參數(shù)資料
型號(hào)： AN-15
英文描述： TOPSwitch Power Supply Design Techniques for EMI & Safety
中文描述： 的TOPSwitch電源電磁干擾設(shè)計(jì)技術(shù)
文件頁(yè)數(shù)： 3/36頁(yè)
文件大?。?/td> 381K
代理商： AN-15
A
6/96
AN-15
3
LISN Bonded to
Reference Plane
Non-conducting
Table
40 cm
80 cm
80 cm
80 cm
minimum
height
PI-1626-111695
Unit
Under Test
Load
This Edge Flush Up
Against Vertical
Reference Plane
PI-1627-111695
0
AC
CURRENT
AC
IN
CIN
V-
L
L
V+
First
Pulse
Steady State Peak Current
Conduction Time
3 mS
ID
Figure 7. Differential Mode Currents Charging Input Capacitor C
IN
.
Figure 6. Typical Conducted Emissions Precompliance Test Set Up.
Figure 6 shows a typical conducted emissions pre-compliance
test setup on a wooden table at least 80 cm high constructed with
non-metallic fasteners
(7)
. The unit under test, LISNs, and load
are all placed 40 cm from the edge of the table as shown. Six
foot cables are used between the unit under test and both the
LISN on the AC input and the load on the DC output. The LISN
and load are each located 80 cm from the unit under test with
excess cable bundled non-inductively. The edge of the table is
placed flush against a vertical reference plane at least two
meters square. The LISN is bonded to the reference plane with
a low impedance, high frequency grounding strap or braided
cable.
In applications where the power supply and load are located in
the same physical package, the cable can be omitted between
the unit under test and the load.
For design, investigation and precompliance testing, a spectrum
analyzer is highly recommended compared to EMI receivers
which are more expensive and more difficult to use. For
conducted and radiated emissions testing, the spectrum analyzer
should have a frequency range of 10 kHz to 1 Ghz, wide range
of resolution bandwidths (including C.I.S.P.R. specified
bandwidths of 200 Hz, 9 kHz, 120 kHz), built in quasi-peak
detector, video filter bandwidth adjustment capability down to
3 Hz or below for average measurements, maximum hold for
peak measurements, and an accurate and temperature
compensated local oscillator capable of centering a 100 kHz
signal in the display with insignificant frequency drift. The HP
8591EM and Tektronix 2712 (option 12)
(8)
are two examples of
lower cost spectrum analyzers sufficient for conducted emissions
precompliance testing.
Peak, Quasi-Peak, and Average
Detection
Power supplies operating from the 50 or 60 Hz AC mains use
a bridge rectifier and large filter capacitor to create a high
voltage DC bus from the AC input voltage as shown in
Figure 7. The bridge rectifier conducts input current for only
a short time near the peak of AC mains voltage. Actual
conduction time is typically 3 mS out of effective line frequency
periods of 8.3 to 10 mS which defines an effective “l(fā)ine
frequency duty cycle” of 30% to 36%. Conducted emission
currents can flow in the AC mains leads (and are sensed by the
LISN) only during the bridge rectifier conduction time. The
conducted emissions signal is actually applied to the spectrum
analyzer or receiver detector input only during bridge diode
conduction time which defines a “gating pulse” with pulse
repetitive frequency (PRF)
(8)(9)
equal to the AC mains frequency
(50 or 60 Hz) and “l(fā)ine frequency duty cycle” just defined. The
“gating pulse” effect due to bridge rectifier conduction time
causes the measured signal magnitude to change depending on
whether peak, quasi-peak, or average detection methods are
used.
A spectrum analyzer or EMI receiver displays the RMS value
of the signal
(9)
. For example, a 100 kHz continuous sinusoidal
相關(guān)PDF資料
PDF描述
AN-16 TOPSwitch Flyback Design Methodology
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
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