online Chinese flyback with driver assemblies questions

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Since my dual 2N3055 driven flyback power supply was accidentally thrown  
away, I was pondering building another until coming across subject  
mentioned assemblies. They're on eBay and elsewhere. Looks like various  
drivers with flybacks. Example: https://tinyurl.com/y4lzxt85 Questions  
would be:

1) Do these have built in diodes? I DO want to be able to drive a HV  
multiplier.

2) Performance/ versatility/ durability comments? Any specific  
recommendations of one over the other, etc? Most seem to fall within the  
$15-$20 US range. The 3055's with flyback and tripler could output 30-40  
KVDC with mA's available. Could one of the prebuilt Chinese units do the  
same?

Might be cheaper to buy than to build another from scratch so your  
thoughts/ experiences appreciated.

Thank you,
Jon

Re: online Chinese flyback with driver assemblies questions
Jon I wrote...
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 Haha, 2n3055, you're talking 45 years ago!!  
 For the last 35 years, we use MOSFETs.

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 It's a shame they never provide schematics or similar
 information.  You do get a nice set of parts, and can
 reverse engineer to get the schematic, and then start
 making changes.


--  
 Thanks,
    - Win

Re: online Chinese flyback with driver assemblies questions
On 11/2/19 8:27 PM, Winfield Hill wrote:
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Interesting that there weren't more responses.  I would have thought  
some folks would have tried them out for the "tinkering" value alone.  
And the cost would have covered just the cost of a single flyback, at  
least of the kind I used to use.  There are also the Chinese Marx  
generators that appear to be driven by these circuits.  They call them  
"levels" when referring to number of stages with what appears to be 20  
stage the highest level (20 level) offered.  They specify "10-15 cm"  
spark lengths with their "6 level" generator which makes sense with a 20  
KV flyback driver circuit.  There are videos around of the Marx  
generators though, but hard to confirm spark lengths claimed.

Well, I had some trouble with the 3055's.  Too much arcing at tripler  
output would burn them out quickly and they way I had everything set up,  
they were a pain to change out.  I finally switched out to a more robust  
transistor and had no more problems, but I couldn't tell you which  
transistor that was now.  It has been some time.


Re: online Chinese flyback with driver assemblies questions
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Many are using the 2n3771, 32,33 series or there about numbers to  
replace the 3055's for more power and reliability.


Re: online Chinese flyback with driver assemblies questions
snipped-for-privacy@earthlink.net says...
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make those last numbers 72 and 73.


Re: online Chinese flyback with driver assemblies questions
Jim Horton wrote...
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 I'm a big user of eBay and AliExpress, and purchase lots of
 high-current and high-voltage stuff, to supplement my pile
 of unusual parts, but I'd not come across the items you found.

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 MOSFETs are more robust than BJTs, in that they can handle
 excess drain voltages, and simply go into a safe avalanche,
 the same as a zener diode (however the breakdown comes with
 ns response times, so the wiring must be low inductance).
 MOSFET gates are vulnerable, but if they're driven with a
 serious gate-driver IC, with low-inductance wiring, they're
 quite robust.  The issue is high RF-frequency during arcing.


--  
 Thanks,
    - Win

Re: online Chinese flyback with driver assemblies questions
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You have to be careful of the ebay China parts. Seems that many of the  
high power and some other parts are not up to what they are suppose to  
be.  

I have bought some things from China via ebay.  Most have been good.

I did buy some RF transistors and they would hardly make any power after  
about 7 MHz and replaced them with some RF Parts company and those had  
the full power at 30 MHz where I wanted to use them.
 Friend bought some rated for about 5 or 10 watts and all 6 of them were  
bad from the start.  The first 2 he put in fried his circuit.  He  
measured the other 4 before instlling them and they were all shorted.

I have seen some pictures of the internals of the  2n3055 transistors  
from China and some had a very small silicon area compaired to the  
'good' ones.  They would test good but probably only good for about 1/2  
to 1 amp.


Re: online Chinese flyback with driver assemblies questions
Ralph Mowery wrote:

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** 2N305s have been around since the mid 1960s and undergone number of chip
 redesigns in that time.  

The  JADEC  specification does not determine the chip itself - only its ove
rall performance. Long as the watts, volts amps, gain and Ft etc are OK you
 can label it as a 2N3055.  

