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voltage reference

Discussion in 'Electronic Design' started by R.Lewis, Apr 6, 2004.

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  1. R.Lewis

    R.Lewis Guest

    I am looking for a voltage reference (anything below 2.0V ) that is
    reasonably repeatable and stable and needs work from -10 to +40c to within
    10% max limit.

    Any ideas for something that doesn't cost the earth - I only need a few K
    pieces but price is very sensitive.
     
  2. LMV431 $0.16/1k for 0°C~70°C , 1.24V nominal.


    Best regards,
    Spehro Pefhany
     
  3. LM317
    1$
     
  4. See:
    http://www.national.com/catalog/AnalogReferences.html
     
  5. R.Lewis

    R.Lewis Guest

    Haven't got that sort of money
     
  6. John Fields

    John Fields Guest

    On Wed, 7 Apr 2004 18:26:52 +0100, "R.Lewis" <h.lewis-not this
     
  7. I am sure for a few K you can get them for 10 cents.
    JP
     
  8. R.Lewis

    R.Lewis Guest

    I am looking (wishing) for 10 cents tops but was rather hoping someone would
    recommend a Vbe of something or a forward diode that would fit my
    requiremnts
     
  9. Jim Thompson

    Jim Thompson Guest

    On Wed, 7 Apr 2004 23:01:16 +0100, "R.Lewis" <h.lewis-not this
    Dreamer ;-)

    ...Jim Thompson
     
  10. 1K pcs. Distributors may sell for more. My suggestion is 0.01 cheaper
    (but you need a resistor) and (possibly more importantly) requires
    something like 1/50 the current.

    Best regards,
    Spehro Pefhany
     
  11. You could MAYBE use an LED (red) or a Vbe multiplier (2 resistors and
    a BJT) and MAYBE meet +/-10% over that temperature range for half that
    cost, but characterizing it probably wouldn't be worthwhile for the
    meagre savings.

    Best regards,
    Spehro Pefhany
     
  12. Jim Thompson

    Jim Thompson Guest

    Why not use one of those CA3083 arrays and build your own bandgap ?:)

    ...Jim Thompson
     
  13. Boris Mohar

    Boris Mohar Guest

    On Wed, 7 Apr 2004 23:01:16 +0100, "R.Lewis" <h.lewis-not this
    Use an LED.
     
  14. Jim Thompson

    Jim Thompson Guest

    How are you going to make a "temp-compensated vbe multiplier"?

    What does a CA3083 sell for? I couldn't find a price on the web.

    If there's interest, I'll design a bandgap around a CA3083... it's
    pretty easy ;-)

    ...Jim Thompson
     
  15. R.Lewis

    R.Lewis Guest

    Do you know of a led that fulfils the 10% requirement ?
    I have not measured any specifically for this task but I seem to remember
    getting a greater that 10% variation in Vf as they come out of the box,
    plus the 2.something mV per degC tempco.
     
  16. Terry Given

    Terry Given Guest

    why stop there? Vbe multiplier with ntc (or ptc) 1st-order temperature
    compensation......
     
  17. Terry Given

    Terry Given Guest

    $0.03 buys you a dual transistor BC847BPN, one NPN the other PNP.....in a
    6-leg SOT23 package - how good a reference can you make with that? crude
    current source driving temp-compensated vbe multiplier.....
     
  18. Terry Given

    Terry Given Guest

    I was looking into a non-linear voltage divider - ntc or ptc at same (ish)
    temp as bjt.
    mostly my point......can you still buy them?
    I am certainly interested.....
     
  19. Terry Given

    Terry Given Guest

    assume an 0.65V forward drop at 25C. -10C gives about 727mV = +11.9%, 40C
    gives about 617mV = -5.1%

    using a Vbe multiplier with a 22k Rcb, and Rbe = 100k NTC paralleled with
    27k, V = 1.349V at -10C = +1.97%, V = 1.323V at 25C and V = 1.373V at 40C =
    +3.82%

    I havent bothered to "design" this, just a quick fiddle with some NTC data I
    happened to have in excel....shows that, over a limited temperature range,
    can do OK with crappy old vbe multipliers and an ntc. If I actually designed
    it (using scientific wild-assed guesses rather than wild-assed guesses) I
    could probably do even better.....

    If you used a BC847bpn with the pnp set up as a crude current source, this
    would run on a very wide input voltage range too....and easily meet the
    $0.17 price requirement
     
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