spice diode model question
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From: Martin Riddle on 20 Dec 2009 18:13 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:9j3ti5ha61p9nb7k16onap6bcl4sc98b4g(a)4ax.com... > On Sun, 20 Dec 2009 14:30:13 -0500, "Martin Riddle" > <martin_rid(a)verizon.net> wrote: > >>I have a diode that I want to model, it's a 85HF20. >><http://www.vishay.com/docs/93529/85hf.pdf> >>This is one of those standard stud mounted rectifiers. >> >>This is the model that I created for it: >>.model 85HF20 D(BV=200 Ibv=.009 Is=1e-3 Cjo=2300p M=0.43 Rs=.00169 >>Tt=100u Eg=1.11 Vj=1.2 Fc=0.5 N=1.1 ) >> >>Cjo was taken for a similar sized schottky . I don't have experience >>with these larger diodes so the model is almost default values. I >>don't >>need the Temperature parameters. Most of the reference books , I have, >>don't deal with the larger diodes. >>Is the Is parameter correct for this model? Any pointers? >> >>I basically need to know if this slow diode will clamp a forward >>voltage >>from a inductor. the model above does work. But its no good if its >>wrong. ( I had another model that didn't work well) >> >>Thanks >> > > If you're concerned about the "forward recovery time" thing, I doubt > that a model will be very useful. You'd really need to test an actual > part to see how it behaves. To complicate life, several of the > different voltage rated versions may at various times come off the > same wafer. > > In general, higher voltage parts have wider junctions, approaching pin > diodes for, say, 600 volt parts, and they tend to be slower turning > on. I've slammed 48 volts across a 600 volt "fast recovery" diode and > it took a couple hundred nanoseconds to ramp up to 50 amps. > > What's your circuit? > > John > > The inductor I want to clamp, is the voltage on is a set of cables. I'm figuring on 100nh or so for each cable, so a 200nh inductor. There will be 3KA flowing thru the cables for 1-20ms. It's the turn off that generates the reversevoltage. So I want to dump that energy into the diode. ( just like a diode across a relay coil) The peak forward current is 1.2kA and decays for a few hundred us, within the Ifsm of the diode. I just want to be sure the diode will conduct within a reasonable amount of time. I have a set of Mosfets that won't like the added drain voltage. I think your right, I need to get the diode and see how fast it will conduct. Cheers
From: Jon Kirwan on 20 Dec 2009 19:01 On Sun, 20 Dec 2009 14:25:45 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >On Sun, 20 Dec 2009 13:03:32 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>I've slammed 48 volts across a 600 volt "fast recovery" diode and >>it took a couple hundred nanoseconds to ramp up to 50 amps. >> >[snip] >> >>John > >Which sounds like 200nH in the wiring ;-) > > ...Jim Thompson Hehe. Indeed. From John's numbers, 48V * 200ns / 50A = 192nH. Jon
From: Martin Riddle on 20 Dec 2009 22:02 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote in message news:da4ti5der5va17dq9i00f5iqbbuqagkktc(a)4ax.com... > On Sun, 20 Dec 2009 13:46:58 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: > >>On Sun, 20 Dec 2009 14:30:13 -0500, "Martin Riddle" >><martin_rid(a)verizon.net> wrote: >> >>>I have a diode that I want to model, it's a 85HF20. >>><http://www.vishay.com/docs/93529/85hf.pdf> >>>This is one of those standard stud mounted rectifiers. >>> >>>This is the model that I created for it: >>>.model 85HF20 D(BV=200 Ibv=.009 Is=1e-3 Cjo=2300p M=0.43 Rs=.00169 >>>Tt=100u Eg=1.11 Vj=1.2 Fc=0.5 N=1.1 ) >>> >>>Cjo was taken for a similar sized schottky . I don't have experience >>>with these larger diodes so the model is almost default values. I >>>don't >>>need the Temperature parameters. Most of the reference books , I >>>have, >>>don't deal with the larger diodes. >>>Is the Is parameter correct for this model? Any pointers? >>> >>>I basically need to know if this slow diode will clamp a forward >>>voltage >>>from a inductor. the model above does work. But its no good if its >>>wrong. ( I had another model that didn't work well) >>> >>>Thanks >>> >> >>The basic Spice diode equation stumbles with Schottky's. >> >>To fit DC, fiddle with IS, RS, IK, N (not M, that's for capacitance) >>_and_ EG. >> >>Hint: EG ~= 0.58 seems to be what most of my models use. >> >>The resulting model is NOT good over temperature. I've had fairly >>good results paralleling diode models with different IS's, etc., but >>it's a tedious curve-fitting process. >> >> ...Jim Thompson > > Also found this page... > > http://www.diodes.com/products/spicemodels/index.php > > ...Jim Thompson Thanks, Forgot about diodes inc. Interesting that Diodes inc bought Zetex. But no models for the power rectifiers. It seems nobody has a model for >10A I found some info on N for power diodes. Its close to 2. Cheers Cheers
