Zener Diode 3.3V 500mW 5% DO35

Rating DC Power Dissipation and TL 75°C Lead Length = 3/8 Derate above = 75°C Operating and Storage Temperature Range

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: Lead Temperature, TL, should be determined from: TL = LAPD + TA. LA is the lead-to-ambient thermal resistance (°C/W) and PD is the power dissipation. The value for LA will vary and depends on the device mounting method. LA is generally to 40°C/W for the various clips and 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 achieved. Using the measured value of TL, the junction temperature may be determined by: TL + TJL. TJL is the increase in junction temperature above the lead temperature and may be found from Figure 2 for dc power: TJL = JLPD. For worst-case design, using expected limits of IZ, limits of PD and the extremes of TJ(TJ) may be estimated. Changes in voltage, VZ, can then be found from: V = VZTJ. VZ, the zener voltage temperature coefficient, is found from Figures 4 and 5. Under high power-pulse operation, the zener voltage will vary with time and may also be affected significantly by the zener resistance. For best regulation, keep current excursions as low as possible.