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Ultrafast recovery diodes

Discussion in 'Electronic Basics' started by oparr, Nov 3, 2005.

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  1. oparr

    oparr Guest

    Currently designing something for which an ultrafast recovery diode is
    recommended but on checking the specs and package types for devices so
    classified at Digikey, I don't like what I see....Current ratings start at
    1A which is much more than I need and SMD package types are typically large
    and bulky SMB or SMA. Forward and reverse recovery times are typically 25 -

    Looking at some switching diodes not claiming to be fast, superfast or
    ultrafast, I see current ratings and package types right up my street.
    Reverse recovery times are as low as 4ns but no mention is made of forward
    recovery times. Two questions...What are all the relevant attributes of a
    ultrafast recovery diode? Why wouldn't a switching diode with a 4ns reverse
    recovery time not be more than suitable as an ultrafast recovery diode?
  2. Jan Wagner

    Jan Wagner Guest

    4ns sounds like a schottky diode or small-signal diode. These are
    all fast and don't have to be explicitly hyped as "ultrafast".

    AFAIK there are no special required attributes or values for
    "ultrafast", "fast", "standard" etc. It depends on the manufacturer
    or reseller and is mostly marketing talk. E.g. the BYW98 (50ns trr)
    diode is called "fast recovery" by ST, but all resellers seem to
    think it's "ultrafast".

    Diodes may also be named "slower" than what they are. For example
    the 1n4148 (max 4ns trr) is usually either called "small-signal" or
    "fast", but haven't seen "ultrafast" anywhere yet.

    And then there's also "soft recovery", but again, what can be
    considered an objective criteria to qualify as "soft recovery"? :)

    So, summary: marketing BS. But okay, I'm not in the
    semiconductor&process business, so maybe someone else can give a
    better answer or correct me here...

    - Jan
  3. Rich Grise

    Rich Grise Guest

    Apparently you've never googled for one yet then. They are used in
    SPSs when Schottkys don't have enough reverse breakdown. They're
    like ordinary silicon diodes, but not with the Schottky doping but
    with doping and other characteristics that minimize reverse carrier
    recovery time, making them "ultrafast", like, switching in times
    comparable to a Schottky or signal diode, but at power diode
    power levels.

  4. Rich Grise wrote...
  5. Guest

    Apparently you've never googled for one yet then.

    Google? What's that?
    Yes, that's about right. Trr is specified at higher current levels
    (typically 500ma as opposed to 30ma). Seems kind of dumb for
    Intenational Rectifier to specify an ultrafast diode (with 1A current
    rating) where current levels never exceed 50ma.
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