Author Topic: Remove ac ripple from ckt  (Read 2207 times)

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Offline A2Topic starter

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Remove ac ripple from ckt
« on: August 05, 2014, 12:38:41 pm »
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.
 

Offline tautech

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Re: Remove ac ripple from ckt
« Reply #1 on: August 05, 2014, 09:13:27 pm »
It is normal to put up to 1000 uF before a linear regulator to reduce ripple.
The boost converter chip datasheet will have recommendations for input and output capacitance.
Often high frequency caps will be needed due to the switching frequency used.
Multi-layer ceramic or tantalum are usually recommended.
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Offline Robby

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Re: Remove ac ripple from ckt
« Reply #2 on: August 06, 2014, 04:43:26 am »
Let me get this straight: the output is +5v but you are seeing +7v?  Is there a .01uf bypass cap where the power leaves and again where it enters the device under test?  Are the wires in a bundle with other voltage sources?  Did you look at the voltage on a scope and see ripple?

EDIT:
Are you trying to pull too much current through the supply?  Use a larger cap, like 4700uf and the see if the ripple has leveled out.
« Last Edit: August 06, 2014, 09:38:23 pm by Robby »
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