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Hello, I am using an intrinsically safe device type 1N5335B Zener diodes. What is the maximum power at 85 degrees Celsius. The diode is mounted to the PCB at a distance of 10mm. Thank you for your response.

The Lead to ambient thermal resistance is something you must determine. It is easy enough to do with a thermal couple and the measuring the power of a device.

Some reference values: (on a 80x80x1.5mm FR4 PCB with a single layer PCB)

Psi L-A (25 mm^2, 1oz PCB) ~ 120 C/W
Psi L-A (600 mm^2, 1oz PCB) ~ 50 C/W

It is a function of your board design and the boundary conditions that the part is subject to.
Answered by:
ON Semiconductor
2015-04-29 12:13:28.76