High voltage diode blowing mysteriously
in [Design]
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From: Jan Panteltje on 5 Jul 2010 06:04 On a sunny day (Mon, 5 Jul 2010 01:20:02 -0500) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <SQeYn.7089$RC5.6665(a)newsfe08.iad>: >"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message = >news:i0r025$ofk$1(a)news.albasani.net... >> Capacitors? Is not 10uF / 250 V too low for 250 V output? >> Maybe a cap starts drawing a lot of current? >> Also check the .47 uF. > >Err, choke input, forward coverter. Yes, so? I would not use a 250 V elco on a 250 V supply. >Peak current is not much greater than average, there are gobs of = >inductance everywhere and only parasitic capacitance. The filter choke = >is bank wound thusly: >http://myweb.msoe.edu/williamstm/Images/Coil.jpg Nice, some HV coil design. >Tim Do not drink while posting :-) I still am not sure what diode[s] yo uare referring to. As somebody mentionioned, use some reference Q1 Q1, D1 D2, T1 T2 etc. Else answering is a bit like playing the lotto. >-- >Deep Friar: a very philosophical monk. >Website: http://webpages.charter.net/dawill/tmoranwms >
From: Jan Panteltje on 5 Jul 2010 06:09 On a sunny day (Sun, 4 Jul 2010 19:57:32 -0700 (PDT)) it happened Nunya <jack_shephard(a)cox.net> wrote in <1e46800c-4459-4386-a7a9-6ec55666765c(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. . .
From: Tim Williams on 5 Jul 2010 06:28 "Ban" <bansuri(a)web.de> wrote in message news:i0s9ev$3qd$1(a)news.eternal-september.org... > If you look at your design, where does the current from the leakage > inductance flow? It twangs through the primary circuit (which is an approximate constant voltage source, making it series resonant with the winding's and choke's parasitic capacitance), which gets sucked up by the snubbers I said are there. There is a measurable and finite overshoot, of about 120V as I stated. This puts the peak reverse voltage around 640V, which is within ratings. There is very little ringing; the damped Q is quite low, maybe 2. The resistors get warm. > there is a big choke and no caps behind the rectifier and > on the other side is the transformer where the current comes from. No way of > going into the ground. > Try my suggestion and look at the voltage with a really high-z 100:1 probe, > then you will see the high peaks. All I have is a 10M probe. Fortunately, the impedance in the area is around 5.6kohms and 47pF (28kohms reactance at the fundamental; much less for harmonics), so this is sufficiently high. Detail: http://myweb.msoe.edu/williamstm/Images/Tubescope_Snubber.png As you can see, there are in fact snubbers across the diodes. Do you see anything that would kill the diodes? Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 5 Jul 2010 06:30 "Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:i0sang$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 -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Ban on 5 Jul 2010 06:48
"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. |