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DC voltage reducer

Erwin Schott
Prodigy 50 points
Other Parts Discussed in Thread: INA116

Hello,

For an application we need a DC voltage reducer that works as follows:

Outgoing voltage = always Ingoing voltage constant minus 1V.

The DC range is 0 – 2V.

We have 8 ports and separate for each port we need it.

  • 0
    TI__Expert 4350 points
    Hi Erwin,

    I'd like to clarify your requirements:
    Vout = Vin - 1 V
    Is the DC range 0 - 2 V for the Vin or Vout?
    Does the Vout need to go negative voltage?
    What is the output current requirement?

    Best,
    Eric
  • 0 in reply to Eric.Preiss
    Prodigy 50 points

    Hi Eric,

    Vout = Vin-1V   -> ok

    DC range 0-2V is for Vin

    Yes, Vout has to go to negative voltage (max -1V).

    Current: application is pH-measurement via impedance-transducer 

    Output current is very less. I approximate 40 - 200mA

    Best,

    Erwin

  • 0 in reply to Erwin Schott
    TI__Expert 4350 points
    Hi Erwin,

    What voltage rails do you have available to use? You'll likely need an op-amp to do this. I'm going to move this post to the Op-Amp e2e forum.

    Best,
  • 0 in reply to Eric.Preiss
    Prodigy 50 points
    Hi Eric,
    24V=
    Best Erwin
  • 0 in reply to Erwin Schott
    TI__Genius 15410 points

    Hi Erwin,

    It sounds like a difference amplifier would work for your application my only concern is that the input impedance of the difference amplifier may effect the performance of the impedance transducer. I'm not familiar with an impedance transducer, can you provide a datasheet of the impedance transducer?

    Why do you need to subtract only 1V off of the input?

    An instrumentation amplifier such as the INA116 can provide a very accurate design for pH sensors. Have you considered this approach?

    Thank you,

    Tim Claycomb

  • 0 in reply to Tim Claycomb
    Prodigy 50 points
    Hi Tim,
    1) Our new measuring pH-transducers give 0-20mA. The subsequent electronic system works with voltage. The current is transformed via 100Ohm precision resistance so we get 0-2V. *)
    2) The primary voltage after the old impedance-transducers stayed within +1V. And again all subsequent electronic systems and software work within the limit. The conversion is time-consuming and so we look for a completed answer.
    3) We frame as a possible solution the described DC voltage reducer:
    - voltage rail 24V=
    - Vout = Vin-1V
    - Vin DC range = 0-2V
    - Vout = max. +1V
    - Current is very less
    The convenience is we only have to put the voltage reducer between Vout and the follow present subsequent electronic systems.
    *) we can use other resistance e.g. 500 Ohm so we get 10V and accordingly we wish to reduce
    Best, Erwin
  • 0 in reply to Erwin Schott
    TI__Guru 62035 points

    Hello Erwin,

    How about the circuit below?  It converts 0-2V into 0-1V and has an input impedance of 1.5MOhms.  It was difficult to understand from your requirement but it seems like the circuit goals are to attenuate a 2V signal into a 1V signal, not necessarily just to subtract 1V from the input.  

    Forum_DCReducer.TSC

  • 0 in reply to Collin Wells
    Prodigy 50 points

    Hello Collin,

    In my reply to Timothy Claycomb I wrote Vout = max. +1V. Sorry I forgot the minus-sign. Vout must be plus/minus 1V.

    The measurement range of an pH-electrode is plus/minus 0,5V.

    So the voltage is not to be sufficient to reduce from 2 to 1V but if a modified above circuit will convert it to minus would be nice.

    For example please see the diagram

      Index A stands for Ausgang = Out and E for Elektrode = Electrode

    In the example 0-20 mA gives via 12,4 Ohm an output 0-248mV. What we need  in that case is an output plus/minus 470mV. So the 0-248mV output has to convert to minus/plus.

    But for generally purpose we prefer an output extended range plus/minus 1V for an input 0 to 2V.

    Regards

    Erwin Schott

  • 0 in reply to Erwin Schott
    TI__Genius 15410 points

    Hello Erwin,

    For an output voltage of +/-1V you will need to use dual supplies, for example +/-15V. You mentioned you have a +24V supply available but do you also have a negative supply rail available? If so, what is the negative supply voltage you have available?

    Thank you,

    Tim Claycomb