Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-01-17
2003-04-15
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06549431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to energy transfer elements and, more specifically, the present invention relates to energy transfer elements having multiple windings.
2. Background Information
FIG. 1
shows an outline schematic diagram of a flyback power supply
101
. The basic operation of the flyback converter
101
is well documented and known to one skilled in the art. The primary switch
103
is controlled through a feedback control signal
105
, typically but not necessarily from the secondary of the power supply as shown. The energy transfer element or transformer
107
windings have a dot polarity that is used to indicate the phase relationship of the winding voltages. During voltage transitions across the windings, the dot end of the windings are in phase.
FIG. 2
is a schematic of a power supply
201
, which expands on the outline schematic of
FIG. 1
by representing the parasitic capacitances
209
that exist between the transformer core and electrical earth, the parasitic capacitances
211
that exist between the input and output windings and the transformer core and also the parasitic capacitances
213
that exist between the input and output windings of the transformer. Usually the transformer core is the ferrite core used in the transformer construction to provide a low reluctance path for the magnetic flux coupling input and output windings of the transformer
207
. As noted in
FIG. 2
, the parasitic capacitance
215
between the output of the transformer and electrical earth in some cases maybe be short circuited depending on the application and or the way in which the electrical noise measurements are made.
During the normal operation of the power supply
201
, the voltages across both input and output windings of the transformer
207
transition in accordance with the standard flyback power supply operation. These transitions generate displacement currents in the electrical earth through the various parasitic capacitances
209
,
211
,
213
and
215
shown. These displacement currents are detected as common mode noise (or emissions) and measured by a piece of test equipment called a Line Input Stabilization Network (LISN). The configuration and connection of this equipment is well documented and known to one skilled in the art.
FIG. 2
also highlights capacitor Cy
217
which is a Y-capacitor, that is commonly used in switching power supplies to reduce the common mode emissions. This component, capacitor Cy
217
, provides a low impedance path for displacement currents flowing between input and output windings of the transformer
207
, to return to their source without flowing through electrical earth. The currents in capacitor Cy
217
are not detected by the LISN and its use therefore acts to reduce common mode emissions.
SUMMARY OF THE INVENTION
An energy transfer element having an energy transfer element input winding and an energy transfer element output winding is disclosed. In one aspect, the energy transfer element input winding is capacitively coupled to the energy transfer element output winding. The energy transfer element is capacitively coupled to electrical earth. One or more additional windings are introduced as part of the energy transfer element. The one or more additional windings substantially reduce capacitive displacement current between the energy transfer element input winding and energy transfer element output winding by balancing the relative electrostatic fields generated between these windings and/or between the energy transfer element and electrical earth by canceling the electrostatic fields generated by all windings within the energy transfer element relative to electrical earth through the selection of the physical position and number of turns in the additional windings. Additional features and benefits of the present invention will become apparent from the detailed description and figures set forth below.
REFERENCES:
patent: 3963975 (1976-06-01), Gauper, Jr. et al.
patent: 4518941 (1985-05-01), Harada
patent: 5579202 (1996-11-01), Tolfsen et al.
Odell Arthur B.
Park Chan Woong
Blakely , Sokoloff, Taylor & Zafman LLP
Power Integrations, Inc.
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