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Voltage doubler,tripler?

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LAN_403

Reaching

Mon Jul 17 2006, 05:10PM

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

okay i searched the web but, nothing i can use,.
i have some big 1200volt igbts here and wanted to build a huge isstc , .here in germany we have a 230volt line so i need a voltage tripler to get the full power out of these bricks. now i was searching for a good circuit for a voltage doubler or tripler but i only found example shematics nothing prooved and stable. with those voltages and currents i definately dont want to "try something" out . so what do you guys usually use in your drsstcs or sstcs? what type of diodes and caps should i use?

hope someone can help me, never needed a doubler or tripler before

Madgyver

Mon Jul 17 2006, 05:50PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Aren't these circuits tested well enough? Or is something wrong with them I am overlooking?

Steve Ward

Mon Jul 17 2006, 06:03PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

You only need a doubler for about 650VDC on 1200V IGBTs. The voltage spikes can be large, so you need the headroom. I would not exceed 800VDC unless you have a really good layout, including snubbers, and special low inductance bus caps with a laminated bus layout etc.. The style of layouts that most DRSSTCs use would not be suitable.

Reaching

Mon Jul 17 2006, 08:05PM

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

mh, okay, everything i wanted was a answer of someone who already build and used a voltage doubler, so he can tell me something about a good capacitor value or current and voltage rating of the diodes,

im so sorry that im not the best in math and cannot calculate everything on my own.

thanks for the help

Steve Ward

Mon Jul 17 2006, 10:18PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

For a large coil, the doubler and the DC bus caps are the same physical caps. Id suggest each cap be at least 350V and 5500uF or bigger probably. The diodes have to be rated for 700VDC, and at least the line current you plan on using (so maybe 20-40A).

The circuit that you want to use is the Greinacher doubler circuit (a) from the link Madgyver provided.

Sulaiman

Tue Jul 18 2006, 10:56AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

If you rectify 230 Vac you get about 320 V dc
A 320 Vdc supply for a CFPR Invertor ('Royer' or zvs) gives about 700 Vrms
that's about 1 kV peak, just nice for your 1200 V IGBTs.
No need for a doubler/tripler etc.

Steve Conner

Tue Jul 18 2006, 11:25AM

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

I used the Greinacher doubler as above to give 600V DC for my OLTC2. I used two 1200uF @ 400V inverter grade electrolytics, and a 92A @ 1200V dual SCR brick, driven by a home-made phase angle controller, in place of the two diodes.

Using SCRs like this allows the voltage to be adjusted without lugging a variac around. But of course plain diodes (with a PIV of at least 800V) and a variac work fine too. I drove the early prototype with a 10A variac and half of a 35A @ 800V bridge rectifier.

Later I added an iron cored choke in series with the AC input, to try and improve the power factor somewhat. The hardest I ever ran it was drawing about 30A RMS @ 240V AC and giving about 7A @ 550V DC out.

I was happy with this arrangement, it never gave any trouble at all. I had a 20A breaker on the incoming line, and if the DC bus got shorted, this always seemed to pop before the SCRs did.

So I'm going to use the exact same circuit for "Odin" except, like Ward says, I won't add any extra capacitors, because the main cap bank (4x 3300uF 420V in series/parallel) can also function as the doubler caps. I'll also not bother with the overcurrent trip that used to shut the SCR gate drive off.

If I wanted more voltage, I think I would scrap the rectifier and build a boost PFC like Ward's, rather than a tripler. If I wanted more power, I'd go to a 6 diode bridge running off 400V 3 phase. If I "Really" wanted to go nuts, I'd feed the 3 phase rectifier into the boost converter. But I think I'll have my hands full even with 600V and 4kW.

EDY19

Wed Jul 19 2006, 07:58PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

How do you go about figuring out the values for the capacitor values? I want to get about 660V (voltage quadrupler) and the current will not be more than 200ma- is there a formula for this?

Steve Conner

Wed Jul 19 2006, 08:09PM

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

The formula I used was "The biggest caps I can get for cheap"

Your tube circuit is low power, but because it's a quadrupler it needs bigger caps than a doubler would have, to avoid too much volt drop. I'd say 220uF or 470uF would be about right.

...

Wed Jul 19 2006, 09:33PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

And if you actually want to caclulate it the formula is given near the bottom of the page linked in the second post.

You just need to decide how much voltage drop you are willing to have, then work backwards to caclulate the values of the caps.

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