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how to get clean 5V from noisy 5V usb power?

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ahgu

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I am using the 5v off the USB connector, I see that it is very noisy. I need it to drive some ADC circuits that requires very clean 5v. LDO regulator need 5.2V to give 5V good power, what else can I do to otbatin good 5V from USB besides putting some 100uF tantulum cap on the supply?
 

You can use an LC filter to filter the 5 V to the ADC reference input. Another method is to use a switching supply to get 5.5 V or so and then use a passive regulator.

Can your ADC operate on a lower reference like 4.7 V produced by a low drop out regulator? This will require you to scale the output by multiplying it by the correction factor 5/4.7 in the logic.
 

If it was my prblem I would use 5-to-5 V dc converter with small LC tanks at both sides of the converter and 10-47uF tantalum decoupling capacitor close to your ADC...
 

ahgu said:
I am using the 5v off the USB connector, I see that it is very noisy. I need it to drive some ADC circuits that requires very clean 5v. LDO regulator need 5.2V to give 5V good power, what else can I do to otbatin good 5V from USB besides putting some 100uF tantulum cap on the supply?
Click to expand...

hi ahgu

Can you evolve a little more, what kind of circuit you want? There are even fabulous ways to obtain precise steady 5volts but tell me a little bit more what environment is this?
 

As the USB voltage is not stable, it's not a good idea to use it for ADC (and voltage reference of ADC) without a voltage regulator. I found one post that is quite similar to your problem here:



Besides, you may try the filter configuration of the following page:
Filtering PC bus power
https://www.epanorama.net/circuits/power_from_pc.html

Another one:
How to "clean up" 5V power supply?
**broken link removed**

May be you should consider to use isolated dc-dc for the power line and optocoupler for the data line, but this would take more space and it's more expensive.

Hope they help.

BTW, pls advise the power consumption of your circuit or application.
 

just want clean 5V off USB power to drive AD converter, that is all.


Is there 4.65 LDO ? Also USB power has a range from 4.4 to 5.5. from the spec.

I really don't want to put a switcher on the circuit board.
 

If it was my prblem I would use 5-to-5 V dc converter with small LC tanks at both sides of the converter and 10-47uF tantalum decoupling capacitor close to your ADC...


what is 5 to 5 vdc converter? do you have values for the LC tank?

thanks
Ahgu
 

DC-DC converter is a small black box (depending on power, it can be not bigger than 14pin dil) that coverts input dc voltage (in your case something around 5V) to isolated output (+5V).
As Ls I would use 10 - 47uH and as Cs 100nF + 10-47uF close to ADC.
 

what kind of inductor should I use? SMT.

HZ0805E601R

LC only good for filtering out High freq noise.
 

ianP:

what about the LC oscillation? resonant freq?
I used the EMI filter , non-resonant, but they are only good for HF.

10uH and 10uF, about 16Khz self resonant freq.
What kind of inductor should I use?
 

I wouldn't worry abot self-resonance in low-pas filter configuration..
As Ls you can use miniaturexial fixed inductors which look alsmost identical as 0.25W resistors or SMD - if you prefer this type..
 

IanP said:
DC-DC converter is a small black box (depending on power, it can be not bigger than 14pin dil) that coverts input dc voltage (in your case something around 5V) to isolated output (+5V).
Click to expand...
If the power consumption is not much, you can use "IC" type of isolated DC/DC converter, e.g. DCR010503 from Texas Instrument.
 

Depends on the noise, you can use decoupling cap to filter high frequency one, then use on chip regultro to reject osme of the rest.
 

I suggest you try an LC filter and carry out some measurements to see if noise decreases. If it does not decrease enough, use larger inductance and capacitance.
Capacitance must consists of 0.1uf in parallel to a 10uf and also in parallel to a 220uf or larger capacitor. You need all these sizes in order to achieve low impedance in a wider frequency range.
 

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