Patent Application
20130049918
The present invention relates to a common mode choke apparatus and method for power converters, and more particularly, to an integrated common mode choke apparatus and method comprising both a common mode choke and a differential mode choke.
A telecommunication network power system usually includes an ac-dc stage converting the power from the ac utility line to a 48V dc distribution bus and a dc/dc stage converting the 48V dc distribution bus to a plurality of voltage levels for all types of telecommunication loads. A conventional ac-dc stage may comprise a variety of EMI filters, a bridge rectifier formed by four diodes, a power factor correction circuit and an isolated dc/dc power converter. The dc/dc stage may comprise a plurality of isolated dc/dc converters. Isolated dc/dc converters can be implemented by using different power topologies, such as LLC resonant converters, flyback converters, forward converters, half bridge converters, full bridge converters and the like.
In a telecommunication network power system, isolated dc/dc converters may generate common mode noise and differential mode noise. More particularly, an isolated dc/dc converter may comprise at least one primary side switch to chop an input dc voltage so as to generate an ac voltage across the primary side of a transformer. In order to achieve a compact solution, the isolated dc/dc converter may operate at a high switching frequency such as 1 MHz. Such a high switching frequency may generate a high and fast voltage swing across the primary side. Furthermore, there may be a plurality of parasitic capacitors coupled between the primary side and the secondary side of the transformer. The high frequency voltage swing and the parasitic capacitors result in common mode noise in an isolated dc/dc converter because the parasitic capacitors of the transformer provide a low impedance conductive path for common mode current derived from the high frequency voltage swing. On the other hand, the switching ripple of the isolated dc/dc converter may generate differential mode noise, which has a major noise component at the switching frequency of the isolated dc/dc converter and a variety of noise components at other frequencies.
In order to control the electromagnetic interference (EMI) pollution from common mode noise and differential noise, a variety of international standards have been introduced. For example, EMI standard EN55022 Class B is applicable to isolated dc/dc converters. In accordance with a conventional technique, an EMI filter may comprise a common mode choke, a differential mode choke, a plurality of common mode bypass capacitors and a plurality of differential mode bypass capacitors. An effective EMI filter can attenuate both common mode noise and differential mode noise so that the telecommunication network power system can satisfy the requirements of EMI standard EN55022 Class B.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention which provide an integrated common mode choke for reducing common mode noise as well as differential mode noise in an isolated power converter.
In accordance with an embodiment, an apparatus comprises a magnetic core, a magnetic plate inserted within an inner circumference of the magnetic core, a first winding coil wound around the magnetic core and a second winding coil wound around the magnetic core.
In accordance with another embodiment, a system comprises a first differential mode bypass capacitor, a second differential mode bypass capacitor and an integrated common mode choke. The integrated common mode choke is coupled between the first differential mode bypass capacitor and the second differential mode bypass capacitor.
The integrated common mode choke comprises a magnetic core, a magnetic plate inserted within an inner circumference of the magnetic core, a first winding coil wound around the magnetic core and a second winding coil wound around the magnetic core.
The system further comprises a first common mode bypass capacitor and a second common mode bypass capacitor. The first common mode bypass capacitor and the second common mode bypass capacitor are connected in series.
In accordance with yet another embodiment, a method comprises inserting a magnetic plate within an inner circumference of a circular ring-shaped magnetic core, configuring a first winding coil wound at a left side of the magnetic plate and configuring a second winding coil wound at a left side of the magnetic plate wherein the first winding coil and the second winding coil are wound in a same direction through the circular ring-shaped magnetic core.
An advantage of an embodiment of the present invention is an integrated common mode choke can reduce both common mode noise and differential mode noise.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The present invention will be described with respect to preferred embodiments in a specific context, namely an integrated common mode choke for an isolated dc/dc power converter. The invention may also be applied, however, to a variety of power converters including both isolated power converters such as forward converters and non-isolated power converters such as buck converters. Furthermore, the invention may also be applied to a variety of power factor correction circuits.
Referring initially to
The integrated common mode choke 100 comprises a common mode choke LCM and two differential inductors, namely LDM1 and LDM2. When a differential current such as the normal operation current of the switching power converter (not shown) passes through the common mode choke LCM, the differential current cancels out in two windings of the common mode choke LCM. As a result, there is no net magnetization of the core of the common mode choke LCM. Consequently, the common mode choke LCM has no impact on the differential current. In contrast, when a common mode noise current passes through the common mode choke LCM, the common mode noise current magnetizes the core of the common mode choke LCM. As a result, the common mode choke LCM show high impedance for the common mode noise current so as to prevent the common mode noise current from polluting the prime power supply (not shown).
Two common mode bypass capacitors CCM are connected in series and coupled between the two outputs of the noise source 102. The joint node of two common mode bypass capacitors CCM is coupled to ground. In accordance with an embodiment, the common mode bypass capacitor CCM has a capacitance value of 2200 Pico Farad (pF). A first differential mode bypass capacitor CDM1 is coupled between the outputs of the noise source 102 and connected in parallel with the common mode bypass capacitors CCM. In accordance with an embodiment, the first differential mode bypass capacitor CDM1 has a capacitance value of 100 Nano Farad (nF). As shown in
A second differential mode bypass capacitor CDM2 is located at the other side of the integrated common mode choke 100. The second differential mode bypass capacitor CDM2 is coupled between the input lines of the prime power source (not shown). In accordance with an embodiment, the second differential mode bypass capacitor CDM2 has a capacitance value of 100 nF. One advantageous feature of having the integrated common mode choke 100 is that combining a common mode choke and a differential mode choke on a single magnetic core can reduce the cost and physical size of the EMI filter shown in
In accordance with an embodiment, the magnetic plate 202 is made of ferrite or the like. In particularly, when the integrated common mode choke 100 is applied to high frequency applications, the magnetic plate 202 made of ferrite may cause low energy losses. On the other hand, in accordance with another embodiment, the magnetic plate 202 is made of powder iron or other powder metal materials. In low frequency applications, the magnetic plate 202 made of powder iron is selected because a powder iron core may have a greater saturation flux density than a corresponding ferrite core. It should be noted that in comparison with conventional partition plates made of insulating materials such as plastics and rubber, the magnetic plate 202 is made of a magnetic material having high permeability. Furthermore, such a magnetic material helps to increase the leakage inductance of the integrated common mode choke 100. The increased leakage inductance makes it unnecessary to employ a dedicated differential mode choke. In fact, the equivalent circuit of the integrated common mode choke 100 shows that a common mode inductance is connected in series with a differential mode inductance. The detailed explanation of the equivalent circuit will be described below with respect to
where N1 is the turns of the first winding coil 204. The equation above shows that the differential inductance of the integrated common mode choke 100 is kind of inversely proportional to the third reluctance R3. In other words, by adjusting the third reluctance R3, the differential inductance is adjusted accordingly. As described above with respect to
Although embodiments of the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