From: John Larkin on 20 Dec 2009 23:29 On Sun, 20 Dec 2009 16:01:52 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Sun, 20 Dec 2009 14:25:45 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: > >>On Sun, 20 Dec 2009 13:03:32 -0800, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>I've slammed 48 volts across a 600 volt "fast recovery" diode and >>>it took a couple hundred nanoseconds to ramp up to 50 amps. >>> >>[snip] >>> >>>John >> >>Which sounds like 200nH in the wiring ;-) >> >> ...Jim Thompson > >Hehe. Indeed. From John's numbers, 48V * 200ns / 50A = 192nH. > >Jon The diode in question is inside this: http://www.highlandtechnology.com/DSS/T220DS.html It's a drift step-recovery (Grehkov) diode, or rather a commercial power diode used in DSRD mode. I assure you that we know exactly what we're doing here, and the diode behaves as described. The inductance of the drive circuit (+48 volts followed by -400) is around 8 nH. The pulser was desiged to rip ions off a microtip in a tomographic atom probe. Google the obvious and learn something. Start here: http://www.avtechpulse.com/papers/thesis/8/ John
From: John Larkin on 20 Dec 2009 23:41
On Sun, 20 Dec 2009 18:13:35 -0500, "Martin Riddle" <martin_rid(a)verizon.net> wrote: > > >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >message news:9j3ti5ha61p9nb7k16onap6bcl4sc98b4g(a)4ax.com... >> On Sun, 20 Dec 2009 14:30:13 -0500, "Martin Riddle" >> <martin_rid(a)verizon.net> wrote: >> >>>I have a diode that I want to model, it's a 85HF20. >>><http://www.vishay.com/docs/93529/85hf.pdf> >>>This is one of those standard stud mounted rectifiers. >>> >>>This is the model that I created for it: >>>.model 85HF20 D(BV=200 Ibv=.009 Is=1e-3 Cjo=2300p M=0.43 Rs=.00169 >>>Tt=100u Eg=1.11 Vj=1.2 Fc=0.5 N=1.1 ) >>> >>>Cjo was taken for a similar sized schottky . I don't have experience >>>with these larger diodes so the model is almost default values. I >>>don't >>>need the Temperature parameters. Most of the reference books , I have, >>>don't deal with the larger diodes. >>>Is the Is parameter correct for this model? Any pointers? >>> >>>I basically need to know if this slow diode will clamp a forward >>>voltage >>>from a inductor. the model above does work. But its no good if its >>>wrong. ( I had another model that didn't work well) >>> >>>Thanks >>> >> >> If you're concerned about the "forward recovery time" thing, I doubt >> that a model will be very useful. You'd really need to test an actual >> part to see how it behaves. To complicate life, several of the >> different voltage rated versions may at various times come off the >> same wafer. >> >> In general, higher voltage parts have wider junctions, approaching pin >> diodes for, say, 600 volt parts, and they tend to be slower turning >> on. I've slammed 48 volts across a 600 volt "fast recovery" diode and >> it took a couple hundred nanoseconds to ramp up to 50 amps. >> >> What's your circuit? >> >> John >> >> > >The inductor I want to clamp, is the voltage on is a set of cables. I'm >figuring on 100nh or so for each cable, so a 200nh inductor. There will >be 3KA flowing thru the cables for 1-20ms. It's the turn off that >generates the reversevoltage. >So I want to dump that energy into the diode. ( just like a diode across >a relay coil) >The peak forward current is 1.2kA and decays for a few hundred us, >within the Ifsm of the diode. > >I just want to be sure the diode will conduct within a reasonable amount >of time. I have a set of Mosfets that won't like the added drain >voltage. > >I think your right, I need to get the diode and see how fast it will >conduct. > >Cheers > > Yikes. High voltage pn diodes have big lightly-doped (intrinsic) regions so act like/are PIN diodes. They turn on and off slow. SiC diodes are a lot faster, assuming you have too much voltage to use schottkies. Infineon? Cree? You'd probably need a few in parallel to handle that current and keep the parasitic inductance down. John |