EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: XaeroDemon on August 01, 2016, 05:45:05 am
-
I am designing a LC filter to filter out DC power from 6s(22.1 nominal voltage) lipo battery.I know the how to calculate Cutoff frequency and Characteristic impedance but I don't know what they should be. Should the be lower as possible.If the Cutoff frequency is low then lot of high frequency will be filter so I guess its good?.I am totally lost and characteristic impedance.lower impedance is better right?.Thank you very much in advance.
-
I am also lost too. ??? I learnt in school a battery is a DC or direct current storage device and viewed with an oscillocsope it's a straight horizontal line. As far as I remember filtering only applies to AC or alternating current circuits. For example in Sri Lanka I think your country follow the british electrical system meaning ac power at 50hz. and so after dc rectification you get 100hz. ripple and that you want to filter although some of the ripple is reduced by the main filter caps. Yes in this case you want to have LC filter. You can find online calculators for this and many more electrical /electronic ones. Or if you are building a battery charger using switchmode circuit. Apart from 100hz. ripple there is also high frequency noise going to the megahertz region.
www.designers-guide.org/design/bypassing.pdf (http://www.designers-guide.org/design/bypassing.pdf)
www.ti.com/lit/an/scaa048/scaa048.pdf (http://www.ti.com/lit/an/scaa048/scaa048.pdf)
www.ti.com/lit/an/snva538/snva538.pdf (http://www.ti.com/lit/an/snva538/snva538.pdf)
www.illinoiscapacitor.com/pdf/papers/filtering.pdf (http://www.illinoiscapacitor.com/pdf/papers/filtering.pdf)
www.changpuak.ch/.../AN1707-POWER_SUPPLY_DESIGN.pdf (http://www.changpuak.ch/.../AN1707-POWER_SUPPLY_DESIGN.pdf)
https://www.ampbooks.com/mobile/amplifier.../LC-ripple-filter (https://www.ampbooks.com/mobile/amplifier.../LC-ripple-filter)
-
The cutoff frequency and input/output Z of a filter design are dependent
on your requirements. Lower or higher values are a function of what you
are trying to accomplish.
In many instances the filter is designed to freq domain criteria, component
sizing, magnetic energy requirements, then the I/O Z levels are dealt with,
eg. their loading effects, or incorporated in the design loading effects as part
of the design.
Its a very broad topic with many fascinating twists and turns, design approaches.
Regards, Dana.
-
Thanks for the info @singapol I get your point bcus in most cases battaries are stable but the in this case I am using LIPO in a quad that requires sudden burst of I which results spikes that needs to be filtered
-
There's so many wrong and right places to put the filter(s), that you might as well show us a block wiring diagram of the devices connected to the lipo.
-
here u go
-
At first guess I think it should go here(red&blue) to protect the AP, GPS and RX from the ESC switching noise.
If the gimbal's servos are powered through the LC filter it will have to carry 4-5 amps safely.
(https://www.eevblog.com/forum/beginners/how-to-cutoff-frequency-and-characteristic-impedance/?action=dlattach;attach=244950)