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參數(shù)資料
| 型號： | AN-17 |
| 英文描述： | Flyback Transformer Design for TOPSwitch Power Supplies |
| 中文描述： | 回掃變壓器設(shè)計(jì)的TOPSwitch電源 |
| 文件頁數(shù)： | 5/12頁 |
| 文件大?。?/td> | 133K |
| 代理商： | AN-17 |
C
6/96
AN-17
5
BIAS
BIAS
(ALTERNATE
LOCATION)
PRIMARY
PI-1678-091395
SECONDARY
(INSULATED)
BIAS
M
M
PRIMARY
(Z WOUND)
ALTERNATE
PRIMARY
WINDING
SECONDARY
SAFETY
INSULATION
TAPE
(a) MARGIN WINDING
(b) C WINDING
PI-1521-091395
Figure 5. Triple Insulated Wire Wound Transformer.
Figure 4. Margin Wound Transformer.
Teflon sleeving with a minimum wall thickness of 0.41 mm
should be used to meet the safety agency requirements. Consider
the core as isolated dead metal (which means the core is
conductive but not part of any circuit and safely insulated from
the consumer). The sum of distance from primary winding (or
lead exits) to the core added to the distance from the core to the
secondary (or lead exits) must be equal to or greater than the
required creepage distance.
Both Z winding (Figure 4a) and C winding (Figure 4b) techniques
for multiple primary layers are shown. Note that the “dot” side
which connects to
TOPSwitch
is buried under the second layer
for self shielding to reduce EMI (common mode conducted
emission currents). Z winding decreases transformer
capacitance, decreases AC
TOPSwitch
losses, and improves
efficiency but is more difficult and costly to wind. The
C winding is easier and lower cost to wind but at the expense of
higher loss and lower efficiency.
Figure 5 shows a new technique using double or triple insulated
wire on the secondary to eliminate the need for margins (insulated
wire sources can be found at the end of this application note).
In double insulated wire, each layer is usually capable of
meeting the electric strength requirement of the safety agency.
In triple insulated wire, all three combinations of two layers
taken together must usually meet the electric strength
requirement. Special care is necessary to prevent insulation
damage during winding and soldering. This technique reduces
transformer size and eliminates the labor cost of adding margins
but has higher material cost and may increase winding costs.
The primary winding is wound over the full width of the bobbin
flange. The bias winding can be wound if desired over the
primary. One layer of tape is usually necessary between
primary or bias and secondary to prevent abrasion of the
insulated wire. The double or triple insulated wire is then
wound. Another layer of tape is added to secure insulated
winding.
Figure 5 also shows an alternate position for the bias winding
wound directly over the secondary to improve coupling to the
secondary winding and reduce leakage inductance (to improve
load regulation in bias winding feedback circuits). Note that
because the bias winding is a primary circuit, margin wound
transformers must have another layer of supplementary or
reinforced insulation between the secondary and alternate bias
winding.
Refer to AN-18 for more information regarding transformer
construction guidelines.
Flyback transformer design now begins by specifying the three
groups of independent variables shown in the spreadsheet
(Figure 6).
Application Variables:
Output power P
, output voltage V
, AC mains frequency f
L
,
TOPSwitch
switching frequency f
(100KHz), minimum
(V
), and maximum (V
ACMAX
) AC mains voltage come
directly from the application.
For efficiency (
η
), start with an estimate based on measurements
in similar power supplies (or use a value of 0.8 if data is
unavailable).
Efficiency can be used to calculate total power loss P
in the
power supply as shown below. Some power losses occurring in
series primary components such as the bridge rectifier, common
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| 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 |
| AN-23 | TinySwitch Flyback Design Methodology |
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