Diode identification?
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From: Arfa Daily on 2 Mar 2007 21:04 "Dave Platt" <dplatt(a)radagast.org> wrote in message news:12uh85jomtt65b0(a)corp.supernews.com... > >flywheeling diode and a 1N4007 would do the job just fine. Does the FET >>source go to ground ? Many power MOSFETS have a diode internally in that >>orientation across from the source to the drain. It gets there as an >>integral side effect of the manufacturing process. > > Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED > or HiperFRED) for MOSFET flyback protection. 1N4007s aren't > particularly fast, and reverse-conduction losses can be significant if > the switching frequency is high (in e.g. an SMPS). That's probably not > all that much of an issue in a solenoid driver, though. That was my thought, and the reason that I suggested a KISS approach with a 1N4007 Arfa
From: John E. on 3 Mar 2007 10:53 Arfa Daily sez: > Not then, I would suggest, a 4.7v zener ... Sounds like it's just a > flywheeling diode and a 1N4007 would do the job just fine. Does the FET > source go to ground ? The source connects to a flame-resistant (blue), less-than 1-ohm, 1/4w(?) resistor (red-violet-gold-gold) that measures about 0.5 ohm. (It should measure 0.27, yes? Maybe candidate for replacement? But maybe it's my Fluke 77's accuracy at that low setting. Resistor doesn't look abused...) The other end of the resistor does connect to ground. > Many power MOSFETS have a diode internally in that > orientation across from the source to the drain. It gets there as an > integral side effect of the manufacturing process. Yes, I've read about the need to short out back-EMF when dealing with relay coils, solenoids, etc. So, 1N4007 it is. An after thought... since the diode was cooked (it actually charred the PCB beneath it) but the resistor and the FET are OK, maybe the diode needs to be boosted to a higher A rating? Thoughts? Thanks to all, -- John English
From: Werty on 3 Mar 2007 11:13 Black ? What size ? I guess 1n4007 1KV , ?1amp , 40 amp surge ____________________________________ On Mar 2, 9:49 am, John E. <incogn...(a)yahoo.com> wrote: > It's shorted, burned on the side against the board, the side of the diode > that has part of the p/n printed (of course)... > > Best I can make out is (reading around the diode: > ITT > 4? > 47 > > Physically it resembles a typical 1A black epoxy rectifier. > > Would this be 1n4147? The "47" is clearly visible, and I think I can make out > a "4" in the first part of the poorly-legible digits. No telling how many > digits between the two "4"s. > > Any possibilities other than 4147? > > Thanks, > -- > John English
From: Eeyore on 3 Mar 2007 11:14 "John E." wrote: > Arfa Daily sez: > > > Not then, I would suggest, a 4.7v zener ... Sounds like it's just a > > flywheeling diode and a 1N4007 would do the job just fine. Does the FET > > source go to ground ? > > The source connects to a flame-resistant (blue), less-than 1-ohm, 1/4w(?) > resistor (red-violet-gold-gold) that measures about 0.5 ohm. (It should > measure 0.27, yes? Maybe candidate for replacement? But maybe it's my Fluke > 77's accuracy at that low setting. Resistor doesn't look abused...) The other > end of the resistor does connect to ground. > > > Many power MOSFETS have a diode internally in that > > orientation across from the source to the drain. It gets there as an > > integral side effect of the manufacturing process. > > Yes, I've read about the need to short out back-EMF when dealing with relay > coils, solenoids, etc. > > So, 1N4007 it is. > > An after thought... since the diode was cooked (it actually charred the PCB > beneath it) but the resistor and the FET are OK, maybe the diode needs to be > boosted to a higher A rating? Thoughts? It seems my post aboutt his didn't reach the group. It's most likely a BZY47-C47 2 watt zener 47V Graham
From: Eeyore on 3 Mar 2007 11:45
Werty wrote: > Black ? What size ? I guess 1n4007 You would be wrong. |