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Filter DC source with 50 mV rms noise?

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adamthole

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I have a 3V DC power supply that is giving me 50 mV of rms noise. I would like to eliminate this noise as much as possible. Is there a calculation that makes it easier to determine what value of capacitor would get rid of most of that noise? When I put a 1000 uF capacitor on the circuit the noise goes away, but I would prefer to use either a much lower capacitor value or something else.

My usable voltage can go as low as 2.7 volts. Does anyone know of a 2.7v precision voltage reference IC that can run off of 3 volts? I can only find them at around 2.5v. (MCP1525 for example)

Thanks!
 
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Some comments:

1. Try smaller capacitors until you find a value that is too small then go back up one size. Hardly scientific but the method works.

2. You can make some estimates but you'll need to understand something about the noise. Is the energy in the noise the result of ripple that would follow an AC rectifier?

3. Linear voltage regulators have some ripple rejection abilities. The ripple rejection can be improved on some of these -check mfrs datasheets.
 
Okay, thanks. I didn't know if there was a rule of thumb or just a guess and check when it came to noise. The noise is caused my a charge-pump.
 
If your charge pump can be made to run faster with an external device, the noise gets easier to filter out. Besides a tantalum cap, use a .1 microfarad monolithic in parallel to help shunt high-frequency ripple to ground.
 
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