1. I have a board, which is getting +8V from a ac-dc power supply.
Input to ac-dc power supply: 220V ac , 50Hz.
output of ac-dc: +5V dc

Now this output contain noise. What I think it will be 50hz noise from power supply riding over +7Vdc.

I have put a 7805 regulator on my circuit which converts +8V to +5V.

What capacitor value should I place on regulator which can remove the noise.


2. In second case, I have a li-ion battery over which a boost converter is fitted, converted its voltage to +5V dc.
It powers my circuit. But since its a boost conveter in contains noise depending upon the its frequency.

How to remove this noise.

 

I would replace the 7805 with a low-drop-out (LDO) regulator such as LF50ABV-DG.

To determine the value of the capacitor you need to specify the load current.

 

Load current on normal mltimeter , which will bypass high frequency reading goes upto 60mA

 

MCU is running at 120Mhz using 16Mhz internal oscillator by PLL

 

Any available Low-Dropout 5V LDO regulator should work (not LM7805 series).
Minimum capacitor values for your specific LDO are shown on the data sheet. Do not go below those values. If there is no "filter capacitor" on the output of the upstream rectifier, then you will also have to add this...

 

I'm fighting a ripple problem on a plating rectifier my self. Just reading around to see how I can repair. 11% ripple from a 5A unit.

Silicon old style rectifier.

 

I'm fighting a ripple problem on a plating rectifier my self. Just reading around to see how I can repair. 11% ripple from a 5A unit.

Silicon old style rectifier.

Your should start a new thread in a case like this...
Read this recent thread.