Author Topic: SSTC issues (gate signal, interrupter-mode, grounding)  (Read 723 times)

Offline Max Seiringer

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SSTC issues (gate signal, interrupter-mode, grounding)
« on: April 12, 2020, 09:54:27 PM »
Hey there!
I am building the Kaizer SSTC1 as my first SSTC project and I ran into some issues.
First off, I based the circiut around the schematics given from http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-i/]http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-i/. I only changed one thing: I didn't have a UCC37322 IC, so I used two UCC37321 and inverted the input-signal for one of those two drivers with the help of a spare input of the 74HC14 IC.
I currently use two lab-supplies for powering the electronics and the coil itsels seperately. Later on, one supply should be replaced with the variac.
The coil has its resonant frequency at 210kHz.

1) When running on low voltage (10V) the circuit works rather good. The only issue is a small spike at the rising edge of the gate-signal. When increasing the input voltage up to 30V, the spike grows and the gate-signal gets very noisy and unclean. At a certain point (above 40V) the frequency jumps to about 600kHz and the supplies go into current limitation. The only way to get the system back to its resonant frequency is to shut it down completely.
The radiated field picked up form the probe of the oscilloscope looks fine, until a certain input-voltage. A significant amount of noise is noticeable at about 30V input.
May this voltage dependent spike have to do something with the Miller-Effect? I checked the GDT with my function generator, the signal looks perfect even with the MOSFETS connected, but without any load connected. The issues only occur when the bridge is connected to the driver.
Another thing I considered is grounding, I tried different methods of connecting the coil to earth with the same results.

2) I have issues when trying to interrupt the circuit. I tired to tie the enable-pins of the UCC37321 ICs directly to ground but the circuit keeps oscillating like usually, no matter what I try. The voltage at the ICs is rather smooth and free from any noise, only very small ripples are noticeable at the voltage-supply for the 74HC14 IC.
What could be the cause of this problem?

Please excuse my english, I'm still learning ;)

Kind reguards,
Max Seiringer

Offline davekni

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #1 on: April 12, 2020, 11:04:35 PM »
Concerning enable pin not working, there's a previous case of exactly that:
https://highvoltageforum.net/index.php?topic=997.msg6869#msg6869

I'm now suspicious that there's counterfeit UCC3732x parts on the market, ones that have enable pin issues.  Counterfeit parts may have other performance issues as well, although non-functional enable is the only one that's come up so far.

For the rest of your post, pictures of your circuitry and wiring will be needed to make any useful suggestions.
David Knierim

Offline Max Seiringer

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #2 on: April 13, 2020, 04:07:57 PM »
Thanks for the fast reply!
I checked all the connections on the PCD several times now, there seems to be no issue.
I got my UCC37321 ICs rather cheap from aliexpress a few months ago. Not a reliable source of components, but at least the MOSFETS turned out to be good. I will test the remaining UCC ICs and post the results later on.

I attached some pictures of my setup, screenshots from the scope will follow soon.

Kind reguards,
Max
« Last Edit: April 13, 2020, 04:14:10 PM by Max Seiringer »

