Voltage signal processing (ac to dc)

[NSKL]

Hello everyone,

I was wondering if someone could point me in the right direction. I have an AC signal generated by a piezo film (used as a vibrational sensor) and I need to process it to get a proportional DC signal. I've tried building a diode bridge and using a AC DC rectifier IC, but all I could achieve is cut the negative part of the piezo film AC output.

Since a picture says a thousand words, please take a look at the attached sketch of what exactly I would like to achieve, and see if you can give me some suggestions.

Thanks in advance,
-Igor

 

[dannix]

sounds like you used a half wave rectifier. You need a full wave bridge rectifier.

 

[NSKL]

Hi dannix, thanks for posting.

I used a db155g briIdge rectifier IC. I thought since it is a BRIDGE rectifier, it must be full wave. Is this not so? Using this IC, I managed to remove the negative part of the AC signal, which is unfortunately far from what I would like to achieve.

I've built a diode rectifier bridge (4 diodes, full wave rectification), but I didn't think in advance and forgot that diodes drop around .6V. When I connected this to the piezo vibration sensor, I got a flat 0v out all the time, since the output of the sensor is always below .6V, therefore the diodes were dropping all the voltage.

Finally, do you believe this is as simple as putting a bridge rectifier IC on the piezo sensor output to achieve what I'm after?

I was looking at suppliers in my area but the choice for bridge rectifier ICs is very limited. I can get the db155g that I mentioned, WO4 and a 2W06. Would any of these be acceptable?

Thanks for help!
-Igor

 

[ericgibbs]

hi NSKL.

Look at this forum link:
You require a precision rectifier for low level ac.

https://www.electro-tech-online.com/threads/ac-bridge.34189/?highlight=opa+rectifier

Web search:

**broken link removed**

 

[crutschow]

Look at this forum link:
You require a precision rectifier for low level ac.

https://www.electro-tech-online.com/threads/ac-bridge.34189/?highlight=opa+rectifier

Web search:

**broken link removed**

Do you want the peak or the average value of the signal?

The first reference circuit above gives the peak of the AC signal.

The second reference has circuits that give the unfiltered rectified signal. Averaging this signal with a low-pass RC filter will give the average DC value of the rectified signal.