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參數(shù)資料
| 型號： | 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 |
| 文件頁數(shù)： | 10/32頁 |
| 文件大?。?/td> | 275K |
| 代理商： | AN-18 |
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AN-18
A
7/96
10
Bias Winding Turns (N
) (D46)
Gapped Core Inductance Coefficient (A
LG
) (C47)
Primary Wire Gauge (AWG ) (D56)
Primary Winding Current Capacity (CMA) (D58)
Secondary Circular Mils (CMS) (C66)
Secondary RMS Current (I
) (D62)
Secondary Wire Gauge (AWG
S
) (D67)
Transformer Construction Steps
Once the transformer parameters have been determined from a
spreadsheet design, the following steps are required to determine
the remaining information needed for transformer construction:
Calculate and select wire sizes using spreadsheet
information and wire table
Pick transformer construction style
Determine insulating tape sizes
Determine insulating sleeving size
Choose method of core gapping
Wire Sizes
Wire sizes for the primary, secondary, and bias windings are
determined from the information provided by the power supply
design spreadsheet. Some extra steps may be necessary to
determine the wire size for a given winding. The wire size
selection process is described below.
Primary Wire Size
The power supply design spreadsheet calculates the insulated
wire diameter for the primary based on the number of primary
turns, the number of winding layers, and the available winding
space on the bobbin. The calculated maximum insulated wire
diameter is shown in cell (D53) of the spreadsheet. The
spreadsheet uses this value to choose an AWG wire size that
comes closest to fitting the bobbin. If the wire size falls between
two standard AWG wire gauges, the spreadsheet will
automatically round down the primary wire size to the next
smaller wire gauge. The resulting primary AWG wire size is
displayed in cell (D56) of the spreadsheet. The spreadsheet
calculates the current capacity of the primary wire (CMA) in
circular mils per ampere and displays the result in cell (D58).
The CMA value should be between 200 to 500 circular mils per
ampere for a practical design. If the CMA is not within these
limits, the design should be adjusted to bring the primary CMA
within limits.
Wire Size vs. Frequency
In some cases, the wire size determined by the spreadsheet will
be too large for use at 100KHz. The wire size that can be
effectively used in a power transformer depends on the operating
frequency. High frequency currents tend to flow close to the
surface of a conductor rather than its interior. This phenomenon
is called the skin effect. The penetration of AC current into a
conductor varies as the square root of the frequency, so for a
higher frequency, currents will flow closer to the surface of the
conductor and leave the interior relatively unutilized. The
result is a higher effective resistance for AC current versus DC
current. To minimize the AC copper losses in a transformer, no
conductor should be used that has a thickness greater than 2
times the skin depth at the operating frequency of the supply. A
graph of usable wire gauge as a function of frequency is shown
in Figure 13. At 100 KHz, the nominal operating frequency of
TOPSwitch
, 26 AWG is the largest wire size that allows full
utilization of the cross-section of the wire. High current windings
at 100 KHz should be constructed using several strands of 26
AWG or smaller wire rather one large diameter conductor, in
order to allow full utilization of the conductor. This is usually
more of a concern for selecting the wire size for a secondary
output winding than for a primary winding.
Secondary Wire Size
The minimum secondary bare wire cross-sectional area is
determined by the spreadsheet from the secondary RMS current,
and is sized for the same current capacity (CMA) as the primary
winding. The resulting minimum wire area (in circular mils) is
displayed in cell (C66) of the spreadsheet, and is used by the
spreadsheet to calculate a secondary wire size. If the secondary
wire size falls between two standard AWG sizes, the spreadsheet
will automatically round the wire size up to the next larger
AWG size. The resulting secondary AWG wire size is displayed
in cell (D67) of the spreadsheet. In many cases, the wire size
picked by the spreadsheet will be too large to satisfy the size
requirements for 100 KHz operation described above. In these
cases, it will be necessary to use several parallel strands of
Figure 13. Skin Depth vs. Frequency.
40
20
15
104
105
Frequency (Hz)
106
107
A
MAXIMUM AWG vs. FREQUENCY
25
30
P
35
Partial
Utilization
Full
Utilization
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| AN-23 | TinySwitch Flyback Design Methodology |
| AN-29 | TOPSwitch-GX Flyback Quick Selection Curves |
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