GENERAL DATA — 1-3 WATT DO-41 SURMETIC 30
θ
JL (t, D) TRANSIENT THERMAL RESISTANCE
JUNCTION-TO-LEAD (
°
C/W)
30
20
10
7
5
3
2
1
0.7
0.5
D =0.5
0.2
0.1
0.05
0.02
0.01
D=0
0.0005
0.001
0.002
0.005
NOTE: BELOW 0.1 SECOND, THERMAL
RESPONSE CURVE IS APPLICABLE
TO ANY LEAD LENGTH (L).
0.01
0.02
0.05
t, TIME (SECONDS)
0.1
0.2
PPK
t2
DUTY CYCLE, D =t1/t2
t1
SINGLE PULSE
∆T
JL =
θ
JL (t)PPK
REPETITIVE PULSES
∆T
JL =
θ
JL (t,D)PPK
0.5
1
2
5
10
0.3
0.0001 0.0002
Figure 2. Typical Thermal Response L, Lead Length = 3/8 Inch
1K
PPK , PEAK SURGE POWER (WATTS)
500
300
200
100
50
30
20
10
0.1
0.2 0.3 0.5
1
2 3
5
10
PW, PULSE WIDTH (ms)
20 30 50
100
RECTANGULAR
NONREPETITIVE
WAVEFORM
TJ = 25°C PRIOR
TO INITIAL PULSE
3
2
1
0.5
0.2
0.1
0.05
0.02
0.01
0.005
0.002
0.001
0.0005
0.0003
TA = 125°C
IR , REVERSE LEAKAGE (µ Adc) @ VR
AS SPECIFIED IN ELEC. CHAR. TABLE
TA = 125°C
1
2
5
10
20
50 100
NOMINAL VZ (VOLTS)
200
400
1000
Figure 3. Maximum Surge Power
Figure 4. Typical Reverse Leakage
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 =
θ
LA PD + TA
θ
LA is the lead-to-ambient thermal resistance (°C/W) and
PD is the power dissipation. The value for
θ
LA will vary and
depends on the device mounting method.
θ
LA is generally
30–40°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 mea-
sured value of TL, the junction temperature may be deter-
mined by:
TJ = TL +
∆T
JL
1–3 Watt DO-41 Surmetic 30 Data Sheet
6-44
∆T
JL is the increase in junction temperature above the lead
temperature and may be found from Figure 2 for a train of
power pulses (L = 3/8 inch) or from Figure 10 for dc power.
∆T
JL =
θ
JL 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
=
θ
VZ
∆T
J
θ
VZ, the zener voltage temperature coefficient, is found from
Figures 5 and 6.
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 2 should not be used to compute surge capa-
bility. Surge limitations are given in Figure 3. 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 3 be exceeded.
Motorola TVS/Zener Device Data
MOTOROLA [ MOTOROLA, INC ]
