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LM393B: Is it possible to set upper and lower hysteresis thresholds without a reference voltage

David Tempesta
Prodigy 60 points
Part Number: LM393B
Other Parts Discussed in Thread: TLV7022, LMP7300

Hi,

I have an application that compares (sorry, kind of obvious) two voltages, however the two voltages are independent of each other, there is no reference or fixed voltage to calculate  hysteresis as seen in the application notes. Is there a way to calculate the hysteresis such that the upper and lower thresholds move but the width of the hysteresis curve stays constant?

  • 0
    Guru 272280 points

    Add a differential amplifier to get the difference relative to a fixed reference voltage.

  • 0
    TI__Guru 52926 points

    Hello David,

    Can you provide the actual expected voltages ranges? AC signal? DC signals? Speed?

    How much hysteresis do you need? We do have comparators with built-in hysteresis, such as the TLV7022 family. Since the internal hysteresis is internally applied after the inputs, the actual input voltages will not affect the hysteresis.

    As Clemens said, it may be simpler/easier to use a simple diff-amp to get the difference then apply a fixed reference.

    Trying to do this with only a comparator would be very complicated and would probably loose overall accuracy. Note that most of the equations assume that the reference voltage is at or near the output mid-point. Moving away from the mid-point distorts the hysteresis symmetry.

    Another device of interest would be the LMP7300 - which has adjustable hysteresis of 0 to 120mV - but watch the allowable input range (1V up to V+).

  • 0 in reply to Paul Grohe
    TI__Mastermind 24310 points

    David

    we have not seen any new input on this post, so I will be closing the thread.

    If you need more support, feel free to reply or open a new thread.

    Thanks

    Chuck