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:

vary and depends on the device mounting method.

tie points in common use and for printed circuit board

wiring.

The temperature of the lead can also be measured using

a thermocouple placed on the lead as close as possible to

the tie point. The thermal mass connected to the tie point

is normally large enough so that it will not significantly

respond to heat surges generated in the diode as a result

of pulsed operation once steady-state conditions are

temperature may be determined by:

lead temperature and may be found from Figure 2 for a

train of power pulses or from Figure 10 for dc power.

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

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

found from Figures 5 and 6.

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 2 should not be used to compute surge

capability. Surge limitations are given in Figure 3. 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 3 be

exceeded.

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Surface Mount Zener Diode