• EEVblog #490 – Peak Detector Circuit

    Fundamentals Friday.
    Designing and measuring basic and precision opamp peak detector circuits.

    Forum HERE

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      • (*steve*)

        Wouldn’t it be better to have a precision rectifier that didn’t saturate the output to the negative rail?

        • Yansi

          really would. One more little diode, problem solved. I wonder, why Dave didn’t mention the openlopp problem and ho to fix that.

      • Warren

        I would love to see an explanation of the op-amp internals, maybe a demonstration of building one from components.

        • huh

          Count me in, that would be a kick ass video. Differential amps, current mirrors etc are building blocks for a lot other circuits.

      • JFA in Montreal

        around 4m30s, you draw (and later on too) the decay curve of the capacitor.
        Shouldn’t it be concave instead of convex, e.g. with the faster decaying rate at the highest voltage, or do you use resistors with a negative value? 🙂

        Ahhh, never mind.

        I love your videos, I learn so much from them…


      • JFA in Montreal

        At 13m46s, you say “it’s gonna take time to charge up this capacitor”.

        However, the capacitor is ALREADY charged, if I understand the circuit correctly. Thus, isn’t the rise time problem caused by the op-amp itself, having a hard time handling the effective open-loop state back into a closed loop mode?

        Mind you, my last electronics class (physics dep’t, 1987) is a little far away…

        • NO, the cap it not charged. I’m talking about a sudden peak value after the cap voltage has been reset.

      • JFA in Montreal

        If my teachers had been as relaxed and enthusiastic as Dave is, I might have turned out becoming an electronic engineer ! Didn’t have that chance, I stuck to physics. Oh well…

        Great inspiration Dave !

      • dentaku

        I just watched this video for the second time and since I’ve learned more about opamps since the first time I finally understand all of it.
        This is very useful. I’m going to try it out soon to see if I can use audio to create control voltages to modulate the frequency of a VCO.

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