Video introduction to Peak Detector circuits - Page 1
Forum section: electronics / beginners

author: w2aew
author_rank: Super Contributor
timestamp: February 02, 2013, 02:49:10 pm
content: Here's a short introduction to peak detector circuits. First looking at a basic peak detector based on a half-wave rectifier, then showing how using an op amp can help eliminate some of the limitations of the basic circuit:If you like this video, you may want to subscribe to my YouTube channel:https://www.youtube.com/w2aewComments and suggestions are always welcome.

author: robrenz
author_rank: Super Contributor
timestamp: February 02, 2013, 05:02:29 pm
content: Great video as usualSome may not realize an opamp can be used as a precision diode.

author: M0BSW
author_rank: Frequent Contributor
timestamp: February 02, 2013, 05:28:58 pm
content: I agree , your video's are always a lesson in understanding electronics, and very enjoyable.

author: w2aew
author_rank: Super Contributor
timestamp: February 02, 2013, 09:47:32 pm
content: Thanks - I'm glad you enjoy them!

author: Axel1973
author_rank: Regular Contributor
timestamp: February 02, 2013, 11:20:09 pm
content: absolutely awesome! As always.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 03, 2013, 01:29:16 am
content: FWIW. AoE also has a section on this particular subject and explained in greater details (i havent watch the above video) including droop and opamp Vus limitation. as always, opamp will have a hard time "super peak detecting" at higher BW.to w2aew.

author: Christe4nM
author_rank: Unknown
timestamp: February 03, 2013, 11:12:37 am
content: Great video! Well explained, at a good pace, short enough while not leaving out any necessary information. Well prepared before shooting it too! (no messing around with probes since your setup is ready to go already)A few questions. I can imagine the opamp doens't really like to have it's output current blocked by the diode in reverse bias if the signal is at its negative half of the cycle. I'm not sure if that's true, but if so, wouldn't it be better to add a second feedback loop with a diode in opposite direction. In that case the opamp can still keep it's inverting input following the non-inverting input. Since it then uses the second feedback loop, the peak detector isn't affected. (Actually you've then build the setup for a precision rectifier circuit). Also, if I remember correctly, shouldn't you add a bit of resistance in the feedback path to the non-inverting input nonetheless? Again I'm not really sure here. I know bits and pieces about working with opamps, but have not yet proceeded into the specifics yet.Apart from that I was thinking that if your input signal is very small, you could consider amplification in the peak detector. For example by adding a voltage divider in the feedback path from the output of the peak detector to the inverting input of the opamp. The opamp will then amplify the signal at the output peak detector into a better measurable range.

author: w2aew
author_rank: Super Contributor
timestamp: February 03, 2013, 02:01:39 pm
content: Quote from: Christe4nM on February 03, 2013, 11:12:37 amAll very good and valid points. The blocked feedback path will generally cause a couple of things to happen. The output slams to the rail when the input drops, which doesn't cause too much of a problem except for potential transient noise and delay in responding. The larger issue is that many op amps aren't stable with a capacitive load. Even for stable op amps, the output will often bang up/down during the charge cycle.So, as you can see, this video is simply an introduction to the concept. There are a lot of improvements that can be made.

author: MikeK
author_rank: Super Contributor
timestamp: February 05, 2013, 04:27:30 pm
content: Thanks, Alan. Good video. Does the output cap affect stability at all? Is the diode preventing it from becoming unstable?