Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Topics - prabhatkumar

Pages: [1]

Solid State Tesla Coils (SSTC) / Distorted gate waveforms

« on: March 03, 2023, 04:51:30 PM »

Hello everyone,
I am trying to build a full bridge circuit based on the Profdc9 PCB pack. Link : https://highvoltageforum.net/index.php?topic=1898.0
I am using the Phase shifted full bridge topology to control the output power( yes I am aware that the standard interrupter method can be used, but this is a part of my college academics which has put the constraint.
I am using isolated gate drivers NCP51561( again pulse transformer is also a great option, but its difficult to add deadtime there. I have added a deadtime of 400nS (I am not sure if this much is actually required, as the board itself has the resistor bypass by schottky diode on it). I think the gate drivers are doing a decent job of driving these charge hungry devices (compared to MOSFETS) without any buffer while maintaining a fast rise time of 100nS of the gate signal and 50nS of fall time.

The IGBTs which I am using is the FGH60N60SMD, based on the recommended device list on Gao's loneoceans website. All these transistors are mounted on a common large heatsink with isolation pads. For test purposes, I am running everything at 100kHz.
I am using a bus capacitance of 1880uF(470uFx4) to give the DC bus to the bridge.

The problem which I am facing is that when I am running the coil at lower voltage, say 30V, then the gate waveform remains relatively clean from any ringing or distortion( gate resistance of 2.2 ohm). But when I increase the the bus voltage to a larger value( like 80V), then the gate waveforms start getting distorted, as in it turns off when it should have been on. And the distortion increases as I increase the voltage, like 370V DC.

I have also added the optional 440CA TVS diode and the gate 18CA TVS diodes on the PCB, but I have not mounted the snubber network.

From my intial observation, this distortion of the low side switch happens exactly when the other diagonal pair in the full bridge turns on. For loading the bridge, I am using a small transformer with ~4mH of primary inductance. Its not supposed to draw any significant current, I have just added it so that the freewheeling of the body diodes actually takes place(not possible in a resistive load).

Another thing is that without any load also attached, the IGBTS get pretty warmed up, and draw some siginficant current while doing absolutely nothing. But surpirisngly, the output looks pretty much perfect except for some ringing to lead inductance.

Now coming to the waveforms.

Rise time

fall time

With 80V on the bus, yellow is VGS of low side switch and blue is the output.

With 360V on the bus, yellow is VGS of low side switch and blue is the output.

Any help/ Suggestions are greatly appreciated. Thank you.

Solid State Tesla Coils (SSTC) / Basic Gate driving doubts

« on: November 19, 2022, 05:37:09 AM »

Hi there everyone,
I have asked several doubts regarding gate driving earlier on this forum and each of them was asked with the intention of making my coil work.
Now, I have sought of taken a dive into the gate driving fundamentals as I have a college reasearch project, where I am desinging a gate driver. So, I have few doubts with respect to the gate driving techniques used in the UD2.7 board.
They are as follows:

1) In this schematic from ud2.7

, Gao says that the main curernt carrying capacitor is the C30( 2.2uF ceramic). So usually for damping the spikes due to inductances and other issues, we put a series resistor with the capacitor. But here he puts a resistor in parallel( and a also a DC blocking cap to prevent resistor burnout in event of saturation). So please me know the reason for placing the resistor in parallel).
2)Now, comming to the buffer stage, the PMOS is capacitvely coupled. Why is it done so? If it would have been in a NMOS then the level shifting was neccsary. But here since the PMOS is already having a LOW VGS(threshold) of like (-1.6V) i.e they would turn off anyting greater than -1.6V.
3)Also, I have doubt reagrding the winding of the pulse transforrmer. I have a very limited sense of understanding the science of transformers and their coupling, so please don't get angry on me

