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 Posted: Mar 08, 2012 - 01:17 PM |
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Joined: Nov 01, 2005
Posts: 6323
Location: Hilversum - the Netherlands
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jayjay1974 wrote:
Plons wrote:
The 1000V+ schottky diode
I don't think you need a Schottky diode , the 0.4V vs 0.7V drop difference is negligible at these voltages.
Agree. But the switching speed requires the use of a schottky. IMO. A fast recovery type is also an option. |
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Posted: Mar 08, 2012 - 01:35 PM |
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Joined: Jun 27, 2005
Posts: 3411
Location: St.Petersburg, Russia
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| In a boost converter straight to 1000, shouldn't the Vds of transistor also be >1000? I don't know, sounds weird to me. |
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Posted: Mar 08, 2012 - 01:50 PM |
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Joined: Nov 01, 2005
Posts: 6323
Location: Hilversum - the Netherlands
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svofski wrote:
In a boost converter straight to 1000, shouldn't the Vds of transistor also be >1000? I don't know, sounds weird to me.
Yep, the transistor as well.
@dak664: that's what I meant with "teh matrix"
I should stop posting after midnight. |
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Posted: Mar 08, 2012 - 04:20 PM |
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Joined: Feb 19, 2010
Posts: 507
Location: Montreal, QC, CA
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svofski wrote:
@hugoboss: because I want to use store-bought 12V (or 9V, or something) wallwart.
But.... Why? Because they look good?
You can still use multiple stage multipliers from 9V but loss is MUCH higher, and there are a LOT more components involved... |
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Posted: Mar 08, 2012 - 04:25 PM |
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Joined: Apr 25, 2006
Posts: 2296
Location: Germany
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I think going from 12v to 1000v directly with a boost
is not so easy, you have an extreme dutycycle.
I also have experienced difficulties in making HV
transformers since the parasitic capacitance of the secondary together with high inductance results
in a low resonance frequency, so you cant operate
at high frequency.
I would suggest a push-pull (two logic-level
MOS transistors primary driven by two non-overlapping PWM outputs from the AVR. This effectively doubles the input voltage. Then I would transform to 250V and use a voltage quadrupler.
(Been there, done that....)
Another remark: It may be that you need a 800V diode
for 400V rectification, depends on the configuration. |
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Posted: Mar 08, 2012 - 05:16 PM |
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Joined: Mar 17, 2005
Posts: 1305
Location: Stockholm, Sweden
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| If I can go from 5V (USB) to 800V with my small solution, it shouldn't be that hard to go from 12V to 1000V? |
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Posted: Mar 08, 2012 - 07:29 PM |
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Joined: Feb 19, 2010
Posts: 507
Location: Montreal, QC, CA
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The problem is not that you CAN go from 5V to 800V, it's mostly that you probably shouldn't, when there is a perfectly good 120V waiting in the outlet.
WHY WHY WHY would you want to take 120V, make 5V from it, then boost it back up to 800V, using 10x as many components??!?! |
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Posted: Mar 08, 2012 - 07:59 PM |
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Joined: Oct 30, 2002
Posts: 5718
Location: The Netherlands
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| You could make it portable then. How did they do this on camcorders that use a tiny CRT for the viewfinder? |
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Posted: Mar 08, 2012 - 09:01 PM |
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Joined: Mar 17, 2005
Posts: 1305
Location: Stockholm, Sweden
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| Probably as I have done. My solution takes 10 components or so, and takes up 2-3 square cm of PCB. Could be smaller if I wasn't interested in having the voltage settable and mesurable. |
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Posted: Mar 09, 2012 - 12:42 AM |
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Joined: Jun 27, 2005
Posts: 3411
Location: St.Petersburg, Russia
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| @hugoboss: because I don't like dealing with stuff in the wall, I prefer it when it's dealt with by certified professionals in the area. |
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Posted: Mar 09, 2012 - 12:47 AM |
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Joined: Feb 19, 2010
Posts: 507
Location: Montreal, QC, CA
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svofski wrote:
@hugoboss: because I don't like dealing with stuff in the wall, I prefer it when it's dealt with by certified professionals in the area.
Hmmm.. Well 800V DC isn't much safer TBH... 800V burns through skin, 120V AC just jolts you (unless you somehow decide to hold on to the wires)... |
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Posted: Mar 09, 2012 - 02:27 AM |
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Joined: Nov 19, 2001
Posts: 917
Location: San Luis Obispo
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hugoboss,
In the OP svofski wrote:
I know how to make 800V from 220V with a regular isolating transformer...
220V is available, not 120V, all more the reason to avoid direct conversion from the line for the minmal power needed.
