Circuit for polarity detection

  1. Can anyone suggest to me a simple circuit constructed using digital gates for polarity detection? The circuit should be able to detect positive, negative as well as zero polarity.

    I need to check the polarity of a dc motor which is controlled by a bidirectional converter. The bidirectional converter has to be controlled in current mode. If any one has ideas regarding the same, i will be grateful.

    But I am not implementing it in real time. I am trying to simulate the logic in MATLAB/Simulink. Can you suggest how I can do the same in Simulink using logic gates? or any other digital gates? The truth table is given along with the schematic for reference as to the expected binary output.

    I have attached the schematic in pdf.

    Thanks and regards


    Attached Files:

  2. jcsd
  3. You have two polarity detectors in your circuit and they are not the same. One has two outputs and the other three. Which one do you want suggestions for? What is the input range for the polarity detector? What do you want to happen if the motor is spinning in one direction and a command, Ec, is given to turn the other direction? Do you want the power to the motor to turn off and allow the motor to coast to a stop or do you want to apply a limited amount of current to the motor in the opposite direction to make it stop and reverse faster? I understand this is a simulation but sometimes simulations lead directly into real products. How will you brake the motor if you want to stop quickly? Do you care if the motor burns up if it should stall?
    Last edited: Dec 6, 2010
  4. Hi there

    i would like suggestions on both the polarity detectors. As for the input range to the polarity detector, do you mean the range within which it detects the signal as positve, negative or zero? i would like the range to be as low as possible. the motor should coast to a stop with minimum losses occurring to the motor while stalling. and the transition from one converter to another should be accompanied by a dead band / transition band during which time the polarity of Ec should remain zero. Converter 1 gets the pulses when id is positive or zero and Ec is positive. Converter 2 gets the pulses when id is negative or zero and Ec is negative.

    Thanks and regards

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