I guess DC adapter filtering seems to work?

Discussion in 'General Electronics Chat' started by mik3ca, Jan 29, 2008.

  1. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    I thought of filtering out my DC adapter power supply for better radio reception, and I think it worked somewhat better.

    Here is how I made my filter:

    I took two fat diodes (diode #1N5 something), and connected the anode of one diode to +ve of the battery, and the cathode to the +ve connection point on my circuit board. Then I connected the anode of the other diode to the -ve connection point on my circuit board, and the cathode to the -ve of the battery. I connected the opposite ends of the two diodes together through 1000uF capacitors. It's like almost making a bridge.

    I wonder if I should make a bridge.

    maybe someone has a better filtering circuit I can make.
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    That is a filter circuit? I'm not sure how diodes are helping things, I'm sure it is attributed to the capacitors alone.

    If you want better filtration, then use a PI filter. This is made using a large capacitor across the supply, then an inductor in series with your circuit, then a capacitor across the circuit.


  3. thingmaker3

    Retired Moderator

    May 16, 2005
    Get rid of the diodes. All they are doing is dropping your supply by 1.4V.

    If your current draw is low enough, use a linear regulator.
  4. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    if I use the PI filter, what are the best values to use for C1, C2, and L1?

    I think C1 and C2 can remain at 1000uF, but I'm wondering about L1. I think that if L1 is too high, then it may end up being a high in-series resistor.
  5. eeboy

    Active Member

    Sep 27, 2007
    Choose L such that it represents a large impedance at or above frequencies you wish to attenuate. Inductive reactance (Xl) is equal to 2*pi*f*L where f is the frequency and L is the inductance.