The doubt is that I understand we have to wind a certain of number of turns(depending on core size, material and operating frequency) to prevent saturation of the transformer. But what is the effect of increasing the number of turns greater than mimimum?
(which is usually the case since we generally wind to the fill the entire core). I have read previously on this forum on this regarding that it will increase the magnetizing inductance and hence the curent also, but I do not understand it.
4) This last question is sort of application oriented. I wish to have deadtime in my final circuit and hence I would generate my signals with deadtime from the controller which I am using. But is it possible to have deadtime through a pulse transformer. I have once tried but at the output all I got was ringing in the output during the deadtime. I thought that passing a zero level through the transformer during deadtime was saturating it, hence I left that part till now. But now as I see it, I think adding deadtime is possible. Also is it possible to have the IGBT's gate pulled to VEE(-7V to -15V) during deadtime?Usually I think it's just pulled to zero volt, but I wanted to have some better noise immunity.
It would be of great help if you all answer such basic questions.
Thank you in advance.

Dual Resonant Solid State Tesla coils (DRSSTC) / Current buffer design

« on: November 07, 2022, 06:57:58 PM »

Hi everyone,
I am in process of designing a gate driver using a pulse transformer for FGH40N60SFD for building a full bridge. Earlier, I had used the FDS4559 dual N-P channel FET as a buffer after my gate driver.
But, now I am out of parts for the dual N-P channel FETs. I have ordered them but its going to a while for them to come. Meanwhile, I was wondering what are the merits/demerits of using a MOSFET based current buffer against a good old BJT NPN-PNP current buffer. The BJTs seem to be much easily available locally and hence I was wondering about using them with my gate drivers.
I am not sure if this is a right observation, but most optocoupler based gate drivers like the HCPL-316 etc. tend to use BJT based current buffer.
I am also interested in the design of the BJT based current buffers like selection of base resistance RB, and other resistances which are absent in a MOSFET based current buffer.
I am attaching a reference current buffer(lone oceans labs 'brick driver' and 'Avago application note' for whose resistance values I am interested in knowing and also why they are even used at such positions.
From lone oceans schematic

, I am interested in the calculations of values of R3 and R2. RG1 and RG2 are, I believe, standard resistors for the turn on and turn off of the IGBTS. Also, what is the significance of R2 here? I have not seen this resistor in many current buffer design, at least not in the Avago application note

Please give me some reference or else some insight into this topic. Thank you

Dual Resonant Solid State Tesla coils (DRSSTC) / controlling the negative gate bias voltage of the Gate drive transformer

« on: September 23, 2022, 05:48:17 PM »

Hi there everyone,
I was wondering if there is a way to control the negative excursions of the gate voltage applied to the IGBTs. Since in most general circuits I see there is +15V, -7V gate bias voltage.
Do all IGBTS( smaller one's) do well with the +-15V excursions?.
I am actually planning to use SiC in a full bridge circuit( not a tesla coil, but a very similar power circuit). So I found online that most SiC gate drivers use a +15 -4V gate drive voltage. Hence I wanted to know if there is a circuit by which we can control the negative excursions of the gate drive voltage.
Thank you.

Solid State Tesla Coils (SSTC) / Gate drive push pull(FDS8958) heating up

« on: February 26, 2021, 09:56:58 PM »

Hello all, I have been working in building a discrete gate drive system just like Loneoceans SSTC4, but then encountered certain observations which I could really not answer.
My setup is as follows. For testing purposes I have used both outputs of my function generator configured as 180 degree out of phase to mimic my tesla coil signals going into it. I am using a TC4427 MOSFET driver since that is the one which is available locally.
Now the output is as expected and is also driving the primary of the GDT without any issue( No load on secondary), but then there are few observations about the current drawn from the power supply.
I have used a input voltage of 15 volts and then using a 9 volt linear regulator to power the TCC4427. Now with the exact same circuit diagram and a frequency of 100kHz, the current drawn from the gate driver was 50-60mA (without the GDT connected). Now as soon as i put the 4.7uF capacitor near the FDS8958, the current drawn from the power supply rises to 120mA. This makes the FDS8958 really toasty very soon though the output remains as good as before. This is the problem which I am not able to explain. How can the circuit draw different current at different capacitances.?
Also please tell me how much current should the circuit draw while idling( not driving GDT)
Thank you.

