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[FAQ] What is Current Transfer Ratio (CTR)?

FAQ: Isolation >> Opto-Emulators >> Current FAQ

What is Current Transfer Ratio (CTR)?

  • What is Current Transfer Ratio (CTR)?

    Current Transfer Ratio (CTR) is a ratio of the current to the output collector input forward current and is represented in a percentage.

    CTR is mainly characterized in analog opto-emulator or optocoupler devices.


    The input forward current (IF) is the current going into the diode while the output collector current (IC) is the current flowing into the output transistor.

    • For CTR > 100%, the IC will be greater than the IF.
    • For CTR < 100%, the IC will be less than the IF.

    How is it represented in datasheets?

    How is CTR measured from a device?

    The diagram below shows the test circuit which is designed to measure the CTR for an analog opto-emulator.

    By applying the input forward current and applying a voltage to the collector-emitter, the output collector current can be measured.