Offline prabhatkumar

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #3 on: April 13, 2020, 04:54:38 PM »
Well Hi there , I am the person whose post was referred by davekni and he very kindly helped me a lot on my own issues .I can completely understand your problem because I went through the same issue . I had also sourced my UCCs from AliExpress by seeing it's low price and unavailability at local markets . But they have a problem that most of the cheap ones enable pin simply doesn't respond and seems like it has no connection internally to the enable pin. This might be the reason that they are sold at such a low price compared to mouser, digikey etc. . But I will tell you what can do to get the coil interrupted. Many people might simply not be in favour of this and yes it's right it's not the best solution . But it worked very well for me.
All you need is a AND gate like 74hc08. We need only 1 AND gate even though it has 4 inside it. Because there are a few connections to be made , I recommend you to build this part along with the 555 or any other interupter ( I used attiny 85 interupter from loneoceans which works decent and we can independently adjust the on time and frequency while also limiting the max on time to some suitable value . By this method you can save a lot of space on the PCB and need only a attiny 85 rather than 555 and few other complementary components). Coming back to the connections , connect the supply and ground to the 74hc08 ( no more than 5 volts or you will try it . A small tip to get 5 volt on the other PCB with interrupter , use the 5 volt output of the attiny if you are opting for that road ) then connect the output from the schmitt trigger which was previously going to the 2 ND pin of the UCC (SIGNAL PIN and obviously cut the track between the signal pin of UCCs and the schmitt trigger.) And now connect the output of the interupter to the 2nd pin of the 74hc08 . The third pin of the AND gate is your final output which you want to feed in the UCCS. But as you using both similar drivers, then you need to feed this signal like before, one directly to one UCC and the other through the 74hc14(inverted one ) to the other UCC to mimmick the inverting action . Try this and tell if this helps .
And another tip for you for the spikes you are seeing. Do not connect to driver side to any power supply source because they tend to pick up noise and then spikes could occur which can the kill the chips on the driver section. I learned this the hard way , I blew up like ir2110 before in a some different attempt and also blew 2 Pairs of UCCs along with several and gates and schmitt trigger.
Simple way to remove spikes. I am not saying Its the best way but it's effective. Use a standard 12 volt lead acid battery ( the small ones you get like 1.2 Ah ones . They aren't very expensive works quite well . Also make sure that you are not powering your driver side above 13 volts because the UCC s max voltage input is 16 volt and even slight spikes in the input voltage could simply kill it. And use a small resistor like 3.9-4.7 ohm on the output of your GDT in series with the DC blocking cap. This will also reduce some unwanted ringing and might save your UCC by limitng the output current to some max if something is wrong( I got this tip from someone on my post before and it works well , haven't killed a single UCC after that )
I am also a learner but still I want to say something about the GDT winding. Your core looks nice and of the correct type ( if I am not mistaken , it seems to be ferroxcube toroid and hopefully your are using the type 3e25 or better than that ) . Your trifilar winding seems to be done correctly but I advise to do it in a more tight manner and also wind the wires more tightly to the core and see if it helps with you noise issue . The wires which go to the mosfets should also be done in twisted pair to reduce stray inductance effect.
Try this and report back.
Hope your project goes well and also your coil looks greatly done.
 
« Last Edit: April 13, 2020, 10:49:01 PM by prabhatkumar »

Offline Max Seiringer

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #4 on: April 13, 2020, 07:47:19 PM »
Thank you for your help!
First off, your guess on the GDT core was spot on. It's a Ferroxcube 3E25.
Using an AND gate to interrupt the coil is a great idea, I will try it out soon.
I already rewound my GDT according to your suggestions and it reduced the ringing quite a bit. However, the series resistor at the GDT made the biggest difference. Running from a battery didn't change much, to be honest the signal looks exactly the same as with the powersupply. I checked the voltage at the driver's input, it looks rather smooth (some ringing with up to 0.3V).
Without the resistor, the signal looks like shown in the pictures below.

20V supply voltage at the bridge.
Red: GS
Yellow: DS


30V supply voltage at the bridge.
Red: GS
Yellow: DS


Just above 30V supply voltage at the bridge.
Red: GS
Yellow: DS

Using a resistor results in a reduction of the ringing measured between drain and source. At 30V at the bridge, the signal looks like the one without the resistor at 20V.
I measured the ringing to be about 6MHz.

I also probed the input signal of the GDT

Red: Output of the first UCC referenced to the driver's ground
Yellow: Output of the second UCC referenced to the driver's ground

Please excuse the quality of the pictures, I am using a cheap USB oscilloscope.

Kind reguards,
Max
« Last Edit: April 13, 2020, 08:25:35 PM by Max Seiringer »

Offline Mads Barnkob

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #5 on: April 13, 2020, 10:27:40 PM »
Hi Max and welcome to HVF :)

Did you try to reverse polarity of your primary coil? It could be that you are running with feedback out of phase with the primary coil. That is a common cause of very-little-output-but-should-have-bigger-output issues with a SSTC.

The coupling between your primary and secondary coil is way too low for a SSTC. That primary coil looks more like something for a DRSSTC or SGTC. See my pictures with primary coil wound directly around the secondary coil with only some 3-4 layers of plastic between them.

How about UCC27423, impossible to get as well? I guess we have to look around for other drivers with enable pin if they are getting hard to souce.
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline prabhatkumar

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #6 on: April 13, 2020, 10:47:55 PM »
Nice to know that the resistor in series helped. And also the oscillations which you see between drain and source should hopefully go when you attach a proper load at the output of the bridge. Use 10 ohm 10w resistor as a load. Careful it gets very toasty hot very quickly . Now hopefully your oscillations should die down quite a bit.
But there is something which I don't understand. The starting two waveforms look fine to me but the third one at voltage just above 30v , why does the signal at the gate start looking sinusoidal type like it's completely changing shape. Is is because you are not zooming in properly or it's just like that. Because if the signal is like that then it's trouble for you and you should stop at this point find the mistake or else you will blow up something else.  And also if you are powering it with something which is not mains referenced like a transformer ( not a variac ) , then put one channel of your scope at the output  and one channel across the low side mosfet not the high side one or else something will blow up. Then please do post the waveforms.
And also as mads said the low coupling could cause trouble
 And I have experienced it before. Initially I tried building kaizer sstc 3 and then I also like you built a very loosely coupled coil but then I could not get the coil to start up. Just by having a good coupling as he said , the coil started working . And also if you have a loose coupling then the antennae will pick up ambient signals in the atmosphere and start oscillating at high frequencies which can cause big trouble for the UCC . I don't know whether it's a coincidence or not , I also was getting 600kHz oscillations when the antennae wasn't able to pickup the signals. I think it's a standard issue with these cheap China UCCs . Best of luck !!


