Precision Diode Wideband AC-DC converter

Thread Starter


Joined Mar 24, 2008
Precision Diode AC-DC converter

  • Qty 2 B1, B2 9V Batteries
  • Qty 2 Battery Clips (BG Micro P/N BAT1098)
  • Qty 1 U1,NJM1465 IC Fast Dual Op Amp (BG Micro P/N ICS 1015)
  • Qty 2 SD1,SD2 IN5822 Schottky Diodes ( BG Micro P/N DIO1N6822)
  • Qty 2 1 R1,R2 2Kohm 1/4W Resistors
  • Qty 2 R2,R3 10Kohm 1/4 W Resistors
  • Qty 1 R4 1Mohm 1/4 W Resistor
  • Qty 1 C4 1.0 uF Cap 16 V or better
  • Qty 3 C2,C3,C5 0.1 uF Capacitors
  • Qty 1 C1 100uF Capacitor 35V or better
  • Qty 1 Solderless breadboard (BG Micro P/N ACS1563)

    Suggested Test Equipment
    • DVM (Digital Volt Meter) or VOM (Volt Ohm Meter)
    • Oscilloscope
    • Function/Signal Generator






    Occationally there is a need to measure frequencies higher than audio ( arbitrary number of 20KHz or greater). I wanted to measure a low level 100KHz signal. DVMs are designed to measure power and aircraft power signals. This means their frequency ranges tend to be (50/60Hz and 440 Hertz (aircraft power)). A wide band AC meter is also useful for measuring both active and passive filters. I selected this circuit from google and modified it trying to improve its performance.

    Theory of Operation


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Thread Starter


Joined Mar 24, 2008
This is an experiment . As stated above it is not complete I am changing the format how I lay this out slightly to see if it is acceptable, I also noticed the things I forgot after I started posting it.

If anyone is interest I am using Libra office to write this, then a combination of Choose all<CNTRL>A and copy and past to write this. Makes revision much faster and easier.
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Joined Jul 31, 2004
Beginners may not understand the intent of the schematic due to lack of familiarity with the two separate commons (symbols). Perhaps an explanation of the two different symbols would help.

Diodes not listed in parts list. Diode symbol looks like that of a Zener diode. I am not familiar with the use of zeners in the precision rectifier circuit.


Joined Sep 17, 2013
With both diodes being inside the feedback loop, have you noticed any performance difference dependent on diode type, i.e normal silicon rather than Schottky?


Joined Mar 30, 2018
I would recommend you use a digital scope to make such measurements – you can then observe the waveform amplitude to check that the rms voltage indicated by the scope is somewhere near correct.

Thread Starter


Joined Mar 24, 2008
Until I get my leg or arm back from the stroke I will not be able to test this, I have a dual trace scope, It is in my garage on the other side of a step. My home is not wheelchair compatible.

Ever study schottky diodes? The do not use the classic PN junction. and have a forward voltage drop of .2-.3 volts and tend to be very very fast.


Joined Apr 23, 2018
Sadly your detector is not going to be linear with frequency the 1u capacitor shunting R1 is going see to that. So its going to be very hard (if not impossible) to sweep over much of a range without having to re-tune the frequency response. However, if your bandwidth is narrow you can fix the response of your detector to suit. Maybe use switched capacitor ranges. Or go wild and use VCF to track your VCO (after pulling C4).

One last problem- your opamp has 4Mz gain bandwidth product- it will run out of puff pretty low down in your pass band.
4Meg/200k is an Av of only 40! This only adds to your frequency response fall off woes.

Life is full off traps...

Thread Starter


Joined Mar 24, 2008
When I built it I will tweak it. You may or may not have picked up that I am mostly bed bound from a stroke 2 years ago. I will get better but it crimps my breadboarding abilities for a while ( I'm working on that) I like to write tech articles, but since my simulator is between my ears I like to test idea before I formally publish them, I also like to design. I have published quite a few chapter in the open source text book on this sit e an will be doing more. I am a very open, if not odd person My history is an open book here on AAC.

Thread Starter


Joined Mar 24, 2008
One of the things I am doing differently is giving BG Micro Part numbers . In the interest of openness I have a business relationship with these folks I do odd jobs for them and get parts in return. Since Radio Shack has mostly gone south I'm filling the vacuum they left behind.