MHST05065 datasheet(6/8 Pages) GE

6 / 8 page

Tyco Electronics Corp.

Technical Note

July 1996

250 W—300 W Board-Mounted Power Modules

Thermal Management for FC- and FW-Series

Module Derating (continued)

Natural Convection With Heat Sinks

Figures 8 and 9 show the power derating for a module

in natural convection with the heat sinks shown in Fig-

ures 6 and 7. Natural convection is the heat transfer

produced when air in contact with a hot surface is

heated, causing it to rise. An open environment is

required with no external forces moving the air. Figures

8 and 9 apply when the module is the only source of

heat present in the system, generating airﬂow of

approximately 10 ft./min. to 20 ft./min. Again, a typical

system with other heat dissipating components will

usually generate higher airﬂows in natural convection.

8-1318

Figure 8. Heat Sink Power Derating Curves

Natural Convection, Longitudinal Ori-

entation

8-1319

Figure 9. Heat Sink Power Derating Curves

Natural Convection, Transverse Ori-

entation

Figures 8 and 9 can be used to predict which heat sink

a module will require in a natural convection environ-

ment, as shown in the following example.

Example 3: Sizing a Heat Sink

What heat sink would be appropriate for a transverse

mounted FW300A1 in a natural convection environ-

ment at 54 V input and 2/3 load with a maximum ambi-

ent temperature of 35 °C?

Solution:

Given: VI = 54 V, Io = 2/3(60) = 40 A, TA = 35 °C

Determine PD (Figure 2): PD = 35 W

Determine Heat Sink (Figure 9):

1 1/2 in. heat sink allows up to TA = 35 °C

203040

100

LOCAL AMBIENT TEMPERATURE, TA (

°C)

1 1/2 in.

1 in.

1/2 in.

1/4 in.

NONE

203040

100

LOCAL AMBIENT TEMPERATURE, TA (

°C)

1 1/2 in.

1 in.

1/2 in.

1/4 in.

NONE

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