High voltage diode blowing mysteriously
in [Design]
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From: legg on 5 Jul 2010 23:14 On Mon, 5 Jul 2010 18:11:46 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Kevin McMurtrie" <mcmurtrie(a)pixelmemory.us> wrote in message news:4c324b1d$0$22128$742ec2ed(a)news.sonic.net... >> Is the part labeled "2 x 10mH 100mA 300T" causing problems when the +/- >> 250V outputs currents aren't balanced? > >It doesn't seem to be. The waveforms on either end look identical and inverted. The currents aren't aall that different. 30mA seems to be enough to cause continuous conduction mode, so it's not trying to play funny on that side. > >Tim If the currents are unbalanced, you may need freewheeling rectifiers to ground, before the choke, on both sides. RL
From: m II on 6 Jul 2010 00:29 Nunya wrote: > STOP posting text with greater than 72 character line length, you > retarded Usenet abusing IDIOT! ============================================ But I say to you that everyone who is angry with his brother will be liable to judgment; whoever insults his brother will be liable to the council; and whoever says, �You fool!� will be liable to the hell of fire. Matthew 5:22 ============================================ father mike
From: Tim Williams on 6 Jul 2010 00:20 "legg" <legg(a)nospam.magma.ca> wrote in message news:6p7536hhm12k3oggp0dsj6te2b8556n7r0(a)4ax.com... > If the currents are unbalanced, you may need freewheeling rectifiers > to ground, before the choke, on both sides. Ah, interesting. The dead time voltages are near zero (give or take a small amount of squiggle), so it seems to be okay. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: m II on 6 Jul 2010 00:32 Nunya wrote: > where some stupid dope like you refuses to use the industry > standard(s). ============================================ But I say to you that everyone who is angry with his brother will be liable to judgment; whoever insults his brother will be liable to the council; and whoever says, �You fool!� will be liable to the hell of fire. Matthew 5:22 ============================================ father mike
From: Tim Williams on 6 Jul 2010 00:37
"Joerg" <invalid(a)invalid.invalid> wrote in message news:89fb8lF7cnU1(a)mid.individual.net... > Best to put them on the schematics. 47pF is almost nothing. Are you sure > this quenches ringing enough? Yes, it gets hardly a cycle before the ringing is too weak to see. > Possibly, because at 75nsec trr these are fairly slow. Slow!? Come on, I know you love dabbling with MHz stuff, but gimme a break, this is only 120k after all! > Since you > probably don't want to spring for four of those Cree super thingamagics > which would totally raid the beer kitty, why the 2x10mH common mode > choke? Tried separate chokes yet? Hmm, "common mode" is a funny way to put it. The negative rail is inverted, so I guess it should be "differential mode". I used that since everyone else uses multiwinding chokes in forward converters. Two chokes would take up more space and be more trouble to wind; this is only one part. I'm not buying them and I'm not mass-producing them, so don't bother going all Joerg on me. ;-) > Of course, if you came into a wad of cash: > > http://www.cree.com/products/pdf/C2D05120.pdf With 45pF at 200V (probably with high Q), I'll need even bigger snubbers. The transistors might not appreciate trying to push around the 455pF "not-recovery" capacitance, either. Actually, 28nC charge is like 0.5A * 50ns reverse recovery, so they'd be just as bad! The only difference is, you get the capacitance back each time, whereas the reverse recovery is heat each time. Anyway, even peak Irr were 0.5A, that's roughly 75ns * 0.5A * 4 diodes * 120kHz * 2/cycle = 36mA effective reverse leakage. At 250V, that's 9W, or 2.25W/diode, but recovery occurs at a few volts, not all 250, so the real power is something else. Evidently it's fairly small, because the diodes don't seem to heat up until the one dies... No one makes 1A SiC rectifiers? What's up with that? Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |