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Maxim > Design Support > Technical Documents > Reference Designs > Amplifier and Comparator Circuits > APP 1867
Maxim > Design Support > Technical Documents > Reference Designs > Automotive > APP 1867
Keywords: current sense amplifier, high-voltage, optocoupler
REFERENCE DESIGN 1867 INCLUDES: Tested Circuit Schematic Description
Optocoupler Extends High-Side Current Sensor to
1kV
By: Roger Griswold
Mar 26, 2003
Abstract: This application note describes the use of a current-sense amplifier along with an optocoupler
to extend the operating voltage range up to 1,000 volts for high-voltage applications. The circuit relies on
the optocoupler's isolation barrier to separate the high-side and grounded side of the 1,000V system. Op
amps are used to eliminate photodiode non-linearity and drift and provide an accurate output voltage
proportional to the load on the 1kV supply.
The task of sensing DC current at high voltage is often problematic. Most high-side current-sensing ICs
available off-the-shelf are good to 30V or 40V. Newer offerings (such as the MAX4080/4081) can sense
up to 76V. For higher voltages, a current-sense amp can be combined with an optocoupler. The high-
side voltage is limited only by the optocoupler's stand-off voltage (Figure 1).
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