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spice diode model question

I have a diode that I want to model, it's a 85HF20.

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

Reply to
Martin Riddle
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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

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
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Reply to
Jim Thompson

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

Reply to
John Larkin

Also found this page...

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...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
                    Help save the environment!
              Please dispose of socialism properly!
Reply to
Jim Thompson

[snip]

Which sounds like 200nH in the wiring ;-) ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

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| 1962 | Help save the environment! Please dispose of socialism properly!

Reply to
Jim Thompson

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

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

Reply to
Martin Riddle

Hehe. Indeed. From John's numbers, 48V * 200ns / 50A = 192nH.

Jon

Reply to
Jon Kirwan

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

Reply to
Martin Riddle

The diode in question is inside this:

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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:

formatting link

John

Reply to
John Larkin

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

Reply to
John Larkin

Glad to and thanks for a link. I also see where Jim was speaking from.

Jon

Reply to
Jon Kirwan

Hehe. Indeed.

John

Reply to
John Larkin

Martin Riddle a écrit :

Well, I just had the same kind of pb to solve, but at somewhat higher currents: full multi-IGBTs 2.5kV bridge with SC current upto the 20kA range. The very well made supply loop (not my design) is around 70nH and the high side IGBT free wheeling diode won't do anything WRT the supply inductance, so we turned to active clamping. I just had some news about the outcome and it clamps very, very cleanly. You have to be very careful and do things well though.

You don't tell what your switches are, but if you're using IGBTs (or MOSFETs if it's low voltage) that might be your ticket.

Oh, and at the huge di/dt involved the wheeling diode also has some

300-400V VF voltage, which too is *not* related to IGBT inductance. 
--
Thanks,
Fred.
Reply to
Fred Bartoli

I see just like a synchronous rectifier in a smps. That?s a little more costly. I'll reserve that idea for last.

Cheers

Reply to
Martin Riddle

=3D.00169

l
1.2kA into 200nH is only 144mJ -- you could just let your monster FETs avalanche and gobble it up.

Or maybe prime the diode with a little d.c., for speed? Hmmm. Nope, can't see a clean way to do that offhand.

-- Cheers, James Arthur

Reply to
dagmargoodboat

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