
12
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 Without Heat Sinks
Increasing airflow over the module enhances the heat
transfer via convection. Figure 25 shows the maximum
power that can be dissipated by the module without
exceeding the maximum case temperature versus local
ambient temperature (T
A
) for natural convection
through 4 m/s (800 ft./min.).
Note that the natural convection condition was mea-
sured at 0.05 m/s to 0.1 m/s (10 ft./min. to 20 ft./min.);
however, systems in which these power modules may
be used typically generate natural convection airflow
rates of 0.3 m/s (60 ft./min.) due to other heat dissipat-
ing components in the system. The use of Figure 25 is
shown in the following example.
Example
What is the minimum airflow necessary for a QW050F1
operating at V
I
= 54 V, an output current of 10 A, and a
maximum ambient temperature of 40 °C
Solution
Given: V
I
= 54 V
= 10 A
A
= 40 °C
I
T
O
Determine P
D
(Use Figure 23.):
P
D
= 8.8 W
Determine airflow (v) (Use Figure 25.):
v = 1.1 m/s (220 ft./min.)
Note:
Pending improvement will lower the power dissi-
pation and reduce the airflow needed.
8-2967 (F)
Note: Pending improvement will lower the power dissipation.
Figure 23. QW050F1 Power Dissipation vs.
Output Current at Room Temperature
8-2968 (F)
Note: Pending improvement will lower the power dissipation.
Figure 24. QW075F1 Power Dissipation vs.
Output Current at Room Temperature
10
1
OUTPUT CURRENT, I
O
(A)
P
D
9
8
7
3
2
2
3
4
5
6
8
10
4
5
6
9
7
V
I
= 36 V
V
I
= 48 V
V
I
= 75 V
SEE NOTE
14
1
OUTPUT CURRENT, I
O
(A)
P
D
12
10
8
2
2
3
4
5
6
8
15
4
6
9
7
V
I
= 36 V
V
I
= 54 V
V
I
= 75 V
10 11 12 13 14
SEE NOTE