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(yè)數(shù)： 20/32頁(yè)
文件大?。?/td> 247K
代理商： AN-16
AN-16
A
6/96
20
or universal inputs is a good assumption. As an example, for a
115VAC input and an output voltage V
of 15V plus the
rectifier forward drop V
of 0.7V, a 16 turn secondary would
be used as the initial value. The primary number of turns N
is
related to the secondary number of turns N
S
by the ratio
between V
OR
and V
O
+ V
D
N
N
V
V
V
P
S
OR
+
O
D
=
×
where V
is the reflected output voltage, V
is the output
voltage and V
D
is the output rectifier forward voltage drop.
Similarly, the number of bias winding turns N
B
can be derived
from
N
N
V
V
V
V
B
S
B
DB
O
D
=
×
+
+
where V
is the bias voltage and V
DB
is the bias rectifier forward
voltage drop.
From the core/bobbin size, it is possible to determine the
outside diameter of the primary wire OD in mm that is required
to accommodate the primary turns in one or two full layers
allowing for margins as appropriate.
OD
BW
N
E
P
=
BW
is the effective bobbin width, which takes into account
physical bobbin width BW, margins M (all in mm), and the
number of winding layers L:
BW
L
BW
M
E
=
×
×
[
]
(
)
2
The closest standard magnet wire gauge that is less than or equal
to this diameter can be selected. Determine the bare conductor
diameter DIA of this wire gauge using information from a wire
table. The next step is to find out if this conductor size is
sufficient for the maximum I
. The current capacity for
magnet wire is specified in terms of “Circular mils per Amp” or
CMA, which is the inverse of current density:
CMA
DIA
I
RMS
=
×
×
×
1 27
.
4
1000
25 4
2
2
.
π
If the CMA is less than 200, a larger gauge wire is needed to
handle the current. This could be accommodated by adding a
second layer if there is only one existing layer and/or by using
a larger core/bobbin and/or a smaller N
. On the other hand, a
CMA greater than 500 would indicate that a smaller core/
bobbin and/or a larger N
P
could be used.
Note that in the AN-17 spreadsheet, DIA is actually derived
from OD using an empirical equation. A practical wire size,
AWG (American Wire Gauge), is determined according to DIA
(see AN-18 Appendix A, Table 2 for wire size information).
CMA is then calculated from AWG.
Another critical parameter that must be checked is the maximum
flux density in the core (B
M
).
B
I
×
L
N
A
M
P
P
P
e
=
×
×
100
A
e
is the effective cross sectional area of the core.
If B
is greater than 3000 Gauss, either the core cross sectional
area (core size) or N
must be increased to bring it within the
2000 to 3000 range. On the other hand, if B
is less than
2000 Gauss, a smaller core or fewer turns on the primary can be
used.
In addition to B
, the core gap length L
required to generate
inductance L
P
with number of primary turns N
P
must also be
checked:
L
A
N
L
A
g
e
P
×
P
L
=
×
×
×
40
1000
1
2
π
The core cross sectional area A
and ungapped effective
inductance A
can be found from the data sheets for the core. L
g
is usually incorporated as an air gap ground into the center leg
of the core and needs to be at least 51
μ
m or (2 mils) for
manufacturability. If L
is less than 51
μ
m, once again the core
size or N
P
must be increased.
One other parameter always required by transformer
manufacturer is the gapped core effective inductance, A
LG
,
which can be determined only after N
P
is fixed:
A
L
N
LG
P
2
P
=
×
1000
As can be seen, the transformer design is a highly iterative
process in itself. When N
is changed, N
and N
will change
according to ratios already established. Similarly, any change
in core size requires a recalculation of CMA, B
M
and L
g
to make
sure that they are within the specified limits.
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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