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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Ok so I'm planning to make a high power "zvs" "flyback" driver (I put flyback in quotes because it does not share anything common with it) to drive a homemade transformer w/ 16kV output and 1200W arcing output as the goal.
Has anyone experimented with the zvs or mazilli driver powered directly from mains?
I want to make the power stage run from rectified mains (325V) to avoid bulky mains transformer. I plan to use gate drivers running from low voltage to drive the gates, I'm wondering if the faster switching wouldn't cause more parasitic oscillations and cause the circuit to be unstable. Also I want to run it with 1200V IGBT's as MOSFETs of this rating are xpensive and hard to obtain. However the IGBT's I'm looking at are TO220 devices, I'm wondering if there wouldn't be any flashover problem between its legs? IIRC they are around 1mm apart, couldn't 1kV+ actually flash over this gap under certain circumstances? And is 1200V rating enough?
Lots of questions, but I really hope to get this thing working as I want to stay away from hard switched designs, these always exploded on me at higher powers...
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Perhaps you should put some anti-parasitic chokes into the circuit, and make them sufficiently different from each other to avoid unwanted oscillatory coupling between them. Good power supply by-passing, short leads, and use of a common earthing point (rather than 'daisy-chaining') will all help with stability too.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I have considered this and so far I have not tried because; 1) The series/dc inductor will be quite large. 2) The primary transformer will be quite large 3) I haven't yet found a use for such power!
I am considering a 'zvs' type oscillator as a CW SSTC primary, just haven't got around to it.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Sulaiman wrote ...
I have considered this and so far I have not tried because; 1) The series/dc inductor will be quite large. 2) The primary transformer will be quite large 3) I haven't yet found a use for such power!
I am considering a 'zvs' type oscillator as a CW SSTC primary, just haven't got around to it.
1200 V is adequate, TO220 sounds a little small.
1) Not too large but more turns of thinner wire will be needed 2) What do you mean by primary transformer? The main ferrite HV power transformer? The 1200W I stated is based on the core size of my xfmr. 3) I did :) Anything from arc drawing and burning things to Jacobs ladder to a Tesla coil (the output will be fullwave rectified and adjustable from 0 to max)
As to the TO220 devices, I'll probably 'pour' something on them, maybe parafin wax or hot glue (after I find it non-conductive) etc. to avoid flashovers between the pins.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Sulaiman wrote ...
I wish you well, and hope to see the working system.
If you like I will crunch numbers as a cross-check, given; operating frequency, core cross-sectional area.
The core is 3.7 cm^2, I don't know the ferrite material number but you can be sure it's for power transformers. The frequency is a variable to experiment with, I'll try different tank capacitor sizes/primary turns and see what works best. However the aim is ~40-60kHz.
I've found a possible problem, I'll be using gate drivers which need below 1.5V on the input to change the output to low, and the IGBTs have ~2V forward voltage drop so theoretically they can not turn the gate drivers low. Will this be a problem in reality? If so what could I do to fix this?
EDIT: What about "angle controller" with a SCR to bring the supply voltage down to say, 200VDC? It would cause bad power factor but I really don't care, and the driver would be quite simpler to build. Just don't think about what happens when the SCR fails short...
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I want to make the power stage run from rectified mains (325V) to avoid bulky mains transformer. I plan to use gate drivers running from low voltage to drive the gates, I'm wondering if the faster switching wouldn't cause more parasitic oscillations and cause the circuit to be unstable.
Steve C. and W seem to have reported some problems, but I don't have clue what could cause them. If drain-capacitor and source-GND connections are kept short I don't see how could Q build high enough to undergo oscillation.
You need to take care though not to overload the tank and drop it's Q too low to oscillate.
You should consider some kind of overcurrent protection. A small CT and a comparator. Even simple SCR saved me a lot of mosfets in halfbridge circuit.
Also I want to run it with 1200V IGBT's as MOSFETs of this rating are xpensive and hard to obtain. However the IGBT's I'm looking at are TO220 devices, I'm wondering if there wouldn't be any flashover problem between its legs? IIRC they are around 1mm apart, couldn't 1kV+ actually flash over this gap under certain circumstances? And is 1200V rating enough?
I'm pretty sure packages are tested for those voltages, and 1kV shouldn't be but a fraction of mm. Just make sure not to get solder, wires and other metal parts much closer than that.
Potting the device probably wouldn't help much as an arc, if it develops would track the package and go through the gap between the potting and package, as you can hardly make a good seal there.
I've found a possible problem, I'll be using gate drivers which need below 1.5V on the input to change the output to low, and the IGBTs have ~2V forward voltage drop so theoretically they can not turn the gate drivers low. Will this be a problem in reality? If so what could I do to fix this?
This was a big problem to me, especially when you consider that voltage drops add! I'm not sure but this may be one of reasons why people have trouble with IGBT's in this circuit.
My idea is to use a PNP transistor series with a pulldown resistor forming an inverter circuit, and put a inverting driver chip or some other circuitry after it.
PNP transistor would react even if base is pulled like a volt under the Ucc and give you large margin of feedback voltage.
For very high frequency operation this also allows using small diodes like 1N4148's in series since forward drop isn't so important anymore.
Haven't tried anything of this yet, just theoretical - sorry!
Hope you'll manage something with this.
EDIT: What about "angle controller" with a SCR to bring the supply voltage down to say, 200VDC? It would cause bad power factor but I really don't care, and the driver would be quite simpler to build. Just don't think about what happens when the SCR fails short...
I wouldn't recommend that especially if you were going to power a tesla coil, your output waveform would be modulated my the short fraction of waveform where SCR's are conducting.
and if you use a filter cap and choke your DC voltage would be greatly dependent on the load.
If I wanted a power supply for royer converter my choice would be PFC buck-boost converter.
It would allow regulation 0-100% and steady DC output. This would actually be my ultimate general purpose HV transformer driver, next step would simply be SLR converter.
Good luck sir, I might join in the project but not sooner than few months, as soon as I get out of the mess here.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Marko wrote ...
... next step would simply be SLR converter.
I've actually considered SLR too, it's pretty simple to get it right, but... There are problems with open circuit output ... and I killed a FET after playing with it a bit, at low power, I'm pretty sure I had everything right. I know this is no excuse, but I think it's not good for anything else than capacitor charging [Tesla coil].
thermite wrote ...
quick side question: who is vladimir mazilli and where is his site or circuit originally published ?
I remember his circuit to firstly appear in a thread called "zvs flyback driver" on the old 4hv.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Today I tried "low voltage" (115VDC) version with 500V FETs and gate drivers. It starts to oscillate as I apply power but as soon as I make the first spark with the transformer, the circuit bursts into MHz oscillations and there is no output from the transformer. I have asolutely no idea what to do with this, I have the tank capacitor soldered directly across the MOSFET terminals. Schematic:
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"zvs" flyback driver on mains?
(the output will be fullwave rectified and adjustable from 0 to max)
