Peak Detector - Reducing Leakage (Op-Amp Basics, episode 7)

Описание: Reducing Leakage Current
Op-Amp Basics, episode 7

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Schematics, as usual, are on the project GitHub: https://github.com/kennykb/kevins-cav...

In this video, we look at the problem of voltage droop in the peak detector circuit of last episode. We learn that it was caused by current leaking charge out of the capacitor that holds the peak voltage.

In the course of tracking down the problem, we learn many lessons about leakge current in high-impedance circuits. We examine a number of ways that current can leak away, and learn about the op-amp specification of input bias current. We find that in our circuit, most of the leakage current was in the diode, and try better and better ways to control it, finally settling on the gate-channel junction of an inexpensive JFET.


00:00 Where is it leaking?
02:41 PSA
04:10 The capacitor?
04:40 The op-amp?
06:52 The world?
07:31 The diode?
08:12 Schottky diode
08:58 Cheap silicon diode
10:04 Low-leakage silicon diode
11:41 Diode-connected JFET
15:22 The reset circuit?
16:06 Next steps


Music:

“Light Sting” Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 4.0 License
http://creativecommons.org/licenses/b...

Images:

"Sailfish" Duane Raver
Public domain
https://commons.wikimedia.org/wiki/
File:Sailfish_(Duane_Raver).png

Video clips:

"Subscribe and Bell Icon" Video by u_r3vm8hrv26 from Pixabay
https://pixabay.com/videos/
subscribe-bell-icon-green-screen-144301/


R82 capacitor data sheet courtesy of Yageo Group - Kemet
LMC6482 data sheet courtesy of Texas Instruments
1N4148 and 2N7000 data sheets courtesy of Vishay Semiconductors
J112 data sheet courtesy of ON Semiconductors


Shout-out to Daniël van der Bent, Andy Kirkham,
Charles Lohmiller, Ray Otwell, John Sheppard and eight
anonyoous donors for their contributions to the Get Fed Up!
campaign. Kevin's Cave People are wonderful!


© 2025 Kevin B. Kenny