JBW050F Power Modules: dc-dc Converter;
36 to 75 Vdc Input, 3.3 Vdc Output; 33 W
Data Sheet
September 20, 2004
Thermal Considerations
Introduction
Thermal Considerations (continued)
Heat Transfer Without Heat Sinks
The power modules operate in a variety of thermal
environments; however, sufficient cooling should be
provided to help ensure reliable operation of the unit.
Heat-dissipating components inside the unit are ther-
mally coupled to the case. Heat is removed by conduc-
tion, convection, and radiation to the surrounding
environment. Proper cooling can be verified by mea-
suring the case temperature. Peak temperature (TC)
occurs at the position indicated in Figure 17.
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.).
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
38.0 (1.50)
generate natural convection airflow rates of 0.3 m/s
(60 ft./min.) due to other heat dissipating components
in the system. The use of Figure 19 is shown in the
following example.
VI(+)
VO(+)
38.0
(1.50)
ON/OFF
+ SEN
TRIM
MEASURE CASE
TEMPERATURE
HERE
Example
What is the minimum airflow necessary for a JBW050F
operating at VI = 54 V, an output current of 10 A, and a
maximum ambient temperature of 70 °C?
CASE
VI(–)
– SEN
VO(–)
Solution
8-716.f
Given: VI = 54 V
IO = 10 A
Note: Top view, pin locations are for reference only.
Measurements shown in millimeters and (inches).
TA = 70 °C
Figure 17. Case Temperature Measurement
Location
Determine PD (Use Figure 18):
PD = 7.7 W
The temperature at this location should not exceed
100 °C. The output power of the module should not
exceed the rated power for the module as listed in the
Ordering Information table.
Determine airflow (v) (Use Figure 19):
v = 0.5 m/s (100 ft./min.)
Although the maximum case temperature of the power
modules is 100 °C, you can limit this temperature to a
lower value for extremely high reliability.
10
9
VI = 36 V
VI = 48 V
VI = 75 V
8
7
6
5
4
3
2
1
0
Note that although the maximum case temperature
allowed is lower than 100 °C under some conditions,
this modules derating is equivalent to or better than the
JW050F. At full load, the JW050F power module has a
higher case temperature rise than the JBW050F.
For additional information on these modules, refer to
the Thermal Management JC-, JFC-, JW-, and JFW-
Series 50 W to 150 W Board-Mounted Power Modules
Technical Note (TN97-008EPS).
0
1
2
3
4
5
6
7
8
9
10
OUTPUT CURRENT, IO (A)
1-0706
Figure 18. Power Dissipation vs. Output Current
Tyco Electronics Power Systems
LINEAGEPOWER [ LINEAGE POWER CORPORATION ]
