參數(shù)資料
型號(hào): AFL5005DW
英文描述: DC to DC Converter
中文描述: DC至DC轉(zhuǎn)換器
文件頁(yè)數(shù): 7/10頁(yè)
文件大?。?/td> 82K
代理商: AFL5005DW
www.irf.com
7
AFL50XXD Series
A conservative aid to estimating the total heat sink surface
area (A
HEAT SINK
) required to set the maximum case temp-
erature rise (
T) above ambient temperature is given by
the following expression:
A
HEAT SINK
T
P
80
30
.
0 85
.
143
.
where
T
P
P
Eff
OUT
=
=
=
Case temperature rise above ambient
Device dissipation in Watts
1
1
T = 85 - 25 = 60°C
and the required heat sink area is
If the worst case full load efficiency for this device is 83%
@ 100W; then the power dissipation at full load is given by
Because of the incorporation of many innovative techno-
logical concepts, the AFL series of converters is capable of
providing very high output power from a package of very
small volume. These magnitudes of power density can only
be obtained by combining high circuit efficiency with effec-
tive methods of heat removal from the die junctions. This
requirement has been effectively addressed inside the de-
vice; but when operating at maximum loads, a significant
amount of heat will be generated and this heat must be
conducted away from the case. To maintain the case tem-
perature at or below the specified maximum of 125°C, this
heat must be transferred by conduction to an appropriate
heat dissipater held in intimate contact with the converter
base-plate.
When operating in the shared mode, it is important that
symmetry of connection be maintained as an assurance of
optimum load sharing performance. Thus, converter out-
puts should be connected to the load with equal lengths of
wire of the same gauge and sense leads from each con-
verter should be connected to a common physical point,
preferably at the load along with the converter output and
return leads. All converters in a paralleled set must have
their share pins connected together. This arrangement is
diagrammatically illustrated in Figure III. showing the out-
puts and return pins connected at a star point which is
located close as possible to the load.
As a consequence of the topology utilized in the current
sharing circuit, the share pin may be used for other func-
tions. For applications requiring only a single converter, the
voltage appearing on the share pin may be used as a “cur-
rent monitor”. The share pin open circuit voltage is nominally
+1.00v at no load and increases linearly with increasing
output current to +2.20v at full load. Note that the current
we refer to here is the total device output current, that is,
the sum of the positive and negative output currents.
1Sil-Pad is a registered Trade Mark of Bergquist, Minneapolis, MN
Thermal Considerations
Since the effectiveness of this heat transfer is dependent
on the intimacy of the baseplate/heatsink interface, it is
strongly recommended that a high thermal conductivity heat
transferring medium is inserted between the baseplate and
heatsink. The material most frequently utilized at the fac-
tory during all testing and burn-in processes is sold under
the trade name of Sil-Pad
4001. This particular product is
an insulator but electrically conductive versions are also
available. Use of these materials assures maximum sur-
face contact with the heat dissipater thereby compensating
for any minor surface variations. While other available types
of heat conductive materials and thermal compounds pro-
As an example, it is desired to maintain the case tempera-
ture of an AFL5015D at
+85°C while operating in an open
area whose ambient temperature is held at a constant +25°C;
then
Thus, a total heat sink surface area (including fins, if any)
of 56 in2 in this example, would limit case rise to 60°C above
ambient. A flat aluminum plate, 0.25" thick and of approxi-
mate dimension 4" by 7" (28 in2 per side) would suffice for
this application in a still air environment. Note that to meet
the criteria in this example, both sides of the plate require
unrestricted exposure to the +25°C ambient air.
(
)
P
=
=
=
100
1
83
.
1
100
0205
.
205
. W
A
=
60
80 20.5
in
HEAT SINK
0.85
=
143
.
2
30
.
563
.
vide similar effectiveness, these alternatives are often less
convenient and can be somewhat messy to use.
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