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參數(shù)資料
| 型號(hào)： | 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(yè)數(shù)： | 7/12頁(yè) |
| 文件大?。?/td> | 133K |
| 代理商： | AN-17 |
C
6/96
AN-17
7
mode choke, and
TOPSwitch
are not associated directly with
energy stored in the flyback transformer core. The remaining
power losses, occurring in the output rectifier and clamp Zener
diode when energy is released from the flyback transformer, are
now defined as secondary loss P
. Loss Allocation Factor Z,
defined below as the ratio of secondary loss P
to total loss P
L
,
is a scaling factor which distributes the losses between primary
and secondary. Loss allocation factor Z is typically between 0.4
and 0.6 which means that secondary loss P
LS
is usually 40% to
60% of total power supply loss P
L
.
P
P
L
O
=
×
η
(
)
1
η
Z
P
P
LS
L
=
Bias voltage V
is determined by the feedback control circuit
and is usually between 10 volts and 30 volts (see AN-16).
For bridge rectifier conduction time t
, 3 milliSeconds is typical
(measure on a similar power supply or set equal to zero for a
conservative first design).
For input filter capacitor C
, start with a standard value in
microFarads between two and three times the output power in
Watts (appropriate for universal or 115 VAC input). For
example: 30
μ
F to 45
μ
F is a suitable capacitance range for a
15 Watt supply. 33
μ
F is the lowest standard value within the
range.
TOPSwitch Variables:
Reflected output voltage V
appears across the transformer
primary when
TOPSwitch
is off and current is flowing through
the secondary and output rectifier diode. Transformers optimized
for
TOPSwitch
applications should be designed with a maximum
reflected voltage V
of 60V or less for the TOP1XX series and
135V or less for the TOP2XX series. For more information,
refer to AN-16.
V
is the on-state
TOPSwitch
voltage from the data sheet
(typically 10 volts) at the specified value for peak
TOPSwitch
drain current I
P
.
Output rectifier forward voltage drop V
depends on output voltage.
For lower output voltages (typically 8 Volts and below) a Schottky
diode is commonly used and V
is typically 0.4 Volts. In some cases,
a Schottky diode can be used for output voltages as high as 12V
depending on input voltage range and transformer turns ratio. For
higher output voltage, an ultrafast recovery PN junction diode is
Figure 7. Bridge AC Current, AC Voltage, and DC Voltage
Waveforms.
normally used and V
D
is typically 0.7 Volts.
Bias winding diode forward voltage drop (V
DB
) is also typically
0.7 Volts
Ripple current to peak current ratio K
determines how far into
the continuous mode a flyback transformer will operate.
Continuous mode transformers optimized for
TOPSwitch
applications operating from 100/115 VAC or universal input
voltage should have a minimum K
of 0.4. Applications
operating from 230 VAC input voltage should have a minimum
K
of 0.6. Discontinuous mode transformers optimized for
TOPSwitch
applications always have a K
RP
equal to 1.0.
K
I
I
RP
R
P
=
Transformer Core/Construction Variables:
The following effective parameters are specified by the core
and bobbin manufacturer in data sheets: cross sectional area A
e
(cm
2
), path length L
(cm), ungapped inductance A
(specified
in either mH/(1000 turns)
2
or nH/T
2
), and physical bobbin
winding width B
W
(mm).
Margin width M, determined by insulation methods and
regulatory requirements discussed above, is usually between
2.5 to 3.0 mm for margin wound or set to zero for insulated wire
wound transformers.
For number of layers L, one or two layers of primary winding
are normally used. Higher number of layers increase cost,
increase capacitance, reduce coupling, and increase leakage
inductance.
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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