High Voltage Forum

Tesla coils => Solid State Tesla Coils (SSTC) => Topic started by: prabhatkumar on March 18, 2020, 03:38:35 PM

Title: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar 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. )
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: ritaismyconscience on March 18, 2020, 05:57:38 PM
Could you send a few pictures?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 18, 2020, 06:28:54 PM
Yes sure !! The only change I made was that replaced the 74 hc14 with cd40106 [ Invalid Attachment ]
The two hanging wires are the wires to be connected to the primary
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 18, 2020, 06:30:33 PM
I can't upload the waveforms at the gates of the mosfet since too bad , the mosfet drivers arent working anymore after the aforementioned problem I encountered.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: johnf on March 18, 2020, 07:02:54 PM
What sort of GDT core have you used??
it might be a powdered iron type that will cause the drivers chips to supply too much current
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 18, 2020, 07:11:47 PM
I don't know the exact type but then I guess its a correct one because the waveforms looked pretty decent at the gate without the bridge supply connected . I also tested the gdt with a function generator on hand and observed the waveforms which also looked acceptable .
 And as I said that this is my second attempt on a building a bridge in a previous attempt I built a ir2110 full bridge without a gdt which also behaved in a similar fashion i.e as soon as I connected the supply voltage for the bridge the drivers failed . And surprisingly none of the mosfets failed ( maybe because I had current limiting on my bench power supply )
I am wondering if it has to do something with the current limiting of my bench power supply for gate driver circuitry because maybe when the gate driver need peak current for switching they just can't get it as my supply goes into current limiting mode.
And maybe also that the primary is not connected so the mosfets are basically operating in open circuit .Also I cannot verify this theories without a concrete solution given by the people replying here as I don't have a lot of ucc ICS to spare( only 1 one more pair to go . And thanks for replying :)!
 PS: LINK FOR THE GDT I USED https://m.aliexpress.com/item/32861649468.html?spm=a2g0n.orderlist-amp.item.32861649468&aff_trace_key=743794a95edc4ceb95f68af9d7a029e3-1584258913329-02359-_etFMgO&aff_platform=msite&m_page_id=6622amp-EQHr2YJdaiHjqhUjjScjvA1584555238490&browser_id=7dd3e04ea5b7412a86b5466a7ba2fc52&is_c=N
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: johnf on March 18, 2020, 07:49:03 PM
I do not see any gate protection on your mosfety gates ie 25 volt transil or zener diodes gate to source.
As you do not know your core parameters you might need to put a resistor in series with your white wire to limit current into your GDT your ucc chips will haqve a max current rating of a few amps select a resistor to limit this current to this max ie if the ucc chip can do 9 amps then a 1.2 ohm series resistor to your GDT you can then measure across this resistor with your scope as long as your circuit is floating away from earth to see how much current is going into your GDT. Ie if you are getting significant number of volt pulses across the resistor then your core has insufficient ui and you are allowing your driver chips to supply past their rating. The scoping of this point will also let you know if the driver chips are behaving ie not high frequency oscillating which does destroy them.
do you have the 1uf ceramic and 10uf electro decoupling caps as per the chip datasheet installed
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 18, 2020, 07:54:25 PM
Thanks for the reply !! I haven't placed the TV's diodes because am just checking if the circuit works for some extent so my voltage is only 12 volts.
I have 1uF ceramic caps installed just beside the ic but no 10uF as is it not there in the kaizer sstc 3 schematic . Though I will add them on my own now to check .
So should I do this test without the power supply to the bridge or with the supply connected to the bridge . Because I think putting no power supply on the bridge side makes no difference as long as the signals at the gates are correct ( basically I don't want to risk another pair of ucc chips ) .
And yes I have put tape around the earth wire of my scope ( I know it's not a good practice but it's only for temporary purpose ) so I will try to take a reading at the input of the gdt .I will upload pics of the waveforms once done.
Also I as said in the previous message this is not the first time I am encountering a similar problem . Because last time when I build a full bridge out of ir2110 in a failed attempt , it had exactly the same problem. But then I never used the gdt . The output of ir2110 was connected directly to the respective mosfets . So could it be something else which we are missing ? Btw what made you select a 1.2 ohm , anything specific ?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: ritaismyconscience on March 18, 2020, 08:12:05 PM
You're using the same power for both the driver and the bridge right? I think HV spikes are getting into your 12V supply, which destroys all the chips.

