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Which of these two designs is better?

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kinjalgp

Active Member
Out of the two +5V regulated power supplies shown, which one do you think is more immune to noise?
I started using the first one in all my circuits, after it solved EMI/NOISE problem in one of my uC based project. I have never tried the 2'nd one nor done analysis of any of these as the circuit was suggested by one of the members of Philips uC forum.
What difference does it make if I connect the C-L-C (Pi) circuit before regulator and after regulator?

Any suggestions/comments/improvements?
 

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Sebi

Active Member
My opinion: the pi-filter in output line need when your circuit generate RF signals/noises (uP also can generate) and make trouble in regulator circuit.
Pi- filter - serial with input - can prevent the incoming RF signals. The DC power cord - as aerial - can receive strong RF signals and make trouble in Your circuits.
 

kinjalgp

Active Member
So will it be more effective if I connec one Pi filter at input of regulator and the other at its output?

What I think is that in the 1st circuit the noise from power chord will pass through the regulator but the Pi filter at its output will block it from reaching the microcontroller. And also the same Pi circuit will also block any noise generated by uC from reaching the regulator. Correct me if I am wrong!
 

seeker

New Member
Hi kinjalgp,

If your voltage regulator circuit is operating in a harsh emi/rfi environment I would use filters on the input and output and also make sure you have a good groundplane throughout to maximize the effectiveness of the filtering.
Also keep all the wires as short as possible (as I'm sure you know:) )

Good luck on your project, Tony
 

Sebi

Active Member
If Your circuit working in RF-noisy environment, and this make a trouble in circuit, two filters always better, but if discovered the noise-source (direction) one enough.
In my practice the noise attack always coming from input.(many dimmers without filter, SMPSU without or not enough filter, RF transmitter and (!) cellular phones nearby the power-cord.)
 

kinjalgp

Active Member
Thanks Sebi and seeker.

Now I think as a general practice, I will use Pi filter at both the sides. This will asuure that I don't have to do any more R&D on problems that arises due to noise, once the circuit it is constructed.

Thanks.
 

adrianospiteri

New Member
I Explain

Hi. Filtering in any circuit is ALWAYS done in primary sections. The first one is thus better since the regulator inputs filtered voltage and regulates it to the correct output.

The second setup although it works as well leaves more noise since the regulator is not capable of filtering certain noise on the input. You can try add a sawtooth to the input and see that with the second setup, the noise ouput is higher than that of the first setup.


ADRIANO SPITERI
 

kinjalgp

Active Member
I think what you say is the other way round. You mean to say that second one is better. Isn't it? By mistake you mentioned second as first and first as second.

Anyways, I think filtering on both sides will increase noise immunity considerably.
 
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