LCR Low Pass Filter

Discussion in 'The Projects Forum' started by czwick, Jul 9, 2012.

  1. czwick

    Thread Starter New Member

    Jul 3, 2012
    8
    0
    Hi,

    I'm building a low-pass LCR filter (you may recognize the below image from a previous thread).

    [​IMG]

    Anyway, I'm unsure as to the exact inductor value I need, if I don't want any frequency past ~500Hz to go through the inductor (my AC component from my PWM will be several mV, but my vcc will be ~2V).

    Thanks!
     
  2. mcasale

    Member

    Jul 18, 2011
    210
    12
    Strange circuit. What IC is that?

    You cannot ensure ALL frequencies above 500Hz are blocked. You need to specify attenuation at certain frequencies. So, where does the filter start filtering, and what is the attenuation at 500Hz, 1KHz, and above?

    You are trying to design a two-pole filter. How do you know you need 2 poles and not just 1, or maybe 3 or more?
     
  3. czwick

    Thread Starter New Member

    Jul 3, 2012
    8
    0
    The chip is an MSP430 low-power line.

    The mic+ line is providing 2V of energy but I'm also trying to drive a 2mV AC signal at 1kHz up it from the PWM as well. So I'm trying to get the DC to go into VCC and the PWM to go up the mic line and not into VCC.

    So I guess I'd like to focus my attenuation at 1kHz. And my current is ~.5mA FYI.

    Thanks!
     
  4. mcasale

    Member

    Jul 18, 2011
    210
    12
    I think we have a disconnect here. When I search for MSP430 I get a TI microcontroller.

    I don't understand what you are trying to do.
     
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