Aging variation data of photocouplers
The optical output of the light-emitting element (LED) decreases with the passage of time. In photocouplers, aging variation of optical output of LED is more dominant than that of optical receiving devices. Therefore, the designer needs to estimate the decrease in the light emission level using the data of aging variation of the adopted photocoupler. The designer calculates the light output change of the LED from the usage environment of the equipment to be used and the total operating time of the LED. It is necessary to reflect this value in the initial value of forward current (IF) of the LED.
* For example, when duty (time duration of light emission) is 50% and working hours are 1,000 h, total operating time is calculated to be 500 hours.
The left-hand figure shows aging variation data of LED optical output.
The right-hand figure shows the operating time when LED optical output drops below a certain criterion.
For example, point A in the left-hand figure and point B in the right-hand figure show aging variation under the same conditions. (IF=50 mA, Ta=40℃, 8000 h).