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1
Quote
1.   Now measurements of scope are correct?
You have explained well exactly what signals you are measuring.  Thank you.  However, those signals are not useful for measuring phase lead.  The signal in front of R2 leads in phase the actual DRSSTC primary current due to L1.  To measure phase lead, one scope channel needs to measure actual coil current, not a signal after phase lead has been applied.  Use either another CT or a resistor in series with the ground lead of your existing CT secondary.

Quote
2.   If low value of R24 delays phase lead then is necessary to put some resistance in series like R2 to prevent wave from distortions and limits input current for AD790 but not to large what I suppose delays the signal?
Low R24 reduces phase lead.  Most drivers do not have any resistor where you have R24.
R2 along with clamp diodes after it are necessary to protect AD790 input from excess voltage.  Distortion after R2 is normal, not a problem.  Phase lead is done before R2.  To avoid distortion on the phase lead circuit, it is normal for R2 to have a much higher value than R1.  For example, UD2.7 uses 51 ohms for R1 and 1k for R2.

Quote
3.    I have not galvanic isolation between logic state and power state. Everything is on the one board. Can it make any unwanted coupling or influence?
Depends on your layout and where power connections are made.  May be fine or may be a problem.  So far I haven't seen anything in your scope traces to indicate a problem.

Quote
4.   You mentioned about 50 ohms resistor and about 30uH coil with 30 ohms reactance. In my LC circuit frequency is about 70-75 kHz so parameters of the burden coil are depend from frequency. There are inductance, resistance, capacity inductance/resistance, own resonant frequency... I thing any simulation would be helpfull to find or design best coil for it?
Oops, my mistake on frequency.  I see your 70kHz frequency in scope traces.  It doesn't change inductance/resistance calculation very much.  You still want L/R to be about 600ns, a bit more at higher frequency.
Yes, I highly recommend simulation!  Simulation allows understanding the circuit better too.  For example, in simulation, you can plot actual primary current and the CT output voltage to compare phase.  My favorite free simulator is LTSpice, but there are many others.

Are you actually using FETs for a DRSSTC?  Or does your schematic show FETs because simulation is easier with FETs.  For the same package size and price, IGBTs handle much higher peak current.  However, IGBTs need 15Vge or higher, so require increasing your gate drive voltage.

Quote
Some strange thing is with negative half wave, because it has about 8-12 volt. I can remove R2 and feedback works/excites but then I have distorted wave in all circuit.
You need better AD790 input protection.  I'll again suggest antiparallel signal diodes instead of zener diodes.  AD790 is specified for input voltage from -Vs to +Vs-2V, so -5V to +3V in your case.  You are lucky to have not burnt your AD790 already!  Diode structures within the AD790 are clamping negative voltage to -5V.
2
Voltage Multipliers / CW Help -- too much info to digest
« Last post by abstruse1 on Today at 06:16:53 PM »
Greetings.  I've been trying to build a CW for weeks now, with almost no luck. I've built several.  I've read the detailed, sophisticated threads that many have posted, but I've not been able to go from those to why my simple CWs aren't working. I've used several drivers. Perhaps someone can help.

My first test is:

1.  Driver is "Monster.com" halogen driver, 12vdc nominal output, 140 watt, freq. around 9kH (but really messy signals on oscilloscope so hard to tell).
2.  6-stage "skeleton" construction (no mounting board) using 12, 1.0 nF, 30kV caps and 12, HRV300, 30kV, 30mA diodes.  Run in mineral oil.

Using just the first stage, I get ~1" arc. Adding 2nd, 3rd, etc. stages makes no difference in arc, until I get to stages 5 and 6, at which points arc gets a bit shorter.

Second test:  Different driver, 25kV, 36 kHz flyback.  About the same results

Third test: Yet another driver, 45kV 60kHz.  About the same results.

I think I'm missing something basic here, but I have no idea what.  I think the outputs from the last two drivers are AC, but they may be pulsed DC.  I say this because the polarity from the drivers is important -- get it backwards and there's no output.

Can anyone help?  Thanx!


3
Thanks davekni!
Your posts is helpfull:-)
My CT is single stage and at this moment I don’t want excess 300A absolutely. I suppose that is impossible in 12V power supply. It just first step for me to make fully proper work of logic.

I do some changes in my AD790 input and I hope correct scope measurements:






 
I put two resistors 180 ohms to check what happen. One man said me that to make possible phase lead the waveform has to be fully sine. Distorted sine wave in any way cannot be leaded.
I did measurments of bridge voltage (1 blue color on diagram) and current yellow directly on terminals of CT connected to AD790. On terminals in front of R2 180 ohms I have fully sine wave, but through I have distorted by 15V zener diodes what is correct. Some strange thing is with negative half wave, because it has about 8-12 volt. I can remove R2 and feedback works/excites but then I have distorted wave in all circuit.

Questions:
1.   Now measurements of scope are correct?
2.   If low value of R24 delays phase lead then is necessary to put some resistance in series like R2 to prevent wave from distortions and limits input current for AD790 but not to large what I suppose delays the signal?
3.    I have not galvanic isolation between logic state and power state. Everything is on the one board. Can it make any unwanted coupling or influence?
4.   You mentioned about 50 ohms resistor and about 30uH coil with 30 ohms reactance. In my LC circuit frequency is about 70-75 kHz so parameters of the burden coil are depend from frequency. There are inductance, resistance, capacity inductance/resistance, own resonant frequency... I thing any simulation would be helpfull to find or design best coil for it?
4
Electronic Circuits / Re: Gate driver for big IGBTs
« Last post by davekni on Today at 05:38:42 AM »
In general it is a great idea.  I did something somewhat similar for my DRSSTC using 40 TO247 IGBTs - four isolated supplies and discrete gate drivers.  I'm using 0-18V with a pair of TO220 FETs for each leg (10 parallel TO247 FETs), as they have no internal gate resistors.  Is 18V/-4V appropriate for your bricks?  Some bricks are specified for +-15V.  That is due to their internal gate resistors without parallel diodes.

