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| 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)計的TOPSwitch電源 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大小： | 133K |
| 代理商： | AN-17 |
AN-17
C
6/96
8
Number of secondary turns N
is a key iteration variable. One
turn per Volt of output voltage is a good value to begin with for
N
S
(for example: start with 5 turns for a +5V output).
The four groups of dependent parameters can now be calculated.
DC Input Voltage Parameters:
Minimum DC input voltage V
depends on the AC input
voltage, bridge rectifier, and energy storage capacitor.
Figure 7 shows how C
charges to the peak of the AC input
voltage during a short conduction time t
. Because of full wave
rectification, C
has a ripple voltage at twice line frequency.
C
must supply the entire average primary current during the
discharge time between the peaks of the AC input voltage.
Minimum DC voltage V
can be found from the following
equation where P
is the power supply output power,
η
is an
estimate of efficiency, f
is line voltage frequency, V
is the
minimum AC mains voltage, C
is the value of the filter
capacitor, and t
is an estimate for conduction time. As an
example, for 60 Hz, 85 VAC input voltage, efficiency of 0.8,
15 Watt output power, 33 uF input filter capacitance, and
estimated conduction time of 3.2 mS, V
MIN
is 93 Volts DC.
V
V
P
f
t
C
MIN
ACMIN
O
L
C
IN
=
×
×
×
×
×
(
)
(
(
)
)
2
2
1
2
2
η
=
×
×
×
×
=
(
)
(
(
.
)
.
)
2
85
2 15
1
2
60
33
3 2
0 8
93
2
mS
F
V
μ
Maximum DC input voltageV
is simply the peak value of
the highest AC input voltage (V
) expected in the
application. Operation from 265 VAC input results in a
maximum DC bus voltage V
MAX
of 375 Volts DC.
V
V
V
MAX
ACMAX
=
×
=
×
=
2
265
2
375
Current Waveform Shape Parameters:
D
is the actual duty cycle occurring when the
TOPSwitch
power supply delivers maximum output power from minimum
input voltage. D
has an upper limit equal to the minimum
value of the
TOPSwitch
Data Sheet parameter DC
(64%).
D
is calculated from reflected voltage V
, minimum DC
input voltage V
MIN
, and
TOPSwitch
on-state Drain to Source
voltage V
DS
:
D
V
V
V
V
MAX
OR
OR
MIN
DS
=
+
(
)
Average current I
is
calculated from minimum DC input
voltage V
MIN
, output power P
O
, and efficiency
η
:
I
P
V
AVG
O
MIN
=
×
η
Peak primary current Ip is calculated from average current I
AVG
,
ripple to peak current ratio K
RP
, and maximum duty cycle D
MAX
:
I
I
K
D
P
AVG
RP
MAX
=
×
×
2
2
)
Ripple current I
R
is calculated from average current I
AVG
, peak
primary current I
P
, and maximum duty cycle D
MAX
:
I
I
I
D
R
P
AVG
MAX
=
×
2
(
)
RMS current I
is calculated from maximum duty cycle D
,
peak primary current I
, and ripple to peak ratio K
. I
can
also be calculated directly from D
MAX
, I
P
, and ripple current I
R
.
I
I
D
K
K
RMS
P
MAX
RP
3
RP
=
×
×
+
(
)
2
1
=
×
×
+
D
I
I
I
I
3
MAX
P
P
R
R
(
(
)
)
2
2
Transformer Design Parameters:
Primary inductance L
(in
μ
H) is determined by the flyback
transformer energy equation defined below. The flyback
transformer stores energy proportional to the square of primary
current. When
TOPSwitch
is on, primary current linearly ramps
up over a current range, defined earlier as ripple current I
, and
increases the energy stored in the flyback transformer core.
When
TOPSwitch
turns off, the stored energy increment
associated with ripple current I
is delivered to the load and
secondary losses (rectifier and clamp). Inductance L
can now
by calculated from output power P
, efficiency
η
, loss allocation
factor Z, peak current I
, switching frequency f
, and ripple
current to peak current ratio K
RP
(which determines I
R
).
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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