Can somebody please explain me how this zvs driver works? / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Can somebody please explain me how this zvs driver works?

previous 1 2 3 next

Move Thread

LAN_403

Ash Small

Tue Jun 26 2012, 02:00PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I assume it's not the resonant frequency of the LC circuit. (or is it?)

I said ringing because I usually refer to a circuit resonating when power is being applied at exactly the correct times. But ringing is just when you change the state of the lc circuit too fast and the current oscillates down on its own. And that is in fact the resonant frequency. I have actually used this as a method to find the resonant frequency of a tank before I had a function gen. Just tap the leads of a power source across the lc circuit while having an oscope trigger and hold. From that data you can just measure out a cycle to get the ~fres.
[/quote1340718652]

Thanks for clearing that up Ben. I usually associate 'ringing' with some unwanted extra oscillation that results in unwanted fluctuations at the gate or base of a transistor. I guess I should have finished my early morning coffee before posting.

Steve Conner wrote ...

As it is a push-pull circuit, you would have to replace the LC tank with some other 3-terminal network to make it complete. You can use a transformer with a saturable core, and delete the DC link choke, to get the ferroresonant version. In this, the oscillation frequency is determined by the supply voltage and the volt-second capacity of the transformer windings.

Are you able to point me in the right direction to read up on this Steve?

As I've mentioned before, the idea of using this setup to drive a GDT intrigues me.

EDIT: I've recently aquired some FX2242 cores which I'm hoping may be suitable for this, although I suspect I may need something with a larger 'window'.

Electorials

Tue Jul 03 2012, 08:48PM

Registered Member #5457 Joined: Mon Jun 25 2012, 06:42PM
Location:
Posts: 14

Alright,

I finally built this circuit but it's not working :(
I tried running it at 12v and 15v but I always have the same problem:

Only one mosfet seems to get warm, the other one is totally cold.
And the output is not working :/

I checked all my wiring 10 times and it seems correct.
I'm testing it with a 6 + 6 turn induction heater coil.

Any ideas?

Greetings,
Electorials

EDIT:
I just noticed that one zener diode is corrected in the wrong way :/
I'll change it tomorrow because it's getting late now.

Could this have destroyed my mosfets? :/ I hope not!

Ben Solon

Wed Jul 04 2012, 03:43AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

if that doesnt fix it, then post a picture of your setup. its hard to find out whats wrong just by saying that your fet burns up. i use igbts for the most part, so my experience doesnt translate becuause the losses are different.

Electorials

Wed Jul 04 2012, 12:43PM

Registered Member #5457 Joined: Mon Jun 25 2012, 06:42PM
Location:
Posts: 14

Allright,

So it seems the zener in wrong polarity didn't kill the mosfet's gate.
(probably because it was pulled to ground all the time when the other mosfet kept conducting).

So that's good news!

But the bad thing is that the circuit draws a LOT of current, testing at 15V, and the mosfets get just as hot as without zero voltage switching.
So it doesn't look like it's working. Also, heating up material with the induction coil goes just as slow as with my simple pwm controller (non zvs)
and it draws like 4 times more current for the same result. Which is totally not what I expect from a nice zvs driver.
The heat sinks are not connected to each other.

I don't know what inductance my coil on the print board is, but I've included some pictures on which you can see it.
The coil gets too hot after 15 seconds. Then I need to stop the driver because else it would overheat.
Same goes for the mosfet's heatsinks. They are small indeed, but at zero voltage switching they should at least last for more than 15 seconds.

The capacitor that I used was a big gray 1ÂµF MKP capacitor (440v) from Vishay. It doesn't even get warm at all, so Or it's just a very good capacitor,
or it's because the circuit isn't working like it should.
I also tried with two of those capacitors in series, and also tried with a 120nF 400V smaller capacitor. Also the same, or worse result.

All pretty odd :/

Some more information: the big resistors are 2 or 3W 470ohm.

13.5 ohm for the two tiny resistors to bring the gates to ground (instead of 10k resistors, but this shouldn't be any problem)

Zener diodes: 1N4742A-TAP high power 12V zener:

Diodes: BYV27-200-TAP ultra fast recovery:

MOSFETS: SIHG73N60E power mosfet:

rdson: 39mOhm
ultra low gate charge
and a suggested application in the datasheet is induction heating.

