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Experimentonomen

Sat Aug 11 2007, 08:32PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

How high current igbtÂ´s are needed for a tiny drsstc, ones that max do 120A pulse wonÂ´t work, eh ?

I got alittle tempted to mame a small drsstc outta a small secondary i wound that is around 1-5MHz.

Would this schemo work ? I sampled some UCCÂ´s so iÂ´ve changed the schemo.

mod edit-oversized images and double posting

CT2

Sun Aug 12 2007, 05:52PM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

1-5MHz is really high for a DRSSTC, but someone on this forum made a really small one so maybe you can look at his to get some ideas. Link If it is really that small then I bet those IGBT's could be made to work with that current rating, getting them to work at the MHz range will be a tough though. Good luck!

Experimentonomen

Sun Aug 12 2007, 05:59PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

These are mosfets, NOT igbtÂ´s! I have two secondaries i could use, either that small MHz one, or a larger one that swings at around 700KHz.

Anyway would the topology in the schemo work ? I borrowed JimÂ´s schemo and modded it abit, would my way of faking a enable pin work ?

Steve Conner

Mon Aug 13 2007, 09:18AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

No, IGBTs will very probably not work in the MHz range, for fundamental semiconductor physics reasons.

Reaching

Mon Aug 13 2007, 09:56AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

meh.

i dont know if switching supply voltage to driver ics with a few hundred hz is common. there are many other ways to interrupt the signal without switching the driver ics on and off. they have a turn on time or a power on time.
why not use a nand gate like a 7400?

you can use on input of a nand for your hf signal, the other input of the nand for your inerrupter, ant voila, the output of the nand is your interruptet hf signal. put a second nand behind that to reinvert the signal for active low.

i build many drsstcs that uses the same principle and they all work without problems. at the moment im on a discrete brick driver and the control electronics are just the same

Experimentonomen

Mon Aug 13 2007, 10:58AM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

As i said in an earlier post, i fixed some UCCÂ´s instead, i will probobly also skip using the small secondary and go with the one i used in the vttc.

The main question however was if my alterations to jimÂ´s circuit would work. Will it or will it not ?

Reaching

Mon Aug 13 2007, 11:40AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

i doubt that it would work. cause the driver ics need say 100ÂµS to fully turn on when enabled with supply voltage, the hf signal within this time is low current an d low voltage, causing the gdt to go mad, and the bridge too. you wont have fun with this circuit, even if it seems to work

Experimentonomen

Mon Aug 13 2007, 01:32PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

I said im gonna use a coil below 1MHz!!!! without topload the secondary is around 700-900MHz, which with a topload should be 400-500KHz, i even bought a large secondary on ebay that resonates @ 275KHz (bought mostly for performande comparison between my diy ones and a factory made one.)

Btw the original circuit is for a tiny drsstc that runs on several MHz, check JimÂ´s drsstc build featured on the 4hv main page, then tell me my coil thatÂ´ll be 3 times larger wont work.

Seriously i am beginning to question the seriousness of this forum, others make stuff that works nicely, but when i take their schem and just move some components around or convert from fullbridge to halfbridge, i get told the components cannot handle the freq and wont work.

And for the CT, i am going to put a burden on it and bias the schmitt trigger just before it turns on to reduce trigger voltage.

Reaching

Mon Aug 13 2007, 02:42PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

i didnt said that a coil at those frequencys wont work. i said i doubt that your interrupter circuit will work, cause the tc4422 have no enable pin, you want to enable them with the supply voltage of the ics.
i said nothing about your halfbridge or feedback circuit or so, only about the parts you added in the shematic.
look at others shematics and compare to yourself. your idea would definatly not work.

yeah, and blow your parts away cause i think you missunderstand some of the members good meanings. so learn by yourself and not from others, try it out...

the first question i tell myself when a member says that my circuit wont work is; why? so i answered yours.

Experimentonomen

Mon Aug 13 2007, 02:56PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

also i said that i have SAMPLED SOME UCCÂ´S WHICH HAVE AN ENABLE PIN as i scrapped my idea of using transistors to chop the Vss of the TCÂ´s. but since everyone is complaining that the circuit wont work, then heres another cidcuit:

link

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