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Constant current sources and capacitance

Discussion in 'Electronic Design' started by john, Nov 14, 2008.

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  1. john

    john Guest

    Hello,

    I am using texas instrument's part number INA2133U and OPA 131 to
    build the constant current source. The following link will take you
    to
    the circuit and data sheet ( page 13, figure 16). The inverting input
    of the amplifier is grounded.


    http://focus.ti.com/lit/ds/symlink/ina2133.pdf


    I used 10uF capacitor in series with the resistor R to stop DC leakage
    current and my load has an impedance in the range of 10Kohm to
    500kohm. My question is there is a chance that the capacitance offered
    by the capacitor and the load will stop the current source to shut off
    and there will be no biphasic wave will pass through the capacitor.

    The biphasic waves are bipolar square waves of frequencies between
    200Hz to 500kHz. Will it better to minimize the DC leakage using some
    trimming scheme at the INA2133 or capacitor will be ok?

    If such thing capacitance exsists acorss the current source than what
    will be its value in my circuit and how can I measure it?

    The value of R is 50KOhm. The Max Dac voltage is +/- 2. 5 volts peak
    to peak.

    Thanks
    Regards,

    John
     
  2. john

    john Guest

    The capacitor is in series with the load.

    John
     
  3. Rich Grise

    Rich Grise Guest

    No. What happens is the capacitor blocks our DC output, charges up, and
    stops at the rail.

    What ever possessed you to put a capacitor in series with a DC output?

    Good Luck!
    Rich
     
  4. john

    john Guest

    Hi,

    So, you are saying that even if the capacitor is fully charged, it
    will not only stop DC but also will not let the ac or biphasic square
    wave pass through it..It will block
    DC and AC both.

    Will it be good idea to add a resistor at the input of the capacitor
    and ground it. The resistor will stop the capacitor to get fully
    charged.

    Thanks
    John
     
  5. john

    john Guest

     
  6. john

    john Guest

     
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