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Reverse Hysteresis in Comparator

Discussion in 'General Electronics Discussion' started by Qube, Jan 3, 2017.

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  1. Qube

    Qube

    1
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    Jan 3, 2017
    Hi,
    currently im making protection of IGBT in voltage inverters by turning off PWM signal in right moment. Im at making PCB stage.
    1. Im using TLC3702, my power supply is 3.3V and my input signal is sinusoidal 0 to 3.3V range. Datasheet says its push-pull comparator, so do I need any other resistor for it to work?
    2.The point im trying to switch states is at lets say 2.965V. This comparator has no built-in hysteresis so i had to do it myself.
    I used: https://www.maximintegrated.com/en/app-notes/index.mvp/id/3616 this site to help me calculate hysteresis.
    My Vref = 2.8. I went trought it and my Vthr and Vthf is 2.976V and 2.954V. (Its little strange that values that comparator is switching has no so much to do with Vref, is that normal?)
    3. Now i want to use 2nd comparator to switch to logic 1 (3.3V) when my input value is below 0.55V. I guess i should swap my input signal with Vref, so i would get Input on "-" of opamp. But the question is what with hysteresis? Should i calculate it the same way? I guess i should leave positive feedback on opamp.
    Or meaby I should use inverting opamp on input signal and do the same i did with 1st one?
     
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