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Messages - profdc9

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21
I will venture an answer to this...

The purpose of the gate resistor is to suppress oscillations of the series LC circuit formed by the IGBT gate capacitor about 3000 pF for the IGBT you have chosen) and the inductance of the connection to the gate.  This is one reason why the connection to the gate should be kept as short as possible, and the signal is carried to the gate using a transmission line of some sort, for example, a twisted pair of a cat 5 cable which has a characteristic impedance of about 100 ohms.  Many gate drive transformers already use cat 5 twisted pairs so this is convenient.  The gate is a load on this transmission line that is very much like a short circuit being a large value capacitor, and the capacitor formed by the two conductors of the transmission line adds only a little extra capacitance to this.   If the gate resistor resistance is too large, the RC circuit formed by the gate resistor and the gate itself has a rise time that is lengthened and therefore slows down the transition of the gate.  If it is too small, you get the oscillations.  So for example, lets say you have 3 cm of trace which has a inductance of perhaps 20 nH.  The impedance of the LC circuit formed by the trace and the gate is sqrt[20 nH/3000 pF]=3 ohms.  To critically damp this LC circuit, you would use a 3 ohm resistor.  This would result in a RC time constant of (3 ohms)(3000 pF)=9 ns.  This does not increase the transition time of the gate that much.  Typically you err a little on the side of a higher resistance, so that 5 ohms is a typical series resistor value.  The value of the resistor is not that critical because in practice it is difficult to measure some of these quantities in-circuit.

Dan

Hi all I am new to the forum. I have built quite a few Spark gap style coils throughout the years and am now trying my hand at my first DRSSTC. I am going to use loneoceans UD2.7 c for the driver and his 80mm Full bridge board for the bridge. I will be using FGA60N65SMD for the igbt's. I am having trouble wrapping my head around calculating the gate resistors values. Could someone point me in the right direction to a good place to read up on this ? I tried using the calculator but I am at a loss as to how to figure out the maximum gate drive current the driver is capable of. Better stated what do I calculated it off of? My assumption is the current of the mosfets that drive the bridge and if so is it x1 since there is a gate resistor per igbt or total current x4?

Any help would be greatly appreciated. Thank you

22
The UD2.9 changes the way that the UD2.7C works.  I modeled it in Qucs (Quite Universal Circuit Simulation) and I attached the schematic below and show the screenshot.

The way it works is a little different than the UD2.7C.  In the UD2.7C (see schematic below), the overcurrent condition clears the second D-latch U7B unconditionally.  This latch output Q is ANDed at U5D, goes through a double NOT gates U8D/U8E and clears U7A, and then is ANDed with the TL3116 outputs at U5B/U5C to turn off the drivers.  The latch U7B can only be reset by another interrupter edge, so once the overcurrent condition happens during a pulse, the driver stays shut off until the interrupter edge reoccurs.

The UD2.9C on the other hand works like this:  When an interrupter pulse comes in at U8C, the diode/capacitor network causes a brief low edge signal.  This sets BOTH U7A/U7B and allows pulses to start.  If J16 is open for not skip pulse operation, when the overcurrent condition occurs, U7A is cleared.  This in turn takes a path through U5B, U8D, U8E, and then resets U7B, similar to what happens in the UD2.7C.  U7A and U7B can only be set again by the rising edge of another interrupter pulse, and so the behavior is the same as the non skip pulse, even though it is arranged a little different.

If J16 is closed, then while the current in the primary is ringing down, once the overcurrent condition clears, the signal from U4 Q is conducted through J16 and allows U7A to be set.  This turns on U7A Q and then if the interrupter pulse is still continuing, the output of U5B is high and so the signal is also clocked in on U7B, reenabling both D-latches and so the driver turns back on until either the overcurrent occurs and U7A/U7B are shut off again, or the interrupter pulse terminates and the output of U5B is low and shuts off U7B.    One other feature is the presence of the transistor Q5.  This transistor prevents another interrupter pulse edge from turning the driver back on if there if at that moment there is an overcurrent condition, so one can not force the driver on excessively and risk damaging the transistors with excessive current.

Typically I don't get a problem with dead time because I use a gate driver transformer to drive the upper and lower transistors with opposite polarity windings.

You can take a look at the simulation below where I verified I could turn the skip pulse on or off depending the connection of the jumper.

