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| 型號： | AN-14 |
| 英文描述： | TOPSwitch Tips. Techniques & Troubleshooting Guide |
| 中文描述： | TOPSwitch的提示。技術(shù) |
| 文件頁數(shù)： | 15/28頁 |
| 文件大?。?/td> | 246K |
| 代理商： | AN-14 |
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AN-14
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6. Optimizing Power Supply Efficiency
Efficiency is typically greater than 80% for most
TOPSwitch
power supplies above 10 Watts. Efficiency can be enhanced to
as high as 90% with the following changes:
Design for higher output voltage (up to 30 Volts). For
example, if a choice is available between output voltages of
12 and 15 Volts, the 15 Volt design will have better
efficiency.
Use Schottky output rectifiers. Universal input voltage
operation will require a transformer designed for 135 V
reflected output voltage V
to keep secondary voltage
stress below Schottky rectifier breakdown rating.
Increase transformer primary inductance for continuous
mode operation to reduce
TOPSwitch
RMS current and
conduction power loss. Figure 6a shows the trapezoidal,
continuous mode Drain current waveform. The ripple
current to peak current ratio (K
) has a practical lower
limit of 0.4 (0.6 for 230 VAC input). To maintain control
loop stability when operating in the continuous mode,
output capacitor size or compensation circuitry may need
to change.
Reduce transformer leakage inductance with split primary
winding.
Remove primary RC damping networks. A properly
designed primary clamp circuit will reduce primary ringing
so that a damping circuit is not necessary.
Remove secondary RC damping network. Proper attention
to PC board layout and selection of EMI filter components
may eliminate the need for the secondary RC damping
network.
Choose higher current bridge rectifier diodes and common
mode choke to reduce power losses due to input current.
Remove minimum load circuit if application allows.
Use higher power
TOPSwitch
with lower R
DS(ON)
.
Add heat sinks to
TOPSwitch
and output rectifier D2.
Refer to AN-19 for more information.
7. Thermal Design
7.1 Heat Sinking
TOPSwitch
, clamp Zener diode VR1, and output rectifier D2 are
the critical power bearing components. Temperature data should
be taken on each of these three components at rated load current
and input voltage in the mechanical package used for the actual
application. Excessive component temperature can be reduced
by selecting components with higher rating, using mounting
techniques with better heat transfer, or adding heat sinks.
Heat sinking
TOPSwitch
is very simple. The TO220 tab is
simply attached directly to the heat sink using a screw, bolt, or
clip. Power supplies in plastic enclosures usually require a
simple, non-safety-isolated, sheet metal stamped heat sink
mounted along the edge of the PC board to transfer heat to the
inside wall of the enclosure. In forced air applications,
TOPSwitch
is also directly attached to a non-safety-isolated, free standing
heat sink located in the moving air path. Applications with metal
chassis or cold plates require safety insulation beneath the
TOPSwitch
tab.
Axial output rectifiers and Zener diodes conduct heat through the
mounting leads. Thermal impedance can be reduced and power
handling improved by mounting axial rectifiers with short leads
to wide copper traces on the PC board. Thermal impedance
through each lead can be different if the die is bonded directly to
one lead and connected to the other lead through a bonding wire.
With vertical mounting, the lead with the lowest thermal
impedance should be kept very short to minimize device junction
temperature. A larger T0-220 style diode can also be used with
the various heat sinks described above.
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PDF描述 |
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| AN-26 | TOPSwitch-FX Flyback Quick Selection Curves |
| AN-35 | LinkSwitch Design Guide |
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| AN002R2-29 | SPDT RF Reflective Switch |
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