I'm very new to electronics and I want to build a basic LC Filter with a 12v regulator and below is my basic schematic. Now i'm sure its incorrect but I want to know why and what i'm missing so I can learn. Basic LC Filter

I'm planning on using the following components:

The power would be provided by either 12.6v or 16.8v from a high capacity lip battery


Change of design: enter image description here


Just to add to Andy's answer (+1 from me).

enter image description here

I've also add a 0.1uF capacitor across the 470uF electrolytic. This is because electrolytics aren't good at filtering high frequencies. Note also where the capacitor grounds are connected. The closer to the regulator the better.

  • \$\begingroup\$ Thank you for your help. So would something like this be suitable uk.farnell.com/tdk/cga2b3x7r1h104k050bb/… \$\endgroup\$ Jan 2 '15 at 12:07
  • \$\begingroup\$ @JosephGregory It has the correct spec (0.1 uF, 50V) - it just depends if you want to use a surface mount device or a through hole style capacitor. \$\endgroup\$ Jan 2 '15 at 12:10
  • \$\begingroup\$ Yeah I want to use a surface mount. Last question and i'll stop bugging you, but do you know what I should look for in Eagle for a capacitor of this size? \$\endgroup\$ Jan 2 '15 at 12:19
  • \$\begingroup\$ @JosephGregory I don't use Eagle myself but the size code for smd caps is a 4 digit number or it will give the dimensions. Take a look at instructables.com/id/… \$\endgroup\$ Jan 2 '15 at 12:34

C1 will block DC - you need to have C1 connected across pin 2 and pin 1 of the output connector SV1.

When you do this it forms a low pass filter that removes high frequency noise from the dc/dc converter's output but there can be a sting in the tail. Without a load, the C and L also can form a highly resonant tuned circuit and some noise (around resonance) can be amplified tremendously. The series resistance of the inductor will tend to reduce this but without looking into the full details and probably simulating the circuit it's hard to tell exactly.

The Farnell page you linked doesn't state the dc resistance by the way.

  • \$\begingroup\$ Also what sort of resistance should I be looking for and why (to be cheeky to help my learn)? \$\endgroup\$ Jan 2 '15 at 12:08
  • \$\begingroup\$ its going to be in the region of an ohm but really it depends on the minimum load current anticipated. \$\endgroup\$
    – Andy aka
    Jan 2 '15 at 14:33

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