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)： 6/32頁(yè)
文件大?。?/td> 275K
代理商： AN-18
AN-18
A
7/96
6
For power supplies using a primary regulation scheme, the bias
winding should be the outermost winding on the transformer, as
shown in Figures 7B and 7D. This maximizes the coupling of
the primary bias winding with the secondary, and minimizes
coupling to the primary, improving the output regulation of the
supply in two ways. With better coupling to the secondary, the
bias winding responds more accurately to output voltage changes,
improving regulation. Also, the resultant poor coupling of the
bias winding to the primary helps to improve regulation by
reducing peak charging of the bias output due to the primary
leakage spike. If the bias winding is only loosely coupled to the
primary, the leakage spike can be filtered by using a small
resistor in series with the primary bias winding, improving the
load regulation of the supply. This is discussed in greater detail
in design note DN-8.
The primary bias winding should ideally form one complete
layer across the width of the bobbin. If the bias winding has
relatively few turns, this can be accomplished by increasing the
size of the wire used in the bias winding, or using multiple
parallel strands of wire. Increasing the fill factor of the bias
winding in this manner improves the shielding capability of the
winding in the case of the secondary regulated supply, and
improves the secondary to bias coupling in the case of the
primary regulated supply.
Secondary Windings
If a transformer has multiple secondary windings, the highest
power secondary should be the closest to the primary of the
transformer, in order to reduce leakage inductance. If a secondary
winding has relatively few turns, the turns should be spaced so
that they traverse the entire width of the winding area, for
improved coupling. Using multiple parallel strands of wire will
also help to increase the fill factor and coupling for secondaries
with few turns. For multiple output secondary regulated supplies,
auxiliary outputs with tight regulation requirements should be
wound directly on top of the regulated secondary to improve
coupling.
Multiple Output Winding Techniques
Instead of providing separate windings for each output in a
multiple output supply, a common technique for winding
multiple output secondaries with the same polarity sharing a
common return is to stack the secondaries, as shown in Figure
8. This arrangement will improve the load regulation of the
auxiliary outputs in a multiple output supply, and reduce the
total number of secondary turns. The windings for the lowest
voltage output provide the return and part of the winding turns
for the next higher voltage output. The turns of both the lowest
output and the next higher output provide turns for succeeding
outputs. For the two output stacked winding example shown in
Figure 8, the relation between output voltages V
1
and V
2
is
given below:
V
V
V
N
N
N
V
D
D
2
1
1
1
2
1
2
=
+
×
+
(
)
V
D1
and V
are the rectifier forward voltage drops for D
1
and
D
2
, respectively. N
1
and N
2
are the winding turns for the V
1
and
V
2
outputs.
The wire for each output must be sized to accommodate its
output current plus the sum of the output currents of all the
outputs stacked on top of it.
Insulation Requirements
Figure 7, in addition to showing optimum winding sequencing,
also shows placement of basic and reinforced insulation to meet
safety requirements and to improve consistency of the finished
transformer.
For the margin wound secondary regulated transformer
(Figure 7A), basic insulation (1 layer of electrical tape) is used
between primary layers and between the primary and the bias
winding. A layer of tape can also be useful between secondary
windings to provide a smooth winding surface from one winding
layer to the next. Reinforced insulation (three layers of tape) is
used between the primary bias winding and the secondary. A
three layer finish wrap completes the reinforced insulation for
the secondary. There are four margins in this transformer: two
for the primary and bias windings, and two for the secondary
windings. Insulating sleeving is used on the start and finish
leads of all windings. In Figures 7A and 7B sleeving is shown
only on the primary finish lead for purposes of clarity. In
practice, sleeving is used on the start and finish leads of all
windings. The sleeving should extend as shown from the inside
edge of the margin to the transformer pin.
For the margin wound primary regulated transformer
(Figure 7B), basic insulation is used between primary winding
layers. As in the secondary regulated transformer, a layer of
tape can be used between secondary windings to smooth the
winding surface. Reinforced insulation is required between the
primary and secondary windings, between the secondary and
primary bias windings, and as a finish wrap on top of the
primary bias winding. In this transformer, there are three pairs
of margins: one pair for the primary winding, one pair for the
secondary winding, and one pair for the bias winding. Start and
finish of each winding are sleeved as described above.
For the triple insulated secondary regulated transformer
(Figure 7C), basic insulation is used between primary layers,
between primary and bias, and between bias and secondary.
The insulation reduces the capacitance of the primary winding
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