JBW050A Power Modules: dc-dc Converter;
36 to 75 Vdc Input, 5 Vdc Output; 50 W
Data Sheet
March 27, 2008
Thermal Considerations (continued)
12
10
8
Heat Transfer Without Heat Sinks
Increasing airflow over the module enhances the heat
transfer via convection. Figure 19 shows the maximum
power that can be dissipated by the module without
exceeding the maximum case temperature versus local
ambient temperature (TA) for natural convection
through 3 m/s (600 ft./min.).
6
MAX CASE TEMP
3.0 m/s (600 ft./min.)
2.0 m/s (400 ft./min.)
1.0 m/s (200 ft./min.)
0.5 m/s (100 ft./min.)
4
2
0
0.25 m/s (50 ft./min.)
NATURAL CONVECTION
0
20
40
60
80
100
120
LOCAL AMBIENT TEMPERATURE, TA (˚C)
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 can typically generate natural convection air-
flow rates of 0.3 m/s (60 ft./min.) due to other heat dis-
sipating components in the system. The use of
19 is shown in the following example.
1-0705
Figure 19. Forced Convection Power Derating with
No Heat Sink; Either Orientation
Heat Transfer with Heat Sinks
The power modules have through-threaded, M3 x 0.5
mounting holes, which enable heat sinks or cold plates
to attach to the module. The mounting torque must not
exceed 0.56 N-m (5 in.-lb.). For a screw attachment
from the pin side, the recommended hole size on the
customer’s PWB around the mounting holes is
0.130 ± 0.005 inches. If a larger hole is used, the
mounting torque from the pin side must not exceed
0.25 N-m (2.2 in.-lb.).
Example
What is the minimum airflow necessary for a JBW050A
operating at VI = 54 V, an output current of 10 A, and a
maximum ambient temperature of 70 °C?
Solution
Given: VI = 54 V
IO = 10 A
TA = 70 °C
Thermal derating with heat sinks is expressed by using
the overall thermal resistance of the module. Total
module thermal resistance (θca) is defined as the max-
imum case temperature rise (ΔTC, max) divided by the
module power dissipation (PD):
Determine PD (Use Figure 18):
PD = 9.5 W
Determine airflow (v) (Use Figure 19):
v = 1.0 m/s (200 ft./min.)
(TC – TA)
ΔTC, max
θca = --------------------
=
------------------------
PD
PD
The location to measure case temperature (TC) is
shown in Figure 17. Case-to-ambient thermal resis-
tance vs. airflow is shown, for various heat sink config-
urations and heights, in Figure 20. These curves were
obtained by experimental testing of heat sinks, which
are offered in the product catalog.
12
10
8
VI = 75 V
VI = 48 V
VI = 36 V
6
4
2
0
0
2
4
6
8
10
OUTPUT CURRENT, IO (A)
1-0697
Figure 18. Power Dissipation vs. Output Current
Lineage Power
LINEAGEPOWER [ LINEAGE POWER CORPORATION ]
