# Need RC filter design for 0to3.3v 50 hz ac signal

Discussion in 'Analog & Mixed-Signal Design' started by Mayuri1234, Sep 29, 2016.

1. ### Mayuri1234 Thread Starter New Member

Apr 7, 2014
3
0
I had designed a RC filter with R=10k and C= 47uF for my 50 hz signal. The DC output is smooth but the signal is getting attenuated.
I have again redesigned the filter with R=10k and C=0.1uF.In this case the output is not getting rectified.

2. ### AlbertHall Well-Known Member

Jun 4, 2014
2,275
449
What frequency do you want to pass through the filter unchanged, and what frequency are you trying to remove?

3. ### hobbyist Distinguished Member

Aug 10, 2008
774
62
Rectification can only work with diodes, if you are filtering out 50 hz , then a full wave rectifier needs to be built then a smoothing capacitor is inserted across the output, to give a better DC output, thats how a unregulated power supply is built.

If your filtering 50hz, to make it smooth DC , then your attentuation will be very high, but your relying on the leftover currents thats getting through, as your DC value. If you were to scope the signal with high resolution, you would see some waveform, because a filter is used for attenuating frequencies not rectifying.

Back to your original request, need help designing a filter for 50hz

first you need to determine some constraints.
1) cutoff frequency, (50hz)
2) resistance of the driving source, you need to make the input impedance at least 10 times larger than the output impedance of the driving source.
3) R=Xc
4) R= {1/(6.28*F*C)}
5) C= {1/(6.28*F*R)}
6) F={1/(6.28*R*C)}

with those equations you can design your RC filter.

Last edited: Oct 3, 2016