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Renesas Electronics America - Knowledgebase

Why the CTR characteristic is not listed in high speed photocoupler?

Latest Updated:10/01/2007


The CTR characteristic is not listed among the electrical characteristics of the PS9117A high-speed photocoupler (IC output, high speed of 10 Mbps). Why is that?


The PS9117A has a function for outputting a digital signal (H/L). The relationship between the input and the output with regard to transmission of this signal is shown in the following truth table.

To change the output from "H" to "L" here, it is necessary to flow an input current of coupled/threshold input current (H → L): IFHL (TYP.: 2 mA, MAX.: 5 mA) or higher in terms of electrical characteristics. When this current is supplied, the output changes from "H" to "L".
To change the output from "L" to "H", make the input current equal to or lower than IFHL.

Since signal transfer is done by controlling the value of the input current in this way, the CTR characteristic is not needed as a design parameter and is therefore not listed.
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Photocouplers / Optocouplers