Peak rectifier

Design of a peak value rectifier with half-wave rectifier (top left)
capacitor, voltage follower (right)
comparator with switching transistor (bottom)

The peak value rectifier is an electronic measuring device with which the maximum value of an electrical voltage is recorded, stored and kept available for further use. The picture shows one possible implementation. The basis for understanding is the behavior of an operational amplifier which, if it is not overdriven, fulfills the two conditions with a very good approximation:

1. no voltage between the inputs
2. no currents in the inputs.

A necessary prerequisite for this is the feedback from the output to the inverting input.

With a positive input voltage , an output voltage is generated in a precision half-wave rectifier - undistorted by the forward voltage of the diode . A high-quality capacitor C is charged with the output voltage . As the input voltage increases, so does the voltage across the capacitor. When the input voltage drops, the diode separates the operational amplifier from the capacitor, and ideally the capacitor maintains its maximum value indefinitely. So that it is not loaded, a loadable voltage is provided by means of a voltage follower for further signal processing . ${\displaystyle u_{\mathrm {e} }}$ ${\displaystyle u_{\mathrm {a1} }=u_{\mathrm {e} }>0}$ ${\displaystyle u_{\mathrm {a2} }=u_{\mathrm {a1} }}$

Detection of the minimum value of a negative voltage requires a different, but similar, circuit with the reverse direction of the diode.

If further voltage peaks are to be recorded, the capacitor must be reset in the meantime. For this purpose, in the circuit shown , the transistor T operating as a switch is brought into the conductive state by a comparator K for as long as is. In a simpler variant, the capacitor is continuously and slightly discharged with a resistor which is so high that a time constant results for a signal with the period duration . ${\displaystyle u_{\mathrm {e} }<0}$ ${\displaystyle T}$ ${\displaystyle RC\gg T}$

Individual evidence

1. ^ Elmar Schrüfer, Leonhard M. Reindl, Bernhard Zagar: Electrical measurement technology . 12th edition. Hanser, 2018, p. 126.
2. ↑ Erwin Böhmer, Dietmar Ehrhardt, Wolfgang Oberschelp: Elements of applied electronics . 16th edition. Vieweg + Teubner, 2010, p. 178.
3. ↑ Hans-Rolf Tränkler: Pocket book of measuring technology . 4th edition. Oldenbourg, 1996, p. 63 f.