Feedback circuit clamps precisely

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< Analog Electronic ~ Feedback circuit clamps precisely

eric

Posted: Thu Oct 05, 2006 11:51 pm Post subject: Feedback circuit clamps precisely

Site Admin Joined: 01 Jan 1970 Posts: 311

A Burr-Brown applicatio0n 61
A linear circuit consisting of an input buffer, IC1a, and output-scaling
amplifier, IC1b, two zener diodes, D1 and D2, and several other
components can supply sharp, precise, bipolar clamp levels with
continuous variable control, from 0 V to ±11 V. A feedback loop
enclosing the amplifiers and zener diodes generates the high
clamping accuracy—see diagram.
Within the limit range of the clamp, ±VL, the zener diodes are off,
and IC1b feeds back its output to the inverting input of IC1a via
R4. At the same time, IC1a drives IC1b via voltage divider RV. The
feedback forces the inverting input of op amp IC1a to equal Ui at
the non-inverting input terminal.
The circuit forces the inverting input of IC1b also to follow Ui.
There is no signal voltage drop across R4, because no current can
flow from it into the inverting input of IC1a. Consequently, the
non-inverting input of IC1b, which defines the potentiometer output
at feedback equilibrium, must also track Ui. In fixed-level limiting
applications, a resistive divider may replace potentiometer
RV. Amplifier IC1a then delivers an output

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