Stan |
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Posted: Mar 16, 2012 - 10:47 AM |
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Joined: Jun 27, 2005
Posts: 3411
Location: St.Petersburg, Russia
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I'm carrying on with the project slowly. So here's the pushpull transformer driver:
https://www.circuitlab.com/circuit/rk4g ... ullador-1/
Yesterday I tried it in real life. It worked nicely, up to some point. The MOSFETs that I had handy didn't have too much stamina, only rated for 20V BRVds. At 3.5 to 5V of input DC I had something like 100-140Vp-p on the output with my random-wounded toroid transformer, loaded on a 15K resistor. At 6V of input voltage the magic smoke was finally released. I imagined that the transformer would kickback at ~ double of input voltage, but what I have observed must have been at least a quadruple. Curious. The simulation doesn't show anything suspicious.
I'm waiting for some more durable MOSFET and I ponder meanwhile. Maybe I'll burn a few more of those puny ones just to see what exactly kills them. |
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Posted: Mar 17, 2012 - 12:38 PM |
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Joined: Apr 25, 2006
Posts: 2296
Location: Germany
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You sometimes can get some nice MOSFETs from old
motherboards. In a push-pull it is important
thet the primaty is very "symmetric", best
is to wind two wires bifilar (together) and the
connect them accordingly. Its also important to
drive the mosfets with enough voltage if they arent
logic level ones.
I am sure we had a thread here about that stuff
some years ago...
Good luck !
Here is the old thread, make 12 Volts from 5 was the application. There is some info about push-pulls
there.
http://www.avrfreaks.net/index.php?name ... ;start=400 |
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Posted: Mar 17, 2012 - 06:17 PM |
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Joined: Jun 27, 2005
Posts: 3411
Location: St.Petersburg, Russia
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The symmetry indeed appears to be an issue. I now have a pair of good old IRF630Ns pushpulling my rather nasty looking coil. Here it is so you could have a laugh:
The primary is 5+5, the secondary is hell knows how many. I picked a coil that I used in some of my previous experiments.
Anyway, running at 80kHz, the smoke does not get released immediately. One of the transistors always gets rather hot pretty quickly, while another tends to stay cool.
Such is the output:
And such is the the drain of the hot transistor:
And the cold one:
 |
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Posted: Mar 17, 2012 - 07:10 PM |
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Joined: Jun 27, 2005
Posts: 3411
Location: St.Petersburg, Russia
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| Update: bifilar-rewound the primary. Running at 80kHz now, both transistors are lukewarm. Awesome! Thanks ossi for the bifilar idea. |
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Posted: Mar 18, 2012 - 12:06 AM |
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Joined: Jun 27, 2005
Posts: 3411
Location: St.Petersburg, Russia
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As I'm moving on to the next step and trying to make the current design repeatable. Any hints on reducing the transients without dramatic redesign efforts? For the reference, after making the primary symmetric, both transistors see the former "hot" picture. A lot of energy seems to be wasted there.
I studied Peret's clock circuit a little bit. There are a lot of secondaries in the design. Initially I planned on getting what I have now, feeding it to a voltage multiplier and then just use a series of resistors to divide the resulting voltages into everything that I need. I'm not really comfortable with transformer design, so I'm trying to minimize the windings parts of the project. The currents in a CRT appear to be ridiculously small, so this plan should work, but what do I know.
Will the regular 4007 type diodes work fine in a multiplier at ~80kHz? |
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Posted: Mar 18, 2012 - 12:47 AM |
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Joined: Nov 01, 2005
Posts: 6323
Location: Hilversum - the Netherlands
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Quote:
Will the regular 4007 type diodes work fine in a multiplier at ~80kHz?
I am afraid not, Svo. The 30us recoverytime is the spoiler.
Nard |
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Posted: Mar 18, 2012 - 01:02 AM |
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Joined: Jun 27, 2005
Posts: 3411
Location: St.Petersburg, Russia
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| Yeah, I was looking at the same figure, Nard and it was worrying me. So I'm going to get some that have "Maximum Reverse Recovery Time: 200nS". I hope those will perform well. Oh dear! |
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Posted: Mar 18, 2012 - 06:26 PM |
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Joined: Mar 27, 2002
Posts: 850
Location: Athens, Hellas
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It is nice to see that you sorted things out! Now, Nard is right about the 1N40xx/1N54xx series; these diodes are too slow for such tasks. For Ultra-Fast solutions there are the UF40xx/UF54xx series at 1.0A/3.0A as well as the MURxxx family, all at 50ns/75ns/100ns. For lower or low voltage rectification with recovery times down to 1ns(!) I prefer the MBRxxx family Schottky diodes.
-George |
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