參數(shù)資料
型號(hào)： AN-18
英文描述： TOPSwitch Flyback Transformer Construction Guide
中文描述： 回掃變壓器的TOPSwitch施工指南
文件頁(yè)數(shù)： 11/32頁(yè)
文件大?。?/td> 275K
代理商： AN-18
A
7/96
AN-18
11
26 AWG or smaller wire to construct a secondary winding that
satisfies both the CM
requirement and the 100KHz maximum
wire size requirement. The total bare area of the paralleled
secondary conductors should be close to the CM
value calculated
by the spreadsheet in cell (C66). If the total bare area is greater
than or equal to the calculated value, the wire size for the
paralleled secondary winding can be used without further
checking. If the total bare area is less than the calculated value
from cell (C66), the current capacity should be checked to make
sure that it remains within the design limits. The current
capacity of the paralleled wires can be calculated from the
formula:
CMA
N
CM
I
S
SRMS
=
×
CMA
is the current capacity of the parallel secondary winding
in circular mils per ampere, N is the number of strands in the
secondary winding, CM
is the bare area of a single secondary
conductor in circular mils (from the wire table in Appendix A),
and I
is the secondary RMS current from cell (D62) of the
spreadsheet.
Bias Winding Design
The wire size for the bias winding will be determined mainly by
space-filling considerations rather than current capacity, as
described in the previous sections on transformer construction.
The wire size of the bias winding should be selected to form as
complete a layer as possible. Usually, it will be necessary to use
a parallel bifilar winding in order to fill the largest possible
space with a manageable wire size. In the Appendix A wire
table, turns per centimeter (TC) values are given for AWG wire
sizes. This data can be used to select a bias winding wire size for
a bifilar winding for a given number of turns and available
bobbin width. The required TC value can be calculated from the
equation:
TC
N
BW
M
B
=
×
×
×
2
10
2
)
TC
is the turns per centimeter capability of the bias winding. N
B
is the number of bias turns from cell (D46) of the spreadsheet,
BW is the bobbin physical winding width in mm from cell (B27)
of the spreadsheet, and M is the margin width in mm from cell
(B28). Once the required TC
is calculated, a wire size is
selected from the Appendix A wire table with a TC greater than
or equal to the calculated value. The largest recommended wire
size is 24 AWG, for ease of winding and termination. If the wire
size used does not form one complete layer, the winding turns
should be wound evenly across the width of the bobbin winding
area.
Choosing a Transformer Construction Type
The transformer construction types shown in Figures 7 and 10
are optimized for margin wound and triple insulated wire
transformer designs for both secondary and primary regulated
power supply designs. These construction types are suitable for
the majority of
TOPSwitch
flyback supply applications. These
figures should be used as examples for specifying the order of
the transformer windings and the placement of the margins and
insulating sleeving (if used), and insulating tape. The
construction type is chosen on the basis of the supply regulation
scheme (primary or secondary) and insulation type (margin
wound or triple insulated wire). Applications requiring the
lowest transformer cost but not the smallest possible transformer
size can use a margin wound transformer. Applications requiring
the smallest possible transformer size should use a triple insulated
wire design.
The construction types shown in Figure 10 are low-leakage split
primary designs, and should be used if the output power of the
supply is greater than 40W. These designs can also be used to
increase efficiency for a lower power supply, but will be higher
cost than a design with a one piece primary winding.
Choosing Insulation Tape Width
For a margin wound transformer construction, three different
insulation tape widths are required. A tape width equal to the
width of the bobbin from flange to flange (BW) is required for
reinforced insulation. This information can be read directly
from cell (B27) of the spreadsheet. A tape width equal to the
width of the bobbin minus the width of the margins is needed for
basic insulation between winding layers and adjacent primary
or secondary windings. This width can be calculated with the
equation:
W
BW
M
TB
=
×
(
)
2
W
is the width of the basic insulation tape, BW is the width of
the bobbin from cell (B27) of the spreadsheet, and M is the
margin width from cell (B28). The third tape width required is
for the margin layers on each side of the bobbin. The width of
this tape is picked to satisfy applicable safety regulations and
entered in cell (B28). Triple insulated wire transformers require
one size of tape for basic insulation, with a width equal to BW.
Insulating Sleeving
In margin wound transformer designs, insulating sleeving is
required on all winding start and finish leads, so that the primary
to secondary isolation provided by the margins is preserved.
The sleeving should have a wall thickness of at least 0.4 mm.
Sleeving for this purpose can be obtained in sizes equivalent to
AWG wire sizes. Usually one size of sleeving, equal to the
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