Consider using two different power supplies. Also definitely add more decoupling capacitors as johnf mentioned.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 18, 2020, 08:14:20 PM
I have dual bench power supply( actually triple with a fixed 5v output on the third ) and all the supplies are isolated from one another so I doubt that will be the cause but I am not sure I am still a newbie so no idea of RF stuff .
Also regarding the high voltage rf created a , I have Slayer exciter running beside the driver so that the antenna could pickup signals and the driver circuitry could begin oscillating which it does properly . It's only when I apply power to the bridge side , the drivers fail.
Also my ucc together take around 200 mA doing the switching job without the bridge supply connected. Is that normal or something wrong here ?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: johnf on March 18, 2020, 09:55:50 PM
12 volts applied to driver chip through a 1.2 ohm resistor will give a max of 10 amps into a dead short negelcting losses in the switch outputs so this is very close to the 9 amps that the driver chip can provide you will need the resistor to be a few watts to allow a short time to do the measurement
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 04:14:34 AM
Ok thanks I will try . But is there something else which you all can think of so that I try that also ?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: ritaismyconscience on March 19, 2020, 04:16:39 AM
Also if you have an oscilloscope, you could check power rails to make sure no voltage spikes are occuring.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 04:33:18 AM
Thanks for the replies everyone !! But all that means is that I will have to sacrifice another pair of ucc chips now
And regarding the power rails spikes , I think I can't take measurement of that when taking the measurement across the resistor at the put of the ucc chips ( since then they both have different
grounds and I don't have a diffrential probe ) .
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 05:02:22 AM
Could I just replace ucc37322 with tc4420 and ucc37321 with ds0026??
I know the pinouts are different but then I will take of that . So will it matter that the ICS are different from another ?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 02:49:59 PM
I think it might need freewheeling diodes on the output, not sure if the IC includes them (you could measure them with a diode checker). Maybe they do have built in diodes but they're not enough for the freewheeling current of your gate drive transformer, who knows.

I've read online that the tc44xx series prefers schottky diodes here or else latchup could still occur, but for the ucc3732x series I've personally had no issues with the UF400x series (UF4004 and below have lower forward drop and less recovery time).

Not saying they can't work without them but its usually standard practice to include some kind of freewheeling path for this kind of transformer drive.


I think I used 10 ohm gate resistors for IRFP260s (that was for flyback frequencies of 40-50khz, the switching rise and fall times should be a small fraction of the total "on" period, gets more important at high frequencies and powers) with 18v zener diodes on the gate, the gate resistor needs to limit the peak currents to less than the max rated of the gate driver chip at the supply voltage. The back to back zeners should be chosen so the worst case they shouldn't allow the gates to reach 20v, but not too low that they start conducting and clipping under normal operation (in practice that's 15-18v imo).

Also the higher power zener diodes 1.3w+ have a lot of junction capacitance, which can slow down switching speeds for SSTC use. This is what worked for me when I built my half bridge resonant flyback driver.

Not saying Mads circuit is wrong, but every build is different and things like parasitic inductance and capacitance differ between what you've built and what Mads built.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 03:32:03 PM
  I guess thats a nice point to have !! I will first upload the waveforms and voltage across the 1.5 ohm resistor as told above and then I will proceed to the modifications which John123 mentioned. So basically I will not connect the supply to the bridge now just to do the above mentioned tests and then verify with you all . Also I am going to use 20 volt TVS diodes instead of the zener for clamping the voltage at the gates. Thanks !!
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 03:55:05 PM
If you've got another power supply spare/battery you can temporarily energize the bridge using it, use a dummy resistor in place of the tesla coil primary. Whilst that doesn't really stress the bridge it'll show you the effect millar capacitance is having on the gate drive waveforms.

Those nice square waves when the main bridge is powered off quickly start looking different when the MOSFETs have got voltage on their drains, if you've got any old switching transformers laying around then connect that in place of the tesla coil primary (load one secondary winding) and see how the inductive loading changes the waveforms (again low voltage like 12v to the bridge, no mains at this point!).