Solid State Tesla Coils (SSTC) / Steve wards UD1.3 driver understanding help

« on: June 22, 2020, 08:49:54 PM »

Hello everyone !! I was just learning about all the logic which is involved in a DRSSTC as compared to SSTC. I could understand the flip flop ( for the ZCS) easily but from a different source( Lone oceans SSTC3 had explained it well ). So now I wanted to understand how to the OCD works even though I wont e using that in a SSTC anyways, but it is still good to know I think as someday I might even plan to upgrade to a DRSSTC.
Now first things first. I am not very experienced when it comes to electronics. Just will start with analog electronics in this semester but I have some very basic understanding. I have decent knowledge of the digital electronics part since it was there in my semester earlier.
Schematic for the UD1.3( attached is screenshot of the same).

So I started wandering around for some explanation of the driver but failed to find it. I stumbled across the Ud1.3 which is used with some changes at many places like lone oceans SSTC4(If I am correct). So here goes my list of questions( Please excuse if they are dumb questions):
1) After the IC2A(74hc08), why is that we need to invert the signal twice and feed the output of each state to the PRE' and CLR' inputs? I know there will be some good brains involved there, but if someone is kind enough to explain by a simple table or a few lines, please do it. Also why is the diode (D7)and resistor(R2) there at the output of IC1A(74hc14). What purpose it is serving there?
I have couple of questions from the UD2.1 as well but that will come after this one is answered.
Thank you !!

Solid State Tesla Coils (SSTC) / STRENGTHENING GATE DRIVE SYSTEM( LONE OCEANS SSTC 4 )

« on: June 15, 2020, 08:29:42 AM »

Hello there everyone. I have completed my first SSTC BUILD and it works reasonably well even at an input voltage of 130v DC. I have noticed and it has been pointed out by pothers in my other post, that my gate drive system is weak in the sense that it cannot maintain the climb without dropping a bit in the miller plateau. The drop is not very significant, but still I would like to make it better and strong enough so that the it can drive IGBT gates also at a voltage of about 15 volts or more. I do have a step up GDT with a ratio of almost 1:1.5, so that's a possible option also.
Now my first inspiration foe the SSTC was the LONE OCEANS SSTC2. Needless to say I went back to his website and found the full bridge sstc 4.
I have very limited parts at the moment and cannot order them also as even big sites like mouser are not shipping anywhere in my country due to lockdown. Neither can I order a ready made PCB from the factory. So only option with me is to do on a perfboard. I have a few tc4420, tc4427, DS0026, mosfet driver ICs which certainly cant supply the requisite current ( tc4420 might be able to do it as its 6A peak driver). I know many well why not using the popular UCC3732X series. Well I used them before in my Sstc build but only to realize that the enable pins don't work, probably because they are rather cheap and Could buy 4 ICs for the price of one as compared with mouser. So now I think that its the fake ICs again that caused the slight weakening of the gate drive system. And also the entire purpose of using the UCC was the enable pins and also 9A peak drive current is not fulfilled.
So on going through the SSTC 4 of LONE OCEANS, i discovered he used gate drive strengthening system comprised of p channel and n channel fets.
LONE OCEANS SSTC 4 schematic:

Now many doubts which I want to get answered.
Firstly the choice of the FETS. He has used some FDS8958 dual N and P channel FETs. Now I dont have the dual channel FETs. I have also read on this forum (mostly it was Mads ) who advised to use the irf540 and irf9540 as a replacement. What i want to know is that is it neccesary for the FETs to be complementary of each other. Cant I use something like irlz44 and irf9540 just because I have them.

2) The next thing I want to know is whether is it possible to ICs like ds0026, tc4427 here. I Know they both are inverting but I will use 1 input of the hex inverter to invert the signal and feed it to the drivers. The reason I ask this that these ICs have 1.5 drive strength on each of the outputs. And Lone Oceans UCC27425 has a drive strength of 4 A. I think it should not matter much as we are anyway using the Fets to increase the drive strength.

