.
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
Uspring wrote ...
Think of the SSTC as sort of amplifier, the input being, where you feed in the antenna signal and the output the secondary top. If you input a sine wave, you'll get out a sine wave, which is somewhat phase shifted against the input. Usually the phase shift will increase for higher frequencies, the output being "later". A late output will cause a late input in the feedback loop, which means, the the frequency will drop, as the next cycle is "late" respective to the previous one. The lower frequency implies less lateness due to less phase shift. So basically the whole system corrects itself by changing the frequency and will run at just the frequency for the feedback to be at the right time.
The resulting frequency might not be the best one for max voltage, though.
I presume then that is why all Steve Ward's DRSSTCs seem to use the a current transformer for feedback in the primary circuit.
I wonder if his mini SSTC could be adapted to use a current transformer rather than an antenna?
Registered Member #46164
Joined: Wed May 07 2014, 08:16AM
Location: California, USA
Posts: 89
Gregary Boyles wrote ...
Uspring wrote ...
Think of the SSTC as sort of amplifier, the input being, where you feed in the antenna signal and the output the secondary top. If you input a sine wave, you'll get out a sine wave, which is somewhat phase shifted against the input. Usually the phase shift will increase for higher frequencies, the output being "later". A late output will cause a late input in the feedback loop, which means, the the frequency will drop, as the next cycle is "late" respective to the previous one. The lower frequency implies less lateness due to less phase shift. So basically the whole system corrects itself by changing the frequency and will run at just the frequency for the feedback to be at the right time.
The resulting frequency might not be the best one for max voltage, though.
I presume then that is why all Steve Ward's DRSSTCs seem to use the a current transformer for feedback in the primary circuit.
I wonder if his mini SSTC could be adapted to use a current transformer rather than an antenna?
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How does the antenna work with the Mini SSTC?