For the antenna just tuck it around the core once, that's usually enough for the oscillator to start doing its thing.

This way you can poke around with a scope and not have to worry about something going bang or high voltages referenced to the mains.

In my experience the gate drive waveforms never look like the perfect square waves when the fets are switching actual power, the trick is to make sure the fets aren't turning off when they shouldn't (going below 10v g-s) or turning on when they shouldn't (rising above the gate-source threshold voltage, usually about 2-3v for most power fets).

The dead time between the two gate drive signals and recovery times of the diodes mod I posted can sometimes cause the gate drive transformer to "wonder".

I'm trying to find the page where someone detailed these problems, I'll post back if I manage to find them for you.

Edit: Found the page, it was actually written about a different gate driver IC but the same could still apply "UC3710 Latch-Up Issue - Update" http://electronsbefree.blogspot.com/p/electronics.html (http://electronsbefree.blogspot.com/p/electronics.html)

More edits: Not sure about your core without looking at waveforms, but it's sometimes luck of draw when it comes to random cores. I've had both bad luck and good luck when it comes to picking randoms (including the hf choke types they slip a few turns around in equipment, often between circuit earth and mains earth and other noise suppression).

What I know to actually work for definate are Fair-Rite 77 5977006401 for flyback frequencies of a few khz up to 100khz, and fair-rite 78 for tesla coil use between 200khz to 500khz. Not saying you have to get these exact cores but something with the same specs as the 78 version for SSTC use.

Random cores can sometimes work, but in my case I had to wind a lot more turns to stop them from making the gate drive chips get hot.

And to your question mixing different gate drive chips, possibly. If one's significantly slower or faster than the other then it could cause delay and phase shift of one of the drive waveforms, this is bad as it might lead to shoot through (a brief point where both fets are on at the same time).

Fiddling with the gate drive resistor on one of the fets could perhaps solve this, often putting a diode in parallel to the gate resistor to enhance the turn off is used to trim switching times.

But speeding up switching comes with its own risks, again it's one of those things other people have had success with but in my case I've always needed to put a resistor in series with this diode or else turning the fet off too fast without some resistance effectively excites an LC tank circuit made up of the fet gate-source capacitance and the inductance of the gate drive transformer = voltage spikes and ringing.

Could you get a picture of the underside of the board? Maybe something could still be accidentally shorted if only the one gate drive transformer is getting hot. Are they definitely UCC37321 and UCC37322 and not the UCC37323 version which is like both built into one package.

Sorry for the wall of text but I went through similar frustration with gate drive transformers back in 2012.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 07:19:56 PM
Thanks John123 for the amazing site and other information your provided. And I can definitely understand the frsutration as it seems to be building up with me also now. The only problem is that in that site they use a 10uF tantalum which i dont have , Is it ok to use a 10uF electrolytic ??
Ok so here I will post the waveform of the various points in the circuit. I am doing this without the power supply connected to the bridge. Also my setup for now is as follows. I have just used a old 9 volt transformer for powering the driver circuit instead of the bench power supply( the slayer exciter is powered by the bench power supply). The voltage at the input after connecting the driver circuit is 12.1 V. I have added the 18 volt TVS diodes(1.5KE18CA) (I still dont  know why the gate voltage reaches 20 volt peak to peak, maybe because no supply and load is there for the current to flow.)
I have also changed the bridge capacitor to a value closer to what i will use actually( I have used a 400 V 150uF) , which I will upgrade later.
Also I have used 1 ohm resistor in series with a 0.47 ohm resistor which should be give around 1.5 ohms total resistance. I also have added another film capacitor of 100nF at the power rails of the UCC , and now I have to say that the ics are colder than before. The film caps definitely perform superior to ceramic ones here.
I have attached the oscilloscope probes to various points to get the measurements , so hopefully you all could point out the problem going in there.I have also attached the pictures of the bottom side of the board and the top also.
The wave forms
1)interrupter output
2)gdt current ( voltage across 1.47 ohm resistor)
3)gate signals( without the tvs diodes here )
4)gate with gdt
5)power line (12volt ripple)
6) Bottom side
7) Top side
8) Current setup(Quite messy)
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 07:42:15 PM
Is it me or does the third image have less voltage amplitude on the yellow waveform than the green one? Are those both gates at the same time?

