0-4mA to 0-3.3V converter

Discussion in 'General Electronics Chat' started by schnnegi, Oct 8, 2008.

  1. schnnegi

    Thread Starter New Member

    Sep 24, 2008
    Hi can anyone help me on this circuit of converting 0-20 mA standard into 0 to 3.3 volt standard.(using opamp or passive method)This signal is being applied to ADC channel of PIC18LF4620 which is driven by 3.3V.
    There should be no drain while applying this I-V converted signal to ADC input.

    When I am applying this (direct connecting preset pot across current i/p whose output is 3.3V) signal to ADC channel voltage is droped to 1.28V so ADC output is 99 instead of 255.
    When I am using Opamp circuit with LM358 the problem faced is
    :---------------I am converting -5V-0- +5V signal into -3.3-0- +3.3V for applying this to power supply for LM358.
    I used 2 OpAmps in inverting mode.the output is saturated.but when i am applying 3.3 V directly i am getting output.
    I checked this using proteus software.But I have -5 -0-+5V source from which i have to convert this into -3.3 -0- +3.3V signal using 1N4148diode and 3.3Vzeners.
    Can any tell me how I can stop this drain of voltage means i am unable to get this voltage range 0-3.3V corresponding to 0-20mA using -3.3-0-+3.3V supply made from 5-0-+5 volt
    Last edited: Oct 8, 2008