
Tyco Electronics Corp.
11
Data Sheet
October 1997
18 Vdc to 36 Vdc Input, 12 Vdc Output; 50 W to 100 W
JC050B, JC075B, JC100B Power Modules: dc-dc Converters;
Thermal Considerations
(continued)
Introduction
(continued)
8-716 (C).f
Note: Top view, pin locations are for reference.
Measurements shown in millimeters and (inches).
Figure 20. Case Temperature Measurement
Location
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.
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.
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 ModulesTechnical
Note (TN97-008EPS).
Heat Transfer Without Heat Sinks
Increasing airflow over the module enhances the heat
transfer via convection. Figure 21 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 Figur e21 is
shown in the following example.
Example
What is the minimum airflow necessary for a JC100B
operating at nominal line, an output current of 8.5 A,
and a maximum ambient temperature of 40 °C
Solution
Given: V
I
= 28 V
I
O
= 8.5 A
T
A
= 40 °C
Determine P
D
(Use Figure 24.):
P
D
= 20 W
Determine airflow (v) (Use Figure 21.):
v = 2.5 m/s (500 ft./min.)
8-1150 (C).a
Figure 21. Forced Convection Power Derating with
No Heat Sink; Either Orientation
8-1249
Figure 22. JC050B Power Dissipation vs.
Output Current
38.0 (1.50)
MEASURE CASE
TEMPERATURE HERE
V
I
(–)
ON/OFF
CASE
+ SEN
TRIM
– SEN
V
I
(+)
V
O
(–)
V
O
(+)
7.6 (0.3)
0
10
20
30
40
100
0
35
LOCAL AMBIENT TEMPERATURE, T
A
(C)
P
D
25
20
10
90
80
70
60
50
4.0 m/s(800 ft./min.)
3.5 m/s(700 ft./min.)
0.1 m/s (NAT. CONV.)
(20 ft./min.)
0.5 m/s(100 ft./min.)
1.0 m/s(200 ft./min.)
1.5 m/s(300 ft./min.)
2.0 m/s 400 ft./min.)
2.5 m/s 500 ft./min.)
3.0 m/s(600 ft./min.)
5
15
30
0.0
0.6
0
2
8
10
12
OUTPUT CURRENT, I
O
(A)
P
D
1.2
1.8
V
I
= 18
V
I
= 27
V
I
= 36
4
6
2.4
3.0
3.6
4.2