Offline davekni

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #7 on: April 14, 2020, 05:54:19 AM »
Max,

Your coil looks very good!  As Mads said, coupling is probably too low for an SSTC.  However, save that primary for a DRSSTC version at some point, as it's so nicely constructed.

Now that you've twisted GDT wires as Prabhatkumar recommended, that should be good.  The series resistor on the GDT input may be too high given how rounded your gate waveforms appear.

The biggest issue I see is inductance on the power wiring to the FET drain and source leads.  That's probably causing the large ringing after rising output edges of the half-bridge.   (It's good that the power wires solder to the FETs close to the package - that minimizes source current induced signals on the gate waveform.)  The caps need to be very close to the FET source and drain connections, and the output connection between the two FETs needs to be short as well.  Copper planes are even better than wires if that's a possibility.

Prabhatkumar,
"All you need is a AND gate like 74hc08. We need only 1 AND gate even though it has 4 inside it."  You are lucky that you haven't fried driver chips or FETs with only one gate driver disabled.  Both driver chip outputs need to be forced low during disabled times.

Max, Since you are using inverting driver chips, NAND gates would be appropriate, one per driver chip.  That way a low enable input to the NAND gates forces the gate driver inputs high, so outputs low.  The inverter for one chip needs to be on the input side of its NAND gate.  Or buy working driver chips if that's an option.

Do you have schottky diodes across the driver chip outputs, especially the output-to-ground diodes?  I've heard multiple times that these chips can't handle much reverse output current, which makes sense looking at their internal schematic.

Good luck!  Thank you for sharing pictures and scope traces.
David Knierim

Offline prabhatkumar

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #8 on: April 14, 2020, 07:54:00 AM »
Sorry for hijacking this thread Max . But this becomes a thing for me also now about what davekni said for the driver chips . Davekni I want to know more about this forced output low during off times .
As much as I understand , if both the driver chips needs to be shut off then could you just explain how does this work in real for the working driver chips and not the fake ones which we have got . Like does it happen like when the enable goes low then driver chips i.e both inverting and non inverting shut off completely . If this is the case , then it means from what in I have done so far , then only one of my chips are shut off during the low period which is the non inverting one ? Please tell any solution using gates because I can't get any genuine driver chips here during the lockdown atleast 
Edit : I tried to use logic and then arrived at the following conclusion , use a AND gate for the non inverting ( or a NAND) UCC and use another output of schmitt trigger to give you the inverted square wave of the resonant frequency which you obtained at first place and then use A DIFFERENT gate to do an AND operation ( or NAND) with the same interuppter signal you are using for the other chip. I hope this might work but davekni or anyone else please do commend on this thing . And Max please try this to see if it works .
« Last Edit: April 14, 2020, 09:43:48 AM by prabhatkumar »

Offline Max Seiringer

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #9 on: April 14, 2020, 09:16:30 PM »
Thank you all for helping!
I tried to shorten the leads to the power supply and it greatly reduced the ringing seen on the DS path. Thanks for this clue!
Concerning the primary... well I always feared that this one is not the appropriate one for an SSTC. However, I wound another primary today.

Don't worry, it's uglier than seen on the picture.
The result was rather dispointing, the coil startet oscillating at 600kHz right away, even at 10V at the bridge. In addition, the signal on the GS and DS path looked pretty horrible.

It looked something like that, but with much less ringing on the DS path.
Red: GS voltage
Yellow: DS voltage

So I went back a step and disconnected the bridge from the supply. I connected one side of my function gengerator to the antenna of the driver, supplied a 200kHz sine wave and had a look at the diffenent stages. One thing I noticed was the input signal at pin 1 of the 74HC14.

The signal is clamped by the diodes, however there is a small spike noticeable at the rising edge. The same spike occurs while operating the coil. Furthermore, the duty cycle is not exactly 50%, the signal is about 60/40 at the input of the UCC ICs. At least the signal between the 74HC14 stages looks fine, actually it looks exactly like the signal as if the coil was powered and self oscillating.

