Need help with alternative opamp

Discussion in 'General Electronics Chat' started by anotheruser1, Apr 28, 2013.

  1. anotheruser1

    Thread Starter Member

    Dec 6, 2011
    Last edited: Apr 29, 2013
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    First of all, you might want to change this Thread's title to "Need help with alternative COMPARATOR".

    According to the datasheet, the TLC2272/74 are rail-to-rail devices on output. The LM393 may not get to V++ on output (it does get to ground).

    compare the stats on and let us know what spec differences concern you.
    why do you not want to use the comparator specified in the drawing?

    The TLC2272 and TLC2274 are dual and
    quadruple operational amplifiers from Texas
    Instruments. Both devices exhibit rail-to-rail
    output performance for increased dynamic range
    in single- or split-supply applications. The
    TLC227x family offers 2 MHz of bandwidth and
    3 V/µs of slew rate for higher speed applications.
    These devices offer comparable ac performance
    while having better noise, input offset voltage, and
    power dissipation than existing CMOS
    operational amplifiers. The TLC227x has a noise
    voltage of 9 nV/√Hz, two times lower than
    competitive solutions.
    anotheruser1 likes this.
  3. crutschow


    Mar 14, 2008
    The reason the TLC2272CP is being used as a single-supply comparator is that it has a CMOS very low bias current input and so will operate with the high resistor values used in the comparator circuit (for example a 30MΩ hysteresis feedback resistance). An LM393 or any other bipolar input amp will likely not work well in that circuit.

    Alternately since TM1 is a low impedance (2kΩ) sensor you could likely reduce the values of all the associated resistors (R4, R5, R6, R19, R20) by a factor of 10 which should then work ok with a comparator like the LM393. If you do, you should also add a 10kΩ pull-up resistor from the LM393 output to +5V to give a good 5V logic high output.
    anotheruser1 likes this.
  4. anotheruser1

    Thread Starter Member

    Dec 6, 2011
    I don't absolutely have to use something different, to keep the price down i wanted to try and use something i already had in my parts collection. Also it seems this chip is a bit harder to come by and fairly pricey in comparison to the lm393. Thanks for the info
  5. anotheruser1

    Thread Starter Member

    Dec 6, 2011
    I think i may just have to buy the chip and forget saving money. I am not comfortable enough with electronics just yet to really modify a schematic that much, i was hopeful that there was a chip that i had that would be plug and play. Thanks for your time