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Did I kill my MOSFETS? (ZVS)

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Tonic

Wed Jul 18 2007, 08:26PM

Registered Member #528 Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166

Sorry for hijacking topic, but would these transistors be suitable for ZVS driver?

IXFH 6N90
Datasheet:

And what parameters in datasheet are important?

Marko

Wed Jul 18 2007, 08:39PM

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

Tonic, if you want to run a royer directly from 230V mains, rather find a 1200V or more rated mosfet. 1000V isn't enough.

I guess you might want something like this, although it probably isn't cheap.

Tonic

Wed Jul 18 2007, 09:44PM

Registered Member #528 Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166

This transistor is the most high-voltage rated MOSFET I can find in my country in low price :( I can buy it for 1.8$ and this price sounded reasonable for me. About main supply, I didn't think about this - I remember 4xVin rule :) I'm thinking about rewounding MOT for 220 DCV.

So, is it suitable? And what parameters are important, with exception of voltage, current, heat dissipation, Rds, fall and rise times?

Myke

Thu Jul 19 2007, 01:11AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Make sure the inductors don't saturate by adding more turns or by changing the core material (ie. air for the energy storage inductor). the MOSFETs might heat up quite a bit at the powers so have a big heat sink. Really thick wires are needed to handle the current.

Sulaiman

Thu Jul 19 2007, 01:30AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Here in UK with 230Vac supply, I intended to make a zvs work directly off the rectified mains
I have some 1200 V 50A igbts and some 1" x 1" x 4" ferrite blocks for the transformer;
I calculated that even with such large ferrite blocks it's not really practical because
the number of turns required to prevent core saturation results in such relatively high inductance
that the available power output wouldn't be worth the effort.

I shall however be making a zvs running directly off the mains soon (a relative term for me)
but I shall be using copper tubing and air (It will be a Tesla Coil primary)
the series / dc inductor is quite large though.

This is one case where careful thought IS required before construction.

Shaun

Thu Jul 19 2007, 07:04AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

I was hoping to get mine into the kilowatt levels with an MOT rewound for around 35 volts, some nice thick wire/solder, and one of my BIG heatsinks (weighs 2 kg!) I have seen someone on youtube do it, with nice results.

I was trying to think of a way to get around the half-wave rectification in my monitor flyback; I was thinking I could wind my primary on two flybacks, but with one upside-down so as not to waste the other half of the wave. Then I could just parallel the + and - of each. This is just something I thought up to double the power, as I want to get as high as possible (in watts

) Has anyone done this before, and is it correct in theory?

Myke

Thu Jul 19 2007, 07:27AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

No it wouldn't work because of how the diodes are arranged. it would be connecting the positive to the - in parallel resulting in a short. You could get it to make a rectified full wave by having the pris wired in anti parallel so that the other half of the cycle is also rectified. At KWs the flybacks you pull from a TV or monitor don't last that long because of internal heating/arcing. The best way to get AC and possibly get KW of power out is by winding your own flyback.

Shaun

Thu Jul 19 2007, 07:32PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

No, I was thinking something like this. I think you might have misunderstood me.

EDIT: oops, reverse the + and - on the HVDC out

Sulaiman

Thu Jul 19 2007, 08:34PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

That is a good arrangement
it balances the load on the primary
and the output will have less ripple (if that matters)

Marko

Thu Jul 19 2007, 08:54PM

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

Hey sulaiman,

[blockquote]Here in UK with 230Vac supply, I intended to make a zvs work directly off the rectified mains
I have some 1200 V 50A igbts and some 1" x 1" x 4" ferrite blocks for the transformer;

[/blockquote]

IGBT's will work with ZVS, but not as well as mosfet's. 1200V mosfets even of mild current rating would be more grateful because of IGBT's slow taily turnoff.

That is one nice of a transformer, and if I needed to use IGBT's on it, I would go for a series loaded ZCS. You could go with cheaper, smaller, 600V IGBT's and still be very happy.
This would probably be most efficient solution since HV mosfets still aren't too developed.

I calculated that even with such large ferrite blocks it's not really practical because
the number of turns required to prevent core saturation results in such relatively high inductance
that the available power output wouldn't be worth the effort.

You are sure in your calculations? Believe me, lights will go dim. You will need to balast such a thing if you want a jacob's ladder..

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