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bibiz999

Feb 2, 2011
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The 1N3710's are 200V zeners in places I'm used to see ordinary switching diodes. Where'd you find this configuration?
I'd also expect the relatively low voltage varistor across the BU to dampen the HV too much. How about placing two of them in series?

I've found it where I found the calculator for the snubber component, i.e. http://www.daycounter.com/Calculators/Snubbers/Snubber-Design-Calculator.phtml , and I was pretty sure those were zener symbol! If simple switching diode would do I'll put some 200V 3A in place.

As for the BU's varistor, I assume two 240V in series act as one 480V?

Thanks.
 

Resqueline

Jul 31, 2009
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Ah, ok, nice site. No, those are actually Schottky diode symbols. Zener symbols don't fold back like that, they only have one angle, and usually only at one side.
I'm sure you'll need more than 200V diodes. I'd use at least 1000V, preferably 1200V, and 1500V if I could get my hands on some.

2 x 240V varistors iin series should be the same as one bigger 480V varistor. Note that this is the sustainable sine AC voltage. The breakdown voltage is much higher.

There's likely no need for more than one snubber circuit, and you don't want to limit peaks to anything much less than 700V.
 

bibiz999

Feb 2, 2011
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I have some 1N5408 diodes at 1000V 3A that I'll use in one RCD Clamping snubber allegedly design to handle: 50V 2A steady and peaks of 800V at 15KHz!
I'll have to find the right combination according to availability of components.
A 100uH inductor, 100nF capacitor and a 1.2M 3W resistor with the 1N5408 diode should do it according to the calculator but ...
Are RF choke the same as regular inductor?

I'll also put two 240V varistor in series parallel to the BU and one to the
MJ3001...

Hopping it will do!

Again thanks for the advice...

Thanks
 

Resqueline

Jul 31, 2009
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The 1N5408 is a rectifier diode, not a switching diode. They're never used professionally for these applications and I'm not sure it would be fast enough.
I''m not experienced enough with snubbing to say if those values are ok, though they all seem to be larger than I think I remember from TV diagrams.
 

davenn

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Sep 5, 2009
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The 1N5408 is a rectifier diode, not a switching diode. They're never used professionally for these applications and I'm not sure it would be fast enough.
I''m not experienced enough with snubbing to say if those values are ok, though they all seem to be larger than I think I remember from TV diagrams.

agreed, they definately wont be fast enough. Schottky or fast recovery Avalanche diodes are needed.

A 1N54xx series will get very hot , very fast and expire soon after. If you dont want to buy new ones pull some from the output stages of the main PSU or from around the output lines of the line out transformer (flyback transformer for you young lads)
in TV's of 10 - 20 yrs old the BY227 to 229 series were the common diode in that area

Dave
 

bibiz999

Feb 2, 2011
43
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agreed, they definately wont be fast enough. Schottky or fast recovery Avalanche diodes are needed.

A 1N54xx series will get very hot , very fast and expire soon after. If you dont want to buy new ones pull some from the output stages of the main PSU or from around the output lines of the line out transformer (flyback transformer for you young lads)
in TV's of 10 - 20 yrs old the BY227 to 229 series were the common diode in that area

Dave

Hi,

Yep I got a SUF30J, it's a fast recovery diode (Trr 35ns) but only 600V 3A. I'll try to find some with a higher voltage I guess. I haven't figured out what to do exactly yet... either add a simple RC or a RCD Clamp snubber, or both. Preferably I would add one or the other but... I've been reading on the subject for the past 2 days and really... It easy to admit I'm a bit confuse cause it's true! I've found a site to compute snubber's values of capacitance, resistance and all but I'm not sure at all about those or about voltage rating of component for example...
Last time I've check, I wanted to put a RC snubber with a 300nF 400V cap (marking says 304J 400AD so) a very big 15ohms resistor (1in long - 1/4in dia. blue/grey ceramic one so I figured 5 W a least) and a SUF30J diode. I'll also add the MOVs so, could it do the trick???I wonder!!

Since I replaced all parts of the cct (flyback, 555, MJ3001 and BU508DF), I'm able to tune it at around 1/2 power. It hisse like hell but no collateral damage other then spike between the flyback pin (0V and surrounding) when I push it... I'll have to insulate them again I suppose!

I'll be back for sure..

Thanks again..
 

bibiz999

Feb 2, 2011
43
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Feb 2, 2011
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Finally...
After adding Snubber, Varistors, Darlington, having splited the cct driver and all, when I pushed the power it blew the MJ3001, potentiometer and the fuse, as it did at the very begining of this thread !
I've decide to add a 1N5408 diode to prevent inductive kickback from the flyback to those components (see cct).
I'm now able to produce a continuous electric arc about 5mm without any blow back! I still need some tuning but there seems to be a light a the end of the tunnel and it might not be a train!

Thanks a lot to everyone who gave me a hand in this, particularly Resqueline...

Ciao!
 

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