Dan



Hello guys, I want to use a skip pulse driver for my Tesla but I'm lazy to design and programming a CPLD driver :p . So I decided to create a skip pulse driver for full bridge drsstc without any programmable devices.
I found peoples who already worked on a logic skip pulse driver ( https://4hv.org/e107_plugins/forum/forum_viewtopic.php?p=1&id=178230#post-178230 and https://highvoltageforum.net/index.php?topic=346.20 ) but I don't understand how they work.

First I begin with the logic of the UD2.7 driver and I added 2 D flip flop. It seems to work on simulation  :D : http://tinyurl.com/yyan2agj


But i have a question about the switching of IGBT : How the driver generate the dead time to not short-circuit the half bridge module ? I didn't find any information on the UD2.7 drive about dead-time generation but I'm using it and it works so I believe it have dead time...


And if you have some advices to improve the skip pulse logic of my driver It will be usefull  :) thank you !

23
Solid state Tesla coils / Re: Flat Secondary Coil on PCB?
« on: May 02, 2019, 02:06:27 AM »
The only thing I can offer here is another reference. This coil is still early days but it is a drsstc.
https://hackaday.io/project/165112-pcbtc-gan-edition

Thanks for the link.  That looks like an awesome project.

Thanks to you both for the info.  It gives food for thought.  I didn't think I was the only one who thought of this, but obviously there's been some movement here. :)

I was thinking of keeping the primary and secondary on separate PCBs so I could stack several secondaries to get more turns, and also I put the sense coil on the other side of the secondary board so that it there is less of a chance of having a coil strike damage the circuity (if it is possible to have a streamer that long).

dan

24
Solid state Tesla coils / Re: Flat Secondary Coil on PCB?
« on: May 01, 2019, 07:34:33 PM »
You wouldn't happen to know of a video of it in use?  I am curious to see how they work.  I was thinking of adding a buck converter before the half/full bridge so that I could modulate the power with an audio signal.

Dan

Hello

I know that such tesla coils work, because they are sold commercially: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TESLA_MINI_v1.2_

In the description you can see the technical data of the coil, it has 120 turns: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TC12_flach

Greetings
Phoenix

25
Solid state Tesla coils / Flat Secondary Coil on PCB?
« on: May 01, 2019, 05:54:26 PM »
I was thinking about designing a small kit-based Tesla coil where rather than the seconary coil being a solenoid, it is a flat spiral.  Of course the secondary inductance goes down, but is there any reason this shouldn't work?  Flat spirals are already used for resonant power transfer applications (e.g. wireless charging and induction cookers).

The board I designed has (I calculate) about 1 mH of inductance.  It is about 150 turns of 0.13 mm wide traces separated by 0.15 mm.  This is the thinnest I could fit in the design rules of the process.

Anyways I was up late last night and drew up a PCB.  The hole in the middle is for a post to put the topload on sticking up from the PCB.  The hole on the edge is to connect the ground.  There is a six turn coil on the back that is used to sense the current in the secondary for feedback purposes.

I was thinking too that I could stack the boards to get more turns and place a thick HDPE insulator between them.    The center of each coil would be connected to the ground of the next in series, and these would be stacked as to be placed over the primary coil  so that the board would intersect  the magnetic field lines of the primary coil.

Here is what I drew up last night:



Any comments about this design?  I want to call it the "Conversation Piece" which would be a little tabletop SSTC coil.  It would be powered by 12-30 VAC.

Dan

26
I made a bobbin using a sheet of high density polyethylene a while back.  I should take a picture of it, but I would have to clean the oil off of it. :)

The sheet was about 6 mm thick.  I cut four 80 mm wide, 150 mm long pieces and made a rectangular long tube with the edges of the pieces glued to each other.  To adhere the polyethylene to itself, I used a butane torch to flame treat the polyethylene so that I could join the four sides together with epoxy.  Then I field off the corners of the rectangle to smooth them somewhat.  I was able to wind 500 turns of 0.25 mm magnet wire around it.  I had some large U-shaped ferrites which then were inserted into the bobbin.

It was one of the first things I did when getting started in high voltage and it was very difficult to get working figuring it out by myself.  After I was done I wrote a document on it.

https://drive.google.com/file/d/0BwFicJLV0O4jYlQ0ejJ6NE9XVE0/view

Dan

27
Solid state Tesla coils / Re: GDT Experiments
« on: March 31, 2019, 05:47:08 AM »
I moved the OC LED backwards so the potentiometers may be better separated, there should be plenty of space now.

