Problems in 2nd order butterworth filter design

Discussion in 'General Electronics Chat' started by sudharshan.panduranga, Feb 26, 2010.

  1. sudharshan.panduranga

    Thread Starter Active Member

    Apr 10, 2008
    61
    1
    Hi....
    I have design a 2nd order butterworth filter (active)for current measurement.
    Please find the attachment.
    In this circuit CT is going to use for the measurement of current.
    Specification:
    Primary of the Current transformer: 0.05A to 1A vary
    Primary turns:5turns
    secondary turns: 1500
    burden resistor :680E.
    Frequency of the butterworth filter=50Hz,
    SEF_1/4 --- connected to controller port.

    Problem:

    At 50Hz design:While injecting the input current to the primary of the CT, the current in the display is not constant.
    eg: If input current is 0.4A, display current is vary around 0.4A+/- 20mA.
    This is happening for 50Hz design of the filter circuit.
    R75,R76=27K, C14, C15=0.1uF SMD

    At 700Hz design: There is no problem in the accuracy. of the readings.
    R75,R76=2.2K, C14, C15=0.1uF SMD

    Please reply.



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