Skip to main content
Renesas Electronics America - Knowledgebase

What is the CTR (Current Transfer Ratio)?

Latest Updated:10/01/2007


What is the CTR (Current Transfer Ratio)?


The CTR indicates the current efficiency between the input and the output in a photocoupler.
This ratio is obtained by dividing the output side current IC by the input side current IF (CTR = IC/IF × 100), and it is expressed in %.
Normally, the CTR (abbreviation of current transfer ratio) is the most important performance measure of general-purpose photocouplers.

The CTR has the following specific characteristics.

(1) It depends on IF (forward current fed to LED).
(2) It is affected by the ambient temperature.
(3) It changes over time.

For details about these characteristics, refer to the following URL.

Suitable Products
Zener Diodes for Surge Absorption
Photocouplers / Optocouplers