Diode identification?
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From: John E. on 4 Mar 2007 05:07 ZY47 diode, from the data sheet: Vz(min) = 44 Vz(max) = 50 I test = 10A Dynamic R @1khz = 24 (typ) Vrev = 24 -- John English
From: Palindrome on 4 Mar 2007 05:21 John E. wrote: > Terry Given sez: > > >>BTW in that position its probably a 47V zener, clamping the peak drain >>voltage. > > > I'd been turning over in my mind that this is indeed a zener, not simply a > "plain" rectifier. It is indeed a 47 volt zener. > > Why was this diode chosen in the design? I'm familiar with the standard diode > being used to short-circuit the back-EMF from the solenoid, but I can't > figure out the purpose of a zener used in this location. The zener does a better, but more expensive, job of protecting the series switching element. It limits both positive and negative transients. A diode across the switched inductor does stop most (but not all) of the switching transient - but doesn't protect the series element from transients on the supply rails, caused by other inductances elsewhere reacting to the sudden change in current. It is usual to combine these sorts of design with reasonably fast (eg tantalum)electrolytics placed locally - to act as energy "tanks" to supply and sink transient power. > > Vdd > /\ > | > | > SS > SS Solenoid > SS > | > +-----+ > | | > | | > BUZ72 | /---/ ZY47 > FET |--+ /\ Diode > -------| | > |--+ | > | | > \ | > 0.27R / | > \ | > | | > | | > /// /// > > I think that should show proper in Courier or Monaco... or Paris (c: > > I must add that Vdd is *reported* to be 42vdc. I was handed this board with > scribbled specs. May be higher or lower or in a parallel universe. > As I and others have written - the diode didn't burn up because of transient energy. There is a supply problem, somewhere. -- Sue
From: Terry Given on 4 Mar 2007 05:44 Palindrome wrote: > John E. wrote: > >> Terry Given sez: >> >>> BTW in that position its probably a 47V zener, clamping the peak >>> drain voltage. >> >> >> >> I'd been turning over in my mind that this is indeed a zener, not >> simply a "plain" rectifier. It is indeed a 47 volt zener. >> Why was this diode chosen in the design? I'm familiar with the >> standard diode being used to short-circuit the back-EMF from the >> solenoid, but I can't figure out the purpose of a zener used in this >> location. > > > The zener does a better, but more expensive, job of protecting the > series switching element. It limits both positive and negative > transients. its pretty hard finding a FET without a body diode, so negative transients are invariably taken care of regardless of the type of clamp circuit. A diode across the switched inductor does stop most (but not > all) of the switching transient - but doesn't protect the series element > from transients on the supply rails, by "series element" you must be referring to the FET. Yep, the zener will protect the FET against voltage spikes on the 42V bus. Of course FETs nowadays are rated for avalanche energy..... caused by other inductances > elsewhere reacting to the sudden change in current. Que? It is usual to > combine these sorts of design with reasonably fast (eg > tantalum)electrolytics placed locally - to act as energy "tanks" to > supply and sink transient power. seeing as Im being a pedantic sod, I'll point out that tantalums are not electrolytics (and vice versa). I once had a serious brain fart in this regard, making a small motor controller at Uni. It ran from a 3-phase supply, and seeing as full-wave-rectified 3-phase AC has ~15% ripple, I figured I didnt need a DC bus cap. Which worked fine, until the first time I turned the H-bridge off with current flowing in the motor :) 30 minutes, 4 FETs and a complete set of gate drive circuits later, I added a large cap. oops. > >> >> Vdd >> /\ >> | >> | >> SS >> SS Solenoid >> SS >> | >> +-----+ >> | | >> | | >> BUZ72 | /---/ ZY47 >> FET |--+ /\ Diode >> -------| | |--+ | >> | | >> \ | >> 0.27R / | >> \ | >> | | >> | | >> /// /// >> >> I think that should show proper in Courier or Monaco... or Paris (c: >> I must add that Vdd is *reported* to be 42vdc. I was handed this board >> with scribbled specs. May be higher or lower or in a parallel universe. > > As I and others have written - the diode didn't burn up because of > transient energy. There is a supply problem, somewhere. > assuming the thing ever worked properly, which it sounds like it did. conceivably a shorted solenoid could have stored enough energy to end up snotting the zener, but as you say, a supply overvoltage would definitely kill it. And it doesnt even have to be that much, just continuous. Cheers Terry
