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Extend current-sense amplifier's input range down to 0V

Posted: 01 Oct 2007 ?? ?Print Version ?Bookmark and Share

Keywords:current-sense amplifier? charge pump? op amp?

In addition to the traditional lead-acid battery, modern electric/hybrid cars often include a large capacitor of 40 farads or more as a backup power source. Located under the rear seat, the large capacitor is used as a backup power supply to power the electronic braking system to safely stop the vehicle in case of engine and battery failure. Lead-acid batteries discharge only down to about 8V, but a capacitor can discharge down to 0V. Therefore, a current-sense amplifier is needed that can measure inputs down to 0V.

Adding a charge pump provides 5V supply rails to the operational amplifier internal to a high-side current-sense amplifier. This modification enables that amplifier to sense currents down to 0V common-mode inputs. The circuit can be modified to accommodate bidirectional current-sense applications.

Please view the PDF document for more information.

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