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Alternative voltage reference?

Discussion in 'Electronic Basics' started by MRW, Jul 23, 2007.

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  1. MRW

    MRW Guest

    Hi! I would like to know if there are other means to setup a voltage
    reference. I came up with this circuit:

    The purpose is to have a voltage divider (via a potentiometer) where
    the output swings from 2.5 to 2V. One way I came up with is by using an
    opamp voltage follower. Is there another way to design a voltage source
    without using an opamp?

    Thank you again everybody!

  2. What's the voltage reference for? (I'm guessing here, but in the
    schematic do you mean that R11 and R20 are to simulate your
    potentiometer and that you already have a 2.5V supply for V2? Do you
    already have 5V and 2.5V supplies already present?)

  3. MRW

    MRW Guest

    Hi Jon, Sorry for not being clear. R11 and R20 are used to simulate my
    potentiometer. I already have a 2.5V source and a 5V source. The
    section highlighted in green is the part that I was referencing.


  4. What's the voltage reference for?

  5. There are series references (essentially 3 terminal voltage
    regulators) and shunt references (essentially integrated
    zener diodes) that can be programmed with 2 or 3 resistors
    to produce clean, stable voltage references, for low current

    For example:
  6. neon


    Oct 21, 2006
    your cicuit is anything but a waste of parts the v-out is as good as Vcc is then you don't need an active amp. those national diodes are very stable as per spec, need more stable then do use an amplifier to supply the current as a stable source. how far do you need to go you bever say
  7. Mike

    Mike Guest

    How about something like this?
    It provides a low Z output drive and only a 100uA load on the 2.5v ref in.

    | +5 |
    2.50v ------- | |
    | | |\| |
    | ---|-\ |
    .-. | >----------- 2.00 - 2.50v
    | |<----------|+/
    5k | | |/| LT1078 etc
    '-' |
    | ===
    | GND
    | |
    20k | |
    created by Andy´s ASCII-Circuit v1.24.140803 Beta
    view with fixed width font.


    When truth is absent politics will fill the gap.
  8. MRW

    MRW Guest

    Thanks, Mike! This looks like a better setup than the one with my
    opamp circuit.
  9. MRW

    MRW Guest

  10. MRW

    MRW Guest

    Nothing special really. I had some old notes that I was reviewing and
    one of the exercise questions that was on it was to come up with this
    type of circuit. Simple really, but I guess it's good practice for the
    fall semester.
  11. You could use an LM317 with a suitable value pot in series with one of
    the voltage setting resistors, calculated to give you the adjustment
    range you want.

  12. Hehe. Well, since it doesn't really need to go anywhere and it is
    about practice, there are a number of options:
    Note that there is no use of the 2.5V supply, here. And it is NOT a
    precision reference and it would be simply horrible over temperature
    changes -- only good for some +/-10C -- as drift per temperature
    changes are in the area of something on the order of 5mV/K or more.

    Another option would be:
    Again, no precision. But better temperature drift -- on the order of

    I picked something like 700uA as the desired current through the 1k
    pot. This was to generate about 0.7V, top to bottom of the sweep of
    the pot, which means you can at least trap your 0.5V in there with a
    little extra so you don't have to nail it precisely. In other words,
    your 1k pot shown will sweep a little wider range than 0.5V. And
    there is nothing precision about any of these, nor temperature
    stabilized. The 2.7k*700uA produces about 1.9V, a pedestal upon which
    the 0.7V range of the pot rests. So roughly speaking, we're talking
    about a sweep from 1.9 to 2.6 volts. Of course, you can tweek things
    a little with R5 in the 2nd circuit and R2 with the first, so that you
    get it centered okay.

    For precision sweep and temperature stability, a different topology
    would probably be used. Of course, you can keep the opamp and use the
    pot as part of a series resistive divider that feeds the (+) input of
    the opamp and use it as a unity gain follower.

  13. MRW

    MRW Guest

  14. Manoj

    Manoj Guest

    Welll i would like to say that there is difference between regulators
    and reference circuits. i refer to using LM317, its a adjustable
    regulator and not a reference circuits.
    But i would add that its better than references made using only
    resistors. they are no reference circuits at all. First write down
    what u mean by a reference circuit. Just a voltage output is not the
    requirements of a reference circuit. It should first be specified like
    whats the stability that would be required, whats teh temperatrue co-
    efficient, what should be change in output voltage if the supply
    voltage changes etc etc.

    If you wish to have a fixed reference circuit, u can try LM336 adn
    things like that.

    well, i would like to reference circuits with just resistors are
    useless in real life.
    LM317 is good if u want some current to be fed to circuits. its not a
    reference but a regulator.

    I hope i didnot offend anyone with my comments

    with regards

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