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Commercial pulse transformers instead of Fair rite 78 toroids?

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LAN_403

Tribologist

Sun Jan 11 2009, 10:29PM

Registered Member #1879 Joined: Mon Dec 22 2008, 04:11AM
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Posts: 40

I did not have any Fair rite 78 so I took a toroid from an old power supply. No idea about composition but when I hooked it up to the USS3732Z pair I got reasonable secondary current when driving the 5.1Ohm resistor so I decided to try it. Seems to work ok so far. I just realized that the mini brute uses 1:2:2 winding. I use Stve Wards 1:1:1 but it seems like it is able to drive the 40N60 anyway. I' re-building it after a arc over to the primary. I will measure the gate voltage more carefully next time around.

I did however find some Murata Pulse transformers 78602/2C

Are they useful as gate drivers? They would look nicer and take less room.

HV Enthusiast

Mon Jan 12 2009, 02:31AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Commercial transformers usually have an enormous amount of leakage inductance. Typically they're no good for this type of use, regardless of what "current" you measure. The more important parameter is what the pulse actually looks like at the IGBT gate.

You also have to look to see if its saturating or not as well.

From a first look, these aren't going to work. You'll need to wind your own.

Tom540

Mon Jan 12 2009, 09:58PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Dr. GigaVolt wrote ...

Commercial transformers usually have an enormous amount of leakage inductance. Typically they're no good for this type of use, regardless of what "current" you measure. The more important parameter is what the pulse actually looks like at the IGBT gate.

You also have to look to see if its saturating or not as well.

From a first look, these aren't going to work. You'll need to wind your own.

Yeah they tend to suck big time. Even the ones meant for driving fets i sampled were HORRIBLE.

HV Enthusiast

Tue Jan 13 2009, 12:41AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Well, they suck because they are designed more so to transfer signals, not power as in the case of driving large MOSFETs and IGBTs.

Typically, you'd have an isolated source to drive the MOSFET or IGBT and just use fiber optics or a gate transformer to send the drive signal over. But to simplify things, we go BRUTE force and drive the MOSFETs / IGBTS directly in most instances except for the largest of IGBTs (i.e. CM600's)

Tom540

Tue Jan 13 2009, 01:03AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Most of the commercial GDT's are made on pot cores. Some of us drive all including the cm600's with GDT's, big GDT's.

hvguy

Tue Jan 13 2009, 06:22AM

Registered Member #289 Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154

Pulse Engineering,

, makes some really nice, low leakage, GDTs. Check out the P0584. I have used this many times to drive CM600s in DRSSTCs.

Tom540

Tue Jan 13 2009, 05:33PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Their website isn't loading for me. Speaking of driving cm600's etc, how is that coil of yours doing? made any recent changes on it?

Tribologist

Wed Jan 14 2009, 12:20AM

Registered Member #1879 Joined: Mon Dec 22 2008, 04:11AM
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looks like the P0584 is nothing more than a toroid on a plastic base anyway. I will take a closer look at the gate as soon as I get the unit back together. I decided to goahead and build some boards with the shut down logic and current sense and also implement the CT as feedback. Up to now I have been using Ward's antenna based design. I probably skip the temp monitoring for now.

Where can I buy the Fair-rite core?

Ulf

Tribologist

Wed Jan 14 2009, 12:25AM

Registered Member #1879 Joined: Mon Dec 22 2008, 04:11AM
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Posts: 40

Can I simply drive the Gate enable at the approximate frequency (240kHz) without providing power to the IGBT when checking or does the Uce come in to play?

Ulf

hvguy

Wed Jan 14 2009, 07:29AM

Registered Member #289 Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154

My large coil is currently collecting dust since the weather is less than ideal for out door coiling (14F right now). I have been spending most of my time working on high power (+5KW) SSTCs.

Those transformers really do work well, and yes Tribologist, they are just a toroid with wire around it in a plastic mount, what did you expect?

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