High voltage diode blowing mysteriously
in [Design]
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From: Joerg on 4 Jul 2010 20:33 John Larkin wrote: > On Sun, 04 Jul 2010 15:28:01 -0700, Joerg <invalid(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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Nunya on 4 Jul 2010 22:57 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!
From: Nunya on 4 Jul 2010 23:01 On Jul 4, 1:52 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: > I have a high voltage power supply Snipped incorrectly formatted post body Cut your line length to the Usenet standard, Mr. Ignore the rest of the world. Some folks need to be whacked upside da head. In HV, you can have multiplier caps that 'appear' to be good, but they are not able to be tested properly at low voltages. I would trade out ALL of the HV multiplier caps.
From: fly on the wall on 4 Jul 2010 23:29 On Sun, 04 Jul 2010 17:33:14 -0700, Joerg <invalid(a)invalid.invalid> wrote: (snip) >You should see the new DIN or whatever standard WRT >designators, it's the epitome of bureaucratic nonsense. (snip rest) No, RoHS and mandating CFL's share the epitome. Everything else is struggling for a place behind them.
From: Tim Williams on 5 Jul 2010 02:09
Not even worth the plonk. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "Nunya" <jack_shephard(a)cox.net> wrote in message news: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! |