Tantalum for decoupling the gate drive ICs? You can substitute it with a low ESR electrolytic of a few hundred uF and above along with some kind of smaller film or ceramic capacitor in parallel, its job is to supply those fast peak currents, without it the supply lines parasitic inductance can cause voltage spikes across the supply pins of the chips.

I decoupled the hell out of my gate drive chips with a combination of spare capacitors I had laying around. I used ceramic, electrolytic (220uF low ESR ones from an old switched mode wall wart secondary side) and film, basically any I could find in the parts box lol. No need to go out and buy new parts, just use what you've got.

Also I remember a forum post on 4hv saying that certain caps don't often work well as the DC blocking capacitor in series with the gate drive transformer primary, something about the capacitance varying with frequency and voltage applied. I used a film capacitor for this, it was 2.2uF pulled from an ATX PSU, for tesla coil use the smaller value is ok but try adding one in parallel and see if it improves the gate switching speeds.

8.7v into 1.47 ohm = 5.918 Amps peak, what does this look like with the regular 12-15v or whatever you're using is supplied? As without these current sense resistors in place and more voltage this could get close to exceeding the 9 amps peak rating. And the MOSFETs need at least 10v to fully turn on or else their on state resistance will be higher and they'll dissipate more power when switching a real load.

The peak to peak gate voltage is ok as its swinging from + 10v to -10v, assuming the ground lead on the scope is connected to the source pin of the fet. It's one of the advantages of a gate drive transformer with bipolar drive, the negative turn off bias stops the miller capacitance from turning the device back on when switching high dv/dt stuff. If peak to peak exceeds 40v then you've got problems, I'd probably change that to display peak instead as it's more useful here.

Apart from that they don't look too bad, a bit slow but no ringing. What's the slayer exciter doing? Is that part of this circuit?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 07:49:45 PM
As I said before the Slayer exciter is just for providing the feedback signal which is then picked up by the antennae.( It is being powered from by bench power supply so completely isolated from the driver .)

And I feel the volatage on both of the waveforms on the gates of the two mosfets are same .
And yes I admit there is a slight damping happening that could be fixed by reducing the series resistor value with gate from from the gdt by a little bit .
And by tantalum I mean the ones used for decoupling of the ICS
So instead of it can I use ceramic and film caps of 100 nf coz I don't have uF caps in a usable size .( I have film mkp type 1uf cap but obviously it's too big )
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 08:27:08 PM
Oh right ok, I forget it uses antenna feedback. btw I edited my previous post on the other page.

The decoupling caps across the IC can be lots of random ones in parallel, that's what I did. It's just there as a low esr energy reservoir for the fast peak current draw until the main filter capacitor can catch up across the PCB parasitic inductance.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 08:45:04 PM
Ok so now what do I do next after adding 2 more 104 caps ??
Like just tell me some way in which I can be sure not to burn my mosfet drivers again while testing . And I hope my core which I used for the gdt is doing okay
Edit :now I know what might be the reason of killing the mosfet drivers i.e overcurrent at the output might cause it as John123 mentioned. But I have small question which might be stupid but please excuse I am a newbie and still learning . You said that the max current is given by 8.7 v / 1.47 ohm. But then should it not be the rms value taken as the voltage here ?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 09:12:45 PM
It's the peak currents which matter too with semiconductors as high peak currents lasting just microseconds can destroy them. The RMS current ie the average current draw measured from the supply will always be much less, for example I've got a flyback driver which can draw a maximum average current of 8-10 amps from the supply but whilst it's doing that the drive mosfet switching the primary coil will see 20+ amps peak.

If you're happy to move onto the next testing step then here's what I'd do next, supply the gate drivers with at least 12v (to fully turn the mosfets on but put a resistor in series to limit the current if anything were to go wrong again, something like 5-10 ohms a few watts.


Now connect the bridge up to a low voltage source and limit the current somehow with a resistor or power supply current limit, again a low ohms power resistor is fine.

Without connecting anything to where the primary coil connects take a look at the gate waveforms, do they look ok with voltage applied to the bridge? are the chips or limiting resistors getting hot?


