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spice diode model question

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

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  1. 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)

  2. 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

    I think your right, I need to get the diode and see how fast it will

  3. Jon Kirwan

    Jon Kirwan Guest

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

  4. Thanks, Forgot about diodes inc.

    Interesting that Diodes inc bought Zetex. But no models for the power
    It seems nobody has a model for >10A

    I found some info on N for power diodes. Its close to 2.


  5. Jon Kirwan

    Jon Kirwan Guest

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

  6. Fred Bartoli

    Fred Bartoli Guest

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

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