Step 4. Check each constant.
Consider whether there is sufficient margin for operating temperature, speed, lifetime design, tolerance of resistor, etc.
Temperature range ⇒ VF, CTR, allowable current, etc.
Load resistance ⇒ switching speed, influence of dark current, etc.
Confirmation of lifetime of the set
The optical output of the input LED of photocoupler decreases with the passage of time.
It is necessary to confirm that the characteristics are satisfied, for which purpose this deterioration during the lifetime target of the set must be included.
The aging variation of the optical coupler can be calculated from input current (IF) and ambient temperature.