The idea with these resistors and low voltage is to prevent damage if anything starts misbehaving and save the chips.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 09:24:24 PM
Thanks for the reply once again !! The thing is that I am currently driving the circuit with a 9 volt transformer . So I get around +10-10 volts across the gdt but if I use a 12 volt transformer the peaks are aas high as 18 volt which might even destroy the ucc drivers once again . And I am fine with mosfets being driven in that high resistance linear region for now . I will see on that issue later . So I will proceed as you said and update about the status tomorrow only if mosfet drivers don't fail .
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 09:26:18 PM
Thanks for the reply once again !! The thing is that I am currently driving the circuit with a 9 volt transformer . So I get around +10-10 volts across the gdt but if I use a 12 volt transformer the peaks are aas high as 18 volt which might even destroy the ucc drivers once again . And I am fine with mosfets being driven in that high resistance linear region for now . I will see on that issue later . So I will proceed as you said and update about the status tomorrow only if mosfet drivers don't fail .

Oh is that a 12v ac transformer or is 12v the DC rectified and smoothed value? What is the voltage of that 12v power supply unloaded? Sometimes these wall warts only put out their name plate voltage at the rated current.

Urm yeah I guess its ok to keep them in the linear region for testing then, just don't pass too much current through them drain to source (it has to do with the mosfet safe operating area too)!
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 09:28:23 PM
When I connect the 12 volt ac transformer, then with a bridge rectified and a 2200uF capacitor on the output the unloaded voltage is as high as 16.2 volts
And I am using a 9 v ac transformer currently so loaded voltage is around 12.1 volt dc
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 09:32:43 PM
When I connect the 12 volt ac transformer, then with a bridge rectified and a 2200uF capacitor on the output the unloaded voltage is as high as 16.2 volts
And I am using a 9 v ac transformer currently so loaded voltage is around 12.1 volt dc

Ah yes that's normal, it's the filter capacitor charging up to the peak of the AC waveform.


Oh crap I just noticed in the datasheet of the gate drive chips you're using:

My cheap solution in this case would be to put a couple of diodes in series with the +16v to drop the volts a bit and then add a 15v zener diode/tvs across the supply rails to clamp any voltage spikes from destroying the chip.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 09:34:09 PM
That's the sole reason I went with a 9 volt ac transformer at the first place now after blowing few chips
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 09:37:11 PM
That's the sole reason I went with a 9 volt ac transformer at the first place now after blowing few chips

Ok I must of glanced over that then sorry, yeah anything above 16v (including brief transient spikes) will blow the gate drive chips. Put a few diodes in series to drop the max volts a bit if you've got any laying around. Then put a zener/TVS across the supply pins near the IC to clamp any voltage spikes.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 09:39:35 PM
Can you just draw a rough diagram sort of to tell me how to put the zeners in the antiparallel configuration for clamping the voltage at 15 volts ( I don't have 15 volt TVS ).
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 09:43:20 PM
Can you just draw a rough diagram sort of to tell me how to put the zeners in the antiparallel configuration for clamping the voltage at 15 volts ( I don't have 15 volt TVS ).

What value of zeners do you have spare? If not have you got any LEDs and how many regular diodes have you got?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 09:45:01 PM
I have an assortment of 1 watt zeners ..so no issue with the values I hope I could get one from that ..and also have leds and plenty of fr107 and 1n4007
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 09:46:08 PM
What voltage zeners do you have?

Here:

It's just a case of dropping the extra volts and clamping spikes on the rail by placing the 15v zener right at the supply pins of the gate drive IC's.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 19, 2020, 10:26:29 PM
Thanks a lot for this . Also do I need to put additional freewheeling diodes at the outputs of the ucc driver as stated above ?

Now all I want is that mads replies and also justifies maybe if there are certain issues with his design or is it just me experiencing these weird issues which no one or maybe very few people encountered beacuse I have done quite a lot of research and then finally thought to take help here as I couldn't find anything which related to the dying of driver chips which I am encountering
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 19, 2020, 10:43:15 PM
Well I always put the freewheeling diodes in on mine, doesn't hurt anything and only helps to protect the output stages of the chips.

I don't think there's anything wrong with Mad's design, it's just the gate drive chips can't take anything above 16v even for a moment. And that transformer was putting out more than that plus brief dv/dt induced voltage spikes.

