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Old 21st December 2005, 09:39 PM   #11
poobah is offline poobah  United States
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Oh...

Your half-bridge instead of full-bridge... OK so the energy is returned to the input via the body diode of the OTHER transistor!

I got it...
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Old 21st December 2005, 10:19 PM   #12
mzzj is offline mzzj  Finland
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Quote:
Originally posted by poobah
Oh...

Your half-bridge instead of full-bridge... OK so the energy is returned to the input via the body diode of the OTHER transistor!

I got it...
I belive he was talking about push-pull with center-tapped primary. Not half or fullbridge .
Edit: not sure afterall, push-pull sounds strange for 240v input, requiring gigavolt(tm) rated mosfets..
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Old 21st December 2005, 10:43 PM   #13
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Yes push-pull with CT primary (is there any other kind?)

So... i get it.

There is no way that this parasitic flyback can bring any recoverable energy to the secondary.

All it does is circulate energy among the primary components, generating more heat.

I'll just have to dissolve the soft parts of the remaining trafos with paint stripper, and rewind them to get rid of the gap.

thanks
Joseph
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Old 21st December 2005, 10:49 PM   #14
poobah is offline poobah  United States
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Joe,

Only a few percent of your energy is being reflected black... of that, about 1% is getting burned up in the diodes. 1% times 3% = 0.03%... not big deal to leave it as is. There is copper loss too but you get the picture. (you really want to rewind those trannies now... don't you?)

Cheers,
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Old 21st December 2005, 11:44 PM   #15
Eva is offline Eva  Spain
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You are just ignoring whatever there is in the secondary side of the transformer...
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Old 22nd December 2005, 12:20 AM   #16
poobah is offline poobah  United States
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Eva,

You are a master of SMPS... please explain???
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Old 22nd December 2005, 02:13 AM   #17
Eva is offline Eva  Spain
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It's not so complex. It's just that the load connected to the secondary side of the transformer may also easily clamp the inductive kickback. Remember that all windings are coupled and the energy stored in the core and the gap may be recovered through any of them.

Furthermore, the classic circuit made of a transformer with a center tapped secondary whose ends are connected to a buck inductor through two diodes causes the transformer to be effectively shorted during the time when the switches of the primary side are off. This means that no magnetisation energy is dumped back to the storage capacitors of the primary side. Think about it.
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Old 22nd December 2005, 04:08 AM   #18
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Thank you Eva

Speaking of modified topologies....


Bi-Forward Converter

if you gurus have already seen this, then ignore this post.

Otherwise... perhaps a new addition to your armamentarium ?

Joseph
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Old 22nd December 2005, 09:11 AM   #19
Eva is offline Eva  Spain
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This paper is quite funny because no way to reset the transformer is provided in the basic schematic, and not a single word about that is said in the entire document... An additional reset winding and a frewheeling diode are obviously required. That topology appears to be more suited for a flyback converter anyway, what makes the difference is just a center tapped primary (showing two independent primaries in the schematic seems quite obfuscated to me).

Also, the converter is drawing pulsed current from mains line at high frequencies, but not a single word is said about that and its consequences. I think that the document should point out that an additional capacitor of up to 1uF is required anyway after the diode bridge in order to provide a low impedance at HF (not required in standard topologies).

PD. it comes from Spain, so I quite understand these deficiencies...
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Old 22nd December 2005, 10:16 AM   #20
mzzj is offline mzzj  Finland
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Quote:
Originally posted by Eva
This paper is quite funny because no way to reset the transformer is provided in the basic schematic, and not a single word about that is said in the entire document... An additional reset winding and a frewheeling diode are obviously required.
Big supprise on academical papers. Sometimes they are intentionally useless, mostly it is just the natural way that they are useless....
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