Dan

28
Solid state Tesla coils / Re: GDT Experiments
« on: March 30, 2019, 07:13:05 AM »
I have to confess I had an ulterior motive for designing the SSTC circuit this way.  I hope to try to use to make an induction heater using the SSTC board.

Basically, use a feedback coil rather than antenna near the workpiece to drive it into resonance.  So I designed it with some stuff that may not have been necessary.  I did not really worry about the dead time but I thought I should look into it after you brought it up.

If you need even less dead time, you can swap R5 and R11 for 4.7k resistors.  The limit is that the overcurrent circuit can only sink 6 mA and so if the resistors are too low resistance, the overcurrent protection does not work.

Dan

29
Solid state Tesla coils / Re: GDT Experiments
« on: March 29, 2019, 02:28:57 PM »
Well you have to realize that there's a lot there in the PCB Pack and it could always use some improvement.  But I wanted to try to create something so that all the circuits one needs could be in one place like Mads with his series of guides.  One of the hardest parts about building a Tesla Coil is trying to figure out where the accurate information is, and this was a struggle for me getting started, so feedback like yours is a big help to try to make the situation better.

As for the dead time issue, here is my understanding of it.  When driving an inductive load like a tesla coil primary, one achieves ZVS (zero voltage switching) for a half/full bridge by having a dead time between the turning off of the upper/lower transistor and turning on the lower/upper transistor.  When both transistors are shut off, there is still current flowing from the inductor.  The current is diverted from the transistor that is now shut off to the the body diode or reverse pack diode of the other transistor.  Since the other transistor is now in forward conduction, its voltage drop is near zero.  So you do get some energy loss from excessive dead time which is current X diode drop voltage X dead time duration.  Now the other transistor is turned on at nearly zero voltage which results in a lower switching loss.   The disadvantage of excessive dead time is you get a little more loss in the reverse diodes but the benefit of ZVS switching for the on condition and a low probability of shoot-through.

Dan 


Well ! This certainly took a different turn, I wanted to make a test circuit for GDT’s, and it resulted in a circuit change !

Dan, thank you very much for your help with this. More than likely I will use this driver in a TC build in the future so thanks for troubleshooting and making changes.

One thing that I am not clear with is jumper settings, so far I figured out AC/DC input jumper, but others are a bit harder to figure out from the schematic ( for me at least ).

I’d like to do a test with FG connected to the antenna input next.

30
Solid state Tesla coils / Re: GDT Experiments
« on: March 29, 2019, 02:23:28 AM »
I have a solution to greatly reduce the dead time.

Replace D3 and D4 with 1N4148.   They are 1N5819 in the design.  I will update the schematic.

It should work much better, here's a screenshot.  The dead time is now 320 ns.

Dan


31
Solid state Tesla coils / Re: GDT Experiments
« on: March 29, 2019, 01:22:05 AM »
I looked on the output of my board.  I get a 880 ns dead time.  I am not sure why you are getting twice as much.  Even this is kind of high for the switching time of the CD40106 with 15 volt supply.  I should probably have a board revision and use a CD4027 and use both the Q and not Q outputs which would change at the same time.  This would also ensure 50% duty cycle, but would add an extra part.

I don't think it's a problem to have zero voltage in the gate drive transformer.  The overcurrent shutoff in fact does exactly this, where it forces both gate drivers low to turn off the MOSFETs. 

I have a plot of the gate drive signal when the antenna port is drive by 200 kHz with a signal generator.  The dead time is long which might lower power output however.



32
Solid state Tesla coils / Re: GDT Experiments
« on: March 28, 2019, 04:36:20 AM »
I don't think it should be a problem.  The body diode of the one MOSFETs should go into conduction after the other MOSFET is turned off.   It is a longer dead time than I have observed but it should probably be ok.

Note that the SSTC should be driven using the antenna feedback.  The built-in oscillator is mostly to "jump start" the oscillation of the Tesla coil.



33
Dual Resonant Solid State Tesla coils / Re: Next Gen DRSSTC
« on: March 25, 2019, 07:35:14 PM »
Apparently there have been updates to the pinout that I have not incorporated into Psoc5-power yet, so you might want to hold off.  You don't need the board if you want to breadboard it.

I could update it if I get an updated pin list.  I haven't looked at the latest PsoC creator project lately to see what the new assignments are.  I think there is support for Ethernet now.

