# spice diode model question

Discussion in 'Electronic Design' started by Martin Riddle, Dec 20, 2009.

1. ### Martin RiddleGuest

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

2. ### Martin RiddleGuest

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

3. ### Jon KirwanGuest

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

Jon

4. ### Martin RiddleGuest

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

5. ### Jon KirwanGuest

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

Jon

6. ### Fred BartoliGuest

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.

7. ### Martin RiddleGuest

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

Cheers