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Marko

Fri Feb 10 2006, 03:58PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I heard a lot about using SCRs in high-power SMPS supplies, but i have no practical schematics or some explanations.
They obivously need to operate at high frequencies and fast turnoff seems impossible to acheive
(using transistors for shorting maybe, or DC blocking capacitors to tear down voltage across, maybe GTO SCR are needed, does somebody have experience with that !dodge
It would be supreme if frequency could go for ~100khz, and drive monstrous TC in double resonant (SCR are still far powerful than IGBTs)

Seems impossible to me as turnoff is very slow, and I havent seen any real schematic of high-power SMPS..???

Just wondering if somebody has experience.

Steve Conner

Fri Feb 10 2006, 05:16PM

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

For frequencies above roughly 25kHz, IGBTs perform better than GTO SCRs. The GTO has a much higher peak current rating, but you can't use this capability at high frequencies, because it also has a much lower di/dt rating than the IGBT. Non-GTO SCRs have a lower di/dt rating still.

It turns out that you can buy surplus IGBT blocks easier than surplus GTO SCRs, too B) and they are more than powerful enough to drive any Tesla coil that any of us has the space and money to build. So IGBTs are our weapon of choice.

Marko

Fri Feb 10 2006, 06:14PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Yes I am aware of that but Im interested how-to, use thiristors (non-gto) most preferably for high power SMPS suplies, al IGBTs do not exist in my country and SCRs (low power) can be bought easily (and cheaply)
If not in TCs i would stay in lower frwquencies, SMPS (high and low voltage) below 50khz...
Maybe I could draw a SCR flyback driver schematic... I have idea to use two SCR and DC blocking capacitor, problem is preventing them to be open both at once..?

Dr. Shark

Fri Feb 10 2006, 07:05PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Where do you live? If it is not too exotic a place I am sure someone from the board would sell you a bunch of IGBTs.
I really dont think SCRs are the way to go...

Marko

Fri Feb 10 2006, 07:18PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

In croatia IGBTs are treasure, i would hang myself if I burn one, after paying sick prices...
Il try to get few trough school and save them for DRSSTC, if I burn them %-6 %-6

Dr. Shark

Sat Feb 11 2006, 03:22PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Well, I just killed 4 IGBTs this afternoon, so I guess I might as well sell some to you. I am in europe too, so I guess there must be a way you can pay for them?

Marko

Sat Feb 11 2006, 06:01PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Il try to get something at school, 200SA600 are bricks but small enough, possible are 30N120 and 40N60 (transistors)...

Its off topic I didnt came here to buy igbts, yust anybody doesnt have a little information (or link maybe) about using SCRs in SPMS applications (just asking..?)

...

Steve Conner

Sat Feb 11 2006, 08:07PM

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

The only switched-mode power circuits I know of that use SCRs, are induction heaters. However the basic circuit is the same as for any other kind of inverter. Dan's Workshop has a page on them that shows circuit diagrams. This is not too easy to find with a search engine: I stumbled across it a couple of months back while looking for something totally unrelated. So I will spare you the "Google Pounce" and I hope the other moderators do the same.

Look down near the bottom.

I have no personal experience with these circuits, except once, when I got a SCR dimmer circuit to oscillate at several kHz by accident.

PS- I have seen board members in Italy and Romania using the Siemens BUP314D IGBTs. I think they are about 7 euro a piece.

Marko

Sat Feb 11 2006, 08:37PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Its connected just like any transistor would be, how did they get sure that SCR doesnt stay shorted trough that coil (doh?)
Il try to do some tests with DC blocking cap and 2 thyristors soon (something like circuit found in atx supplies)

Thanks anyway conner :)

So I will spare you the "Google Pounce" and I hope the other moderators do the same.

I would really not ask without torturing google first... :)

Steve Conner

Sun Feb 12 2006, 11:33PM

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

The circuit is the same as for a transistor, but the load is special. Because it's resonant (contains L and C) the current is supposed to reverse of its own accord and turn the SCR off.

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