That's why the 15v zener/TVS should be literally soldered across the supply pins of the IC to catch any fast spikes, I have a feeling the extra capacitors you installed across them might also be helping to dampen transient voltage spikes on the supply rails (especially if it made them run cooler).

To scope the supply rail spiking use the little ground spring instead of ground wire, it may only be for a very short period like in the nanoseconds and have very fast edges. Regular switchable x1, x10 scope probes should be on x10 to get maximum bandwidth (unless you've got some fancy probe).
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 20, 2020, 05:03:53 AM
So now I will do the recommended changes and be back again hopefully if everything is right .And yah I am aware of that spring method to measure the noise but then I think I will just go ahead with the modifications proposed. Also another thing which might give some clue is that whenever the gate driver ICS died the schmitt trigger (c40106)also died with it. So does it have to do something with this or just a matter of coincidence ?
PS : Previous to this , I was giving supply to the driver by the bench power supply which had regulated 12 volt with current limiting so it rules out the chances of ICS dying due to spiking .
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: John123 on March 20, 2020, 11:57:13 AM
You could have the the most expensive and best power supply in the world and the voltage spikes will still appear on the circuit board, it's down to physics and the parasitic inductance of the various wires and PCB traces.

The gate drive chip outputs are switching really fast with fast edges, even with capacitors close the parasitic series inductances effectively creates a boost converter on the supply pins of the chip. These spikes won't show up on the power supply, as far as your power supply is concerned there's a steady 12v across its output terminals. it's the reason why commercial circuit boards are often plastered with capacitors of all shapes and sizes many in parallel with each other (especially computer motherboards).

Some videos on the subject, the chips being used doesn't matter as its the same across the board but just gets worse and worse with faster speed switching and currents (like the 9 amp peak currents of the gate drive IC's).
https://www.youtube.com/watch?v=9EaTdc2mr34 (https://www.youtube.com/watch?v=9EaTdc2mr34)
https://www.youtube.com/watch?v=VfCu-siq0-Y (https://www.youtube.com/watch?v=VfCu-siq0-Y) (at 6:00 when he removes the ceramic capacitor, that's when the effects of parasitic inductance kicks in).
https://www.youtube.com/watch?v=1xicZF9glH0 (https://www.youtube.com/watch?v=1xicZF9glH0)
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 20, 2020, 12:29:27 PM
I agree to John123 that spiking can be present . Niether is my my power supply a fancy one like all rigol and keysight or any other popular manufacturer of good power supplies . Mine is cheap one ( but still I feel it's expensive beacuse my budget very restricted on such things) .
Another issue which arised now is that after doing the mods ( adding freewheeling diodes across the outputs of the chips ( I used uf4007 ) , is that now my half bridge current through the primary of the gdt looks somewhat funny . Beacuse what happenes now is that the current through the gdt goes higher in amplitude than it it goes below the zero reference line , which I think might cause problems so till now also I didn't attach a supply to the bridge. I also couldn't fit more decoupling capacitors as the space is now completely taken by the freewheeling diodes. I have 100 nf film and 1uf ceramic across each of the ucc chips
 Please tell me if I do need to add more ) . I will put the waveform right here . [ Invalid Attachment ]  [ Invalid Attachment ]
I did the mods by referring this schematic as told in the forum above ( I also used the 1 ohm resistor between vcc and 12 volt and ground and 12volt , so is that causing any issue ) . [ Invalid Attachment ]

I sincerely request you all to put views on why is the half bridge signal turning on longer for one side while not so for the other side ?. Is it normal so that i can proceed with connecting a load and low voltage power supply to the bridge with a resistor in series to reduce the current.If not normal then please put some solutions and also why is happening so
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: davekni on March 21, 2020, 04:25:49 AM
The 1-ohm resistors in the ground (pin 3) gate driver leads are a big problem.  Current spikes during switching can easily move the ground high enough to switch the logic state seen on the driver's input.  Ideally there's a good ground plane to which the drivers both connect, along with the circuitry driving the inputs.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 21, 2020, 04:27:45 AM
So is that making my waveform slightly unequal on each side ??
http://electronsbefree.blogspot.com/p/electronics.html
Here it's written why we need the resistors
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: davekni on March 21, 2020, 05:25:49 AM
The 1N5819 diodes are a good idea.  Most gate drivers aren't used with inductive components on their outputs.  All the rest is likely compensating for poor circuit board layout and/or poor component performance (high ESR capacitors in particular).  That exact fix happened to work for some particular layout.  The ground resistors in particular will cause problems in most uses, and may be the cause of your specific issue.

