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)： 2/32頁(yè)
文件大?。?/td> 275K
代理商： AN-18
AN-18
A
7/96
2
Wire Table
A wire table provides dimensional and electrical characteristics
for magnet wire, and is used to select appropriate wire sizes for
transformer design. There are three major wire sizing systems:
AWG, SWG and metric. All wire sizes used in this application
note are based on AWG sizing. A wire table is provided in
Appendix A with data on AWG wire sizes from 18 gauge
through 44 gauge. SWG and metric equivalents to AWG wire
sizes are also shown. A wire table is also available in
reference 5. Wire tables can be obtained from some of the
magnet wire manufacturers listed in Appendix A.
Transformer Construction Materials
The following paragraphs describe the basic materials needed
to construct switching power supply transformers.
Ferrite Cores
Appropriate ferrite materials for 100KHz flyback transformers
are TDK PC40, Philips 3C85, Siemens N67, Thomson B2,
Tokin 2500 or other similar materials. A wide variety of core
shapes are available. E cores are the best choice for transformer
cores for reasons of low cost, wide availability, and lower
leakage inductance. Other core shapes and styles such as the
ETD, EER and EI are also usable. A chart of suitable ferrite core
types for various power levels and transformer construction
types can be found in Appendix A.
Bobbins
Bobbins for off-line flyback transformers should be chosen
with regard to the safety creepage distances required by the
applicable safety regulations. Particular areas of consideration
are the total creepage distance from primary pins to secondary
pins through the core, and the creepage distance from primary
pins to the secondary winding area. With some bobbin styles,
extra insulation may be necessary to meet the creepage
requirements. Bobbins should preferably be made from
thermosetting materials such as phenolic resin in order to
withstand soldering temperatures without deformation.
Polybutylene or polyethylene terphthalate (PBT, PET) and
polyphenylene sulfide (PPS) are also acceptable materials,
though more sensitive to high temperatures than phenolic
resins. Nylon should be avoided if possible, as it melts easily
at the temperatures required to effectively terminate the
transformer windings to the pins on the bobbin. If Nylon
bobbins are used, they should be made with glass reinforced
resin with a temperature rating of 130C.
Insulating Materials
A common insulating material used in transformers is polyester
or Mylar, available in sheet or tape form. This material is also
manufactured as an adhesive tape that is particularly useful in
transformer construction. US manufacturers of this tape
include 3M, Tesa, and CHR. For creepage margins in
transformers, it is desirable to use a thick tape so that the
required build for a margin can be achieved using relatively few
layers. Several manufacturers make a polyester film/mat tape
that is useful for this application.
Magnet Wire
Some typical domestic manufacturers of magnet wire are
Belden, Phelps Dodge, and Rea. The preferred insulation for
magnet wire is a nylon/polyurethane coating. This coating
burns off in contact with molten solder, allowing the transformer
to be terminated by dip tinning in a solder pot. This type of
insulated magnet wire is available from almost all manufacturers
under various trade names: Solderon, Nyleze, Beldsol, etc. The
insulating coating should be “heavy” or “double” to better
withstand the stress of handling and the winding process.
Ordinary enameled wire or polyimide wire insulation should
not be used, as these types of insulation must be stripped
mechanically or with chemical stripping agents in order to
terminate the wire to the transformer pins.
Triple Insulated Wire
Triple insulated wire can be used to simplify and reduce the size
of transformers where safety isolation is required. The type of
triple insulated wire useful for transformer construction consists
of a solid wire core with three distinct and separable layers of
insulation. Three manufacturers of triple insulated wire are
listed in Appendix A.
Sleeving
Insulating tubing is used to insulate the start and finish leads of
windings in a margin wound transformer. The tubing should be
recognized by the applicable safety agencies, with a minimum
wall thickness of 0.4 mm to meet thickness requirements for
reinforced insulation. The tubing should also be heat resistant,
so that it does not melt when exposed to the temperatures
required to solder the transformer lead wires to the pins on the
bobbin. Materials commonly used for sleeving include Teflon
tubing or polyolefin heat shrink tubing.
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