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Dr. Dark Current

Thu Aug 28 2008, 06:31AM

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

Well for marx gen and arc drawing you need current limiting anyway, so you can wind it like you said (secondaries opposite, primary in the middle) or the traditional way (secondary opposite primary).

rp181

Sat Sept 27 2008, 08:02PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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I finally got around to doing something, I wound two secondaries. Each has ~174 turns on 30AWG wrapping ware (not magnet wire, it has a thin PVC insulation. Coil form is 1.5in PVC. I have both secondaries across from each other.For the primary, i put 4 , each 3 turns each (12AWG). Two are under one secondary, the other two under the others. Would this method work? I wanted a split primary, then i could change the out put voltage by doing 1 pri, 1 sec, 1 pri 2 sec, 2 pri, 1 sec, etc. To drive it, i wanted to start with a half bridge of IGBT's, and upgrade to a full bridge later. would it be feasable to use these:http://www.st.com/stonline/products/ literature/ds/11731/stgw30nc60w.pdf, to run direclty from mains?

Dr. Dark Current

Sat Sept 27 2008, 09:47PM

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

rp181 wrote ...

would it be feasable to use these:http://www.st.com/stonline/products/ literature/ds/11731/stgw30nc60w.pdf, to run direclty from mains?

yes, but you'll need clamping diodes on the IGBTs.

rp181

Sun Sept 28 2008, 03:37AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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thanks for saying that, i also have stgw30nc60wd, but i didnt know the difference betwwen the two, the d version has a diode =)

Dr. Dark Current

Sun Sept 28 2008, 11:43AM

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

rp181 wrote ...

thanks for saying that, i also have stgw30nc60wd, but i didnt know the difference betwwen the two, the d version has a diode =)

They will work, but not to their maximum possible power because the diode is only 15A. For full powers I'd rather use the diodeless type and add an external ultrafast recovery one (>40A, 500V)

rp181

Sun Sept 28 2008, 02:37PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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i have a 30 amp 600v (i think) diode that im using for nothing that i can use. Would that explain over heating? My boost converter uses that IGBT, and gets very hot in a few seconds, would it work if i replaced with a STGW30NC60W and have an external diode?

Dr. Dark Current

Sun Sept 28 2008, 03:51PM

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

rp181 wrote ...

i have a 30 amp 600v (i think) diode that im using for nothing that i can use. Would that explain over heating? My boost converter uses that IGBT, and gets very hot in a few seconds, would it work if i replaced with a STGW30NC60W and have an external diode?

The internal diode should not present heating issues but rather an "early failure".
IGBTs DO get hot in e.g. flyback converters (boost converter falls into this category) because they switch with tail current that is related to input current, not output. Also because of high forward drop (>2V), they are not suitable for low supply voltages because they'll burn a lot of power. (Hopefully someone can explain this more clearly).
Try to replace it with suitably rated FET and you'll probably see big decrease in heating.

The diode should be OK if its a fast (preferrably ultrafast) type.

rp181

Sun Sept 28 2008, 06:47PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
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ive ran this IGBT before with the same boost converter and it didnt even get warm, but once i soldered it to a board, it gets hot. I think its because i forgot to put a voltage regulator, so the gate is only getting power from a 9v. This happned before, and when i switched to the comp PS, it ran cool.
Back on topic, for the driver was looking at TI's PWM controllers, would this be sutible?
UC28025N
or
UC28023N
It says ones for full bridge (25 one)

Dr. Dark Current

Sun Sept 28 2008, 07:00PM

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

rp181 wrote ...

ive ran this IGBT before with the same boost converter and it didnt even get warm, but once i soldered it to a board, it gets hot. I think its because i forgot to put a voltage regulator, so the gate is only getting power from a 9v. This happned before, and when i switched to the comp PS, it ran cool.

9V is too low, the IGBT does not turn on fully and wastes power in the linear region. I prefer to use 15V or more for the gates.

rp181 wrote ...

Back on topic, for the driver was looking at TI's PWM controllers, would this be sutible?
UC28025N
or
UC28023N
It says ones for full bridge (25 one)

You understand it will not drive the bridge directly, and will need low/high side driver (GDT etc.), right?

I would use a SG/KA3525 or even the classic TL494, with the outputs boosted with gate drivers and fed into a GDT.

rp181

Sun Sept 28 2008, 07:56PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

Ya, i was going to put it throught a gate driver and a GDT. Will it affect the ferrite core if i clamp it together with 2 aluminium bars and 2 threaded steel rods?

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