After discovering fake Motorola power BJTs in 1982, I began cutting the top
s of dead and suspect TO3 examples to see what was inside.

Verrry interesting ....  

In the case of 3055s, older examples use a large chip with solid metal bond
ing attachments. Later ones, particular from Motorola use a much smaller ch
ip with aluminium wires. Nothing wrong with either.  

Some of the fakes I came across were 2N3055s relabelled as the vasty better
 MJ15003 types. Others turned out to be high voltage switching devices with
 tiny chips and even power Darlingtons - visible by the presence of a small
er transistor on the same chip.  

One particularly egregious fake from India had two chips inside, wired in p
arallel in a desperate attempt to meet the Motorola spec. But that idea doe
s not work.

Another fact that I uncovered is that Motorola like to change the chips ins
ide their power BJT devices without warning.  Devices sold since the 1990s  
as the classic 2N3773 or MJ802 types are in fact MJ15003s relabelled.  

Fine for new designs, which is all Motorola ever consider, but can cause al
l sorts of strange behaviours in older ones. Repairers beware.  

Plus the price is double or triple that of the more recent part.  

Anecdote:  

A famous audio engineer from the UK called Doug Self got trapped by this.
  

He published a design in Wireless World magazine for a "Blameless Amplifier
" using MJ802 and MJ4502s from a stock of old ones he had. It had vanishing
ly low THD.

When folk built his design using the parts and PCB as specified they could  
not achieve nearly the same result.  

Lots of weeping and gnashing of teeth went on in the letters pages.  

Nobody ( but me it seems) figured out the cause was Motorola being deceptiv
e.  


.....  Phil  



Re: online Chinese flyback with driver assemblies questions
On Sunday, November 3, 2019 at 5:06:36 PM UTC-5, Phil Allison wrote:
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The term is JEDEC. Can't you get anything right?

Re: online Chinese flyback with driver assemblies questions

 Michael Terrell Scumbag troll wrote:

-----------------------------------


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** So what.

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** That the best you can do - fuckwit ?  

   Wot a stinking low life you are.  


.....  Phil  

Re: online Chinese flyback with driver assemblies questions
On Monday, November 4, 2019 at 6:54:24 PM UTC-5, Phil Allison wrote:
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Yawn. You aren't man enough to ever admit that you're wrong, so you project all of your faults on others. Exactly what I expected from you.


Re: online Chinese flyback with driver assemblies questions
Yo, Bogan, Mr. Terrell may not be my most favorite person, but on his very worst day of his entire life, he is happier, a better human being and far more worthwhile than you on the very best day of your life.  

I expect that a diet of Sausage Rolls and Foster's Beer has that effect - oh, right. I expect that you cannot afford the sausage, only the rolls. Sorry about that.  

Peter Wieck
Melrose Park, PA  


Re: online Chinese flyback with driver assemblies questions
On 11/3/19 2:46 PM, Ralph Mowery wrote:
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It's a shame China parts can be so varying in quality, but I too am not  
immune although in a different capacity: faucet vacuum aspirators.  I  
had a really nice glass one, US made, that would pull up to at least 28"  
Hg with standard faucet pressure, then one day my carelessness broke it.  
  It was a Kimax?  and they were no longer available, so I decided to  
try a stainless steel aspirator from China.  It could hardly pull 15"  
Hg, a far cry from the advertised 28-30" Hg!  I contacted the seller and  
got an immediate refund with no argument, so I'll bet, at least in this  
instance, that there were a lot of insufficient aspirators.  That wasn't  
the only one I tried as I tried out several other metal ones, but none  
would pull vacuum like the glass one did.  That's when I finally decided  
on a single stage pump but, after 2 years, that Chinese made pump has  
leaked.




Re: online Chinese flyback with driver assemblies questions
On 4/11/19 5:53 am, Winfield Hill wrote:
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An AliExpress search for "Flyback Driver Circuit" comes up with the same  
item in the top few hits: <https://www.aliexpress.com/item/32769816552.html

Re: online Chinese flyback with driver assemblies questions
On 11/2/19 3:48 PM, Jon I wrote:
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Yes, they do have built in diodes so you won't be able to drive a  
multiplier.

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If you can still find a flyback without built in diodes, go with the  
better mosfet circuit recently discussed.  The hard part would be  
finding the flyback.


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