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Help understanding and deciding on DRSSTC

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Ken M.

Sat Apr 12 2008, 10:17PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

So basicly attempting to make a DRSSTC with a 2"x8" secondary, and trying to use TO-247's, just won't happen..huh?

I was thinking a TO-247 style would work as far as switching since Wiki mentions FGA40N60UFD

and if its max switching speed is = to the inverse of all the Rise and fall times as well as delays it ~should~ handle 3.6MHz. Even though I can still see where you are going, in the fact that the faster you make something switch the faster and hotter it gets.

However if my theory holds (unlikely) then that would mean that this IGBT

Could work since it could switch at ~4MHz, this one I especialy think could work since it can handle 200KHz @ 390V 18A and I think if I'm only gonna push or trry to push 70V max then it could run at 400KHz at 50A or more, This one

is slower but could still handle 3MHz.

HV Enthusiast

Sun Apr 13 2008, 12:15AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Take a look at Figure 4 for the datasheet.

Ken M.

Sun Apr 13 2008, 02:13AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

OK so for:

FGA40N60UFD @ 400KHz 300V only about 2.5A
HGTG30N60A4D Doesn't even look like it can handle 300KHz but For 390V @ ~290KHz 8A
OK the other one is a mosfet....

So it looks like non of these can handle it....But waitI was looking at Ward's Schematic for his .5 DRSSTC which is what I'm basing mine on and it shows him using HGT1N40N60A4D

And As far is it looks My choice of HGTG30N60A4D

and it seems to be the closest I can find in a 247...even though you said it won't work, but it can handle more power dissapation.

So then what would be advised?

Bennem

Sun Apr 13 2008, 01:20PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Ken,

My last three DRSSTC's (also based on Steve Wards design)
used the HGT1N40N60A4D IGBT and operated at
200KHz, 360Khz and 450Khz and work fine with that IGBT.
Though as Dan said the losses are greater at this high frequency.

Mel

bob golding

Sun Apr 13 2008, 06:03PM

Registered Member #1084 Joined: Mon Oct 29 2007, 08:58PM
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Posts: 28

hi ken,
filter caps

Ken M.

Sun Apr 13 2008, 06:25PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

With the execption of a variac, and or The various electronic Variacs is there any SIMPLe way to avoid or less'n inrush currents, Like Ward I'm making my DRSSTC to be portable and easy to setup, basicly a small portable table top model without lugging around a variac or making a some what complicaticated electronic variac.

As for the IGBT's, I can't use a TO-247, and that I'm stuck forking out a good bit of cash for some Isotops?

Josh Johnson

Sun Apr 13 2008, 09:41PM

Registered Member #793 Joined: Sun May 20 2007, 06:50PM
Location: Minneapolis, MN
Posts: 35

Just to be clear in the 'inrush current' has nothing to do with the IGBTs or any part of the switching circuitry. It's between the supply caps and the wall.
Here is your circuit during run-time and then what it looks like just after you turn-on the supply.

The uncharged capacitors appear to the wall as dead shorts so a huge amount of current rushes in to charge them. a.k.a in-rush current. The current gets less as the caps charge.
To reduce in-rush current you can add an inductor (choke) to the input say where F1 is in the circuit. Actually the transformer you have shown in your circuit will help to limit in-rush but I don't think it will give you enough power.
Also you can put a resistor where F1 is and switch it to a short circuit with a relay when the caps get charged enough.

HV Enthusiast

Sun Apr 13 2008, 09:44PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Ken M. wrote ...

With the execption of a variac, and or The various electronic Variacs is there any SIMPLe way to avoid or less'n inrush currents, Like Ward I'm making my DRSSTC to be portable and easy to setup, basicly a small portable table top model without lugging around a variac or making a some what complicaticated electronic variac.

As for the IGBT's, I can't use a TO-247, and that I'm stuck forking out a good bit of cash for some Isotops?

As long as you have big capacitors on your DC power supply, inrush current is going to be an issue.
You'll have to deal with this some way or another.

As far as output control goes, you can always vary the pulsewidth from 0 (OFF) to your full pulsewidth.
Just keep in mind, in this scheme, its not turning the coil on SOFT. If you have a problem, you are still applying full voltage across your bridge
even at short pulsewidths, so its still has the possibility of BANG.
With a variac, if there is a problem, you can usually sense it at very low voltage first.

To be honest, no reason not to get a variac. Its probably one of the cheapest components in a DRSSTC. You can get a used one for less than $50.00 on EBAY.

Dan

Tom540

Mon Apr 14 2008, 04:38AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Hmm, I would say that you should definitely use to-247 IGBT's on a small coil like that. The hgtg20n60's are going to be better than the 30n60's because for some reason they have a higher pulsed current and can run fine at 400Khz.

About that circuit you're using. There is absolutely no reason to use the 74HC109 flip flop. It costs more than a 74HC74 and has more pins that aren't being used that will just be tied high. The hc109 is a more specialized flip flop and has extra states but for the DRSSTC controller they aren't needed.

I'm not even sure you'd need a variac for a coil that small. Your bus caps will not need to be that big.

Ken M.

Mon Apr 14 2008, 09:10PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

I only had the HC109 cuz thats what Steves Schem had, I though the same thing after looking at teh datasheet, I'll see what I have sitting around but iff not I can always try TI's samples again =P.

Also, Whats the difference between N-Channel IGBT's and, IGBT's?

One other thing Because I'm looking to make this be VERY neat and tidey, I'm gonna try and use Dan's Express PCB company and would have 2 extra boards for the driver and power section, maybe even an interruptor boards but haven't gotten that far, So If anyone would be interested gimme a PM. I haven't orderded them yet, haven'tr even set them up yet TBH.

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