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Schottky diode

Started by Michael November 23, 2015
What is Schottky diode turn on time? 
I know that it is very low (have always been low enough for me). Until now that is... I am looking for more quantitative information
Reason for this posting:
Prototype with MBRX140-TP diodes behaves differently from the product board with 1N5819HW. The diodes are used to keep inductive load driver output "contained" between power rail and GND.
Both boards are laid very similarly and very carefully; PS is very carefully decoupled.  Prototype (uses MBRX140-TP) works fine, product board (uses 1N5819) keeps failing because output swings way above power rail.
Neither diode datasheet has turn on time information.
Any insight will be appreciated.
Thanks
On 11/23/2015 09:46 AM, Michael wrote:
> What is Schottky diode turn on time? I know that it is very low (have > always been low enough for me). Until now that is... I am looking for > more quantitative information Reason for this posting: Prototype with > MBRX140-TP diodes behaves differently from the product board with > 1N5819HW. The diodes are used to keep inductive load driver output > "contained" between power rail and GND. Both boards are laid very > similarly and very carefully; PS is very carefully decoupled. > Prototype (uses MBRX140-TP) works fine, product board (uses 1N5819) > keeps failing because output swings way above power rail. Neither > diode datasheet has turn on time information. Any insight will be > appreciated. Thanks >
Interesting. The turn-on delay in a PN diode arises because the E field is initially shielded out by free carriers between the contact and the junction. Those aren't normally present in a Schottky, which is part of the point--instantaneous turn-on. I use 1N5819s in prototype SMPSes all the time, and haven't noticed any voltage overshoot. How long does the overshoot last? How hard are you hitting the diode? Is it possible that you got counterfeit 1N5819s? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Monday, November 23, 2015 at 10:02:29 AM UTC-5, Phil Hobbs wrote:
> On 11/23/2015 09:46 AM, Michael wrote: > > What is Schottky diode turn on time? I know that it is very low (have > > always been low enough for me). Until now that is... I am looking for > > more quantitative information Reason for this posting: Prototype with > > MBRX140-TP diodes behaves differently from the product board with > > 1N5819HW. The diodes are used to keep inductive load driver output > > "contained" between power rail and GND. Both boards are laid very > > similarly and very carefully; PS is very carefully decoupled. > > Prototype (uses MBRX140-TP) works fine, product board (uses 1N5819) > > keeps failing because output swings way above power rail. Neither > > diode datasheet has turn on time information. Any insight will be > > appreciated. Thanks > > > > Interesting. The turn-on delay in a PN diode arises because the E field > is initially shielded out by free carriers between the contact and the > junction. Those aren't normally present in a Schottky, which is part > of the point--instantaneous turn-on. I use 1N5819s in prototype SMPSes > all the time, and haven't noticed any voltage overshoot. > > How long does the overshoot last? > How hard are you hitting the diode? > > Is it possible that you got counterfeit 1N5819s? > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > > hobbs at electrooptical dot net > http://electrooptical.net
The overshoot lasts ~1/2 of 125MHz period ringing (it is not measurement artifact, believe me). I have a picture of this thing swinging 14V avove rail (ouch!) for ~3ns. The peak current is, say, 3-5A. Counterfeit parts?? This is something I haven't though about. The world we live in... Would anybody pull these tricks with (very cheap) 1N5819? What is the chance of getting counterfeit parts from reputable supplier (Digi-Key)?
On a sunny day (Mon, 23 Nov 2015 07:11:22 -0800 (PST)) it happened Michael
<mk617435@gmail.com> wrote in
<340aa6b2-e4ed-4460-87b3-cd8c575b4482@googlegroups.com>:
> >The overshoot lasts ~1/2 of 125MHz period ringing (it is not measurement artifact, believe me). I have a picture of this thing >swinging 14V avove rail (ouch!) for ~3ns. >The peak current is, say, 3-5A. >Counterfeit parts?? >This is something I haven't though about. The world we live in... >Would anybody pull these tricks with (very cheap) 1N5819? What is the chance of getting counterfeit parts from reputable >supplier (Digi-Key)?
Can you do a differential measurement across the diodes (ch1 - ch2) If the pulse is not there, then it is likely PCB. Yes, fake parts are everywhere.
