14
Lucent Technologies Inc.
Data Sheet
May 2000
dc-dc Converters; 36 to 75 Vdc Input, 3.3 Vdc Output; 33 W to 50 W
QW050F1 and QW075F1 Power Modules:
Thermal Considerations
(continued)
Heat Transfer with Heat Sinks
(continued)
8-2380 (C)
Figure 28. Heat Sink Power Derating Curves;
Natural Convection; Transverse
Orientation
8-2381 (C)
Figure 29. Heat Sink Power Derating Curves;
Natural Convection; Longitudinal
Orientation
8-2382 (C)
Figure 30. Heat Sink Power Derating Curves;
1.0 m/s (200 lfm); Transverse Orientation
8-2383 (C)
Figure 31. Heat Sink Power Derating Curves;
1.0 m/s (200 lfm); Longitudinal
Orientation
These measured resistances are from heat transfer
from the sides and bottom of the module as well as the
top side with the attached heat sink; therefore, the
case-to-ambient thermal resistances shown are gener-
ally lower than the resistance of the heat sink by itself.
The module used to collect the data in Figures 26 and
27 had a thermal-conductive dry pad between the case
and the heat sink to minimize contact resistance. The
use of Figures 26 and 27 are shown in the following
example.
10
20
30
40
50
60
LOCAL AMBIENT TEMPERATURE, T
A
(
°
C)
100
0
P
D
70
80
90
0
18
14
12
16
20
10
8
6
4
2
1 IN. HEAT SINK
10
20
30
40
50
60
LOCAL AMBIENT TEMPERATURE, T
A
(
°
C)
100
0
P
D
70
80
90
0
18
14
12
16
20
10
8
6
4
2
1 IN. HEAT SINK
10
20
30
40
50
60
LOCAL AMBIENT TEMPERATURE, T
A
(
°
C)
100
0
P
D
70
80
90
0
18
14
12
16
20
10
8
6
4
2
1/1NO HEAT SINK
10
20
30
40
50
60
LOCAL AMBIENT TEMPERATURE, T
A
(
°
C)
100
0
P
D
70
80
90
0
18
14
12
16
20
10
8
6
4
2
1/1NO HEAT SINK