Thanks for your reply Mic3. I apologise for my ignorance; though I believed my subject to be related to this thread.
i have attached a file with my design for a full-wave rectifier with smoothed out DC output and integrated Common Mode Rejection. I hope this circuit will be of use to the members. The circuit has good linearity from 10 mV up to 2.5 Volts with frequency ranging from 50 Hz up to 100 kHz. I have found the accuracy to be less than 5 mV. The circuit works well in simulation, and as constructed hardware . I would apprecaite any comment and suggestions.

regards
Nader

 

Nad,

Just build the circuit in figure 3 and put a capacitor in parallel with a resistor on its output:

http://sound.westhost.com/appnotes/an001.htm

 

Mic3

you are quite right. That will work; though, it will only give smoothed half-wave rctified. Furthermore, I found that this method is very limited in its range, and Opamp saturates at higher voltages above 500mV. My circuit needs to measure the voltdrop across a shunt with input currents varying from 10 mA to 10 Amps. Sorry for discussing this issue in this thread. Should I start a new one? I am only trying to share my experiences and ideas with others and be of help if I can; bearing in mind that I am new to Opamp design.

Many thanks for your replies and suggestions.
Nader

 

If you design it properly then it won't saturate at 500mV.

What is the power supply for the op amp?

Will you sense an AC current?

 

Welcome to AAC, nad. We discourage thread hijacking, as it leads to consufion. Always start a new topic in its own thread.

This is the thread that got hijacked - http://forum.allaboutcircuits.com/showthread.php?t=9821&page=2.

A note - your circuit is overly elaborate. The "original" out of the National Semiconductor op amp circuits collection followed by an inverting stage with a 1 - 10 uF cap across the feedback resistor gives excellent results. Your 2200 uF cap is going to seriously strain the poor op amp trying to push current onto and off of that monster.

 

The simple circuit does not need "millions" of resistors.

 

I disagree with this circuit because if you don't use a resistor between the capacitor and the output of the first rectifier then the capacitor will discharge rapidly.