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Article: Optoisolators compute watts and volt-amperes.
- Article from:
- EDN
- Article date:
- February 21, 2008
CopyrightCOPYRIGHT 2008 Reed Business Information, Inc. (US). This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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W Stephen Woodward, Chapel Hill, NC
Edited by Charles H Small and Fran Granville
A decade or so ago, I designed a simple circuit that included a quad optoisolator arranged in a full-wave analog-multiplier bridge (Figure 1 ). It sensed and calculated watts of ac-power consumption and ignored any reactive component in the load. The circuit's principle of operation relies on the fact that the LEDs of the bridge, like any other device with a semiconductor junction, have a dynamic conductance that's directly proportional to current: approximately 19 mS (millisiemens)/A at 25[degrees]C. Both the line voltage and load-current-proportional sense voltage, which ...