(Copied in from other thread)
Doug Coulter wrote:Price has nothing to do with patent-ability, and Spellman among others has published this design for a few of their supplies going back decades. Nuff said?
Feel free to find one. If you do, I'll paypal you $20.
But suit yourself, now you can go sue Spellman, Glassman, and others who used this trick way long ago
Doug, there's no need to be like this. They either have done it, or they haven't. If they have, it is prior art, unpatentable. I did the searches and nothing came up. I did more than that and hunted further literature. Nothing that I found. Maybe there is. But I searched for a long time, and came up with no such previous use of multiple supplies feeding one stack.
It's obvious once you see it, but nothing quite like this in such a simple form has been done that I have found.
Feel free to prove me wrong and get your $20 off of me.
Show me an example of a single stack of stages being fed by multiple capacitively coupled power sources that share a common ground, and come collect your $20!...that last cap having to be very high voltage (and thus higher joules)
I run 100pF/30kV link capacitors up to 30kV, then two of those (50pF/60kV) on further stages up to 60kV. Gee. 0.1 J. Big joules....
And you do need a decent sized ac feed-in cap if you want any regulation worth talking about - with a non-stiff supply, feedback regulation is a very tough loop to close without it hunting or oscillating.
I've put the detail into the patent. If you do not wish to read or believe the results, nothing much I can do about that.
If you bother to try this out for yourself, rather than simply dismiss it without generating any numbers, you'll discover that the link caps only impact efficiency, not ripple current and regulation. You can disagree all you like, but I've done it, measured it, written it up. Try it, you'll see for yourself.
The reason is quite simple if you think about it - as the input AC oscillates, the cap follows the phase. As the cap lags behind the input AC, say in the negative going stroke of the input cycle, so the voltage across it goes up considerably, because it is undergoing a 'differential' charge. As it reverses and goes back the other way, however much it was on the 'wrong' side of the lower potential of the stage in the negative going cycle, so it will be equally effective on the top of that stage's potential in the positive going cycle.
So the cap can lag on each stroke, but the potential by which it 'lags' adds up constructively in the next half-cycle.
Basically, the link capacitor can see double the peak to peak volts or more in the applied AC, and that's fine because it makes no difference to the ripple voltage so it makes them more effective if they undergo
more voltage deviation and the full pk-pk volts during a cycle, whereas the 'storage' caps, in series with the load, you want those to undergo
as little voltage deviation as possible. As the energy content is the voltage squared, you can see immediately why the link caps can be really small in comparison with the storage caps.
Using smaller caps for the 'coupling' merely causes them to undergo much higher duty cycles. Clearly you'd be able to take that too far and cause them to fail. But the ceramic disc types I use (100pF/30kV, retail purchase price of $0.40 each) do fine and do not appear to overheat at all under a 5mA load. (100pF at 40kHz is ~40kOhm impedance... I guess that means about 0.3W per cap when carrying 3mA?)
If this was well-known and understood, I'd expect to see the building and recommendations for CW stacks to include this detail, because, as you say, HV caps are expensive. In the tests I have done, it suggests you can substantially reduce the capacitance of half the caps (the caps not in series with the load) in a CW stack without ANY effect on the
output at all. You might have to turn up the input a little to accommodate work losses in those link caps, but if they are of sufficient quality and can handle the RMS current they are exposed to, then any increase in input is marginal. I have found it to be essentially unmeasurable (maybe a little loss noticed, but measurements are below statistical significance to report).
IF course, had you done the legally required searching for prior art the USPTO requires (but most ignore) you'd already know all this. It's up there.
$20 in it for you if you show me a real document showing this.
Having said that, double the volts and current and you might have something you could run a fusor from and it'd be a boon to amateurs, who don't have to pay a bit of attention to patents on things for their own use anyway.
Doug, do you really have an understanding of this patent? Just read it. There's clearly stuff you haven't read, maybe there might be something that will surprise you!
You can double the volts and current easily, simply by having 4 of these and putting them together. There's even a diagram to make this plain-and-simple to understand. They can be serialed (with sufficient isolation in the caps and inverters) and paralleled, no problem. This is a key part of the advantage they bring. Just have a small pile of them, and set them up in any order and configuration you like to achieve your HV electrical requirements of the day. High current - parallel them all. High volts, serial them. A bit of both - use them individually, or in pairs. Whatever.
This idea is all about flexibility to achieve a specific HV load requirement, and the capacity to make use of mass-produced low cost components.