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NTC/PTC Thermistor Reading conversion

Discussion in 'Electronic Design' started by Neil, Nov 24, 2003.

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  1. Neil

    Neil Guest

    I have a setup that currently takes in a reading from an NTC
    thermistor on a board as a safety lock-out if the board temperature
    gets too high. The latest design has switched to using a PTC
    thermistor due to some space/cost constraints.

    I have a setup all ready that read in the old NTC thermistor - and the
    PTC design may be temporary so I don't really want to modify it too
    much. Is there anything in existance that takes in a signal from a
    PTC thermistor and gives an output representing what the NTC would
    have given? If not how difficult would it be for me to design this?
    What would that involve?

  2. Robert Baer

    Robert Baer Guest

    Ther are a number of ICs that have a *linear* voltage output
    porportional to temperature (most in degrees Centigrade).
    And some makers have them available in SOT-23 which is about a small
    as you can get without going to COB.
  3. A good overtemp safety circuit will also be arranged to
    lock-out at an apparent undertemp. This is done so that
    it failsafes for sensor open or short circuit.

    Such a circuit is then also easy to swap between NTC and
    PTC sensors, just change some passive bridge values, as
    required for the possible differing sensor resistances,
    and adjust the "overtemp/undertemp" tripping points.
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