I don't directly monitor Vce, but do estimate power and die temperature using current sense and simulated Vce.  There's more details in the first post too, but here's one post describing that:
https://highvoltageforum.net/index.php?topic=798.msg5332#msg5332
5
Electronic Circuits / Gate driver for big IGBTs
« Last post by TMaxElectronics on Today at 02:15:25 AM »
I thought I'd make a post about a little project I've been working on for a while :)

It's a gate driver made specifically for gates of large IGBTs (like the one Steve gave away a while back). Nothing special at the moment, but I do want to include de-saturation detection at some point, and maybe even measure dissipated power (accurately measuring the current would be an issue for that though). The goal is more or less to just be able to source much more current than integrated gate driver ICs could, with a convenient isolated logic level input for control from any old FPGA/CPLD/whatever.
I'll probably make a github repo and document it properly at some point so people can replicate it if they want to.

The low and high voltage sides are bridged because I fried the last digital isolator I had by soldering it in wrong way round... ::)


The driver itself is powered from a 10W flyback converter with 18V and 4V (winding ratios didn't work out for 5V) output. Well at least the transformer is dimensioned for 10W, but the sot23 mosfet would probably get a little cooked running at that power level continuously ;) I'm not even sure how much power I'll actually need for driving the IGBTs in the end though, so it might actually be quite overkill ::)
I've wound the transformer on one of the cheap aliexpress bobbin and core sets, which I really like. It's regulated from a feedback winding and driven by a pic12f1572 running a pid loop. The primary mosfet is extra-low gate charge and seems to be happy running from the PICs pin directly even at 250kHz. With the pic it would also be quite easy to make the drive voltage adjustable via RS485.
At 500mA current on the 18V rail I got a surprisingly high efficiency of 91% with the mosfet reaching a marginal 95°C according to the thermal camera.

For the output stage I'm using a SO-8 mosfet with one P and one N channel mosfet, driven by a normal gate driver. That seems to work fine, except for around 100ns of cross-conduction when the output switches off... might need to add some diodes there.
I have two different resistors for charge and discharge at the moment even though I don't know if I'll need them, because the big drivers I've seen do the same. My plan is to handle dead times in the driver logic so if its for that its not needed.

I ran a burn in test with a 470nF cap on the output (with additional 1 ohm 5W gate resistors). Things got a little toasty drawing 7W but it happily drove the cap at 50kHz.
I'd say the performance is decent, except for the overshoots. My guess is that those are from the inductance of the wire wound power resistors (measured as ~1uH :-[).




And finally here's the performance driving an actual IGBT (IXXN110N65C). The ones that kept blowing up in my coil :P



What's your guys verdict? What sort of test can/should I run on it to see if it works ok in all circumstances? :)
And what do you think about using SMA as the output connector? It should be very low impedance and is nice and robust.
6
Vacuum Tube Tesla Coils (VTTC) / Re: Modified VTTC for induction heating
« Last post by dbach on July 24, 2021, 11:38:33 PM »
Dear Mads,

This certainly helps! I will enjoy reading thru this thanks so much!
7
Vacuum Tube Tesla Coils (VTTC) / Re: Modified VTTC for induction heating
« Last post by Mads Barnkob on July 24, 2021, 11:29:15 PM »
It should not be a problem to find tube based induction heater designs, as almost all large industrial induction heaters in the MHz range are still based on tubes.

I might just have the book you are looking for here: https://kaizerpowerelectronics.dk/tools/file-archive/?drawer=application_notes*induction_heating
8
Electronic Circuits / Re: repair of Panasonic microwave inverter
« Last post by Twospoons on July 24, 2021, 10:41:38 PM »
Are these drivers a single IGBT quasi-resonant topology like induction stoves?

It would seem that way based on the schematics I've seen. The only power devices in this inverter are the one IGBT and the diode bridge.  With a single switch pushing 1kW I can't see how else it could be done - the way the transformer is built would lead to considerable leakage inductance, and the only sensible way to handle that, at that power level, would be a quasi-resonant topology.

So far everything is still running, after cooking dinner last night. And I still have a set of spares if it dies again.

And like most appliances these days I guess its designed to outlast the warranty, and not much more.  So they can sell you another one.
https://en.wikipedia.org/wiki/Phoebus_cartel <- this is why consumers get screwed over, and the world has a waste problem.
9
Vacuum Tube Tesla Coils (VTTC) / Modified VTTC for induction heating
« Last post by dbach on July 24, 2021, 09:18:42 PM »
Hello all,

A person on a HV discord server recently modified his VTTC for induction heating and it worked quite well. I would like to do a tube based project as I have siliconed myself out with a drsstc and this seems like a perfect project. does anyone here know of any tube based induction heaters that might be more efficient then a modified vttc one? There is barely any info online so help would be appreciated!

Thanks, Davis.
10
Electronic Circuits / Re: repair of Panasonic microwave inverter
« Last post by Mads Barnkob on July 24, 2021, 08:08:36 PM »
Are these drivers a single IGBT quasi-resonant topology like induction stoves?

A single IGBT driver for 2300W is not designed to live more than 2 years required warranty life, might even be shorter. My own experiments with the induction stoves, is that the IGBT blows up by the slightest change of load impedance at maximum power. A short overload could properly kill a MWO inverter in the same way if the magnetron can suddenly pull too much current? I am however not sure it works that way? (put more stuff in, its more loaded, or metal)
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