Dan

34
Solid state Tesla coils / Re: Chinese MOSFETS/IGBTS
« on: March 25, 2019, 05:09:01 PM »
Yes that is the GM328.  I have one of those as well.  They're excellent little diagnostic devices.  I was thinking of something like this, but more specialized to power MOSFETs and IGBTs.

Dan


The differences in the copper backs will outweigh the differences in the silicon.  Have you guys seen these cheap little testers?:



From here:

https://www.ebay.com/itm/172557508334

That is a quick, cheap, non-destructive way to weed out the fake FETs.  The Rds number is usually off by a fair amount, so to further test I put 10A through one and measure the voltage drop.

35
Solid state Tesla coils / Re: Chinese MOSFETS/IGBTS
« on: March 24, 2019, 04:37:50 PM »
I wonder if there's some simple tests that could be built into a device for identifying MOSFETs and IGBTs, kind of like the GM328 component tester that you can get on ebay cheaply.

For example, without really high voltages/currents being applied, one can look at:

1.  Gate capacitance with a grounded source/emitter
2.  Threshold voltage
3.  On/off time could be done by sending a periodic square wave to the gate, and then putting the drain voltage and gate voltage into a logic gate.  Using an AND logic gate measures the on-time which is measured using the duty cycle of the time that both the gate and drain are high logic level, and the off time is measured by a NOR gate, which measures using the duty cycle the time the gate and drain are both low logic level.
4.  By using a current sense resistor, the phase lag between the collector or drain current and the emitter-collector or source-drain voltage can be measured so the switching losses can be estimated, again using the duty cycle measured using a logic gate.
5.  Collector-emitter saturation voltage for an IGBT or Rds for a MOSFET.
6.  Body diode or reverse diode forward voltage.

To avoid damaging the device and to keep the costs of such a device down, I am avoiding anything that directly measures the maximum voltages or currents a device can handle.

A cheap device to identify fakes could help alleviate the problem.

36
Dual Resonant Solid State Tesla coils / Re: UD 2.7C Build
« on: March 24, 2019, 03:22:14 PM »
Beautiful assembly job!

By the way, if you attach a 3.5 mm female plug to the Sound +/- input, you can try out the sound interrupter feature.

Make sure you adjust the minimum Ignore Interval and Pulse Width when you use it so that you don't try to pulse the coil too often or too long.  Start with a short pulse width if you have any doubt.

Also, you can hook an earphone up to the digital + output if you want to listen to your interrupter before you use it with the coil, or you can look at it on your scope.

Also, you can solder header pins into the ISP connector if you want to use the board with a AVR programmer directly so you don't have to use a separate fixture.

Dan

Interrupter is almost complete, Attiny85 is missing because programming is a bit more complicated than I expected.
But, it is partially functional without  the Attiny, enough to check if UD2.7 is working correctly.

I connected them together using a bit of fibre optic cable, and to my horror UD did not react to the input ! Input signal LED stayed firmly off.
After a bit of scoping and tracing the signal I discovered that I did not solder one side of D13.
Note to self: Missing solder joints are bad for functionality
After I soldered the diode, signal LED came on and started flickering in sync with the interrupter.

So far I confirmed that the UD powers up ok, and receives the signal.
I need to check if the outputs for GDT’s work correctly, is it possible to do that without C33 and the inductor in place ?

37
Solid state Tesla coils / Re: Chinese MOSFETS/IGBTS
« on: March 22, 2019, 06:39:37 PM »
You might be able to use them as low current/low voltage devices, but it's too easy to take a small die and put it in a big package.  Big dies cost more but are the ones that have the high voltage and/or current ratings.  Often you can find substitutions of fakes where the substitute superficially behaves like the real part, for example, LM358 dual op-amp for TL082, or one pin compatible logic family for another.  Sometimes, the substitutions are rejects of the real part that don't meet specifications, but might be sufficient for hobbyist purposes.  Occasionally, the parts are other parts relabeled which is easy to find.  But things like high power MOSFETS/IGBTS are almost invariably fakes because its too easy to substitute small die parts for large die parts.

You might try lcsc.com which might save you some money over digikey/mouser.  I think they have more to lose by counterfeiting because they are trying to establish a reputation as a parts supplier.

