KEPCO KFD 6-25-28W - Manual (Page 13)

KFD 6-25-28/060801
9
using a one half inch fin heat sink oriented along the length. Consider the following:
For an air flow of 150 ft./min. using the same D.C. to D.C. Converter as in the last example and with a 0.5
inch heat sink with fins oriented along the length, refer to the thermal resistance plot. From Figure 14 the
thermal resistance is 1.3°C/W.
After the delta change in case temperature is calculated, the actual case temperature is determined by the
following:
18.7 DETAILED THERMAL MODEL
The thermal resistance previously includes heat transfer by conduction, convection, and radiation, from the
entire module to the surrounding environment. Typically the KFD power module is soldered to a vertically
oriented printed wiring board. Most of the heat transfer is by convection and radiation from the top mount-
ing surface of the module. Significant amounts of heat are also removed by convection from the sides of
the module, by conduction by the printed wiring board, and by convection off of the opposite side of the
printed wiring board
18.8 RADIATION HEAT TRANSFER
Radiation is not dependent upon the air flow over the power module, but on the temperature difference
between the module and the surrounding environment. For a particular KFD power module,
θ
R
due to
radiation can be determined experimentally. For the KFD high power modules operating at Tc=95°C and
Ta=25°C,
θ
R
(Radiation Resistance) =15°C/W
18.9 HORIZONTAL ORIENTATION
In some applications the power module is operated in natural convection and oriented horizontally. In that
situation
θ
TOTAL
=4.8°C/W for the overall module thermal resistance (including the base plate resistance).
19.0 FUSING CONSIDERATIONS
The encapsulated KFD Power Module can be used in a stand alone operation, or as an integrated part of
a complex power architecture. To achieve maximum safety and system protection always use an input line
fuse. To aid in the proper fuse selection for a given application, information on inrush energy and maximum
current is provided in the KFD specifications. It is also recommended to refer to the fuse manufacturer's
∆ TC PD θ ) ( =
∆ TC 35.2 1.3 ( ) 45.8 ° C = =
TC TA ∆ TC + ( ) 50
°
C 45.8 C + ( ) 98.8
°
C = = =
CAUTION
THE KFD MODULE IS NOT INTERNALLY FUSED; AN INPUT
LINE FUSE MUST ALWAYS BE USED