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)： 14/36頁(yè)
文件大?。?/td> 381K
代理商： AN-15
AN-15
A
6/96
14
capacitance) cause additional voltage peaking and ringing at
frequencies typically between 3 MHz and 12 MHz. The
TOPSwitch
Drain, transformer primary, and Drain clamping
components connected to the Drain node will drive displacement
currents to earth ground through transformer capacitance or
stray capacitance. This displacement current returns
“backwards” through the line and neutral conductors back to
the
TOPSwitch
Drain driving node as a common mode emission
current. The displacement currents generated by the drain
voltage waveform cause spectral energy in the form of a
common mode conducted emission currents to be concentrated
at the switching frequency and 3 MHz to 12 MHz resonant
frequency (f
1
) of the indicated ringing voltage waveform.
Common mode emission currents will be lower with
TOPSwitch
when compared with discrete MOSFET implementations
because
TOPSwitch
has a controlled turn on gate driver to
reduce dv/dt. Common mode emissions currents are also lower
because the
TOPSwitch
TO-220 tab is connected to the relatively
quiet source pin while a discrete MOSFET has the noisy drain
“transmitting” node connected directly to the tab (and heat sink)
“broadcasting antenna”.
Diode Voltage Waveform
The diode voltage waveform V
is also characterized by fast
voltage changes and fast rise and fall times. Parasitic circuit
elements (transformer leakage inductance and diode capacitance)
cause additional voltage peaking and ringing at frequencies
typically between 20 MHz and 30 MHz. The diode voltage
waveform will drive displacement currents to earth ground
through transformer capacitance or stray capacitance. The
displacement currents generated by the diode voltage waveform
cause spectral energy in the form of common mode emission
currents to be concentrated at the switching frequency and
20 MHz to 30 MHz resonant frequency (f
2
) of the indicated
ringing voltage waveform.
Secondary Current Waveform
Secondary current I
begins to flow as soon as
TOPSwitch
turns off. Current starts at a peak value and decreases linearly
at a rate determined by secondary inductance and output voltage.
This trapezoidal (or triangular) current waveform is characterized
in the frequency domain by a spectrum with a fundamental at
the switching frequency and harmonics determined by the
relative squareness of the waveform. Additional ringing
superimposed on the waveform is related to the drain source
voltage V
waveform previously discussed. This composite
current waveform can cause significant magnetic fields to
radiate if the current path defined by the PC board layout
encircles a large physical area. Spectral energy in the form of
a common mode emission current would be concentrated at the
switching frequency and 3 MHz to 12 MHz resonant frequency
(f
1
) of the indicated ringing current waveform.
Figure 28. Examples of Typical Flyback Power Supply Waveforms Causing EMI.
IPRI
VDRAIN
ISEC
C
LOAD
VIN
VDRAIN
-
IPRI
+
ISEC
PI-1724-121895
+
-
VDIODE
VDIODE
f1
f2
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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