help hight quality regulating dc voltage

Thread Starter

arenwi

Joined Dec 29, 2014
37
Hi again,

Now I ´m trying to obtain the most linear signal that is possible from a baterry of 4.5 volts to 1.5 volts (with low current less than 100 mA).

I will use this 1,5 volts for powerin an electret measurement microphone. The noise of the power will be in the output signal of the microphone and after to be amplified (40 dB) it generate me a big error in mi peak to peak max values detector.

I start using an low voltage regultor from microchip (studing a lot of data sheets I thougt it could ve a good option).
http://www.microchip.com/wwwproducts/Devices.aspx?product=MCP1700

I´m using the recomendated schematics from microchip (option 1) and after that a low pas filter aded by me (option 2), ussing electrolitic capacitors and tantalum capacitors, with no diferences.

IMG_5689.jpg

But the results are not what I hope, you can see a small noise signal od 10 t0 12 mV.

Captura de pantalla 2015-05-14 a la(s) 01.28.54.png

I need to reduce this noise making the signal more stable and make mi measurement microphone more stable.

Any ideas?? many thanks
 

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AnalogKid

Joined Aug 1, 2013
9,161
Measuring low noise values is very difficult because the scope can act as an electric field receiver and pickup all kinds of interference. For precise noise measurements, get rid of the ground lead on your scope probe and replace it with a direct connection to the shield cylinder near the tip. The total loop length from where the probe tip touches the signal to where the probe ground touches the circuit ground should be less than 10 mm. Also, measure across a 0.1 uF ceramic capacitor from the regulator output to GND.

ak
 

crutschow

Joined Mar 14, 2008
26,974
What does the scope signal look like when you connect the scope directly to the ground?

Try making the capacitor much larger after the 1kΩ resistor (say 470μF or more).
 

Thread Starter

arenwi

Joined Dec 29, 2014
37
MAny thanks for your fast answers... Like some users are thinkung this noise is from the osciloscope, conecting directli the + of teh probe and the ground I have the same noise. This is an tektroniks osciloscope and this is internal noise???? Incredible

I was making different test with another osciloscope, and old analog hameg and the results are really better. I use the same cirquit with electrolitic capacitors in the top measurement and tantalum in the second measurement (we are seen the ac voltage with 5 mvolts of scale).
I thaught that the tantalum will be better but it semss that not. That is a very hight quality signal.IMG_5695.JPG

Any body know if the noise of mi new digital osciloscope is normal?? (you can see in the first post)


Many thanks
 

crutschow

Joined Mar 14, 2008
26,974
Digital scopes tend to have a higher noise level than the old analog scopes so are not good for measuring low noise levels.
If the digital scope has a bandwidth selection for the input, then using the lowest bandwidth will help.

For low frequency noise suppression, tantalum caps are generally no better than aluminum (they are both electrolytic type).
The capacitance value of the capacitor is the main factor that affects the noise in your circuit.
 

Thread Starter

arenwi

Joined Dec 29, 2014
37
Thank you very much crutschow. i was thinking about it more than 15 days until I had decided to post it and in less than one day ....

Your help is wonderfull

:)
 

ScottWang

Joined Aug 23, 2012
7,004
Mcp1700 - The Input Operating Voltage Range: 2.3V to 6.0V.
1. How many volts of the input?
2. Disconnect the input of Mcp1700 from Vin, and connecting input to GND, measuring input and output with O'scope.
3. Adding a 220uf~470uf/10~16V and 0.1uf/50V to the input of mcp1700 and measuring the input and output with O'scope.
 

Thread Starter

arenwi

Joined Dec 29, 2014
37
Hi scottwang, many thanks for your help, it was a problem with the noise of the osciloscope who is biguer than the Mcp1700

many thanks
 
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