Opamp based ideal diode peak detector of small AC voltage - Page 1
Forum section: electronics / projects

author: eneuro
author_rank: Super Contributor
timestamp: August 20, 2014, 03:33:24 pm
content: Hello,Just made simple peak detector cicrcuit with LM324 opamp amplifier, but trying to figure out if I can use other opamps of this quad opamp to exchange this small voltage rectifier diode marked in orange on this schematics without using -5V to 5V opamp power supply Vcc?Just watched this nice Dave vblog about precision peak detectors and while I have small AC voltages it could be nice reuse Shottky BAT85 diode I've used as recifier there with another opamp from LM324 if possible, but diode reverse current protection is not needed-only remove this Vf voltage drop in rectifier diode.However, those AC inputs marked by red & blue colors in my simulation schematics, where peak detection input is, while I'm using LM324 powered by 0V-5V looks like it might be issue and I'm not sure if this opamp based ideal diode rectifier can work without -/+5 power supply?LM324 has input voltage marked as -0.3V to 32V, differencial input voltage 32 and power supply Vcc +/-16V or 32V in its absolute maximum ratings datasheet parameters...BTW: Those opamp power supply concerns when dealing with AC signal input voltages, especially when opamp have to work as rectifier in peak detection circuit makes me crazy while there are different types of opamps and endless posibilities to connect it to external components, but sometimes I need detect something in analog world and convert it to MCU ADC voltage levels above single LSB, so it looks like it is not possible to escape from those strange analog opamps

author: Dongulus
author_rank: Regular Contributor
timestamp: August 20, 2014, 04:15:32 pm
content: The LM324 can run on a single supply or a split supply. Don't look at the absolute maximum ratings; those are the range of values that the part can tolerate without damage.The first page of thedatasheetsays that the amplifier can be powered by voltages down to 3V for a single supply, and +/- 1.5V for a split supply.For an op-amp running on a single supply, you need to create a "virtual ground" reference point that is half-way between your supply voltage and your circuit's GND.This websitehas information about about how to build a virtual ground point for a single supply op-amp.

author: macboy
author_rank: Super Contributor
timestamp: August 20, 2014, 04:36:29 pm
content: To remove the forward voltage drop of the diode, put it inside the feedback loop of the op-amp.One minute on google should give you the right idea.

author: eneuro
author_rank: Super Contributor
timestamp: August 20, 2014, 06:00:37 pm
content: Quote from: Dongulus on August 20, 2014, 04:15:32 pmAbsolute ratings and operating temperature this is what I'm interested first when using new component in new not tested before configurationThere single powered LM324 is used to detect sound, but using microphone and peak detection is after amplifier using diode and there is no negative input voltages I guess.My question is not how to connect opamp with diode and feedback to make such peak deetction circuit like in this Dave video below, but I'd like to use LM324 opamp with single power supply 5V only without -5V one.I know how to make virtual ground but not sure if needed and unfortunatelly my simple circuit simulator gives me strange outputs when this precision peak detection circuit with diode on opamp output negative fedback is used, so maybe it is time to switch tospice?

author: macboy
author_rank: Super Contributor
timestamp: August 20, 2014, 06:11:44 pm
content: For such a simple circuit, the most accurate and fastest simulator is a breadboard, wire, and components

author: eneuro
author_rank: Super Contributor
timestamp: August 20, 2014, 08:51:28 pm
content: Quote from: macboy on August 20, 2014, 06:11:44 pmI do not like breadboard and for simple circuits single layer PCB prototypes are better while one look and whole circuit and its connections are visible when back lighted from the bottom and ready to connect external antenas, coils and piezoOn thesefew pages of precision rectifierbook is version of improved "Superdiode", as well as full-bridge precision rectifier and AC voltage measurementsFinally I've found this interesting precision rectifier circuit based on cheap TL072, but it is not such easy choose proper opamp, while there are many traps and slow opamps might be useless in some cases.In this precision rectifiers overview there are many references and examples including a few single power supply, but it is tricky and sometime diodes matching needed.Precision rectifiers application notes review by Rod ElliotThose precision rectifier circuits looks simple but so many traps and dependencies

author: dannyf
author_rank: Super Contributor
timestamp: August 20, 2014, 10:40:42 pm
content: Rod Elliot has a nice collection of precision rectifiers (pretty much the same as peak detectors) on his website.Google him.

author: eneuro
author_rank: Super Contributor
timestamp: August 21, 2014, 12:34:47 am
content: Quote from: dannyf on August 20, 2014, 10:40:42 pmHopefully found his website before (this schematics I've choosen with TL072 opamp is from his conclusions and one of recomendations) and now added "by Rod Elliot" to link I've provided in my previous postHe did great research in this subject and it is easier choose something to test