MHST05065 datasheet(7/8 Pages) GE

7 / 8 page

Tyco Electronics Corp.

Technical Note

July 1996

250 W—300 W Board-Mounted Power Modules

Thermal Management for FC- and FW-Series

Basic Thermal Model

Another approach for analyzing thermal performance is

to model the overall thermal resistance of the module.

This presentation method is especially useful when

considering heat sinks, since their performance is also

typically given as a resistance. Total module thermal

resistance (

θ) is deﬁned as the maximum case temper-

ature rise (

∆Tc,max) divided by the module power dis-

sipation (PD):

θ = ∆Tc,max / PD

This can be represented as an equivalent circuit as

shown in Figure 10. In this model PD,

∆Tc,max, and θ

are analogous to current ﬂow, voltage drop, and electri-

cal resistance, respectively, in Ohm's law. Also,

∆Tc,max is deﬁned as the difference between the inlet

ambient temperature (TA) and the module case tem-

perature (Tc) as deﬁned in Figures 3 and 1 respec-

tively.

∆Tc,max = Tc – TA

8-695

Figure 10. Basic Thermal Resistance Module

For FC- and FW-Series 250 W to 300 W BMPMs, the

module's thermal resistance values versus air velocity

have been determined experimentally and are plotted

in Figures 11 and 12 for a unit without a heat sink and

for the various heat sink conﬁgurations (see Figures 6

and 7). Note that the highest values on the curves rep-

resent natural convection. In a system with free-ﬂowing

air and other heat sources, there may be additional air-

ﬂow.

It is important to point out that the thermal resistances

shown in Figures 11 and 12 are for 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 will generally be

lower than the resistance of the heat sink by itself. The

data in Figures 11 and 12 were taken with a thermally

conductive dry pad between the case and the heat sink

to minimize contact resistance (typically 0.1 °C/W to

0.3 °C/W).

8-1320

Figure 11. Case-to-Ambient Thermal Resistance

Curves, Longitudinal Orientation

8-1321

Figure 12. Case-to-Ambient Thermal Resistance

Curves; Transverse Orientation

BMPM

= BMPM

THERMAL

RESISTANCE

100

200

300

400

500

600

0.0

0.5

3.0

3.5

4.0

4.5

AIR VELOCITY, (ft./min.)

2.5

2.0

1.0

1 1/2 in. HEAT SINK

1 in. HEAT SINK

1/2 in. HEAT SINK

1/4 in. HEAT SINK

NO HEAT SINK

1.5

100

200

300

400

500

600

0.0

0.5

3.0

3.5

4.0

4.5

AIR VELOCITY, (ft./min.)

2.5

2.0

1.0

1 1/2 in. HEAT SINK

1 in. HEAT SINK

1/2 in. HEAT SINK

1/4 in. HEAT SINK

NO HEAT SINK

1.5

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