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Renesas Electronics America - Knowledgebase

How can the maximum junction temperature be calculated?

Latest Updated:01/01/2009


The maximum junction temperature is not stated on the data sheets of photocouplers and optical MOSFETs. How can the maximum junction temperature be calculated?


The maximum junction temperature of photocouplers and optical MOS FETs differs when power is applied and when it is not applied.
When power is not applied, the maximum junction temperature is the upper limit of the maximum rating of the storage temperature, as in general semiconductor devices.
When power is applied, the maximum junction temperature is lower than when power is not applied due to a high-temperature degradation phenomenon unique to optoelectronic devices. The characteristics curve of the power dissipation vs. the ambient temperature below shows the value.
Extending the sloping line of the characteristics curve, the power dissipation would be 0 mW at about 125°C.
If internal dissipation occurs near the sloping line within the allowable range of the operating ambient temperature, the junction temperature is assumed to be around 125°C. 125°C is therefore the maximum junction temperature when power is applied.

See the explanation provided at the following link for details of the maximum junction temperature.
Suitable Products
Blue-Violet Laser
Optical Sensors
Optical Storage Devices
Fiberoptic Devices
Photocouplers / Optocouplers
Solid State Relays (OCMOS FETs)