A newb with questions about filters

Discussion in 'General Electronics Chat' started by boogie, Jan 11, 2010.

  1. boogie

    Thread Starter New Member

    Jan 10, 2010
    25
    0
    Hi everyone
    I've recently found this website (what an amazing place) and spent the last couple of weeks studying the E-book. So far so good...
    I now got to the filters section and I have a few question I was hoping some of you can help me with:

    1. In section 2 (low pass filters) in chapter 8, it is said that "the inductive low-pass filter is often preferred in AC-DC power supplies to filter out the AC “ripple”". If I'm not mistaken the ripple is usually created by a capacitor filter which is usually placed after the diodes bridge (at least that's the way I see it done in most wall-warts). How and why does an inductor smooth out that ripple? does it come after the capacitor or instead?

    2. In section 6 (resonant filters) in chapter 8 a resonant band pass filter is displayed (the one which is said to be popular for radio). My question is, how can I make it more selective? (sharper/steeper). Am I wrong to assume it has to do with the Q? If I'll use a lower resistance R1 will it be more selective? will it increase the Q?

    3. Why do we need R1? Is it to prevent a short circuit during times when the frequency is low and the inductor behaves as a short circuit?

    4. Am I wrong to assume that an inductor's internal resistance contributes to a lower Q?

    5. I'm a guitar player and we commonly use effects pedals which often have some sort of control over the frequency response (knobs for lows/mids/highs) - what is the common way to create these? what kind of filters do they use? often there is a notch is the mids - how is this achieved?


    These are a lot of question - I know ... but I really need your help.

    Thanks

    Shiron
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Both the capacitor and the inductor filter ripple by storing energy and releasing it during the dead times. Where they inject the energy is a bit different however.

    There is also the issue with large capacitors having a bit of problem with high frequencies (the exact capacitance at as specific frequency depends on the capacitor, they have a freq response). Coils do too, but they are more likely to block high frequency components due to their location in the schematic.

    You can also think of the combo of both as a better grade of low pass filter than by themselves, the Q goes up. DC is the ultimate low frequency if you think about it.

    You might show a link or a schematic of what you're having trouble with. There are folks that can explain it better than me.
     
  3. boogie

    Thread Starter New Member

    Jan 10, 2010
    25
    0
    Well, I'm even more confused now... :( I can understand how using both a capacitor and an inductor will create a resonant band pass filter but I can't understand how they'll be used to create a low pass filter. Sadly I don't have a schematic, I'm referring to what the e-book said (see my quote).

    Also, does anyone have an answer to questions 2-5?

    Thanks
    Shiron
     
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