I'd also like to thank you for the advice on interrupting the coil. I will try it out as soon as i get some AND/NAND gates, as it turns out I'm running out of material :(

Kind reguards
Max

Offline davekni

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #10 on: April 14, 2020, 09:23:26 PM »
During operation the GDT input is a +-12V square wave, turning one FET on and the other off during each half-cycle.  To stop operation, the GDT needs 0V input.  0V across the GDT is accomplished by both UCC driver chips outputting 0V.  (It would theoretically work to have both UCC driver chips output 12V, but low is stronger, so is better for forcing 0V.)

Here's a couple circuit sketches for gating inputs to UCC chips with non-functioning enable inputs.  Top one is for the normal case with one UCC37322 and one UCC37321.  The lower case is for both chips being UCC37321 (inverting) as you (Max) have.  This isn't the only possible gating, as the same logic could be accomplished with AND or OR or NOR gates instead of NAND as I've used here, but the necessary inversions would be different.


David Knierim

Offline Mads Barnkob

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #11 on: April 14, 2020, 09:52:19 PM »
Another classic SSTC misbehavior cause is ungrounded unused inputs on the logic ICs. You can get quite a lot of internal crosstalk from open inputs on a 74HC14 to the gates in use. 

That is about the only reason I can think of, to get a higher frequency back than the resonator has, or you just have some unique setup where it locks to the 3rd harmonic instead of the fundamental.
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline davekni

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #12 on: April 14, 2020, 10:21:46 PM »
With only 10V on the bridge, I wonder if the antenna is managing to pick up the gate-drive signal more than the intended HV from the coil?  Another possibility might be the Tesla secondary ground connection coming loose.  Neither of these are from any experience, just ideas.

Driving the antenna directly with a signal generator is going to place a high load on the signal generator output.  The generator is feeding clamp diodes through 0.1uF, which is under 10 ohms at 200kHz.  I'd suggest adding some series resistance, perhaps 1k, between the generator and antenna node.  That might fix the duty-cycle error you are seeing.
David Knierim

Offline Magneticitist

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #13 on: April 27, 2020, 04:08:49 AM »
Reading about your enable pin dilemma which I currently share, I went back and checked to see that even though I ordered a SINGLE new UCC27322 from an ebay seller I had received 6 of them thinking I must have ordered 6. It sort of makes sense now that none of the enable pins work on them. The same thing goes for the single 27321 I had ordered from a different seller. It may not be wise to purchase any more of those unless they come from a trusted person with some to spare.

Offline ritaismyconscience

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #14 on: April 27, 2020, 06:11:09 AM »
Wouldn't be surprised if the sellers are remarking cheaper drive ICs like the TC4420. If they actually made the chips, it would be trivial to add a few gates.
« Last Edit: April 27, 2020, 06:13:24 AM by ritaismyconscience »

Offline prabhatkumar

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #15 on: April 27, 2020, 01:33:05 PM »
What I would suggest that even after so much troubleshooting and help from others , if it isn't helping then why not completely scrap that idea off. You were originally building kaizer sstc 1 if I am correct , why not build the sstc 2 ?. Mads has also provided with complete PCB layout which is even quite compact and I have also used it with some modifications like more filtering at the UCCs , addition of diodes to prevent flyback due to switching of inductive load( GDT here) . All these modifications could be done without any change on the PCB , you just need to solder from the other side ( I could send a picture of my board if you want ) . This way the issue of picking up noice might also reduce.

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Re: SSTC issues (gate signal, interrupter-mode, grounding)
« Reply #15 on: April 27, 2020, 01:33:05 PM »

 


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Mugi30
May 18, 2020, 10:05:14 PM
post Re: What's the best way to trigger these things?
[Capacitor Banks]
johnf
May 18, 2020, 09:03:11 PM
post Re: What's the best way to trigger these things?
[Capacitor Banks]
John123
May 18, 2020, 07:50:08 PM
post Re: Powerful easy to build MIDI Interrupter
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Max
May 18, 2020, 04:15:16 PM
post Re: Freewheeling diodes are burning (Now other problems)
[Solid State Tesla Coils (SSTC)]
hip424
May 18, 2020, 03:13:14 PM
post Re: How to get rid of stuff?
[Sell / Buy / Trade]
klugesmith
May 18, 2020, 06:31:25 AM
post Re: Building a bigger DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ritaismyconscience
May 18, 2020, 03:18:40 AM
post Re: What's the best way to trigger these things?
[Capacitor Banks]
davekni
May 18, 2020, 02:26:27 AM
post Re: What's the best way to trigger these things?
[Capacitor Banks]
rikkitikkitavi
May 17, 2020, 11:17:06 PM

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