From: Palindrome on 4 Mar 2007 06:07 Terry Given wrote: > Palindrome wrote: > >> John E. wrote: >> >>> Terry Given sez: >>> >>>> BTW in that position its probably a 47V zener, clamping the peak >>>> drain voltage. >>> >>> >>> >>> >>> I'd been turning over in my mind that this is indeed a zener, not >>> simply a "plain" rectifier. It is indeed a 47 volt zener. >>> Why was this diode chosen in the design? I'm familiar with the >>> standard diode being used to short-circuit the back-EMF from the >>> solenoid, but I can't figure out the purpose of a zener used in this >>> location. >> >> >> >> The zener does a better, but more expensive, job of protecting the >> series switching element. It limits both positive and negative >> transients. > > > its pretty hard finding a FET without a body diode, so negative > transients are invariably taken care of regardless of the type of clamp > circuit. Hence why I wrote "series switching element" rather than FET. If the designer was brought up designing using pnp/npn transistors, he may have always protected them this way. > > A diode across the switched inductor does stop most (but not > >> all) of the switching transient - but doesn't protect the series >> element from transients on the supply rails, > > > by "series element" you must be referring to the FET. Yep, the zener > will protect the FET against voltage spikes on the 42V bus. Of course > FETs nowadays are rated for avalanche energy..... > > > caused by other inductances > >> elsewhere reacting to the sudden change in current. > > > Que? The power distribution and supply system connected to the load will, itself have a transient response (eg have series inductance) and may easily overshoot following step changes in load. > > It is usual to > >> combine these sorts of design with reasonably fast (eg >> tantalum)electrolytics placed locally - to act as energy "tanks" to >> supply and sink transient power. > > > seeing as Im being a pedantic sod, I'll point out that tantalums are not > electrolytics (and vice versa). "Tantalums Tantalum capacitors are also electrolytic, constructed with a very porous anode made with tantalum powder. This powder is pressed into a pellet form with a tantalum wire inserted." http://www.electronicproducts.com/print.asp?ArticleURL=itw.may2006.html > > I once had a serious brain fart in this regard, making a small motor > controller at Uni. It ran from a 3-phase supply, and seeing as > full-wave-rectified 3-phase AC has ~15% ripple, I figured I didnt need a > DC bus cap. > > Which worked fine, until the first time I turned the H-bridge off with > current flowing in the motor :) 30 minutes, 4 FETs and a complete set of > gate drive circuits later, I added a large cap. oops. > > >> >>> >>> Vdd >>> /\ >>> | >>> | >>> SS >>> SS Solenoid >>> SS >>> | >>> +-----+ >>> | | >>> | | >>> BUZ72 | /---/ ZY47 >>> FET |--+ /\ Diode >>> -------| | |--+ | >>> | | >>> \ | >>> 0.27R / | >>> \ | >>> | | >>> | | >>> /// /// >>> >>> I think that should show proper in Courier or Monaco... or Paris (c: >>> I must add that Vdd is *reported* to be 42vdc. I was handed this >>> board with scribbled specs. May be higher or lower or in a parallel >>> universe. >> >> >> As I and others have written - the diode didn't burn up because of >> transient energy. There is a supply problem, somewhere. >> > > assuming the thing ever worked properly, which it sounds like it did. > > conceivably a shorted solenoid could have stored enough energy to end up > snotting the zener, but as you say, a supply overvoltage would > definitely kill it. And it doesnt even have to be that much, just > continuous. I'd go for the continuous - every time where component and circuit board burning were evident. -- Sue
From: Terry Given on 4 Mar 2007 06:46
