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DESIGN AND DEVELOPMENT OF MEDICAL ELECTRONIC ...

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ISOLATEDPOWERINPUTJ4ISOLATED SIDENON-ISOLATED SIDE1 VCC234 +9V_ISO-9V_ISO+9V-9V+9VJ3123C10NON-ISOLATEDPOWER INPUTLM385-1.2-9V_ISO48ISOLATEDSIGNALINPUTR106.8kD2R910kJ1BNC12II VCC<strong>OF</strong>FSETADJUSTR82kR318kGAINADJUSTIC50.1uFIR41.5kR51kR72k-9V_ISO234 5C2.01uF+9V_ISOIIC120pFR21k+9V_ISO213R610k-9V_ISOR11kQ12N2222I+ C447uF341IC22 5IL300876+ C647uFR142kMaintain: 5mm AirClearance8mm CreepageDistanceR156.8kR1220kIC3LM74123-9V4 5-+-+7 1C7.01uF6IC1LM741I+ C310uF+9VR1110kReinforced IsolationBarrier7 1+9VR1318kC9.01uF6C8.01uF8.01uFD14LM385-1.212J2BNCNON-ISOLATEDOUTPUTFigure 3.13 Unlike the open-loop isolation amplifier of Figure 3.8, the output of IC1 in this closed-loop circuit is not simply a current proportionalto its input voltage. Rather, part of the LED’s optical flux is detected by the second photodiode and used to provide feedback to theop-amp current source. Since the stability of a photodiode is not usually a concern, and since the characteristics of both photodiodes areclosely matched during manufacture, the transfer characteristic of the complete circuit is highly linear regardless of LED nonlinearity, aging,temperature, or LED drive current dynamics.117

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