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Registered Member #3704
Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92
TwirlyWhirly555 wrote ...
I used plastic laminate sheets round my mini SSTC to stop flash overs ,
9" arcs from a 2"x2.8" secondary keep going down before that :P
Wow, that sounds like a very small coil...
Once again, I've rethought my secondary. I would really prefer to use the one I already have, but that means fres would be higher--around 273.6kHz. I think that's still well in the acceptable range, though I don't have experience with this. perhaps someone else can verify....?
The current idea is to use my 4.5" x 19" secondary and make a small (3" x 10") toroid out of 3" aluminum dryer duct. Based on JavaTC, these are the results I get:
I also downloaded JavaTC and edited the HTML file so that I could view the entire graphic without it overlapping text:
The ratio looks a little better, and it doesn't require me to use up more wire than I need to.
Registered Member #3704
Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92
Sigurthr wrote ...
Why not just shrink the tank cap or increase tap range on primary?
I'm just building a basic SSTC for the time being, so there isn't a tank cap. But I'm trying to figure out the best size of secondary and topload to get a resonant frequency of between 200 and 300 kHz (ideally).
I thought so but couldn't figure out why you were worried about the target frequency so I assumed you might be trying a hybrid type construction, switchable between DR and SR.
I wouldn't stress over the actual resonant frequency then. I've made successful SSTCs up to 1.1MHz that hard switch the FETs in CW at several hundred watts of power. Use what secondary and topload you want to, what difference does it make if it is 230KHz or 290KHz? Just my 2 cents. =)
Registered Member #43278
Joined: Sat Feb 22 2014, 09:18AM
Location: Sydney
Posts: 9
DerStrom8 wrote ...
By the way, the image JavaTC creates based on the information seems to be in the wrong place for me. Does anyone else have this issue?
DerStrom8 wrote ...
I also downloaded JavaTC and edited the HTML file so that I could view the entire graphic without it overlapping text:
The ratio looks a little better, and it doesn't require me to use up more wire than I need to.
You might want to go back and check that you have entered the various heights correctly into JavaTC. The only times that I have had trouble with the graphic like you have shown, the fault has been entirely mine. I strongly suspect (but have not verified) that JavaTC will give you a lower Fres if it has been lead to believe that your coil is going to operated partly buried ...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
1100MHz! And I thought designing a 60MHz, 1kW resonant vacuum tube oscillator was a challenge.
(...I know, I just had to.)
BTW. FETs can switch really fast, but it's often the active feedback schemes which limit the useful frequency range, caused by delays and phase shifts in the loop. For higher frequencies, self-excited oscillators are the way to go. But the basic PLL circuit can be used well over 1 MHz, the direct amplifying feedback will work well to maybe 500 kHz.
Registered Member #3704
Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92
Sigurthr wrote ...
I thought so but couldn't figure out why you were worried about the target frequency so I assumed you might be trying a hybrid type construction, switchable between DR and SR.
I wouldn't stress over the actual resonant frequency then. I've made successful SSTCs up to 1100MHz that hard switch the FETs in CW at several hundred watts of power. Use what secondary and topload you want to, what difference does it make if it is 230KHz or 290KHz? Just my 2 cents. =)
In a way you're correct--I will eventually want to switch it over to a DRSSTC--but for the time being I'm just making a plain SSTC. I am trying to make it as easy as possible to switch over though, which is why I'm trying to keep the resonant frequency within a decent range.
1100 MHz, eh? That must have been an interesting build
mbd wrote ...
You might want to go back and check that you have entered the various heights correctly into JavaTC. The only times that I have had trouble with the graphic like you have shown, the fault has been entirely mine. I strongly suspect (but have not verified) that JavaTC will give you a lower Fres if it has been lead to believe that your coil is going to operated partly buried ...
I was wondering if that was the case, that I was entering the heights incorrectly. For height 1 (Low-voltage end) I put in 1 inch, assuming it would be 1 inch off the stand, and for height 2 (high voltage end) I entered the height of the coil +1". I think I must have made a mistake in this part somewhere.
Dr. Dark Current wrote ...
1100MHz! And I thought designing a 60MHz, 1kW resonant vacuum tube oscillator was a challenge.
(...I know, I just had to.)
BTW. FETs can switch really fast, but it's often the active feedback schemes which limit the useful frequency range, caused by delays and phase shifts in the loop. For higher frequencies, self-excited oscillators are the way to go. But the basic PLL circuit can be used well over 1 MHz, the direct amplifying feedback will work well to maybe 500 kHz.
Very good to know. I'll probably still keep the frequency low because I eventually plan on swapping the FETs out with IGBTs when I swap over to the DRSSTC, and I will want to change as little as possible for the rest of the coil.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
All the heights in the JavaTC are relative to the ground plane. This includes the primary coil, secondary coil, topload, etc. Enter something like 20" for the bottom height, this will work well. Also, make sure you enter the ground plane and wall dimensions about correct.
Another problems beginners could have with JavaTC: -Coil dimensions are entered by the radius, not diameter -Wire Dia / AWG switch in secondary coil wire size -When using metric units, people sometimes have trouble entering all the dimensions in centimeters (especially the wire sizes)
If you've entered data of a secondary coil you already have, always check the DC resistance after completing the calculation. If it's off, you've made a mistake somewhere.
Registered Member #3704
Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92
Dr. Dark Current wrote ...
All the heights in the JavaTC are relative to the ground plane. This includes the primary coil, secondary coil, topload, etc. Enter something like 20" for the bottom height, this will work well. Also, make sure you enter the ground plane and wall dimensions about correct.
Another problems beginners could have with JavaTC: -Coil dimensions are entered by the radius, not diameter -Wire Dia / AWG switch in secondary coil wire size -When using metric units, people sometimes have trouble entering all the dimensions in centimeters (especially the wire sizes)
If you've entered data of a secondary coil you already have, always check the DC resistance after completing the calculation. If it's off, you've made a mistake somewhere.
I will try raising up the LV end of the coil to about 20" and will get back to you.
In the meantime, I've been looking around at some IGBTs for when I convert it into a DRSSTC. I have been looking at 600V >30A continuous models, and I found a fairly cheap one on Mouser:
I don't want to buy it unless you guys think it will work. Are there any other specs I should look at before deciding to purchase? Looking at the datasheet (link: ) it looks like these should be able to switch fast enough and the diode recover quickly. I'm planning to buy 10 of them, so that I have plenty of backups if anything goes wrong (which it probably will )
I'll get back to you on the JavaTC calculations. I also want to make sure that I have all the measurements correct.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The part you posted is a relatively slow one. Have a look at the following part numbers:
HGTG20N60A4D (a relatively old transistor, but still fast even for today's standards and should be rugged) (or other HGTG...A4D models) FGH40N60SMD (a more modern part) (or other FGH...SMD models) STGW30NC60WD (or other STGW...WD models)
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First SSTC design - Need some critique
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