Dan

38
Dual Resonant Solid State Tesla coils / Re: UD 2.7C Build
« on: March 06, 2019, 04:27:03 PM »
The fiber optic connector is from Industrial Fiber Optics.  You can get it from digikey

https://www.digikey.com/products/en?keywords=IFE97

The plastic fiber is not easy to find.  It might be better to order both the IFE97 and the plastic fiber from Industrial Fiber Optics directly, but it is more expensive.

If you want to attach your own fiber optic output rather than using the LED, there is a port J15 with +V, zero volts, and a digital output.  You can build a simple circuit with a NPN transistor and the LED of your choice instead on a little external perfboard with literally three components (resistor, transistor, and LED).

Dan

I studied loneoceans’s instructions on initial power up of the board, nowhere did he mention that GDT’s must be connected, he even mentioned that if there is no GDT’s connected, there should be no signal on the outputs.
So, I gathered enough courage to power up my board, I set my power supply to 24V DC at 200mA max.
To my relief, blue LED came on, and there was no smoke leaks anywhere, current draw 0.02 A.
So far, so good  :)

While I was procrastinating whether to power it up or not, I built an enclosure for it.
PCB’s for the interrupter are on their way, most of the components are available locally. Only problem is fibre optic connector - can’t find it anywhere.

39
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: March 04, 2019, 12:58:48 AM »
I made a board for the CYC8KIT-059 based UD3

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/Psoc5-power

so you don't have to etch a board.

Dan

That's right, 500kHz is the maximum for the UD3.

Perfboard is not ideal for a high current gatedriver. I would prefer SMD mit big ceramic decoupling to keep the switching noise out of the driver.

I drive my SKM400 with a 13 to 10 GDT with 24V on the GDT driver so you get 18V at the gate.
Thanks for the suggestions!I'll try to etch a PCB and use 10uF THT X7R capacitors,two in parallel for each N-P MOSFET pair(IRFZ44NPbF and IRF4905PbF).If I succeed to modify an ATX PSU,then I can change the gate drive voltage.
I also received a CY8CKIT-059 board and checked your UD3 firmware,but some files are missing.Do you have a simpler firmware something like the UD2.7 or I should make one on my own?

the universal driver can do 500khz but the SKM400 probly can not what frequency is your coil? your snubber will not work if you are soldering to aluminuim. at least bridge the cap connection to the screws with copper at the end of your assembly
The SKM400 bricks definitely can't do 500kHz,but hopefully they can 150kHz.I plan to enhance the MMC connections or even make a completely new one if this fails.The snubbers are good,1uF and mounted directly to the bricks with the screws.

40
Dual Resonant Solid State Tesla coils / Re: UD 2.7C Build
« on: March 01, 2019, 03:55:35 PM »
Yes the OneTesla code is there.  You will need an AVR programmer and avrdude, which costs $5 on ebay, and the hex file is already there.   There are instructions in the folder with the software.

Dan

The standard interrupter has four modes:  standard test mode, which is basically pulsing the interrupter periodically for a particular pulse length, burst mode, which is to try to get briefer, more intense sparks, the MIDI interrupter, which can be used for playing MIDI files from a computer through USB, and the external audio sequencer, which if you play a tone like, for example, from a guitar, will generate a set of pulses with controlled length.  You can see it in action here

The code for the ATTiny, is that the onetesla usb midi code that you have a folder backwards in the same git? I did not find a clear description of which software was for it.

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September 15, 2019, 08:22:47 PM
post Re: My second DRSSTC
[Dual Resonant Solid State Tesla coils]
erdal
September 15, 2019, 02:09:17 PM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
AlexanderHun
September 15, 2019, 10:39:29 AM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
ElectroXa
September 14, 2019, 07:01:28 PM
post Re: adventures in homemade flyback bobbins.
[Transformer (ferrite core)]
AlexanderHun
September 14, 2019, 06:59:13 PM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
AlexanderHun
September 14, 2019, 06:43:15 PM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
ritaismyconscience
September 14, 2019, 06:35:32 PM
post Homemade HV transformer
[Transformer (ferrite core)]
AlexanderHun
September 14, 2019, 05:05:00 PM
post Re: UD2.7 Gate Signals
[Dual Resonant Solid State Tesla coils]
profdc9
September 14, 2019, 04:50:10 PM
post Re: UD2.7 Gate Signals
[Dual Resonant Solid State Tesla coils]
coilinator
September 14, 2019, 08:42:55 AM