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ZVS Fly back driver PCB and updated schematics

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LAN_403

Dr. Dark Current

Fri Jun 08 2007, 10:02AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

just a small question, I haven't constructed this "improved" version of the driver, where do you wind the extra 3+3 turns? It is on the flyback core, air cored or on some external core? Thanks

Danielle

Fri Jun 08 2007, 04:40PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

on the fly back core but the PCB isn't updated I have a new one now ill post later.

Danielle

Sat Jun 16 2007, 06:50PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
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Posts: 267

I finally finished the board and I have driven the fly back I can drive it at 1- 120V the IGBTs blew at 100v I think a combination of transience and over current the arc looked like a MOT arc at full power take a look at the pics I think I put it together well I like it that I can run it at all voltages the arc is when I had it at 10v.

Danielle

Mon Jun 18 2007, 04:03PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
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Posts: 267

Hi I have been experementing with this and now I just keep plowing IGBTs should I ad more turns around the primary of the flyback or should I have it connected to an inturupter? Thanks for the help.

...

Mon Jun 18 2007, 04:55PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

You should learn how the circuit works so you can fix the problem.

To start, keep in mind that the switches need to be rated at at least pi (3.5x) times the input voltage, assuming that everything is in tune.
From there I would suspect you wimpy series choke, I for high power runs I would say you need way more turns.
From there you can look for core saturation, which can be best found by running the circuit off an isolation transformer and scoping across the tank cap, and making sure it is a nice clean sine wave.

Marko

Mon Jun 18 2007, 11:19PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Guys, everyone, how do you expect massive 30N60 IGBT to work properly with 470 ohm gate resistors? HGTG30N60a4d has at least 15nF gate capacitance wich gives RC time constant of 7 microseconds!

At typycal frequencies I would imagine you to run the royer this could be more than half of period, so your IGBT's probably aren't turning on at all!

For such large devices you need really small resistors and dissipate huge amounts of power (wich is a natural trait of such gate drive system).

For those IGBT's you will need something around 20ohms, not more that 33 ohms to get fair rise times close to their delays and each resistor needs to be 10 Watt beast.

In such occasions I would probably place a driver chips on IGBT gates and pull their inputs up with high value resistors to keep things nice and cool.

I also don't understand those LR 'snubbers' (or whatevewr they are). They seem to originate from hvwiki but I really don't see a point in them except burning additional power.

Colin 99

Thu Jun 21 2007, 03:04AM

Registered Member #192 Joined: Fri Feb 17 2006, 03:08AM
Location: Canada
Posts: 44

I see your point! My ZVS works well but I'm generating alot of heat off the the heatsinks and big arcs. I'm using 30N60s on my ZVS driver too, but if I used 20 ohm gate resistors, it would require hugh zeners, (I'm using a 36 volt battery supply). Obviously the circuit (gate driver) would have to be modified to allow for fast gate charging. I've heard of other people using a separate supply for the gates, maybe that is the way to go. Does anyone have suggestions?

If we could turn on the 30N60s faster; they might not dissapate as much heat.

BTW: I think those LR snubbers that you are refering too are suppose to be a second (3 +3 turn) primary, but once you add 100 ohms in series with that, I can't see how it's suppose make the ZVS better.

Marko

Thu Jun 21 2007, 09:01AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Yeah, you should definitely use another low-voltage supply for the zeners.
Something between 12-15V is ok.

But *still* you are going to need really small high-wattage resistors to charge the gates quickly enough. Still, if I already have separate power supply I would just go with gate drivers.

Danielle

Fri Jun 22 2007, 08:57PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

I lowered the resistance on the gate and I am going to try it with a gate driver chip but when I put a scope on the gate I don't see anything and the arc goes away. I also won't be running it strait from the 12v supply. I have separate supply currently and now am using a 35A 1000V full wave rectifier because the 8 A blew apart for my high current one. I did think of using a 5.2 ohm 5W on the gate but decided it not necessary, but as the IGBTs heat up and blow I am going to try that. The best arcs so far were 6" at 64V 7A and then the IGBTs both blew.

Marko

Sun Jun 24 2007, 06:53PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Rocketry you can't use the oscilloscope on that circuit without isolation transformer, you are creating a short by grounding the mosfet sources.

Also, your power draw at 64V is insane. That is almost 40V/turn wich i'm sure for that you are deeply in saturation considering your resonant cap value. Something like 10V/turn is still a lot but more reasonable. Check this out regarding saturation flux density.

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