EDIT: I was also going through The legendary driver UD1.3b of Steve Ward.
Steve wards schematic:

Also in Steve's design he used 2x10uF (C11 and C14 as dc blocking caps in parallel with a 10 ohm resistor to reduce ringing. The problem is that I understand that he used such big values so that gates of some chunky IGBTs could be run with ease, so can i reduce this capacitor value. I have some
3uF mylar caps probably and chunky 4.7uF film caps. I also dont have ceramic caps higher than 1uF.
picture of the 3uF cap:

I also came across Laci's post, reading through all the pages and then also saw that used a so called h bridge GDT driver based on ir2110 and irfz44. He said that results were good enough but certainly not the best due to ringing etc, and also that he lost quite many ir2110 ( reason still unknown), before finally giving up.
Post Link: https://highvoltageforum.net/index.php?topic=165.20

schematic for the h bridge GDT driver from the same post:

I think this schematic has a flaw, notice the high side of the bridge where there no bootstrap capacitors even no fast charging diode like uf4007, maybe that is the reason for his circuit failing.
Now I wont mind trying that method I am almost on the verge of completing the full bridge on ir2110, I have completed and checked the halfbridge section and it works fine I think. Only thing is that the ir2110 is drawing pretty good current like 120 mA and is getting hot. So please let me know if there is some error or is that the normal current draw by these ir2110 ICs.

Please answer my queries. Thanks in advance.

Solid State Tesla Coils (SSTC) / SSTC DRIVER WITH NON FUNCTIONAL ENABLE PIN FOLLOWUP

« on: June 06, 2020, 10:10:59 AM »

Hello all !! This post is a followup to my earlier post where I had reported non functional enable pins of the UCC327321 and UCC3322. Now after getting workaround with logic ICs ( AND GATE AND INVERTERS), I have made the requisite changes and then made some tests. I have few doubts on how things should be and what i am getting practically on the oscilloscope. Post from where this started
https://highvoltageforum.net/index.php?topic=997.msg6869#msg6869
suggested fix i tried
https://highvoltageforum.net/index.php?topic=1034.0
The schematic if you dont have time to read all this :

1) I have followed the Kaizer SSTC3 schematics and used the same board with a few changes ( Adding more filtering near the UCCs and also some diodes on the output of the driver ICs to prevent latch up. In the scheme the input from the antennae gets fed to the schmitt trigger( I use CD40106 instead of 74hc14). Then the output of the first schmitt trigger is fed into another to effectively get a nice square wave of the resonant frequency. Now what I have a doubt in is that at the input of the first schmitt trigger , the voltage there is a 1.1 volt approx, which I think is due to the fact that the voltage is clamped by the two germanium diodes(1n60) even though the bridge side of the driver is not powered. Due to this the schmitt trigger treats it as high level and hence after inverting we get around 0 volts at the output of the first schmitt trigger. Now this signal is sent tot eh second schmitt trigger and it outputs a continuous logic high( as input is logic low). This is the signal which is fed to the first and gate along with the interrupter signal. Now whenever the interrupter is on the and gate output is also high. This is sent to one the UCC now according to the scheme. Please tell if i need to directly connect the output of the first schmitt trigger to the input of the first and gate or the previously mentioned setup is correct and also if the signal going to the UCC is correct or not. I am attaching my scope shots for reference:
a)Green is Input to Schmitt trigger 1, Yellow is interrupter output

b)Green is OUTPUT of Schmitt trigger 1, Yellow is interrupter output

2) I have also scoped the output of the drivers and found that they work as they should. The only thing which worries me is that normally force the output of both the drivers to 0 , to stop the working of the coil when the interrupter is sending a logic zero ( oR off during that time). Here in my case i am getting both the chips outputting logic 1 which is fine because in the push pull it doesn't really matter whether both the chips output zero or one, only thing is that the should be same.
So do I need to rectify this or leave it as it is because what i think is outputting logic 1 continuously will stress up the UCC for no good reason. Also is it related t the previously mentioned problem of the interrupter logic and resonant frequency being fed in tot he schmitt trigger twice. ?? I am attaching the scope shots for reference.
a)Driver chips output

b)how the actual pulses look like

c)Yellow is output of inverting chip , green is interrupter signal.

d)zoomed in shot of the above mentioned.

