How to limit a opamp's output?

Discussion in 'Homework Help' started by pedroca1, Oct 9, 2016.

  1. pedroca1

    Thread Starter New Member

    Oct 9, 2016
    Hi everyone,

    I have a signal (called Y) that is a sawtooth wave and goes to 5V to -5V. I also have a temperature sensor (called T) that spits two values: 6V or 0V. When T = 6V, that signal Y must be 0 and when T = 0V, Y should remain unchanged!
    My professor gave us this challenge and we can only use opamps and resistors... I have thought to use a comparator opamp and use Vcc+ = GND and Vcc- = Y, but I can't do this because Y isn't a constant voltage. That is the only thing I could think to solve this challenge...
    I want to limit Y's wave using T, how can I do this?
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Welcome to AAC!
    The moderators will probably move this thread to the 'Homework help' forum where it belongs.
    Do you have dual-polarity supplies available for the opamp/comparator?
  3. pedroca1

    Thread Starter New Member

    Oct 9, 2016
    Oh, that's ok. Sorry for that, I'm new here :x
    Yes, I do!
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
    I think you have to build a logic gate.

    For example. If you use good rail to rail op amp. You use output of sensor T as power source for the op amp that is configured as buffer.

    For example.
    Put NOT gate between T and positive power supply of the buffer op amp. When T is 6 volts (I assume Logic 1), the output of NOT gate will be 0 volts (Logic 0). Then you feed the output of NOT gate to the positive power supply of buffer op amp, right now this is 0 volts. Since the positive power supply of the buffer op amp is 0 volts, the positive portion of sawtooth wave will be destroyed and you will see just the 0 volt flat line, in other words a positive portion of Y will be 0 like you want. The negative portion of swatooth wave will still be present because we did not modify the negative supply of the op amp.

    Bottom line. The way I see this working is that you pass signal Y though buffer op amp, and you switch the buffer op amp On and Off based on the output of sensor T.
    Last edited: Oct 11, 2016
    atferrari likes this.