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Old 9th August 2005, 07:16 AM   #31
subwo1 is offline subwo1  United States
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Quote:
Originally posted by mzzj

Hint: look for used oil burner ignition transformers, 10kV (+-5kV center-tapped). Or neon light transformers.
Could a flyback transformer work if the primary drive were adjusted to lower the voltage as needed?
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Old 9th August 2005, 07:32 AM   #32
Eva is offline Eva  Spain
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It would work but I want 50Hz AC. Anyway, I have remembered that someone gave me an old neon lighting transformer some time ago and I have just found it (under a pile of other scrap stuff). Should it be in good condition most of the work would be already done
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Old 9th August 2005, 07:56 AM   #33
subwo1 is offline subwo1  United States
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Sometimes things in those piles of old parts come in handy. I have numerous previously wound toroids, e-cores, etc. and various and sundry parts which I have accumulated. It is nice being able to maintain as much momentum as possible and not be delayed when trying out design ideas.
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Old 9th August 2005, 09:15 AM   #34
mzzj is offline mzzj  Finland
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Chocoholic, what do you use for "operating voltage" for half-bridge or flyback?
" the actual r.m.s. or d.c. value shall be used;
if the d.c. value is used, any superimposed ripple shall not be taken into account;"

Rms voltage of waveform at transformer primary?

And what pollution degree you use/assume?
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Old 9th August 2005, 09:16 PM   #35
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Quote:
Originally posted by mzzj
Chocoholic, what do you use for "operating voltage" for half-bridge or flyback?
" the actual r.m.s. or d.c. value shall be used;
if the d.c. value is used, any superimposed ripple shall not be taken into account;"

Rms voltage of waveform at transformer primary?

And what pollution degree you use/assume?
You are right.
For the flyback it would be sufficient to calculate the RMS value.
Even with the reflected voltage and leakage peak going up around 750V peak in worst case... the RMS value would remain around 450V, instead 600V that I had assumed.
For a boost topology I calculated 500V DC, as
my plans were considering a 480V DC rail.
So the isolation requirements would be pretty much the same in both topolgies .

My pollution degree was 2. Isn't that the common assumption for
non sealed indoor electronic equipment?
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Old 9th August 2005, 09:48 PM   #36
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Quote:
Originally posted by Eva


Chocoholic:

I don't like your idea of stepping down mains to 12V through a conventional transformer and then stepping it up back to the voltages required by your amplifiers. It sounds bulky and quite inefficient to me.

I would prefer stepping up 12V (10..15V) to 300V (250..375V) in an unregulated way (simple, smaller and more efficient). That +300V bus may be also powered from rectified mains (skipping PFC stage since you seem not likely to enjoy the added complexity and you can't sell your equipment anyway). Bulk storage capacitors should be placed on that +300V bus (they are required for mains rectification anyway, and this already requires a lot of capacitance, furthermore 400V capacitors store more joules per euro in less space, and peak currents when using 12V power are dramatically reduced). And then, a full or half bridge regulated converter powered from the +300V bus would follow (preferably using IGBTs since their losses doesn't increase proportionally to I^2 like in MOSFETs but to I).
I also do not really get a state of the art feeling....


But it is perfectly simple and as the heavy 12V caps are existing anyway, because of the car supply option.... A single torroid + rectifier seems to come not heavier, not bulkier... , than my set up
with boost + halfbridge + proper filtering.

I could skip the boost, you are right. And go for a halfbridge converter only. But this solution would not be perfectly simple and also not perfectly state of the art. ... and less fortunate for 120V/230V... Somewhere inbetween.... hm....

Currently none of the solutions is really giving me the kick.


From technical side the boost+halfbridge would be the best.
BTW: I already finished the stepped gap choke for the PFC.
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Old 9th August 2005, 09:58 PM   #37
mzzj is offline mzzj  Finland
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Quote:
Originally posted by ChocoHolic


My pollution degree was 2. Isn't that the common assumption for
non sealed indoor electronic equipment?
Umm, guess so. Just got this standard to my hands today so I am not any sorta expert.

How about epoxy potting your trafo, then you could use pollution class 1 creepages and best CTI values?? No need for vacuum-potting tough as its only for against pollution

btw, I dont have any clue about different material CTI values because I dont have access to that xxxx standard where they are specified. Do you have this standard? I would be intrested to hear some examples.
arrgh, would need tons of publications to cover just en60065 and its references
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Old 9th August 2005, 10:18 PM   #38
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Sorry... I also don't have the CTI details. That's why I considered the worst. From what I know some FR4 PCB material offer CTI above 600.
May be also coated FR1 or CEM1? I don't know.
Also several high quality isolation tapes. But bobbins often are poor...
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Old 9th August 2005, 10:49 PM   #39
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The stepped gap choke is a doubled EVD 36.
43 turns of 150x0.1 silk covered HF litz,
wound in three layers with interlayer isolation.
At low currents L=1.1mH.
At levels above 0.7A it changes to 330uH and remains stable
up to all area saturation at around 17A.
If heated to 100C, this saturation may happen around 12A, which is
my worst case requirement at 120V.

...hm, somehow I am curious...
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Old 9th August 2005, 10:56 PM   #40
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Sorry, I should mention:

White trace is the voltage across the choke: 100V/div
Coloured trace is the current through the choke: 5A/div
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