Solid State Tesla Coils (SSTC) / CORE FOR GDT AND CT

« on: April 13, 2020, 03:02:15 PM »

Hey there everyone !! I had successfully made my first sstc and I am very pleased with it's performance . I know I am not making big arcs but then this was only a learning experience and I had it. But during the lockdown I was thinking to study more on drsstc and then also choose a core for the CT, GDT and capacitors for the mmc. I don't want to make like deadly arcs which are 4 feet long . My secondary is only 10 inches tall and has a diameter of around 4.2 inches. It has got 1400 turns. In real life ,I get a resonating frequency of 238.5 kHz. I will run the coil without the toroid.
So now for the main question , I was reading the forums for the core for GDT and CT , and found that mads replied that he uses this :
https://www.mouser.in/ProductDetail/EPCOS-TDK/B64290L674X830/?qs=sGAEpiMZZMt1hubY80%2Fs8DEvGx1xc7EcUsoMlWTaffs=
I also found that many people use this core:
https://in.element14.com/ferroxcube/tn32-19-13-3e25/ferrite-core-toroid-3e25/dp/3057008
I also found another toroid from ferroxcube which has a different coating ( epoxy ), compared to the above cores . These two cores have the same material 3e-25 . But strangely though the coated one has a bigger diameter and a higher Al value still being a little cheaper from the other . I don't know a lot about the cores so please enlighten me on this . I would prefer to order the cheaper one with epoxy coating as I could save like 4 usd on 20 pieces . Also will the high Al of 7.3 uH of this core be suitable for the gdt. Link for the 2nd ferroxcube core
https://in.element14.com/ferroxcube/tx36-23-15-3e25/ferrite-core-toroid-3e25/dp/3057021
Also sorry for the inconvenience as the prices are mentioned in INR and not in USD

As a standard rule of thumb ( as far as I know ) , the Al value should be above 5000 as mads has said in his drsstc design guide.
Now I could also source any of the above cores , the epcos being a little bit more expensive because it has got a slightly larger diameter, I am thinking on the ferroxocube one.
But while browsing I found a page on digikey where there is a large number of cores given with materials like N30, T-35, T-65 etc
Now I would go for the core diameter and the Al value mentioned aside each core , it is right or also do we need to look for the other properties of the core . If yes then please can someone share a link to a page or briefly explain the main difference between the types like T-35, T-38 etc . I will attach the link to that page which has the different cores given.
https://www.digikey.com/catalog/en/partgroup/toroid-core-type/23563
THANKS !!

Solid State Tesla Coils (SSTC) / Interuppter code help for sstc (LONEOCEANS SSTC2 )

« on: April 05, 2020, 05:20:57 PM »

Hello there everyone !! I was on my way of building my first sstc originally from kaizer sstc 3 , but then i encountered many issues for which I already started 2 new topics an with the help of fellow members on this forum, I was able to fix them to a good level and proceed. Back then I was using my function generator as source for generating the interrupter signal. But now to pack up everything I need a standalone interrupter . For that i tried many 555 circuits but was satisfied with none, since i want to adjust frequency and duty cycle both( I came across a 555 circuit in which there are two cascaded 555 to change the duty and frequency but what happens actually is that it is never an independent control of it, when i change frequency duty also gets affected and vice versa.). So then i stumbled across the lone oceans sstc 2, he was using an attiny 85 interrupter. But now I am not able to undesrstand many parts if his code. If anyone can then please explain me the same. I will attach a link to the code file directly.
http://www.loneoceans.com/labs/sstc2/ATtiny85_SSTC_Interrupter_63.ino
I will list down the things which i am not able understand.
1)Right where he writes user definable variables, how does he decide what the maximum on time can be(32768/5) ??
2)In the create other variables part, what is critical frequency and how is it calculated??
3) In the part where he decides the frequency{Freq= 1+ vbps + 4)/4}, why did he add 4 to it ??
4) Also how the are the clock settings essential here, there is a link in the code on how to change the system clock settings( 1 MHz OR 8 MHz).
Else if you are super generous then a humble request , can you also explain the bottom part in brief

And if there are other suggestions for any other interrupter , then please do mention it. Thanks !!

