Zener Diode Power Dissipation and Denating

Zener Diode are specified to operate at a maximum power called the maximum dc power dissipation P_D (max). The power dissipation defined,

P_D=VzIz.

The maximum power dissipation of a zener diode is typically specified for temperature at or below a certain value (50^o C). The maximum power dissipation is reduced according to a derating factor.