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)： 9/36頁(yè)
文件大小： 381K
代理商： AN-15
A
6/96
AN-15
9
Subclass
Y1
Y2
Y3
Y4
Peak Impulse
Voltage V
applied before
endurance
8.0 kV
5.0kV
none
2.5 kV
radiated emissions specifications. Using short leads and short
PC traces for all Y-capacitor connections is critical to meet both
conducted and radiated emissions specifications.
In two-wire 230 VAC or universal input applications, a single
Y1-safety capacitor can be directly connected between the AC
mains or bridge rectifier output to the SELV secondary. The
single Y1-capacitor will also meet the electric strength voltage
requirement (for 230 VAC mains connected power supplies,
typically 3,000 VAC for one minute). Y1-capacitors with a
value of 1000 pF are available from Murata
(14)
(ACT4K-KD
series, DE1110 E 102M ACT4K-KD), Roederstein
(15)
(WKP
series, WKP102MCPE.OK) and Rifa
(12)
(PME 294 series, PME
294RB4100M). In general, Y1-capacitors are not used in 3-
wire applications.
Y2-capacitors do not meet reinforced insulation requirements.
In a single component failure safety investigation, one Y2-
capacitor may be replaced with a wire jumper to see if an electric
shock or fire hazard condition will exist. In most 2-wire
applications, a series combination of two 2200 pF Y2-capacitors
are commonly used between primary and SELV outputs so that
a short circuit failure of one Y2-capacitor creates no safety
hazard. A series connection of two Y2-capacitors is also
necessary to meet the electric strength requirement (for 230
VAC mains connected power supplies, typically 3,000 VAC
for one minute). In 3-wire applications, the Y2-capacitor may
be directly connected between AC mains or bridge rectifier
output and earth ground because the earth ground wire will
safely shunt the fault current created by a shorted Y2-capacitor.
Y2-capacitors rated at 250 VAC are available from a variety of
vendors including Murata, Roederstein, Panasonic, Rifa, and
Siemens. Figure 13 shows impedance plots for various sizes of
Y2-capacitors with short leads and one plot for a large Y2-
capacitor with long leads. Y-capacitors perform most of the
high frequency filtering from 10 MHz to 200 MHz. Note that
capacitor resonant frequency is usually 40 MHz or higher
unless artificially reduced with long leads or long PC traces.
Long leads and long PC traces can also cause emission currents,
though low enough to meet conducted emissions specifications,
to radiate sufficient energy from the power cord to exceed
I
(
)
Frequency (Hz)
100
10M
1M
100K
10K
1K
100
10
1
0.1
1K
10K
100K
1M
10M
40M
4700pF
2200pF
1000pF
330pF
4700pF
(LONG LEADS)
P
Figure 13. Y2-Capacitor Impedance.
In 115 VAC applications, a series combination of two Y2-
safety or two Y4-safety capacitors can be directly connected
between the AC mains or bridge rectifier to the SELV secondary.
Y3-safety capacitors are not normally used.
Safety specifications such as UL1950, UL544, and IEC950
limit the amount of fault current that can flow when a safety
ground connection has been opened or one component has
failed (Y1-capacitors, because of their construction, are excluded
from the failed component test). For example, UL1950 specifies
that information technology equipment with Class I or three
wire input (line, neutral, and earth ground), 240 VAC, 60 Hz
input must have a leakage current no higher than 3.5 mA if earth
ground is opened or one component has failed short which
restricts Y-capacitor maximum value below 0.039
μ
F (or
39 nF). For class II or two wire input (line, neutral, with no earth
ground), leakage current must be less than 250
μ
A with one
failed component which restricts Y-capacitor size to under
0.0028
μ
F (2.8 nF or 2800 pF) for 240 VAC, 60 Hz input.
Capacitor and input voltage tolerance must also be taken into
DUT
PI-717-032192
LINE
NEUTRAL
GND
Leakage
Currents
Figure 14. Typical Safety Measurement Setup.
Test Voltages for
Quality Approval,
Periodic and
Lot-by-Lot Testing
4000 VAC
1500 VAC
1500 VAC
900 VAC
Rated
Voltage
(VAC)
< 250 V
> 150 V
< 250 V
> 150 V
< 250 V
< 150 V
Type
of
Insulation
Bridged
Double Insulation or
Reinforced Insulation
Basic Insulation or
Supplementary Insulation
Basic Insulation or
Supplementary Insulation
Basic Insulation or
Supplementary Insulation
Table 4. Y-Capacitor Subclass.
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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