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1% zener diodes?

Discussion in 'Electronic Design' started by Michael, Jul 24, 2007.

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  1. Michael

    Michael Guest

    Hey there - is there such a thing as a 1% zener diode? They all seem
    to be about 5%. I was looking to make a 10V vref and the best I was
    able to find was the Digi-Key EDZTE6110BCT-ND, which is accurate to
    2.3%. This just strikes me as odd - and makes me wonder if I'm looking
    in the wrong place or something.

    I did, however, discover that there are actual 10V vref chips out
    there - so I'm planning on going with one of those.

    -Michael
     
  2. You're assuming that these devices start to conduct
    at 10.00V sharp ? This is not the case anyway. The
    specified conduction voltage is defined at 1mA.

    And yes, a 10V reference is a different device.

    Rene
     
  3. Zener diodes are actually in a breakdown region.. so unreliable,
    not accurate etc by nature.

    10V reference? A LM317 with 2 resistors or a 10 turn poti will
    make any reference you like, for less money with better temp stability,
    then a zener, possibly for less money too.
    All that with more power....
     
  4. Michael

    Michael Guest

    Well, my knowledge of them was that you would always put a resistor
    inline with them to give it a proper bias current so that you would
    hit the exact right voltage. I need the 10V to connect to the non-
    inverting input of an Op-amp (OP747). Thus I'm not worried about a
    current drain on the line.

    -Michael
     
  5. whit3rd

    whit3rd Guest

    No. Zener diodes are mass-produced and sorted into 10% and 5%
    bins, but if you require 1% accuracy you need a laser-trimmed
    resistor (at least) in addition to bias current regulation and
    other niceties. 10V 1% references are trimmed ICs, not
    discrete zeners.

    REF-01 is a typical such part; see

    http://www.analog.com/en/prod/0,2877,REF01,00.html
     
  6. D from BC

    D from BC Guest

    Even if 1% tolerance did exist, I think the thermal drift (due to self
    heating and a range of ambient temperatures) would make the 1%
    pointless.
    D from BC
     
  7. Jim Thompson

    Jim Thompson Guest

    TL431 ??

    ...Jim Thompson
     
  8. James Arthur

    James Arthur Guest

    The 10V reference chip is a better choice, but I once had a set of
    precision zeners at either 1 or 2% increments, IIRC.

    Once upon a time zeners were king as reference diodes. The 1n829a,
    for example: 6.2V, 5ppm/C.

    Cheers,
    James Arthur
     
  9. Guest

    Only at 7.5mA - to get all the precision that you paid for with the !
    N829, your needed a precision resistor biased from the reference
    voltage to keep the current stable at just the right value. See

    http://www.ortodoxism.ro/datasheets/motorola/1N823.pdf

    and note that the temperature stability is specified at 7.5mA
    +/-0.01mA - the better the diode the closer you've got to hold the
    current to 7.5mA to maintain that stability.
     
  10. In general, zeners make piss poor regulators.




    --
    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
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  11. Precision voltage reference zeners are pretty much a thing of the
    past. You were limited to a certain voltage (around 6.2V) and forward
    current (quite a few mA, IIRC) to get zero (nominal) tempco-- as
    determined by the physics. ICs are much better for most applications
    requiring much accuracy, and are reasonably priced.
    The LM4040 is an inexpensive shunt (two active pins, just like a
    zener) reference that might do your job, and it's available in 10V
    with tolerancces of 2%, 1%, 0.5%, 0.2% and 0.1%, and spec'd at 150uA.
    Tempco is nothing special (100 or 150ppm/K for all tolerances, but
    still far better than what you'd get with an uncompensated 10V zener.

    Of course if you can use a series reference that might save you a
    part, but they tend to be a bit more expensive.


    Best regards,
    Spehro Pefhany
     
  12. Joerg

    Joerg Guest

    In them days I preferred the uA723 when I needed precision. Sometimes I
    still do that :)
     
  13. Guest

    At Cambridge Instruments, twenty years ago, we liked the Linear
    Technology voltage references

    http://www.ortodoxism.ro/datasheets/lineartechnology/1019fcs.pdf

    5ppm/C and available with tight tolerances. Farnell doesn't seem to
    stock the 10.00V part, but does have the 5.00V voltage part for about
    $15 each in small quantities.

    When I last looked, Thaler could do better, but their parts were
    appreciably more expensive.

    http://www.thaler.com/thcpdf/vre310.pdf
     
  14. Jamie

    Jamie Guest

    I found the 723 seem to have a lot of failed units out there for
    what ever reason?
    THey just seem to fail and go into full output..
    that's not very good if you don't have crowbar protection.
     
  15. Joerg

    Joerg Guest

    I usually do have a crowbar but I have never seen that phenomenon, and
    it's been decades. What happened a lot in my teenage days was that chips
    showed up from "re-labelers" and other shady sources, often at regular
    electronics stores. Never seen a uA723 from there but I did end up with
    a batch of uA741 that were totally out of spec. This is very frustrating
    for a teenager who isn't a chip expert yet.

    The 723 is alive and kicking, and very reliable. Look at any linear
    brick supply from Condor or PowerOne. I just bought a few for a
    prototype and sure enough they still use the good old 723. By default
    they usually have a crowbar but not so much out of concern for the 723,
    it's to protect against a pass transistor that shorts out.
     
  16. Rich Grise

    Rich Grise Guest


    I once read somewhere that you could put an ordinary forward-biased
    silicon diode in series with a zener and their tempcos would tend to
    cancel out, albeit they didn't say how well. :)

    Cheers!
    Rich
     

  17. The only 723 failures I can recall resulted in low or no output.
    I've only seen a few bad ones, but loads of them in equipment and
    modular power supplies.

    i agree about the crowbar. Anyone who builds that type of supply
    needs OVP.

    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  18. Winfield

    Winfield Guest

    I also have a set of 1% zener diodes, but for real-world
    use they're nearly useless, because they have to be used
    at the exact specified test current. That's why I still
    have 'em, never found a good way to use them!
     
  19. Jim Thompson

    Jim Thompson Guest

    Use the zener to reference an OpAmp style current mirror when sources
    current to the zener.

    The "magic" is in how to get it to start ;-)

    I built a chip long ago which did that using the E-B junction as the
    zener. Not for much accuracy, but for significant PSRR in the bias
    system.

    ...Jim Thompson
     
  20. D from BC

    D from BC Guest

    That is an IC full of transistors.
    D from BC
     
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