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Large DRSSTC [update]

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Linas

Mon Feb 13 2012, 03:41PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

I am using 1 (or 0,5R) in series to inductor, 15R shunt for LR , and 12T inductor (d=1cm).
CT was 1:200 (like Finn )
i don't have any capacitor in series, CT goes directly to ad790 2 leg with LR and R network.
is it possible to kill ad790 if input goes higher than supply, but still lower than max supply voltage ?
( maybe i have half dead ad790, since it working if i test with generator and not working in drsstc )
or maybe i have to weak feedback somehow, and ad790 can catch up, but making bigger resistance near ad790 made no effect, ( and i can see voltage difference with scope on +- leg respect to 0 )

ScotchTapeLord

Mon Feb 13 2012, 04:57PM

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

I would clamp the input to the supply voltage. It's possible that the inputs are clamped, but that is not suggested by the datasheet nor is it likely as the input impedance is very high. It either works or it doesn't.

This might be your problem. I imagine it's possible it applies to comparators as well as op-amps.

A lot of datasheets for comparators/op amps specify that they are immune to input-overvoltage induced phase reversal, though AD790's datasheet does not.
You don't need a very high voltage going into your comparator, especially if you buffer it with something from the 74hc series.

That's a nice comparator with a fast latch. I think I'll include it in my next Digikey order.

Linas

Mon Feb 13 2012, 05:44PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

no, this is not a case here.
i get nothing on output, maybe some time spikes, that's it.
I know that this driver was working with high power ultrafast igbt (1200V 400A half bridge bricks ) but with CM600 it just don't, and i don't know why

teravolt

Mon Feb 13 2012, 07:59PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi Linas. is this the prdictor circuit that you are using

The fasest I've ever had CM600's up to is about 100kz. how do they respond with your new driver

Linas

Mon Feb 13 2012, 08:25PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

teravolt wrote ...

hi Linas. is this the prdictor circuit that you are using

The fasest I've ever had CM600's up to is about 100kz. how do they respond with your new driver

i have around 40-50KHz Fo.
Yes, circuit is same, just have 1k resistors in ad790 for 5 leg to +5v.
ok, i found two differences, one is i have +-12V (instead of +-15V, it shouldn't be a case here)
and also i am using simple inductive resistors for LR network, not non-inductive like Finn did

teravolt

Tue Feb 14 2012, 02:56AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi linas, i asume all of your subsytems like fet drivers are turning your igbts on when the interuptor is going.I would check that first. are you getting a feedback pulse from the zero cross transformer. Is your phasing is corect to the AD790? If yes is the pulse making it to pin 7 you may have to adjust the threshhold on R10 as you are running the interupter. When your getting a pulse out of the AD790 you will have to make adustments to the 4 trimmers connectd to IC5 to get the feedback to the UCC37322. It might be a bitch make all those adjustmens on Finns circuit.

Linas

Tue Feb 14 2012, 05:54AM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

as i said before, it works with old Steve Ward driver.
And i have just 2 timing resistors and one for offset ( some don't use all of them, and still getting what they want )
Phase of CT is right, because after set of timing i reverse it, and do it again, with no luck

Goodchild

Tue Feb 14 2012, 03:32PM

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

You probably just don't have enough lead. Try adding some more L or R depending on the type of phase lead circuit you are using. I say this because your signal is not supper bad looks like it just needs a tinny bit more lead to we working perfectly.

Linas

Tue Feb 14 2012, 04:04PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Goodchild wrote ...

You probably just don't have enough lead. Try adding some more L or R depending on the type of phase lead circuit you are using. I say this because your signal is not supper bad looks like it just needs a tinny bit more lead to we working perfectly.

Problem is, that video was made with old fast bridge, i can't even get into osculation

teravolt

Tue Feb 14 2012, 05:15PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

does the CM600 driver work have you tested past 50khz?

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