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Tyco Electronics Corp.

Technical Note

July 1996

250 W—300 W Board-Mounted Power Modules

Thermal Management for FC- and FW-Series

The goal of thermal management is to transfer the heat

dissipated by the module to the surrounding environ-

ment. The amount of power dissipated by the module

tion below:

Also, module efficiency (

η) is defined as the ratio of

output power to input power as shown by the equation

below:

The input power term can be eliminated by the combi-

nation of these two equations to yield the equation

below:

η) / η

This equation can be used to calculate the module

power dissipation. However, efficiency is a nonlinear

current (Io). Typically, a plot of power dissipation versus

output current over three different line voltages is given

in each module-specific data sheet. This is because

each module has a different power dissipation curve. A

typical curve of this type is shown below in Figure 2 for

a FW300A1 Power Module (5 V output voltage).

8-1313

Figure 2. FW300A1 Power Dissipation vs. Output

Current

Module Derating

Experimental Setup

The derating curves in the following figures were

obtained from measurements obtained in an experi-

mental apparatus shown in Figure 3. Note that the

module and the printed-wiring board (PWB) onto which

it was mounted were vertically oriented. The passage

has a rectangular cross-section. The clearance

between the top of the module and the facing PWB was

kept constant at 0.5 in.

8-690a

Figure 3. Experimental Test Setup

V = 72 V

V = 54 V

V = 36 V

70

60

50

40

30

20

10

0

0

102030

40

50

60

FACING

PWB

AIR VELOCITY

AND AMBIENT

TEMPERATURE

MEASURED

HERE

AIRFLOW

PWB