On 11/23/2015 10:11 AM, Michael wrote:
> On Monday, November 23, 2015 at 10:02:29 AM UTC-5, Phil Hobbs wrote: >> On 11/23/2015 09:46 AM, Michael wrote: >>> What is Schottky diode turn on time? I know that it is very low >>> (have always been low enough for me). Until now that is... I am >>> looking for more quantitative information Reason for this >>> posting: Prototype with MBRX140-TP diodes behaves differently >>> from the product board with 1N5819HW. The diodes are used to >>> keep inductive load driver output "contained" between power rail >>> and GND. Both boards are laid very similarly and very carefully; >>> PS is very carefully decoupled. Prototype (uses MBRX140-TP) >>> works fine, product board (uses 1N5819) keeps failing because >>> output swings way above power rail. Neither diode datasheet has >>> turn on time information. Any insight will be appreciated. >>> Thanks >>> >> >> Interesting. The turn-on delay in a PN diode arises because the E >> field is initially shielded out by free carriers between the >> contact and the junction. Those aren't normally present in a >> Schottky, which is part of the point--instantaneous turn-on. I >> use 1N5819s in prototype SMPSes all the time, and haven't noticed >> any voltage overshoot. >> >> How long does the overshoot last? How hard are you hitting the >> diode? >> >> Is it possible that you got counterfeit 1N5819s? >> >> Cheers >> >> Phil Hobbs >> >> -- Dr Philip C D Hobbs Principal Consultant ElectroOptical >> Innovations LLC Optics, Electro-optics, Photonics, Analog >> Electronics >> >> 160 North State Road #203 Briarcliff Manor NY 10510 >> >> hobbs at electrooptical dot net http://electrooptical.net > > The overshoot lasts ~1/2 of 125MHz period ringing (it is not > measurement artifact, believe me). I have a picture of this thing > swinging 14V avove rail (ouch!) for ~3ns.
Oh. That's pretty well outside the range of usual uses for a 1N5819!
> The peak current is, say, 3-5A.
Well, even with a sinusoid, getting 14V from a 4A current at 125 MHz needs only L = Vpeak/(dI/dt) = 14/(2*pi*4A*125e6) = 4 nH. That's an easily believable value for a 1N5819--it's equivalent to about 5mm of wire.
>Counterfeit parts?? This is something > I haven't though about. The world we live in... Would anybody pull > these tricks with (very cheap) 1N5819? What is the chance of getting > counterfeit parts from reputable supplier (Digi-Key)?
Well, it doesn't look like they need to be counterfeit to explain the effect. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Monday, November 23, 2015 at 10:30:02 AM UTC-5, Phil Hobbs wrote:
> On 11/23/2015 10:11 AM, Michael wrote: > > On Monday, November 23, 2015 at 10:02:29 AM UTC-5, Phil Hobbs wrote: > >> On 11/23/2015 09:46 AM, Michael wrote: > >>> What is Schottky diode turn on time? I know that it is very low > >>> (have always been low enough for me). Until now that is... I am > >>> looking for more quantitative information Reason for this > >>> posting: Prototype with MBRX140-TP diodes behaves differently > >>> from the product board with 1N5819HW. The diodes are used to > >>> keep inductive load driver output "contained" between power rail > >>> and GND. Both boards are laid very similarly and very carefully; > >>> PS is very carefully decoupled. Prototype (uses MBRX140-TP) > >>> works fine, product board (uses 1N5819) keeps failing because > >>> output swings way above power rail. Neither diode datasheet has > >>> turn on time information. Any insight will be appreciated. > >>> Thanks > >>> > >> > >> Interesting. The turn-on delay in a PN diode arises because the E > >> field is initially shielded out by free carriers between the > >> contact and the junction. Those aren't normally present in a > >> Schottky, which is part of the point--instantaneous turn-on. I > >> use 1N5819s in prototype SMPSes all the time, and haven't noticed > >> any voltage overshoot. > >> > >> How long does the overshoot last? How hard are you hitting the > >> diode? > >> > >> Is it possible that you got counterfeit 1N5819s? > >> > >> Cheers > >> > >> Phil Hobbs > >> > >> -- Dr Philip C D Hobbs Principal Consultant ElectroOptical > >> Innovations LLC