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參數(shù)資料
| 型號(hào)： | AN-16 |
| 英文描述： | TOPSwitch Flyback Design Methodology |
| 中文描述： | TOPSwitch的反激式設(shè)計(jì)方法 |
| 文件頁數(shù)： | 19/32頁 |
| 文件大?。?/td> | 247K |
| 代理商： | AN-16 |
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A
6/96
AN-16
19
package,
(specified in the
TOPSwitch
datasheet), and from
heat sink to ambient,
(usually specified in the heat sink data
sheet). If a package without a heatsink tab is used, such as an
8 pin DIP, then a typical die to ambient thermal impedance,
,
for a board mounted part can be found in the data sheet for these
calculations. It is recommended that the die temperature be kept
below 100
°
C under all conditions.
Step 11. Check minimum I
of the selected
TOPSwitch against required I
. Increase K
RP
, if
possible, for least continuous operation.
Using continuous mode operation at low line decreases the peak
current required for a given output power, allowing the use of
a smaller
TOPSwitch
. However, if so desired, a trade-off
between
TOPSwitch
and core size can be accomplished by
increasing the K
value. Larger K
allows the use of a smaller
core at the price of a larger
TOPSwitch
, as larger K
implies
less continuous operation and lower inductance L
, but higher
peak current I
. This is very important when the best suited
(smallest possible)
TOPSwitch
that can be chosen for a design
still ends up with significant extra current capability. It is then
best to trade this extra current capability for a reduced core size
by using a higher K
RP
. In addition to affecting the size of the
transformer core, K
also influences supply efficiency. Larger
K
results in higher primary RMS current I
and higher
TOPSwitch
conduction loss while lower K
results in lower
I
and lower
TOPSwitch
loss. For applications with tight
physical size/weight limitation and/or efficiency requirements,
an intermediate K
value can offer the optimum solution
between cost and performance.
Although this design method is designed to use the highest
possible K
once
TOPSwitch
is first chosen, the flexibility is
certainly available for other design options. Experienced
engineers should make their own judgment on K
RP
value based
on the specific requirements of their application.
Step 12. Determine primary inductance L
P
Because the energy transferred from primary to secondary each
switching cycle is simply the difference between 1/2 x L
x I
P
and 1/2 x L
x (I
- I
)
2
. The primary inductance L
P
can be
expressed as a function of I
P
, K
RP
, f
S
, P
O
,
η
and Z:
2
L
P
I
K
K
f
Z
P
O
P
RP
RP
2
S
=
×
×
×
×
×
×
η
+
10
1
1
6
2
(
)
η
η
η
is the efficiency and Z is the loss allocation factor. If Z=1, all
losses are on the secondary side. If Z = 0, all losses are on the
primary side. Z is simply the ratio of secondary loss to total loss. If no
better reference information is available, Z should be set to 0.5.
Step 13. Chose core and bobbin as a function of P
O
based on AN-18, Appendix A, Table 2 and determine
A
e,
L
e,
A
L
and BW from core and bobbin catalog
AN-18 Appendix A provides a table of recommended core
types for various power ranges. Notice that there are two
transformer construction types shown in the table. For single
output designs, a triple insulated secondary simplifies
transformer construction and allows the use of the smallest size
core and bobbin for a given output power. Margin winding,
which is suitable for both single and multiple output secondaries,
will require wider bobbins and therefore, longer/taller cores. If
there is no specific form factor requirement, it is best to start
with the smallest EE type core for the power level. EE cores are
usually the least expensive type. The two digit number following
the core type indicates the core size in mm. For 100KHz
operation, the selection of core material is not very critical.
TDK PC40 material is a good first choice. Other ferrite
materials with similar characteristics are available from many
manufacturers. Lower frequency core materials such as Philips
3C85 and its equivalents will also work at 100 KHz, and could
be used if there is a cost advantage.
Once a core has been selected from the catalog, a suitable
bobbin can be easily identified.
Manufacturer specified core parameters A
L
A
and bobbin
parameter BW are usually found in the same catalog.
Step 14. Set number of primary layers L and number
of secondary turns N
S
(see Step 16 to 22)
Step 15. Calculate number of primary turns N
P
and
number of bias turns N
B
(see Step 16 to 22)
Step 16 to Step 22. Check B
, CMA and L
. Iterate if
necessary by changing L, N
S
, core/bobbin until within
specified range
In addition to the selection of core and bobbin, a total of nine
parameters must be specified in the construction of a transformer:
primary inductance Lp, core gap length L
,
number of turns for
primary N
, secondary N
and bias N
, wire outside diameter for
primary OD and secondary OD
S
, bare conductor diameter for
primary DIA and secondary DIA
. Because the bias winding
carries very little current (typically less than 10 mA), the wire
size of the bias winding is never a problem.
Except for L
, the above parameters are all interdependent. A
good starting point is to pick a number for the secondary turns.
Using 1 turn/volt for 100/115 VAC and 0.6 turn/volt for 230 VAC
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AN-17 | Flyback Transformer Design for TOPSwitch Power Supplies |
| AN-18 | TOPSwitch Flyback Transformer Construction Guide |
| AN-19 | TOPSwitch Flyback Power Supply Efficiency |
| AN-20 | Transient Suppression Techniques for TOPSwitch Power Supplies |
| AN-22 | OBSOLETE when inventory is depleted. 10% tolerance no l |
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