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Can I use MOSFET or TO-247 IGBT to build a small DRSSTC?

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hsieh

Mon Feb 21 2011, 12:54PM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I decided to build a very small DRSSTC but I can't afford IGBT bricks.But I have a lot of MOSFET and TO-247 packaged IGBT like this

and

Can I use steve's DRSSTC.5 and replace the IGBT brick with TO-247 packed IGBT or MOSFET?I have ever seen some people do so, will this work?

Which driver is better?

thanks

Gregory

Mon Feb 21 2011, 04:47PM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226

Yeah! You can use TO-247 I'm able to do 90cm with a half-bridge of this IGBTs.. And I know people that make the same with MOSFETs, the IRFP260.

Keep the inductance high and the capacitance low, to get a high impedance tank circuit and low current peaks

I think the best driver is the DRSSTC-.5, or the steve ultimate driver..

ScotchTapeLord

Mon Feb 21 2011, 05:50PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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Posts: 635

Typically DRSSTCs use IGBTs. Small ones can certainly run off 247 packages. MOSFETs are much lossier at high currents, which is an important characteristic of the DRSSTC, so go with IGBTs.

dmg

Mon Feb 21 2011, 06:19PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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I wouldn't trust mosfets in a DRSSTC.
IIRC a mosfet has some decent on resistance, where power dissapated is given by I(squared) times (on resistance). so as you go up in current, your losses just get worse. (not linearly either, as for that squared part)

an IGBT however should act more like a diode when its switched on, so that your loses are going up linearly as the current your pushing in them increases, and will maintain a fairly level voltage drop.

Im not sure, but I think mosfets can't be run into saturation like IGBTs, if you saturate IGBTs (lowers that voltage drop) and have them soft switch (which DRSSTCs already do, hard switching them in a DRSSTC will have some pretty nasty effects, IE *boom*.), they deal far better with pulsed high currents then mosfets can. but carefull doing this, as the gate can fail easly if not properly protected (Keeping IGBTs saturated that is).

Luca

Tue Feb 22 2011, 08:47AM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

GBD wrote ...

an IGBT however should act more like a diode when its switched on, so that your loses are going up linearly as the current your pushing in them increases, and will maintain a fairly level voltage drop.

This is a common misconception about IGBT on characteristic... It is almost true only at very low currents, but If you look at the Vce vs Ic curve of any IGBT you realize that at high currents the voltage drop across C-E is neraly proportional to the collector current. So, even IGBTs have a sort of "Ron" which is much smaller than the Ron of an equivalent mosfet, for this reason the conduction losses are smaller.
Regards,

Luca

hsieh

Tue Feb 22 2011, 09:58AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

What Can I use if I can't find TVS diode 1.5KE220 in steve's circuit?
and should I connect a diode on C.E pin of my IGBT?

ScotchTapeLord

Tue Feb 22 2011, 01:41PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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Luca- The voltage drop does rise somewhat proportionally, but by a very small factor. For example, in this datasheet

the voltage varies from .5V to 4V in saturation... which is a small enough change where we can consider it constant. (4V @ 600A equates to .0067 ohms, whereas .5V @ 10A equates to .05 ohms, so the voltage drop is much more constant than the on resistance)

As for the TVS, I feel that they are very important. Many experience total failure soon after a blown TVS. I'd suggest using an equivalent voltage and power TVS elsewhere if you cannot find that specific model.

hsieh

Wed Feb 23 2011, 12:25AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

If I really can't find TVS diode,can I use Gas Tube Arresters?

Gregory

Wed Feb 23 2011, 01:05AM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226

I think not, because it will not work at the frequency of a DRSSTC. But you cab try with some normal 5W zeners..

Goodchild

Wed Feb 23 2011, 06:04AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

You know I have found that TVS is not really needed if you follow a couple of simple rules:

1. Keep your bus layout low inductance
2. Use good snubber caps close to IGBTs
3. Don't exceed 2/3 Max V of your IGBTs

I don't use TVS on any of my DRs or QCW for that matter and I have never had a failure from over voltage.

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