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dc to dc converter chip

Discussion in 'General Electronics Discussion' started by Dkcorey, Mar 23, 2012.

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  1. Dkcorey

    Dkcorey

    3
    0
    Mar 23, 2012
    I'm trying to convert a voltage that varies between 0-50mv dc to a linearly corresponding voltage between 0-5 vdc.

    Is there an IC that will do this?

    Thanks

    dave corey
     
  2. BobK

    BobK

    7,682
    1,687
    Jan 5, 2010
    Yes, an opamp. You want to make a non-inverting amplifier with a gain of 100. This is quite simple. Use the non-inverting amplifier with feedback configuration shown in this article, with Rv = 99 * Rg to get a gain of 100.

    http://en.wikipedia.org/wiki/Operational_amplifier

    Bob
     
  3. Dkcorey

    Dkcorey

    3
    0
    Mar 23, 2012
    I was going to use an opamp, but I understand that they need a both positive and a negative power supply. Is there a way around that?
     
  4. timothy48342

    timothy48342

    218
    1
    Nov 28, 2011
    If you have a nice solid supply voltage greater than 5V dc and also a small varying dc voltage signal in the 0-5mV range, then yes, easy, all you need is to amplify it as BobK described.

    However if all you have is the varying 50mV as your only power source and you want to step it up to 5V, that's a lot tougher. (a LOT tougher)

    Stepping up a dv voltage can be done in a couple ways, but you don't have much to work with to start. And you not going to get someting for nothing. If your voltage go up by a factor of 100, then the available amps will drop by a factor of at least 100. (power and energy can't increase.)

    If your starting voltage was higher, and strong, you could power an inverter to get ac(with some losses), step it up to whatever av voltage you need (and there's where the drop in amps takes place) and then rectify back to dc. (more losses there)

    But I don't know if there are any invertor circuits that can run on less than 50mV. Also how strong of a voltage signal is that? What is the "source resistance" or what is the max amps when at 50mV and does that value (those values) change as the voltage changes?

    If you can't answer the last question easily, then describe your source more. Is this a generator, thermocouple, solar cell, potatoe?

    I'm not saying it can't be done.
    --tim
     
  5. BobK

    BobK

    7,682
    1,687
    Jan 5, 2010
    opamps can be run off a single supply, in fact, I have never seen one that had 3 power connections (+V -V and gnd). The reason dual supplies are used is that the output can never really reach gnd. In older opamps they are limited to as much as 2V away from V- and V+.

    What you want is a rail-to-rail opamp that can run off 5V. Rail-to-rail means that the output voltage can swing all the way from 0v to 5V when powered by 5V. However, it cannot really reach all the way to the rails, it will be a few 10s of millivolts off if you try to draw any current at all from it. If that is acceptable, you can use a single supply.

    If you really need 0 to 5V you will need to use dual supplies of about +-7V for non-rail-to-rail or +-5.5 V for rail-to-rail amps. Pay attention to the output swing parameters in the datasheet.

    Bob
     
  6. Dkcorey

    Dkcorey

    3
    0
    Mar 23, 2012
    Got it!! Thanks for the help guys.... DC
     
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