APPLICATION NOTE:

Since the actual voltage available from a given zener

diode is temperature dependent, it is necessary to

determine

junction

temperature

under

any

set

of

operating conditions in order to calculate its value. The

following procedure is recommended:

/W)

lead temperature and may be found from Figure 3 for a

train of power pulses or from Figure 4 for dc power.

For worst-case design, using expected limits of Iz, limits

Changes in voltage, Vz, can then be found from:

from Figures 2.

Under high power-pulse operation, the zener voltage will

vary with time and may also be affected significantly be

the zener resistance. For best regulation, keep current

excursions as low as possible.

Data of Figure 3 should not be used to compute surge

capability. Surge limitations are given in Figure 5. They

are lower than would be expected by considering only

junction temperature, as current crowding effects cause

temperatures to be extremely high in small spots

resulting in device degradation should the limits of

Figure. 5 be exceeded.