How are your 3732x chips actually wired?  The reference you pointed to shows driver chips with single ground pins.  Did you wire the 3732x grounds together, then through 1-ohm to ground, or is it only the output side with 1-ohm resistors and the input side directly grounded?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 21, 2020, 05:34:59 AM
I am attaching a reference schematic from mads own website which I followed and made a pcb of it . And by the way I have used uf4007 instead of the in5819 as I heard they are better here .
The grounds are wired together and then through 1 ohm resistor they are grounded.
EDIT: I am attaching some waveforms of the gates of the two mosfets and the current through the GDT. I have also increased the resistance of the series resistor though the GDT for measuring the current through it and also restrict the current through to a certain value.
Now my problem is that as it can be seen in the wave forms that the voltage at gates of one mosfet (YELLOW COLOUR) rises to a higher value then it goes below it ( The difference is around 0.5 V). So is that much of variation allowed or something is wrong ??
EDIT 2: I have now tested it with a voltage of 5 volt which is separate unit ( Its a low power wall wart), from the bench power supply i am powering slayer exciter with. The input to the bridge is hence 5 volt with a series 22 ohm resistor to prevent any over current if it happens. Now the drivers DIDN'T BLOW. But then again gate waveforms didn't look very promising as one side is rising higher than the other . So I am not yet sure to increase the input voltage to the bridge. Also I notice ringing is dominating now .Please have look and tell what is wrong and how could it be made better.New wave forms after powering the bridge
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: davekni on March 21, 2020, 06:36:58 PM
How are you measuring GDT current?  You mentioned increasing a resistor in series with the GDT.  What value is that resistor?  Are you measuring current by using a differential scope probe on the resistor?  I see 2.27V peak, but don't know how to translate that to amps.

Looking back to the beginning of your post, I see that this is driving a pair of TO247 parts, not a larger IGBT brick.  The gate capacitance and therefore current may be low enough that the 1ohm ground resistors aren't causing issues.

The uf4007 diodes are plenty fast, but aren't schottky, so have higher forward voltage drop.  They aren't as useful for protecting the gate driver outputs as 1N5819 or similar schottky parts are.  However, they likely do contribute some to protection.

I wouldn't be concerned about the 0.5V gate-drive voltage asymmetry.  That could easily be due to the duty cycle not being exactly 50% and/or the non-linear gate capacitance of the TO247 IGBTs (or FETs - I didn't search back to see which you are using).

The ringing is presumably a result of the IGBT switching.  Hard to say if ringing will scale up enough at higher IGBT voltage/current to become a problem.  The key will be good low-inductance bypass and bulk capacitance across the IGBT half-bridge power rails.

Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 22, 2020, 04:39:50 AM
Thanks for the reply davekni. I am using an oscilloscope whose ground terminal I insulated so that I I can take non ground reference measurements without a differential probe. I am using a 2.7 ohm resistor in series to the gdt. Also I have 5.6 ohm resistor on the gates of the mosfets and regarding the voltage asymmetry , it almost fixed itself I don't know why that happened at the first place but it's still there a little bit but then as you said I don't need to worried about this
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: davekni on March 22, 2020, 05:17:51 AM
The gate-drive signal may be low enough impedance to work with a floating scope.  In general, a scope's floating ground still has quite a bit of capacitance to the power line, primary in the power supply's EMI filtering, perhaps 10nF.  I'd recommend against connecting the "floating" ground to any signals with significant source impedance.  The scope ground impedance may be causing the asymmetry, or at least contributing to it.

