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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dr. GigaVolt wrote ...
i use CST-206 type current transformers which are small and cheap for this purpose and they are good for at least 500A peak current on the primary at 100-300kHz.
well, I can't see how this would work for a non-DR coil. When drawing arcs, the primary current starts to resemble a triangle wave with the switching transitions at maximum current. If you sampled the current, it would just rise and never cross zero again -> blown bridge.
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
@Frosty90 No you couldn't. The delay depends on the input amplitude, whenever that is the primary feedback it works ok as the currents are pretty high - but not for secondary one. The shunt produces the same delay as the antenna so seems it's worth a try - with a generic stepup ratio of ~10 the startup will be smooth and will require no startup oscillator. Drew this tonight - was pretty sleepy so forgot the reverse diode, but at least the point is clear :)
@Dr. GigaVolt Of course the primary-fed CT is the best choice for DRSSTCs - but not for ISSTCs like I said above - the generally triangular magnetizing current would screw it up for sure, so it would lock onto the frequency of the primary vs DC blocking cap resonance.
Registered Member #1617
Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139
Lithiumord:
I dont really understand what you mean by "the delay depends on the input amplitude", if this is the case, why should it not work for a fixed power level? Or could you use another feeback CT to sense the current and adjust the shift register clock acordingly? Although this probably defeats my original purpose, to keep it as simple as possible.
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
I mean: a CT should be loaded, if the input current is too low it will induce a lag. Now how can you hold a constant power level in a non-CW system? ;) Also why messing around the shift registers etc if you can just use a shunt? By the way, the shift register is not a time machine lol - it can only produce delays, now how would a delay help to compensate another delay? ;)
Registered Member #1617
Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139
"not a timemachine" lol, yeah what i meant was you could add 360 degrees of phase shift plus or minus enough to compensate for the delay. so the delay of all your drive electronics plus ct etc meant your drive signal was delayed by say 5 degrees, you could set your shift register for a delay of 355 degrees, thus going backwards through time, and emerging from the past in phase with your secondary I should have made myself more clear! Ok so if the input currentis too low it will introduce a lag. how low is too low? could one not design a CT or purchase (i really dont want to) one to do the job? but yeah your right a current shunt would be easy.
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
360deg offset - huh, it has an issue ;) For example, the system does the first period open-loop and measures the feedback frequency. Let's say it gets the unloaded secondarie's 100kHz, therefore 10us. It uses those 10us for the next cycle, and it's ok, but at some point the spark starts to form up and those 10us get too low. But - the proper offset will be induced only for the next cycle, so - you fail to get the system running in sync with the secondary on the startup part. Also I have no idea how are you going to set it all up ;) If you can tolerete the lags in the startup - well, there is no reason to have the disadvantages of the direct feedback, you can use a PLL. If not - the feedback has to be accurate!
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