Palindrome wrote: > Terry Given wrote: > >> Palindrome wrote: >> >>> John E. wrote: >>> >>>> Terry Given sez: >>>> >>>>> BTW in that position its probably a 47V zener, clamping the peak >>>>> drain voltage. >>>> >>>> >>>> >>>> >>>> >>>> I'd been turning over in my mind that this is indeed a zener, not >>>> simply a "plain" rectifier. It is indeed a 47 volt zener. >>>> Why was this diode chosen in the design? I'm familiar with the >>>> standard diode being used to short-circuit the back-EMF from the >>>> solenoid, but I can't figure out the purpose of a zener used in this >>>> location. >>> >>> >>> >>> >>> The zener does a better, but more expensive, job of protecting the >>> series switching element. It limits both positive and negative >>> transients. >> >> >> >> its pretty hard finding a FET without a body diode, so negative >> transients are invariably taken care of regardless of the type of >> clamp circuit. > > > Hence why I wrote "series switching element" rather than FET. If the > designer was brought up designing using pnp/npn transistors, he may have > always protected them this way. its surprising how much stuff ends up being designed that way - "because", rather than having a good reason. > >> >> A diode across the switched inductor does stop most (but not >> >>> all) of the switching transient - but doesn't protect the series >>> element from transients on the supply rails, >> >> >> >> by "series element" you must be referring to the FET. Yep, the zener >> will protect the FET against voltage spikes on the 42V bus. Of course >> FETs nowadays are rated for avalanche energy..... >> >> >> caused by other inductances >> >>> elsewhere reacting to the sudden change in current. >> >> >> >> Que? > > > The power distribution and supply system connected to the load will, > itself have a transient response (eg have series inductance) and may > easily overshoot following step changes in load. > now thats a nicely worded sentence. >> >> It is usual to >> >>> combine these sorts of design with reasonably fast (eg >>> tantalum)electrolytics placed locally - to act as energy "tanks" to >>> supply and sink transient power. >> >> >> >> seeing as Im being a pedantic sod, I'll point out that tantalums are >> not electrolytics (and vice versa). > > "Tantalums > Tantalum capacitors are also electrolytic, constructed with a very > porous anode made with tantalum powder. This powder is pressed into a > pellet form with a tantalum wire inserted." > http://www.electronicproducts.com/print.asp?ArticleURL=itw.may2006.html > ya got me :) common usage of "electrolytic" refers to ye olde carboxylic acid-style electrolytes, for whatever reason tantalums are always called tantalums. >> >> I once had a serious brain fart in this regard, making a small motor >> controller at Uni. It ran from a 3-phase supply, and seeing as >> full-wave-rectified 3-phase AC has ~15% ripple, I figured I didnt need >> a DC bus cap. >> >> Which worked fine, until the first time I turned the H-bridge off with >> current flowing in the motor :) 30 minutes, 4 FETs and a complete set >> of gate drive circuits later, I added a large cap. oops. >> >> >>> >>>> >>>> Vdd >>>> /\ >>>> | >>>> | >>>> SS >>>> SS Solenoid >>>> SS >>>> | >>>> +-----+ >>>> | | >>>> | | >>>> BUZ72 | /---/ ZY47 >>>> FET |--+ /\ Diode >>>> -------| | |--+ | >>>> | | >>>> \ | >>>> 0.27R / | >>>> \ | >>>> | | >>>> | | >>>> /// /// >>>> >>>> I think that should show proper in Courier or Monaco... or Paris (c: >>>> I must add that Vdd is *reported* to be 42vdc. I was handed this >>>> board with scribbled specs. May be higher or lower or in a parallel >>>> universe. >>> >>> >>> >>> As I and others have written - the diode didn't burn up because of >>> transient energy. There is a supply problem, somewhere. >>> >> >> assuming the thing ever worked properly, which it sounds like it did. >> >> conceivably a shorted solenoid could have stored enough energy to end >> up snotting the zener, but as you say, a supply overvoltage would >> definitely kill it. And it doesnt even have to be that much, just >> continuous. > > > I'd go for the continuous - every time where component and circuit board > burning were evident. it all depends on how much transient energy there was. when working with big stuff, components can (and do) disappear completely. If any form of arc develops as a result of some transient phenomenon, its pretty easy to burn big holes in things. and a transient that snots the zener will make it fail short-circuit (unless it disappears), at which point it will then fry. however such pontification is essentially meaningless; the supply rail needs to be checked.... Cheers Terry |