I hope you can do something with this information.

Pictures of my setup:

Greetings,
Electorials

m4ge123

Wed Jul 04 2012, 02:11PM

Registered Member #4118 Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140

The inductor you're using looks like a common-mode choke pulled from a mains input filter. Try using an iron powder one instead. The ones you can commonly find are yellow with a white bottom (#26) and green with a blue bottom (#52).

Electorials

Wed Jul 04 2012, 02:56PM

Registered Member #5457 Joined: Mon Jun 25 2012, 06:42PM
Location:
Posts: 14

m4ge123 wrote ...

The inductor you're using looks like a common-mode choke pulled from a mains input filter. Try using an iron powder one instead. The ones you can commonly find are yellow with a white bottom (#26) and green with a blue bottom (#52).

I can't seem to see the difference between ferrite and iron powder cores. They look just the same to me :/
but I got these two inductors:

The blue one I have already tested, and the results are just as bad as with the toroidal coil.
The black inductor does the same; also doesn't work.

Update:
If I try this driver with a flyback transformer, the spark isn't big at all, but it sounds like it makes a 50Hz buzz
(probably because it draws so much current from my supply that the flattening capacitor gets discharged too quickly)

Forty

Wed Jul 04 2012, 03:16PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

The test I usually use to see whether a core is powdered iron or ferrite is to scratch through the coating in a small place (on a toroid) and see if you can scratch the core as well as see what color it is. Powdered iron will be softer, easier to scratch, and a lighter color usually. I've seen some antique ferrite cores that are kind of flaky, but most modern ones are super hard.

Electorials

Wed Jul 04 2012, 03:22PM

Registered Member #5457 Joined: Mon Jun 25 2012, 06:42PM
Location:
Posts: 14

It looks like pretty hard to scratch both of those coils.
But I don't think I have any other :/

Would it really be so bad to use a ferrite core?

Ben Solon

Thu Jul 05 2012, 05:08AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Ferrite will saturate almost immediately, so it's no good for any application with even small dc currents.

If you get an arc, no matter how small, then it is switching(even if it is poor switching). One problem that popped up in my igbt zvs is that when one device broke in such a way that it didnt conduct, the other would maintain some switching which could be seen on the collector/drain as a half sine wave.

Do you have a scope? Try to find some way of measuring what's going on. It would. E the easiest way to see what's going on. As of right now the only thing that comes to mind is that one fet is eternally on and heating, causing sagging of the power supply, while the other switches normally. This would explain the low power arc with 50hz buzz- class a operation amplitude modulated with the dc link ripple. Can you check that again just to make sure?

Electorials

Thu Jul 05 2012, 08:51AM

Registered Member #5457 Joined: Mon Jun 25 2012, 06:42PM
Location:
Posts: 14

I don't have a scope :/
but if one FET is stuck and the other switching, then the one heatsink should get a lot hotter than the other. But that doesn't happen; the produced heat in both heatsinks seems identical.

Update:
I connected the two Gates to ground, and then applied power to the circuit.
No current flows trough the mosfets.
This means they are still in tact, and are not stuck in their Conducting state.

DC voltage across the capacitor while operating is 13mV. -> good right?
AC voltage I cannot measure since my multimeter is made for 100Hz max.

Another update:
Woaah! I'm getting somewhere!!

This is what was the problem:

The coil on the right was the one which I used to use for induction heating.
I thought like "it's a small driver, so I need a small coil"
and by the way, I always read everywhere that I needed like 5-6 turns on each side

That turns out to be totally wrong. I've just tested it now with the new coil (on on the left in the picture)
and the current is a Lot lower now, and heating goes super-fast :D
It has 8 + 8 turns, and the diameter is a lot larger.

Only thing I still need to work on is the inductor on the print board. That one still gets too hot after 20 seconds.
I think it just needs to be an inductor with thicker wire, but I don't have cores which are large enough for fitting some thicker wire windings :/

Finally it's starting to go in the right direction :D

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob