Precision Rectifier Circuit to detect peaks

Question

I have a question about speed at detecting peaks.

Essentially, my question is that I have a precision rectifier with a capacitor equipped to the end of it to smooth the incoming full bridge rectified wave, which works 100%.

however I am concerned, as the application is to play audio through this and capture the current peak. I am worried that the peaks won't be captured in time as audio changes very quickly worst case 1/20kHz.

I understand I need a resistor to discharge the cap so it can change on the next cycle, however when I put a low value resistor (For a faster discharge time) it doesn't reach my peak value anymore oppose to using a big resistor or no resistor which is important as the next stage is a comparator with a fixed Vref to compare to.

How do I balance this? I need a resistor value that can discharge the capacitor fast enough for incoming music in order to capture the peaks of that instant moment. Or is that the trade off?

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

C2 is too big for this sort of application. The OPA350 is only capable of 80mA of output current and it takes a long time to charge the 680uF cap. You then also need then a very small R3 value to discharge it rapidly between peaks.

Set C2 at about 2uF and R3=100k Ohm

That will give you reasonable peak capture and a decay time in the 200mS range. If you need to make this voltage available elsewhere you could add another OPA350 as a buffer.

^{simulate this circuit – Schematic created using CircuitLab}