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| 型號： | AN-16 |
| 英文描述： | TOPSwitch Flyback Design Methodology |
| 中文描述： | TOPSwitch的反激式設(shè)計方法 |
| 文件頁數(shù)： | 24/32頁 |
| 文件大?。?/td> | 247K |
| 代理商： | AN-16 |
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AN-16
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PI-1615-021296
FEEDBACK
VIN
TOPSwitch
DRAIN
SOURCE
CONTROL
T1
D2
C1
RL
NS
NP
VO
Figure 1. Basic Flyback Converter Circuit.
Appendix A
TOPSwitchFlyback Fundamentals
This appendix explains the operation of a flyback power supply
using the
TOPSwitch
power integrated circuit.
TOPSwitch
is
a monolithic device combining a high voltage power MOSFET
switch with all the analog and digital control circuitry required
to implement isolated, regulated, and protected switching power
supplies. Designing the power supply is greatly simplified
because few external components are required. The high
switching frequency of 100 KHz reduces the size of the power
supply by allowing the use of smaller energy storage components.
The
TOPSwitch
was designed for use in isolated power supplies
or DC to DC converters. Power levels up to 50 Watts can be
delivered from AC voltages of 85 to 265 VAC, or 100W with
a 195 to 265 VAC input range. Operation from lower input
voltages is also possible with reduced levels of output power.
The flyback power supply is described in detail. Ideal and non-
ideal circuit operation is explained. The difference between the
discontinuous and continuous mode of operation is discussed.
The benefits of high frequency operation are presented. Other
types of power supplies using both linear and switching
techniques are examined and compared with the flyback
topology.
The Flyback Power Supply
The flyback topology, shown in Figure 1, is recommended for
off-line, isolated, power supply applications. The flyback
supply has a low parts count, wide input voltage range, inherent
feedback voltage sensing, single or multiple output voltage
capability, output voltages that can be higher or lower than the
input voltage, and ability to provide both positive and negative
voltages.
Almost all off-line switching power supplies require isolation
between primary and secondary components to satisfy the
requirements of domestic and international safety regulations.
This isolation, along with any necessary voltage transformation,
requires a power transformer. Most switching power supplies
also need an inductor as the energy storage component and also
as part of the low pass filter required to transform the pulse
width modulated switching waveform into a DC output. The
flyback topology is attractive for low power isolated switching
power supplies because the transformer is combined with the
inductor in a single magnetic component providing energy
storage, isolation, and voltage transformation. As compared to
other topologies such as the forward converter, the flyback has
the fewest magnetic components and the lowest parts count,
resulting in the lowest cost. The flyback topology retains these
advantages at power levels up to 100 watts, or output currents
up to 10 amperes. Component stress levels above 100 watts or
10 amperes output current require the use of more expensive
components, allowing other topologies to become more cost
effective.
Another important advantage of the flyback topology is that a
feedback voltage proportional to the output voltage can be
obtained directly by adding a “feedback” winding to the power
transformer. This means that secondary side regulation can be
accomplished on the primary side of the power supply without
using an optocoupler or similar isolation device between the
primary and secondary circuitry. Single or multiple, higher or
lower, positive or negative output voltages are primarily a
function of the construction of the power transformer.
Comparison to Other Techniques
Alternatives to flyback power supplies for low power
applications include linear supplies and other switching
topologies such as the buck converter and the forward converter.
These are briefly examined below. Additional information can
be found in some of the references listed at the end of this
appendix.
Linear Power Supplies
The linear power supply is characterized by the use of an AC
line frequency (50-60 Hz) transformer, rectifier, filter, and
linear regulator as shown in Figure 2. This type of power supply
is inexpensive and reliable but suffers from the following
disadvantages:
Largest size
Highest weight
Poorest efficiency
Narrow input voltage range
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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