Solid State Tesla Coils (SSTC) / No current flowing through half bridge (kaizer sstc 3)

« on: March 22, 2020, 04:32:28 PM »

Hey there everyone . So I am on way building my first sstc from kaizer's site (sstc 3). So I had earlier started a new topic with gate drivers ICS dying ( Ucc37321) which seems to be now resolved . But now another issue popped up is that whenever I try to power the bridge side of my sstc there seems to be very little or almost no current which is constant (18mA) . There also seems to be a horrible oscillation (or ringing) . I will upload the waveforms here .
Please tell me why isn't there any current flowing even though I have like a 10 ohm resistive load on the output without the usual
DC blocking cap. My mosfets seems to be switching well but there seems to be nothing happening . Even if my change my load to 1 ohm , nothing changes and also there are quite a few spikes in the drain source voltage which indicates very less current flowing. I am powering my driver circuit with a 12 volt battery . I am powering the bridge with a 18 volt transformer with a bridge rectifier. Is it beacuse my gate voltage is around 10.7 volt and not 12 volt ??
Waveforms :

Green is drain and source voltage , yellow is gate and source

Green is current though gdt measured with a series resistor of 2.7 ohm.yellow is gate source voltage .

Green is current through gdt and yellow is drain source voltage

Solid State Tesla Coils (SSTC) / Gate drivers ICS Dying( UCC37322 and UCC37321 )

« on: March 18, 2020, 03:38:35 PM »

Hey !! i tried making the sstc 3 from the kaizer electronic site
(http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-iii/). This is my first post here (and also the first post on any electronics forum, so please excuse my faults here ).
I made the pcb from the express pcb file you provided by conventional toner transfer method at home. The pcb is working and I verified with a scope without the bridge supply on ( Only 12 volts was fed for the oscillatory part ( with drivers ics, gdt and the mosfet in place), only thing i didn’t connect the primary wires to the tesla coil . I checked it by running a slayer exciter on the same tesla coil to be used with the half bridge later with antenna in close vicinity ( 3-4 cm from the coil ). The wave forms were as expected just with a slight damping which could be fixed by reducing the gate limiting resistor( i used 5.6 ohm originally ) . But as soon as i connect the supply to the bridge( just 12 volts to check) , bang !! my driver circuity went in the current limiting mode and immediately the top ucc became hotter than normal. ON checking everything i realized this is not the only victim of this crash but also my 74hc14 inverter went bad i.e I dont have any pulses at the base of the driver ics. Now believe me i tried to build a full bridge with ir2110 before and burnt like 10 ir2110 before with the same issue, as soon as i connect the supply i goes bang !!( at least the ir2110 worked till the supply voltage was raised till 25 volts dc).
So please help me out as i dont have the money to invest on lot of ucc ics they are very expensive and also not available where i live ( I have to order them from mouser).
PS: Is it because the the primary was not connected anywhere or somehting else which i am not aware of . Also the the entire electrncs drive circuitary is connected to a 12 volt lab bench power supply (with current limiting on . I restricted the cureent to maybe 500mA ). And also the circuity was consuming 200 mA with no supply on the bridge side . The drivers were oscillating as they should with feedback from the slayer exciter.

EDIT: For those of you all who dont have the time to scroll the 3 pages of this post, I will tell what fixed the issue. The thing was i powering the tesla coil( SLAYER EXCITER USED HERE FOR FEEDBACK PURPOSED ONLY FOR CHECKING THE DRIVER) and my driver circuit
from a single bench power supply with 3 independent(isolated outputs. the power supply was hy3005-3 or similar ones sold there). As noob I am with electronics, I thought that it would work out fine, but as pointed in this post below by ritaismyconscience, the high voltage noise got back into the supply though the wires and interfered with other channels also and there must be huge voltage spikes which could have blown the ucc chips and the schmitt trigger. But then I the powered the slayer exciter and the driver circuit with simple old iron transformers laying around and then it worked out fine. Also go through this post as there are many other things suggested below like adding resistor to the outputs of the gdt which is better than no resistor of course etc. )