Optics, Electro-optics, Photonics, Analog > >> Electronics > >> > >> 160 North State Road #203 Briarcliff Manor NY 10510 > >> > >> hobbs at electrooptical dot net http://electrooptical.net > > > > The overshoot lasts ~1/2 of 125MHz period ringing (it is not > > measurement artifact, believe me). I have a picture of this thing > > swinging 14V avove rail (ouch!) for ~3ns. > > Oh. That's pretty well outside the range of usual uses for a 1N5819! > > > The peak current is, say, 3-5A. > > Well, even with a sinusoid, getting 14V from a 4A current at 125 MHz > needs only > > L = Vpeak/(dI/dt) = 14/(2*pi*4A*125e6) = 4 nH. > > That's an easily believable value for a 1N5819--it's equivalent to about > 5mm of wire. > > >Counterfeit parts?? This is something > > I haven't though about. The world we live in... Would anybody pull > > these tricks with (very cheap) 1N5819? What is the chance of getting > > counterfeit parts from reputable supplier (Digi-Key)? > > Well, it doesn't look like they need to be counterfeit to explain the > effect. > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > > hobbs at electrooptical dot net > http://electrooptical.net
Agree. Somewhat. dI/dt=4A/4ns=10^9 A/s; L=V/(dI/dt)~14nH - ~20mm of 1mm diameter wire. The layout is much better than that. Another argument: MBRX140-TP in identical package does not misbehave. Regards Michael
On Monday, November 23, 2015 at 9:46:50 AM UTC-5, Michael wrote:
> What is Schottky diode turn on time? > I know that it is very low (have always been low enough for me). Until now that is... I am looking for more quantitative information > Reason for this posting: > Prototype with MBRX140-TP diodes behaves differently from the product board with 1N5819HW. The diodes are used to keep inductive load driver output "contained" between power rail and GND. > Both boards are laid very similarly and very carefully; PS is very carefully decoupled. Prototype (uses MBRX140-TP) works fine, product board (uses 1N5819) keeps failing because output swings way above power rail. > Neither diode datasheet has turn on time information. > Any insight will be appreciated. > Thanks
OK I first need to warn you that most of my ideas are a bit crazy. (So take them with a grain of salt.) But I would guess a turn on time of some diode capacitance, times whatever the effective resistance is. Perhaps one has less C and or resistance. George H.
On Monday, November 23, 2015 at 10:44:55 AM UTC-5, Michael wrote:
> On Monday, November 23, 2015 at 10:30:02 AM UTC-5, Phil Hobbs wrote: > > On 11/23/2015 10:11 AM, Michael wrote: > > > On Monday, November 23, 2015 at 10:02:29 AM UTC-5, Phil Hobbs wrote: > > >> On 11/23/2015 09:46 AM, Michael wrote: > > >>> What is Schottky diode turn on time? I know that it is very low > > >>> (have always been low enough for me). Until now that is... I am > > >>> looking for more quantitative information Reason for this > > >>> posting: Prototype with MBRX140-TP diodes behaves differently > > >>> from the product board with 1N5819HW. The diodes are used to > > >>> keep inductive load driver output "contained" between power rail > > >>> and GND. Both boards are laid very similarly and very carefully; > > >>> PS is very carefully decoupled. Prototype (uses MBRX140-TP) > > >>> works fine, product board (uses 1N5819) keeps failing because > > >>> output swings way above power rail. Neither diode datasheet has > > >>> turn on time information. Any insight will be appreciated. > > >>> Thanks > > >>> > > >> > > >> Interesting. The turn-on delay in a PN diode arises because the E > > >> field is initially shielded out by free carriers between the > > >> contact and the junction. Those aren't normally present in a > > >> Schottky, which is part of the point--instantaneous turn-on. I > > >> use 1N5819s in prototype SMPSes all the time, and haven't noticed > > >> any voltage overshoot. > > >> > > >> How long does the overshoot last? How hard are you hitting the > > >> diode? > > >> > > >> Is it possible that you got counterfeit 1N5819s? > > >> > > >> Cheers > > >> > > >> Phil Hobbs > > >> > > >> -- Dr Philip C D Hobbs Principal Consultant ElectroOptical > > >> Innovations LLC