Stable optocoupler

  
A circuit stabilizes the current-transfer ratio (CTR) of an optically coupled isolator used as a linear transducer. The optocoupler produces a voltage output that is proportional to—but electrically isolated from—the voltage input. However, the output voltage is directly affected by changes in the CTR, and the CTR can change substantially with temperature and current. To a lesser extent the CTR changes with time over the life of the optocoupler. The circuit employs a feedback circuit containing a second optocoupler.
Stable optocoupler  - schematic

The feedback signal tends to oppose changes in the overall CTR.




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