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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 |
| 文件頁數(shù)： | 28/32頁 |
| 文件大?。?/td> | 247K |
| 代理商： | AN-16 |
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AN-16
A
6/96
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time. This means that
(
)
(
)
(
)
(
)
V
V
L
D
f
V
V
D
N
N
L
f
IN
DS ON
×
P
S
O
D
×
S
P
P
S
×
=
+
×
×
2
1
(4)
Solving for V
O
, one obtains the expression
V
V
V
D
D
N
N
V
O
IN
DS ON
(
S
P
D
=
×
×
(
)
)
1
2
(5)
As long as the power supply is running in the continuous mode,
it can be seen from the above expression that there is no direct
dependence of the output voltage on the output loading. To a
first order, the duty cycle of the supply will remain constant as
the load is changed, and the initial value of the primary current
waveform will change instead.
The primary inductance of the power transformer, output loading,
and the
TOPSwitch
off time determine continuous or
discontinuous operation. This dependence is shown in
Equation (2). The boundary of continuous versus discontinuous
operation is defined by the equation
I
V
V
f
L
N
N
V
V
OB
IN
O
S
P
S
P
IN
O
=
×
×
×
×
×
+
2
2
2
(6)
Where I
OB
is the output current at the boundary between
continuous and discontinuous operation.
This equation is derived by assuming that the integral of the
output current of the power supply over the entire switching
cycle is exactly equal to the integral of the transformer secondary
output current over the off time period. This means that during
the off time, the transformer delivers exactly enough energy to
balance the energy delivered to the load over the entire switching
cycle, with no energy left over, and runs out exactly at the end
of the off time.
If the output current is greater than the right hand side of
Equation (6) , the supply is operating in the continuous mode.
If the output current is less than or equal to the right hand side
of the equation, the supply is operating in the discontinuous
mode. A smaller transformer primary inductance will give up
the energy stored in the magnetic field at a faster rate and result
in discontinuous conduction mode. Conversely, a larger primary
inductance will not give up all the energy stored in the core each
cycle and operate in continuous mode. If the load current is
reduced below I
, the supply will run in the discontinuous
mode. Also, if the input voltage is increased for a given load,
the supply can transition to the discontinuous mode, as I
OB
increases with increasing input voltage.
Non-ideal Model (Discontinuous and Continuous
Mode)
The circuit for the non-ideal flyback power supply and the
associated waveforms for the discontinuous and continuous
operating modes are shown in Figures 8 and 9. The non-ideal
flyback has three additional parasitic circuit elements: two
inductors and one capacitor. The inductor L
is the leakage
inductance of the primary winding on the power transformer.
The inductor L
KS
is the leakage inductance of the secondary
Crossover
Interval
PI-1617-021496
VIN
LKP
RL
VO
-
+
+
VDS
-
+
-
IPRI
ISEC
VIN
VDRAIN
Leakage
Spike
Voltage
1
Interval
IPRI
2
3
VP
ISEC
Slope = di/dt
VIN+VOR
0
DRAIN
SOURCE
CONTROL
D2
C1
LKS
CDRAIN =
COSS+CXT
Figure 8. Non-ideal Flyback Converter Waveforms - Discontinuous Mode.
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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