Choosing a Capacitor and Inductor

Discussion in 'General Electronics Chat' started by darunium, Mar 16, 2012.

  1. darunium

    Thread Starter New Member

    Mar 16, 2012
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    Hi All,

    To caveat this I am no EE, sorry if my question is silly! Any help is really appreciated!

    I am trying to probe a load with both a DC bias via one instrument and an AC bias via another (I've tried putting them in series in a variety of configurations, but that hasn't worked out because of the way that the internal electronics on the instruments connect to grounds).

    The method I would like to imploy is two loops, one for DC current and one for AC current, but to isolate them from one another I'd add an inductor to the DC loop, and a capacitor to the AC loop.

    My load is in the Mohm-Gohm range. My DC bias 10-800mV. My AC bias 2-10mV at 500-1500Hz.

    My question is: what qualities of the inductor and capacitor should I look for?

    My understanding is that I would want a high inductance and high capacitance based on the idealized impedance formulae:
    [​IMG]
    [​IMG] (wikipedia)

    but in practice do I just want the highest L and C possible or should I be careful about that? To remind my load is in the 100kOhm-1Gohm region, so I want my capacitor to provide <1kOhm resistance to the 1kHz signal, and the inductor to provide <1kOhm resistance to the DC signal, as well as minimal noise in both.

    Thanks for any advice!

    Darunium
     
  2. darunium

    Thread Starter New Member

    Mar 16, 2012
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    I should also add that I'm curious about other capacitor and inductor properties I should look for - does the material matter? The maker? Other qualities?

    Thanks!
     
  3. darunium

    Thread Starter New Member

    Mar 16, 2012
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    Here is a picture of what I mean:
    [​IMG]
     
  4. darunium

    Thread Starter New Member

    Mar 16, 2012
    4
    0
    no advice?
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,605
    Darunium: just saw your post. This sounds something similar to things I have seen done back in my power supply days when incoming inspection had to test inductors when driving them with both AC and DC signals.

    Everything you've said about picking the values seems correct. As 1K << 1M you can safely ignore the setup in your measurements.

    Are you having any problems or just double checking before spending any money?
     
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