diangonal half bridge, so a switch at either end of the winding.
250,000+ of them suggest they are flybacks.the open-loop regulation comes from the flyback mode, when both primary switches turn off. the pair of primary diodes then clamp the leakage spike to the input rail, and if more energy is stored in the core than the load needs, the excess energy is returned to the primary supply by said diodes.
Cheers Terry
Whether it's a flyback or forward converter depends on the way the output diode is connected, no?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
That's sort of a commodity part... lots of them in the Mouser and Digikey catalogs. I used one in a 900 volt hv supply I posted some time back...
================
+9-------///////ct///////--------to c-w multiplier chain | | | | d -----g 2N7002 s | | | | gndThe 2:1 stepup greatly improves the available flyback boost ratio.
The gate drive was tiny-logic schmitt oscillator. One version had closed-loop hv regulation with one additional transistor.
John
I guess it's a flyback if all the energy is stored in the inductor before being transferred into the load.
John
OK, let me try to restate my perspective one more time:
I AM NOT USING THESE TRANSFORMERS AS FLYBACKS. OTHER TOPOLOGIES DO EXIST.
The simple square-wave inverter needs no feedback loop and has no startup problems. Since inductance is so high, these parts could be run in the audio range, although 50-70 KHz seems about right. We often deliberately slow down the fet gate drives to reduce noise, which doesn't work as well in a flyback.
Custom magnetics don't make a lot of sense unless volume is huge, as yours seems to be. The time and hassle spent in engineering is hard to earn back over less than tens of thousands of parts, so we use a stock transformer or inductor whenever we can.
John
dui4
hen3 dui4
(I taught myself Mandarin recently)
Cheers Terry
Dont beat about the bush John, tell us whether or not you intend using these as flyback transformers. dont be shy :)
wrt startup: depends on output capacitance, no? I guess there is a fair amount of leakage, so it looks less like a short.
Absolutely! If cheap is good, cheaper must be better :)
I often use planar cores, for that reason - standard cores, DIY custom windings.
In this particular case its not all about volume (but I am using about 8 of these per design), but rather about what happens when things go horribly wrong. an inductorless buck-derived converter isnt so happy running into a dead short.
The last lot I did were exactly as you described, and they worked well. I had a PLD, so it generated the oscillator, which I could control the duty cycle (narrow pulses at startup), and no feedback. It worked very well, BUT when I deliberately blew up an IGBT (10-20 desats in quick succession) it snotted the gatedrive completely (look ma, no zetex transistors) and buggered the supply too - tiny bjt didnt like switching into what was essentially a dead short.
So I figured next time round, I'll specifically consider what happens then. this new design is also cheaper :)
Cheers Terry
Hey, chickens are off-topic in my thread.
John
not even chicken chow-mein?
Cheers Terry
Empty calories. But we had some VietNamese BBQ chicken on Sunday that was memorable.
John
Don't rush me. I need a chance to think it over.
Who cares? Just let the 2N7002's grunt. But right, a rectified square wave doesn't need a lot of filter caps like a flyback does. And none of that silly right-half-plane nonsense for us, no siree.
We do worry about a shorted channel on the 16-channel boards. One fix is a small source resistor shared between the fets, with appropriately scaled gate drive (~~4 volts works) so the fets will current-limit if the load is shorted.
Power electronics is a nuisance when things go wrong.
John
Gamun
Cheers Terry
:)
fair enough, too. Something I learned a long time ago: Aint no laws against slavery in electronics. Yay for m*cp
good thinking. Nowadays I throw in one more transistor, and run peak current mode control. I also monitor average gate voltage, so I can shut the whole thing off if it sits at low duty cycles. The PCMC protects the junction for a long enough time that its easy to notice and do something.
Yes. "Component no longer there" is a common failure mode.
Its made me rather careful. I once sat beside a flywheel that self-destructed with 1MJ of stored energy. came close to s*****ng my pants, but luckily the containment all worked well (the kind of "luck" that involves careful worst-case-scenario design). It certainly got the attention of everyone in the factory :)
and whats the deadliest near-miss I've seen? A guy nearly lose his head in a wicked storm, when a sheet of roofing iron flew over his shoulder - he was running, and the iron went by a LOT faster. 2' to the right and he'd have been bisected :(
Cheers Terry
Très bon... err.. hao3 ji2 le!
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
You are far, far too kind. I have several friends who are fluent in mandarin, and I recently spent 3 weeks there on a consulting job. Before I went there, I could say "hello", "thankyou" and "goodbye", albeit so badly I'm sure it was only thru context that anyone understood me (sigh chair?!)
My good friend Paul spent my first weekend there teaching me, and making me do all the speaking. After the first week, I could get around - eat, sleep, travel, shop, swear at beggars (isnt PK a great insult? OK its cantonese), all the fun stuff. Dice games taught me the numbers :)
Now I have a dictionary, and a Berlitz phrase book & CD, which I've ripped to the MP3 player I bought for this purpose (long flights are boring). I listen to the CD every time I'm driving.
The mandarin phrase book is terrible, as it doesnt use pinyin, but rather an american-phoneticised mutation. This has actually been very helpful, as I am slowly translating that crap into pinyin.
There are lots of chinese here in NZ (12.5% or so), and I quite often get to conduct entire transactions in Putonghua. It surprises the hell out of most chinese, that a white guy would bother to learn such a thing.
It will be a while before I can have a real conversation, but I'll get there. the writing isnt exactly easy either (yi, ar, san are OK, the rest is harder), but the language structure is fun.
I also write emails in pinyin, after first apologising (qing wen wo de putonghua bu hao), as I need the practice.
Zai4Jian4 Terry
Should be: dui4 bu qi3 wo3 de ... ;-)
Ditto. I'm working more on the characters these days. A bit of a hard slog, but it's coming.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Ah, I see, Xiexie. I have no shame, and am happy to experiment and be corrected. Qing Wen is essentially "please ask" so should preface a question.
One of my mates can read 10,000 characters, which is no mean feat. Another can read and write chinese emails. Me, Im just happy I can recognize ge :)
I cant believe I waited so long to learn another language. Still, there is no time like the present.
Back to writing 8051 machine code....hilarious, I'm using a hex editor, and hand-compiling. I've been arguing with a programmer about some of his crappy code, and so far am winning, by dint of hacking the bin file directly. I sorted out the inability to generate a 76kHz square wave problem (moral: never let computer programmers design anything; get an engineer), now I am figuring out why the LEDs flash at power-on.
Cheers
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