Optics, Electro-optics, Photonics, Analog > > >> Electronics > > >> > > >> 160 North State Road #203 Briarcliff Manor NY 10510 > > >> > > >> hobbs at electrooptical dot net http://electrooptical.net > > > > > > The overshoot lasts ~1/2 of 125MHz period ringing (it is not > > > measurement artifact, believe me). I have a picture of this thing > > > swinging 14V avove rail (ouch!) for ~3ns. > > > > Oh. That's pretty well outside the range of usual uses for a 1N5819! > > > > > The peak current is, say, 3-5A. > > > > Well, even with a sinusoid, getting 14V from a 4A current at 125 MHz > > needs only > > > > L = Vpeak/(dI/dt) = 14/(2*pi*4A*125e6) = 4 nH. > > > > That's an easily believable value for a 1N5819--it's equivalent to about > > 5mm of wire. > > > > >Counterfeit parts?? This is something > > > I haven't though about. The world we live in... Would anybody pull > > > these tricks with (very cheap) 1N5819? What is the chance of getting > > > counterfeit parts from reputable supplier (Digi-Key)? > > > > Well, it doesn't look like they need to be counterfeit to explain the > > effect. > > > > Cheers > > > > Phil Hobbs > > > > -- > > Dr Philip C D Hobbs > > Principal Consultant > > ElectroOptical Innovations LLC > > Optics, Electro-optics, Photonics, Analog Electronics > > > > 160 North State Road #203 > > Briarcliff Manor NY 10510 > > > > hobbs at electrooptical dot net > > http://electrooptical.net > > Agree. Somewhat. > dI/dt=4A/4ns=10^9 A/s; L=V/(dI/dt)~14nH - ~20mm of 1mm diameter wire. The layout is much better than that. > Another argument: MBRX140-TP in identical package does not misbehave. > Regards > Michael
I populated (working) prototype with "counterfeit suspected" parts (1N58190). The ringing (there is always some) is barely distinguishable (only with glasses on) from the one with MBRX140-TP. :o(
On 11/23/2015 10:44 AM, Michael wrote:
> On Monday, November 23, 2015 at 10:30:02 AM UTC-5, Phil Hobbs wrote: >> On 11/23/2015 10:11 AM, Michael wrote: >>> On Monday, November 23, 2015 at 10:02:29 AM UTC-5, Phil Hobbs wrote: >>>> On 11/23/2015 09:46 AM, Michael wrote: >>>>> What is Schottky diode turn on time? I know that it is very low >>>>> (have always been low enough for me). Until now that is... I am >>>>> looking for more quantitative information Reason for this >>>>> posting: Prototype with MBRX140-TP diodes behaves differently >>>>> from the product board with 1N5819HW. The diodes are used to >>>>> keep inductive load driver output "contained" between power rail >>>>> and GND. Both boards are laid very similarly and very carefully; >>>>> PS is very carefully decoupled. Prototype (uses MBRX140-TP) >>>>> works fine, product board (uses 1N5819) keeps failing because >>>>> output swings way above power rail. Neither diode datasheet has >>>>> turn on time information. Any insight will be appreciated. >>>>> Thanks >>>>> >>>> >>>> Interesting. The turn-on delay in a PN diode arises because the E >>>> field is initially shielded out by free carriers between the >>>> contact and the junction. Those aren't normally present in a >>>> Schottky, which is part of the point--instantaneous turn-on. I >>>> use 1N5819s in prototype SMPSes all the time, and haven't noticed >>>> any voltage overshoot. >>>> >>>> How long does the overshoot last? How hard are you hitting the >>>> diode? >>>> >>>> Is it possible that you got counterfeit 1N5819s? >>>>
>>>> hobbs at electrooptical dot net http://electrooptical.net >>> >>> The overshoot lasts ~1/2 of 125MHz period ringing (it is not >>> measurement artifact, believe me). I have a picture of this thing >>> swinging 14V avove rail (ouch!) for ~3ns. >> >> Oh. That's pretty well outside the range of usual uses for a 1N5819! >> >>> The peak current is, say, 3-5A. >> >> Well, even with a sinusoid, getting 14V from a 4A current at 125 MHz >> needs only >> >> L = Vpeak/(dI/dt) = 14/(2*pi*4A*125e6) = 4 nH. >> >> That's an easily believable value for a 1N5819--it's equivalent to about >> 5mm of wire. >>
<snip>
> > Agree. Somewhat. > dI/dt=4A/4ns=10^9 A/s; L=V/(dI/dt)~14nH - ~20mm of 1mm diameter wire. The layout is much better than that. > Another argument: MBRX140-TP in identical package does not misbehave.
