BZX79C30 datasheet(41/42 Pages) MOTOROLA

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1N5333B through 1N5388B

Motorola TVS/Zener Device Data

6-137

5 Watt Surmetic 40 Data Sheet

Devices listed in bold, italic are Motorola preferred devices.

VZ, ZENER VOLTAGE (VOLTS)

1000

100

0.1

100

0.1

100

120

140

160

180

200

220

VZ, ZENER VOLTAGE (VOLTS)

T=25

°C

Figure 9. Zener Voltage versus Zener Current

VZ = 11 thru 75 Volts

Figure 10. Zener Voltage versus Zener Current

VZ = 82 thru 200 Volts

APPLICATION NOTE

Since the actual voltage available from a given zener diode

is temperature dependent, it is necessary to determine junc-

tion temperature under any set of operating conditions in order

to calculate its value. The following procedure is recom-

mended:

Lead Temperature, TL, should be determined from:

TL = θLA PD + TA

θLA is the lead-to-ambient thermal resistance and PD is the

power dissipation.

Junction Temperature, TJ, may be found from:

TJ = TL + ∆TJL

∆TJL is the increase in junction temperature above the lead

temperature and may be found from Figure 4 for a train of

power pulses or from Figure 5 for dc power.

∆TJL = θJL PD

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 = θVZ ∆TJ

θVZ,thezenervoltagetemperaturecoefficient,isfoundfrom

Figures 2 and 3.

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.

Data of Figure 4 should not be used to compute surge capa-

bility. Surge limitations are given in Figure 6. They are lower

than would be expected by considering only junction tempera-

ture, as current crowding effects cause temperatures to be ex-

tremely high in small spots resulting in device degradation

should the limits of Figure 6 be exceeded.

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