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407244748

Power Modules: dc-dc Converters; 36 to 75 Vdc Input, 5 Vdc Output; 50 W to 150 W

Tyco Electronics 

Data Sheet

July 1999

JW050A, JW075A, JW100A, JW150A Power Modules:

dc-dc Converters; 36 to 75 Vdc Input, 5 Vdc Output; 50 W to 150 W

Thermal Considerations (continued)

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.).

Thermal derating with heat sinks is expressed by using

the overall thermal resistance of the module. Total mod-

ule thermal resistance (θca) is defined as the maximum

case temperature rise (∆TC, max) divided by the module

power dissipation (PD):

θca =

∆TC, max

-------P-----D--------

=

(TC – TA)

---------P-----D----------

The location to measure case temperature (TC) is

shown in Figure 26. Case-to-ambient thermal resis-

tance vs. airflow is shown, for various heat sink config-

urations and heights, in Figure 32. These curves were

obtained by experimental testing of heat sinks, which

are offered in the product catalog.

8

7

1 1/2 IN. HEAT SINK

1 IN. HEAT SINK

6

1/2 IN. HEAT SINK

1/4 IN. HEAT SINK

5

NO HEAT SINK

4

3

2

1

0

0

0.5

1.0

1.5

2.0

2.5 3.0

(100) (200) (300) (400) (500) (600)

AIR VELOCITY, m/s (ft./min.)

8-1153 (C)

Figure 32. Case-to-Ambient Thermal Resistance

Curves; Either 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 Figure 32 had a

thermal-conductive dry pad between the case and the

heat sink to minimize contact resistance. The use of

Figure 32 is shown in the following example.

Example

If an 85 °C case temperature is desired, what is the

minimum airflow necessary? Assume the JW100A

module is operating at VI = 54 V and an output current

of 20 A, maximum ambient air temperature of 40 °C,

and the heat sink is 1/2 inch.

Solution

Given: VI = 54 V

IO = 20 A

TA = 40 °C

TC = 85 °C

Heat sink = 1/2 in.

Determine PD by using Figure 30:

PD = 17 W

Then solve the following equation:

θca =

(TC – TA)

---------P-----D----------

θca =

(85 – 40)

---------1----7----------

θca = 2.6 °C/W

Use Figure 32 to determine air velocity for the 1/2 inch

heat sink.

The minimum airflow necessary for the JW100A mod-

ule is 1.3 m/s (260 ft./min.).

Tyco Electronics Corp

15

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