Unless I'm misunderstanding, the overshoot lasts half a cycle, so it has to go up and back down in that 4ns. Thus I think you're optimistic by a factor of 2, and 7 nH is an easily believable figure for a 1A diode. (You're really abusing that 1N5819--its abs max rating is 1.5A for repetitive pulses of <50% duty cycle.) That could easily be caused by the internal construction of the diode, e.g. bond wires. It could also be an LC resonance inside the diode package. The 1N5819HW has almost twice the capacitance (50 pF vs 30 pF) of the MBRX140, and 50 pF and 7 nH resonate at 270 MHz. Anyway, the two are just about exactly the same price--7 cents for the MBRX140 vs 8 cents for the 1N5819HW in reels from Digikey--so why not just use the one that works? Cheers Phil Cheers Phil Hobbs
> Regards > Michael >
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On 11/23/2015 11:50 AM, Michael wrote:
> On Monday, November 23, 2015 at 10:44:55 AM UTC-5, Michael wrote: >> On Monday, November 23, 2015 at 10:30:02 AM UTC-5, Phil Hobbs >> wrote: >>> On 11/23/2015 10:11 AM, Michael wrote: >>>> On Monday, November 23, 2015 at 10:02:29 AM UTC-5, Phil Hobbs >>>> wrote: >>>>> On 11/23/2015 09:46 AM, Michael wrote: >>>>>> What is Schottky diode turn on time? I know that it is very >>>>>> low (have always been low enough for me). Until now that >>>>>> is... I am looking for more quantitative information Reason >>>>>> for this posting: Prototype with MBRX140-TP diodes behaves >>>>>> differently from the product board with 1N5819HW. The >>>>>> diodes are used to keep inductive load driver output >>>>>> "contained" between power rail and GND. Both boards are >>>>>> laid very similarly and very carefully; PS is very >>>>>> carefully decoupled. Prototype (uses MBRX140-TP) works >>>>>> fine, product board (uses 1N5819) keeps failing because >>>>>> output swings way above power rail. Neither diode datasheet >>>>>> has turn on time information. Any insight will be >>>>>> appreciated. Thanks >>>>>> >>>>> >>>>> Interesting. The turn-on delay in a PN diode arises because >>>>> the E field is initially shielded out by free carriers >>>>> between the contact and the junction. Those aren't normally >>>>> present in a Schottky, which is part of the >>>>> point--instantaneous turn-on. I use 1N5819s in prototype >>>>> SMPSes all the time, and haven't noticed any voltage >>>>> overshoot. >>>>> >>>>> How long does the overshoot last? How hard are you hitting >>>>> the diode? >>>>> >>>>> Is it possible that you got counterfeit 1N5819s? >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>>> >>>>> -- Dr Philip C D Hobbs Principal Consultant ElectroOptical >>>>> Innovations LLC Optics, Electro-optics, Photonics, Analog >>>>> Electronics >>>>> >>>>> 160 North State Road #203 Briarcliff Manor NY 10510 >>>>> >>>>> hobbs at electrooptical dot net http://electrooptical.net >>>> >>>> The overshoot lasts ~1/2 of 125MHz period ringing (it is not >>>> measurement artifact, believe me). I have a picture of this >>>> thing swinging 14V avove rail (ouch!) for ~3ns. >>> >>> Oh. That's pretty well outside the range of usual uses for a >>> 1N5819! >>> >>>> The peak current is, say, 3-5A. >>> >>> Well, even with a sinusoid, getting 14V from a 4A current at 125 >>> MHz needs only >>> >>> L = Vpeak/(dI/dt) = 14/(2*pi*4A*125e6) = 4 nH. >>> >>> That's an easily believable value for a 1N5819--it's equivalent >>> to about 5mm of wire. >>> >>>> Counterfeit parts?? This is something I haven't though about. >>>> The world we live in... Would anybody pull these tricks with >>>> (very cheap) 1N5819? What is the chance of getting counterfeit >>>> parts from reputable supplier (Digi-Key)? >>> >>> Well, it doesn't look like they need to be counterfeit to explain >>> the effect. >>> >>> Cheers >>> >>> Phil Hobbs >>> >>> -- Dr Philip C D Hobbs Principal Consultant ElectroOptical >>> Innovations LLC Optics, Electro-optics, Photonics, Analog >>> Electronics >>> >>> 160 North State Road #203 Briarcliff Manor NY 10510 >>> >>> hobbs at electrooptical dot net http://electrooptical.net >> >> Agree. Somewhat. dI/dt=4A/4ns=10^9 A/s; L=V/(dI/dt)~14nH - ~20mm of >> 1mm diameter wire. The layout is much better than that. Another >> argument: MBRX140-TP in identical package does not misbehave. >> Regards Michael > > I populated (working) prototype with "counterfeit suspected" parts > (1N58190). The ringing (there is always some) is barely > distinguishable (only with glasses on) from the one with MBRX140-TP. > :o(
Yeah, it's never the cheap simple thing that went wrong. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net