LC filters

[Kevin Weddle]

LC filters have good attenuation at low frequencies and are less suitable at higher frequencies. 40db/decade is the attenution. Is -3db the nominal attenuation for unwanted frequencies? Should the final attenuation be more or less than -3db in order to be finished with filtering.

[indulis]

Do the math and plot the transfer funtion, then you will know (and should understand) what it does.

[Kevin Weddle]

For example, a passband amplifer can have as little as 20db/decade roll-off. A cascaded passband amplifier can have a much higher roll-off. I normally see many filters in a circuit, is it to achieve an exact amount of filtering? I have 120Hz 10mVpp ripple coming from my 7805 voltage regulator, should I filter it out?

[audioguru]

I have 120Hz 10mVpp ripple coming from my 7805 voltage regulator, should I filter it out?

10mV p-p is very small. If you want less ripple then increase the value of your main filter capacitor.

[Hero999]

I have 120Hz 10mVpp ripple coming from my 7805 voltage regulator, should I filter it out?

No, there's no need to filter out just 10mV of ripple.