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Do I need a 50/60Hz notch filter for battery powered devices?

up vote 14 down vote favorite

Given that battery powered devices are not plugged in the mains power, can I assume that there will be no 50/60 Hz frequency noise?

This question came up while thinking about what the circuit for a portable ECG monitor would look like and it seemed obvious that the 50 Hz notch filter could be eliminated. But is it so?

Thank you

2 Answers

up vote 4 down vote accept

If you are talking about power inputs. There will be no ripples in a battery powered system to be filtered. You don't need to use a filter.

But a parallel capacitor can be useful for reducing instant voltage change during power off/on.

up vote 3 down vote

Batteries are DC, the − and + poles do not alternate, therefore there is no frequency in batteries. Unlike AC, where − and + do alternate between poles. Depending on where you live, the mains will be 50 Hz or 60 Hz. The UK is 50 Hz and the USA is 60 Hz for example. So, you don't need a 50 Hz filter.


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Do I need a 50/60Hz notch filter for battery powered devices?

up vote 14 down vote

Given that battery powered devices are not plugged in the mains power, can I assume that there will be no 50/60 Hz frequency noise?

This question came up while thinking about what the circuit for a portable ECG monitor would look like and it seemed obvious that the 50 Hz notch filter could be eliminated. But is it so?

Thank you


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up vote 9 down vote

If you are talking about power inputs. There will be no ripples in a battery powered system to be filtered. You don't need to use a filter.

But a parallel capacitor can be useful for reducing instant voltage change during power off/on.

edit

Due to things like a battery's internal resistance, doesn't that only hold true if the size of the battery is large enough that fluctuations in load current only produce insignificant fluctuations in voltage? Putting a filter between battery and load should help smooth out these load induced fluctuations. - BeowulfNode42 Jul 17 at 7:15

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