2.27V on 2.7 ohms is under 1A peak, so under 1V peak across the 1-ohm ground resistors.  That's low enough to avoid unintended logic switching.  I still recommend against any ground resistor.  If the chip needs current limiting or spike filtering, the supply resistor should be sufficient.  Since the two chips switch opposite directions, there's a supply resistor in series with the gate drive signal for every transition.  Double the supply resistors to 2 ohms each if you want the same total resistance as 1 ohm ground and 1 ohm supply.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 22, 2020, 05:57:24 AM
The gate-drive signal may be low enough impedance to work with a floating scope.  In general, a scope's floating ground still has quite a bit of capacitance to the power line, primary in the power supply's EMI filtering, perhaps 10nF.  I'd recommend against connecting the "floating" ground to any signals with significant source impedance.  The scope ground impedance may be causing the asymmetry, or at least contributing to it.

2.27V on 2.7 ohms is under 1A peak, so under 1V peak across the 1-ohm ground resistors.  That's low enough to avoid unintended logic switching.  I still recommend against any ground resistor.  If the chip needs current limiting or spike filtering, the supply resistor should be sufficient.  Since the two chips switch opposite directions, there's a supply resistor in series with the gate drive signal for every transition.  Double the supply resistors to 2 ohms each if you want the same total resistance as 1 ohm ground and 1 ohm supply.
Hey devkni thanks for the quick reply . But I am a newbie yet , so there a quite a lot of things I didn't understand in your statement. What do you by that the voltage is low to avoid any unwanted switching.
Second : and there isn't any supply resistor in series to chip . So it's it required ??
And what do you mean by 1 ohm ground and 1 ohm supply in the last line .
And what exactly happens with a high impedance load and a floating scope connected across it ?
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: davekni on March 23, 2020, 12:12:36 AM
From your post yesterday you mentioned that you were following this recommendation:
http://electronsbefree.blogspot.com/p/electronics.html
And from your next post yesterday:
"The grounds are wired together and then through 1 ohm resistor they are grounded."

Did you add only the ground resistors from the electronsbefree schematic?  I see no need for either ground or supply resistors.  However, if you are going to include resistors as per electronsbefree, I recommend adding only the supply resistors, not the ground resistors.  This is in response to your question "And what do you mean by 1 ohm ground and 1 ohm supply in the last line".  Those 1 ohm resistors are the ones in the electronsbefree schematic, which I thought you had copied.

The resistors in series with the driver chip grounds are a problem only if the voltage across them is high enough to make an incoming logic 1 level (+5V) look like a logic 0.  In other words, if the gate-drive chip ground spikes up to 3 to 4V, then a 5V logic input will be only 1 to 2V above it's 3 to 4V ground, so will register as a logic 0.  For 1-ohm ground resistors, it would take 3 to 4 amps to reach that voltage.  Your gate-drive currents appear to be just under 1A (2.27V / 2.7 ohms).  That will create spikes on the gate-drive grounds of just under 1V, not enough to cause trouble.  You could scope the ground pins (voltage across the 1-ohm ground resistors) to verify that voltage spikes are low enough.

Concerning your question: "And what exactly happens with a high impedance load and a floating scope connected across it?", the issue is current flowing through the scope probe "ground" lead.  Even with the scope "ground" isolated from the power line safety ground, the scope "ground" will have capacitance to the power line hot and neutral leads.  This capacitance will inject some line-frequency (50 or 60Hz) current into the circuit at the node connected to the scope "ground".  The capacitance will also load down higher-frequency signals, as current from the signal is fed through the scope ground, through the scope's capacitance, then through the hot and/or neutral power leads to ground at the line breaker panel.

How much problem the scope "ground" current is depends on circuit impedance and scope "ground" impedance.  Larger scopes that draw more line power are likely to have more capacitance from hot and neutral to "ground".  You could experiment by scoping a floating signal as you've been doing, but add a resistor between the scope "ground" and the signal, say 10k ohms.  Compare the traces with 10k in series with the "ground" and separately with the 10k in series with the probe tip instead.  If the two scope traces look roughly the same, then your scope "ground" load is less than I'm guessing, so less of a problem.
Title: Re: Gate drivers ICS Dying( UCC37322 and UCC37321 )
Post by: prabhatkumar on March 23, 2020, 04:27:02 AM
Thanks a lot davekni for the reply and explaining so well. By the way now I am experiencing another problem that the bridge doesn't supply any current even though it appears to be switching . I have started a new topic ( NO CURRENT THROUGHB HALF BRIDGE )about that so it would helpful if you could have aook in to that also . Thanks !
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