How to get a ripple free output low pass filter?

[pran.thakur]

hi
i am using ad 736 as precision rectifier to measure ac mains current using shunt resistance tecnique.
i wnt to know that how can i get ripple free o/p that is pure dc voltage which can fed to microcontrolar.
(please specify the value of R and C for low pass filter)

 

[FvM]

Re: rms to dc converter

Strictly spoken, you can't get a ripple free output of a low pass filter. You do a trade-off between ripple and response time,
as discussed in the AD736 data sheet. To achieve a true ripple free output with finite response time, averaging over full mains
frequency cycles (e.g. by the processor) would be the most effective method.

 

[keith1200rs]

rms to dc converter

Page 14 of the datasheet gives a table of suggested averaging and filter capacitor values for different signal types. 150uF for the averaging and 10uF for the filter would seem appropriate for your application, I would have thought.

Keith

 

[pran.thakur]

rms to dc converter

can u please specify the circuit for converting the input ac vtg to equivalent output pure dc using AD 736.thanks.

 

[keith1200rs]

Re: rms to dc converter

can u please specify the circuit for converting the input ac vtg to equivalent output pure dc using AD 736.thanks.

I'm confused by the question! The AD736 takes an AC signal and turns it into a DC RMS one. The connections to do this are described in the datasheet, e.g. figure 18.

Keith.

 

[pran.thakur]

Re: rms to dc converter

Thanks
bt fig 18 is to complicatd.
Can i use fig 11 without voltage divider ckt.

In my project when i connect shunt to ac mains with load of 100 watt bulb then i got 4mv reading across shunt using multimeter.
I want to measure this 4mv using microcontroler so i need to convert this 4mv into dc then fed to adc and then to microcontroler..
Plz help me to design this ckt

 

[keith1200rs]

Re: rms to dc converter

I'm more confused! Figure 11 is a graph in my data sheet - I have linked to the latest one on Analog Devices' web site.

www.analog.com/static/imported-files/Data_Sheets/AD736.pdf

Keith.