It seems to me that flyback SMPSes use pulsed DC instead of AC. Is this true?
For example, here, the transistor simply turns on and off, providing pulses to the transformer, right?
Would SMPSes be more efficient if their transformers were fed high-frequency AC instead of high-frequency pulsed DC (for example, by using an H-bridge to provide a negative voltage across the transformer primary for the second half of each cycle)?
Thanks,
Michael
High Frequency chopped DC is equal to High Frequency AC.
I.T. I.S. A.C.
w.
Yes. But flybacks take fewer external parts. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
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| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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I love to cook with wine. Sometimes I even put it in the food.
Oh! It's a cost-savings thing, then.
Thanks,
Michael
One big motivation is higher frequency allows smaller cheaper reactive components.
The penalty is running into transistor switching times, ferrite losses and rectifier Trr.
Not studied this area - but I think semi-resonant SMPSUs are the answer to that.
If I understand it correctly - they're sort of AC transformer drive instead of DC pulses.
Really big (like kilowatt) switching supplies are often forward converters, with symmetric square-wave drive, no DC component, into the transformer. No DC in the transformer core is more efficient.
There are also some clever resonant designs that run real AC (sine waves) through the magnetics.
Small, cheap supplies work well with the flyback topology.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Ok, thanks!
Forward Converter... new vocabulary words for today :)
Michael
Forward converters don't have to be as big as the examples JL mentioned.
The early PC/AT psus were often flyback, but forward converters became pretty much the standard once the ratings got to around 200W.
There's plenty of off the shelf controller chips to chose from and also plenty of appnotes with example circuits. The SG3524 is just one of many that springs readily to mind.
The KA7500 is popular in ATX supplies, so there may be a free development sample gathering dust in the loft. AFAICR: the TL494 is another common choice.
Those 3 part numbers will find manufacturers that have other similar parts on offer.
A few more
Forward
Flyback
Buck
Boost
Cuk
Sepic
Resonant
Cockroft-Walton
Royer
Baxandall
(there must be more)
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
image150a.png
ESM_power_B.pdf
There are. Not least many sub-categories of the above!
Flybuck
ICL7660-style flying capacitor
Tesla coil
thunderstorm ;)
Cheers
Phil Hobbs
yes.
It's not a transformer... it's an inductor with two windings.
That won't work with a flyback, but with a forwards converter* it would work, but now you have twice the switch losses.
(*) where the secondary and primary windings conduct simultaneously eg: Royer.
-- \_(?)_
A good intro to switched mode:
-- \_(?)_
his true?
pulses to the transformer, right?
equency AC instead of high-frequency pulsed DC (for example, by using an H- bridge to provide a negative voltage across the transformer primary for the second half of each cycle)?
a.png
Ooh thanks!
Michael
I'd be interested to see a 6MV supercapacitor and a buck that can bring that down to national grid type voltages.
Apparently US power companies have for some time been experimenting with EHV DC distribution lines. Last I heard they were reaching for 1MV in an attempt to find the tradeoff between corona discharge on EHV DC compared to capacitive losses on lower voltage AC distribution.
I think LTC or somebody makes what is basically a flying-inductor converter.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
It is true.
But "Alternating current (AC), is an electric current in which the flow of electric charge periodically reverses direction, whereas in direct current (DC, also dc), the flow of electric charge is only in one direction".
So the High Frequency AC which is flowing in a transmising line is not AC at all. It is the impulsing current. Do you agree? S*
napisal w wiadomosci news: snipped-for-privacy@googlegroups.com...
Your flyback is using the impulsing current.
But the term "impulsing current" was used by Tesla. Up to now the Tesla name is absent in textbooks about radio. Do You know that Tesla was "Father of radio":
I disagree. AC REVERSES polarity (hence the "Alternating" in Alternating Current). Pulsed DC does not.
Sometimes names are not precise. The High Frequency AC in the radio mast is not symetric AC. So it is practically the Pulsed DC. S*
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