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Low Vf diode

Discussion in 'Electronic Design' started by Eeyore, Oct 17, 2006.

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  1. Eeyore

    Eeyore Guest

    I'm looking for a small-signal diode ( minimal Vrrm and If required )
    with the smallest possible Vf @ ~ 1mA.

    Any pointers ? I'm thinking Schottky ( leakage isn't an issue ) but I'm
    not familiar with what's readily available.

    Graham
     
  2. john jardine

    john jardine Guest

    For years Farnells have been doing the quaint, gold bonded Germanium, OA91.
    It's 0.32V @1ma. Just looked at a Schottky BAT85 though and find it's
    exactly the same!.
    john
     
  3. Phil Allison

    Phil Allison Guest

    "Eeyore"

    ** Try Germanium for the lowest Vf.

    Maybe a nice gold bonded one like the OA47 or AAZ15.

    Around 0.23 volts at 1mA.




    ......... Phil
     
  4. Greg Neill

    Greg Neill Guest

  5. Eeyore

    Eeyore Guest

    Funny that ! I was wondering about Ge.

    I wonder how they compare at say 10uA ?

    Graham
     
  6. Eeyore

    Eeyore Guest

    Cheers Phil.

    Graham
     
  7. Eeyore

    Eeyore Guest

  8. John Perry

    John Perry Guest

    Others have mentioned schottky, germanium, and active circuits. The
    only thing I've ever heard of any lower are biased diodes and, for the
    ultimate, the "back diode".

    If you've got plenty of bucks to spend, try American Microsemi and
    Herotek, both of whom claim to sell back diodes.

    John Perry
     
  9. Tom Bruhns

    Tom Bruhns Guest

    The slewing, of course, is always a problem when you get to high enough
    frequency. There's a cute circuit, though, that isn't quite as
    accurate but close, and doesn't have that problem. The basic idea is
    that you feed your signal in through a diode, to a resistor to a
    negative supply. The R-D node goes to an op amp (+) input. The op amp
    uses a matched diode feeding back from output to the (-) input, and an
    equal R to the neg. supply, so that the output tracks the input. Add
    one more diode, from the input R-D node to ground, so your input is
    ignored if below ground (or other reference of your choice). Or drive
    the second input counter-phase for full wave rectification. May or may
    not be useful to you, but I've found it to get around that slew-rate
    problem nicely when you don't need super DC accuracy. The op amp only
    needs to change direction suddenly, not slew half a volt suddenly.

    Cheers,
    Tom
     
  10. I suggest you search for parts called zero bias diodes.
    these are very low forward drop Schottky diodes such as:
    http://www.macom.com/DataSheets/MA4E2200 Series.pdf
     
  11. Eeyore

    Eeyore Guest

    I've never heard of this. What is it ?

    Graham
     
  12. Eeyore

    Eeyore Guest

    Nice trick.

    But I need the accuracy !

    Graham
     
  13. Eeyore

    Eeyore Guest

  14. Robert Baer

    Robert Baer Guest

    Naturally you know that a "back diode" is a tunnel diode where the
    peak current is the same as the valley current.
    Net result is equivalent to a diode with zero forward voltage and
    about 500mV reverse "breakdown".
     
  15. Robert Baer

    Robert Baer Guest

  16. I'm not a solid state physicist, but there is quite a range
    of doping and metal contact choices that make Schottky
    diodes. Some of the choices that produce diodes with low
    reverse voltage capability also produce low forward drop. I
    think most zero bias diodes have a reverse voltage
    capability rated in single digits.
     
  17. PeteS

    PeteS Guest

    These are the people I get my PIN diode RF switches from, and they do
    indeed have incredibly low forward drops.

    I've never had a failure with a Macom part.

    Cheers

    PeteS
     
  18. Joerg

    Joerg Guest

    Hello Phil,
    Or the OA91. That saved my old Minolta SRT after Mercury cells went
    unobtanium. Needed to drop 200mV but no more. Works like a champ again.
     
  19. I believe you can still buy them in Canada. Or so I've heard.
     
  20. Joerg

    Joerg Guest

    Hello Homer,
    Sure, but I also wanted to be a good steward towards the environment.
    Plus after a further mechanical mod we can now buy a new battery for
    that camera at pretty much any supermarket.
     
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