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spice diode model question

M

Martin Riddle

Jan 1, 1970
0
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
 
M

Martin Riddle

Jan 1, 1970
0
John Larkin said:
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
 
J

Jon Kirwan

Jan 1, 1970
0
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
 
J

Jon Kirwan

Jan 1, 1970
0
On Sun, 20 Dec 2009 13:03:32 -0800, John Larkin

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/

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

Jon
 
F

Fred Bartoli

Jan 1, 1970
0
Martin Riddle a écrit :
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

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.
 
M

Martin Riddle

Jan 1, 1970
0
Fred Bartoli said:
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.

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

Cheers
 
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