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參數(shù)資料
| 型號： | AN-20 |
| 英文描述： | Transient Suppression Techniques for TOPSwitch Power Supplies |
| 中文描述： | 暫態(tài)的TOPSwitch電源抑制技術(shù) |
| 文件頁數(shù)： | 3/8頁 |
| 文件大?。?/td> | 112K |
| 代理商： | AN-20 |
A
6/96
AN-20
3
+1
-1
0
0
-10
+10
V
V
∝
160V
∝
450V
-20
-30
-40
PI-1716-120595
Vo
VDIODE (ENVELOPE)
Figure 5. Output Voltage and Envelope of Diode Voltage Waveform
During Normal Mode Transient Surge.
Circuit Countermeasures
The following circuit countermeasures have been shown to
improve
TOPSwitch
power supply operation under transient
spike or surge voltage conditions.
TOPSwitch
ST202A power
supplies have been demonstrated to successfully operate through
both ring wave and 1.2
μ
S/50
μ
S surge voltages with peak
voltages up to 3 kV with the following circuit modifications.
All common mode countermeasures apply to differential mode
transient test conditions as well.
Common Mode Countermeasures
Eliminate all PC Board arcing! Dim the lights and closely
examine the PC board during testing for signs of arcing between
PC traces or conductors. Change the PC layout temporarily
with trace cuts and jumpers to increase the spacing and make
permanent changes on the PC board artwork. Slots in the PC
board can be used to increase effective clearance.
Replace common mode choke with wider bandwidth style. One
example of a wide bandwidth common mode choke is shown in
Figure 6. Note that each common mode inductor is wound in
two series connected sections to reduce capacitance. Two
section construction also divides or splits the transient test
voltage to reduce voltage stress and prevent arcing between
common mode choke windings. Use 10 mH to 33 mH common
mode chokes such as the Panasonic ELF-18D290X series for
output power under 20 Watts and ELF-18D2XX series for
output power over 20 Watts. (Toroidal common mode chokes
are not recommended.)
The differential mode configuration shown in Figure 4 applies
the transient test voltage across both AC mains conductors. The
TOPSwitch
power supply output should be connected either
directly to earth ground or AC coupled through a capacitor to
earth ground. This transient test voltage causes high differential
mode transient currents which can overcharge the power supply
bulk energy storage capacitor (C1 in Figure 7) or high voltage
DC bus (V+) to a high value. During transient testing, directly
measuring the V+ high voltage DC bus is dangerous and can
lead to equipment damage. Fortunately, the V+ high voltage
DC bus can be measured indirectly on the secondary side of the
power supply. Figure 5 shows the ST202A power supply
output voltage and the envelope of the output rectifier (D2 in
Figure 7) anode voltage during a differential mode test. The
anode voltage is useful because the envelope above reference is
proportional to power supply output voltage V
and the envelope
below reference is proportional to the V+ high voltage DC bus.
During the transient test, input capacitor C1 and the V+ high
voltage DC bus is charged from 160 VDC up to 450 VDC but
the
TOPSwitch
simply operates through with just a minor
output voltage correction.
Some differential mode transient test voltages are capable of
charging input capacitor C1 up to a voltage sufficient to cause
the bridge rectifier diodes to enter avalanche breakdown which
essentially clamps the high voltage DC bus (V+). Sometimes
the fuse opens, sometimes the bridge rectifier fails and then the
fuse opens. In the worst case scenario, the transient test voltage
charges up input capacitor C1 to a sufficiently high DC bus
voltage (V+) that
TOPSwitch
Drain voltage rating is exceeded.
0.8
13.0±0.5
21.0±1.0
10.0±0.5
16.0±1.0
2
3
PI-1635-111695
Figure 6. Spool Wound Common Mode Choke (Dimensions in mm).
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