High voltage diode blowing mysteriously
in [Design]
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From: Jan Panteltje on 5 Jul 2010 06:49 On a sunny day (Mon, 5 Jul 2010 05:30:03 -0500) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <fviYn.9492$3%3.2848(a)newsfe23.iad>: >"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message = >news:i0sang$llm$1(a)news.albasani.net... >>>Tim >> >> Do not drink while posting :-) > >Well, considering you seem to have writing/comprehension problems, I'll = >go easy on you and give you a visual aid. :-) >http://myweb.msoe.edu/williamstm/Images/Tubescope_Snubber.png > >Tim PK, great, well maybe that other poster has a point mentioning huge voltage peaks. I could imagine bottom of 102T spiking positive while left bottom connection of 300T spiking negative. Maybe you think that is damped by the other positive diodes, but then that 300T reverses the phase :-) If top left of 300T goes positive, then also bottom left of 300T will go negative. But I would check caps first. >-- >Deep Friar: a very philosophical monk. >Website: http://webpages.charter.net/dawill/tmoranwms >
From: Hammy on 5 Jul 2010 08:49 On Mon, 5 Jul 2010 12:48:28 +0200, "Ban" <bansuri(a)web.de> wrote: > >"Tim Williams" <tmoranwms(a)charter.net> schrieb im Newsbeitrag >news:xtiYn.9491$3%3.9373(a)newsfe23.iad... >"Ban" <bansuri(a)web.de> wrote in message >news:i0s9ev$3qd$1(a)news.eternal-september.org... >> If you look at your design, where does the current from the leakage >> inductance flow? > >It twangs through the primary circuit (which is an approximate constant >voltage source, making it series resonant with the winding's and choke's >parasitic capacitance), which gets sucked up by the snubbers I said are >there. > >There is a measurable and finite overshoot, of about 120V as I stated. This >puts the peak reverse voltage around 640V, which is within ratings. There >is very little ringing; the damped Q is quite low, maybe 2. The resistors >get warm. > >> there is a big choke and no caps behind the rectifier and >> on the other side is the transformer where the current comes from. No way >> of >> going into the ground. >> Try my suggestion and look at the voltage with a really high-z 100:1 >> probe, >> then you will see the high peaks. > >All I have is a 10M probe. Fortunately, the impedance in the area is around >5.6kohms and 47pF (28kohms reactance at the fundamental; much less for >harmonics), so this is sufficiently high. > >Detail: >http://myweb.msoe.edu/williamstm/Images/Tubescope_Snubber.png >As you can see, there are in fact snubbers across the diodes. > >Do you see anything that would kill the diodes? > >Yes, the puls from the leakage inductance cannot flow into the snubbers >because the 10mH inductance behind will block that current. If you put a >capacitor across the rectifier output, the spikes can be absorbed. Also this >will prevent this point being pulled negative by the 10mH choke, which will >double the voltage across the diodes. >Make some tests with 2 probes in differential mode to see the true voltage >across the diodes. > You need to take differential measurments. I plugged in some estimates based on an absouloute output voltage of 500V and they do indeed see 1.9KV. http://i48.tinypic.com/2ec3z89.png
From: Nunya on 5 Jul 2010 10:54 On Jul 5, 3:09 am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Sun, 4 Jul 2010 19:57:32 -0700 (PDT)) it happened Nunya > <jack_sheph...(a)cox.net> wrote in > <1e46800c-4459-4386-a7a9-6ec556667...(a)e29g2000prn.googlegroups.com>: > > >On Jul 4, 1:52 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: > >> I have a > > > STOP posting text with greater than 72 character line length, you > >retarded Usenet abusing IDIOT! > > What is your problem, there is no limit to line length in Usenet, so it >is up to the artistic capabilities of the creator of the posting to format >the text anyway they want, in fact newsreaders who garble that text > by reformatting violate the principle of conservation of of creativity, > so take that. > You're an idiot. Usenet has always been that way. You not knowing that after all these years, shows everyone just how little attention you pay to the details. The "that" which "you take", Jan, is the fact that you are an utter idiot where knowing about Usenet is concerned. You also lack skill in electronics. We already knew that, however. All the blank lines after your stupidity is more proof that you do not know anything about that which you blather on about. So, FOAD, Blather boy.
From: Joerg on 5 Jul 2010 13:08 Nunya wrote: > On Jul 4, 5:33 pm, Joerg <inva...(a)invalid.invalid> wrote: >> John Larkin wrote: >>> On Sun, 04 Jul 2010 15:28:01 -0700, Joerg <inva...(a)invalid.invalid> >>> wrote: >>>> Tim Williams wrote: >>>>> I have a high voltage power supply, >>>>> http://myweb.msoe.edu/williamstm/Images/Tubescope_Supply2.png >>>>> under reasonable load (140VDC link voltage; Vadj set for 230V output; 3A heaters, fractional mA at -2kV, 100mA at +230V, 35mA at -230V). It runs cool and smooth for about a minute (aside from the snubbers, which get quite hot), then suddenly the output drops dead and the current limit starts squealing. One of the negative output diodes is failing shorted. (Good thing the current limit keeps it from nuking the transistors.) >>>>> Until failure, the diodes run cool (aside from what heat they pick up from the snubbers). The waveforms show 120V overshoot, which is well within ratings (1000V diode with about 600V peak reverse). I can't imagine it's an avalanche thing, as the reverse voltage is low and, until failure, the diodes run cool. I'm still more confused that it's consistently the negative side diode (three have died so far), which is the lighter loaded side. >>>> I don't see any snubbers of clamps on the upper right transformer where >>>> it says 102T. >>>> BTW, it helps to turn on designators. TR1, Q5, R6, and so on. >>> TR? A transistor is Q. A transformer is T. >>> John >> Sir, yes, Sir! <clicking heels, saluting> >> >> On mil schematics that's the case but civilian ones are all over the map >> in that respect. You should see the new DIN or whatever standard WRT >> designators, it's the epitome of bureaucratic nonsense. Designators >> different for the same type of component and depending on its function. >> >> I just had one that said TR, another one XFMR. >> > And BOTH are incorrect designations. They can be used in item > descriptions (xfmr), but reference designators have an industry > standard > and your remark that they do not is noncorrect in all circles excpet > those > where some stupid dope like you refuses to use the industry > standard(s). > So, essentially you hang out in some stupid clics. Designators have > had variances based on device function. Diodes are a perfect example. > We see "D1" or "CR1", where "CR" was derived from "Cathode > Rectifier". Just FWIW: What you call stupid clics are often rather large and successful enterprises, the products of which even you will experience on a regular basis. Like when you are going places ... -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 5 Jul 2010 14:09
Tim Williams wrote: > "Joerg" <invalid(a)invalid.invalid> wrote in message > news:89cg7iFchaU3(a)mid.individual.net... >> I don't see any snubbers of clamps on the upper right transformer >> where it says 102T. > > Ran out of room to draw them. The note just above indicates the > nature of said snubbers. > Nope. No capacitance values, no resistor values. >> BTW, it helps to turn on designators. TR1, Q5, R6, and so on. > > "Turn on"? I draw these in Paint. Refdes are a hassle ;) > <gasp> ... oh well. > Call 'em "high voltage diodes", and not "low voltage schottky", "EHV > diodes" or "FWB". I'll know exactly what you're referring to, just > as well as "D17-D20" or whatever. > Did you scope the voltage at the transformer secondary? And the current into the diodes, with a current transformer? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |