专利汇可以提供Method and apparatus of capacitor divider based offline AC-DC converter专利检索,专利查询,专利分析的服务。并且An AC/DC power converter has, as its first stage, a capacitor divider and rectifier and, as the second stage, a switch mode power supply. This configuration may be suitable for low power low voltage aerospace applications. The benefits of the circuit may include small reactive component size; near sinusoidal input current, low EMI emissions resulting from low inrush current; intrinsic current limiting that may eliminate the need for short circuit protection; and low overall component count.,下面是Method and apparatus of capacitor divider based offline AC-DC converter专利的具体信息内容。
We claim:
The present invention generally relates to the field of power supplies and more particularly to the field of power supplies that convert alternating current to low power, low voltage direct current.
In a typical AC power system in an aircraft, there are many low power low voltage control circuits that require a DC voltage directly from the AC lines. The AC line voltage generally provided by aircraft power systems usually has a frequency of 400 Hz at 115V. For variable frequency systems, the frequency is usually in the range of from 360 Hz to 800 Hz. In many cases, the power required for such low power low voltage control circuits is very small. However, in conventional AC/DC power supply design, the input capacitor required to interface the control circuit with the aircraft power supply system is a high voltage, high capacitance part, which tends to be bulky when compared to the size of other control circuit components. This dramatically increases the physical size of the AC/DC power supply.
This problem has been dealt with in several different ways. The most common approach before introduction of the switch mode power supply has been the circuit 100 shown in
For low power applications, this circuit has been replaced by a flyback converter design.
Other designs have been promoted, which address different aspects of the problem. The disclosure of U.S. Pat. No. 4,665,355, issued to McCollum et al. describes an off-line capacitor divider power supply, which supplies regulated DC voltage levels referenced to the AC voltage source output terminal to a load such as the control and drive circuits of a solid state power controller. The power supply design is that of a linear power supply which is good only for a fixed frequency, fixed input voltage and a fixed load. When either the input voltage or the frequency changes, the design will suffer from poor efficiency, overheat, and loss of regulation.
The disclosure of U.S. Pat. No. 4,910,654, issued to Forge, describes an AC to DC conversion circuit, in which the first stage comprises a diode bridge rectifier coupled to a capacitor divider that in turn serves as input to a switch mode power supply. The disclosed circuit addresses the problem of burning out the current limiting resistor connected to the input terminal of the AC to DC converter stage of the switch mode power supply by removing the resistor and substituting a non-dissipative capacitive divider circuit which charges the filter or storage capacitors while the input relay is open. It does not address the problem of large value capacitors in the circuit.
The disclosure of U.S. Pat. No. 5,282,126, issued to Husgen, describes a starter circuit for a switched mode power supply, in which a capacitor divider is used to receive the pulsing DC voltage provided by a bridge rectifier. The use of the capacitor divider serves as both a smoothing device for the pulsing DC voltage and eliminates the need for transistor and collector resistance rated for high voltages and large currents. However, it does not address the problems of complexity, high part counts, and large value capacitors.
Hence, it can be seen that there is a need for a power supply for aircraft electrical systems in which the conversion circuit that is small in size. Associated with the space requirement, it is desirable to have as low a component count as possible to reduce inventory requirements for spare parts and to have high reliability to reduce the probability of failure at critical times. Furthermore, close proximity of the aircraft components with each other may promote interference between systems, so that low EMI emissions may also be desirable.
In one aspect of the present invention, an AC/DC power converter is provided, where it is coupled to an AC voltage source having a ground terminal and a power terminal, for supplying regulated DC voltage levels to a load. The AC/DC power converter may be comprised of the following components: a first stage with a capacitor divider, the capacitor divider further comprised of a plurality of capacitors connected in series between the AC voltage source ground terminal and the AC voltage source power terminal, a selected capacitor from the plurality of capacitors with a capacitor power terminal and a capacitor ground terminal, such that the capacitor terminals provide a voltage across the selected capacitor; a rectifier receiving the voltage across the capacitor power terminal and the capacitor ground terminal and providing a unregulated DC voltage across a rectifier output terminal and a rectifier ground terminal; and a second stage switch mode power converter having an output power terminal and an output ground terminal, the second stage receiving the unregulated DC voltage from the rectifier and providing a regulated DC voltage across the output power terminal and the output ground terminal.
In another aspect of the invention, if isolation is not required, the second stage switch mode power converter may take the form of a buck converter, having an output power terminal and an output ground terminal. The buck converter receives the unregulated DC voltage from the rectifier and provides a regulated DC voltage across the output power terminal and the output ground terminal.
In another aspect of the invention, if isolation is required, the second stage switch mode power converter may take the form of a forward converter, where the forward converter receives the unregulated DC voltage from the rectifier and provides an isolated regulated DC voltage across the output power terminal and the output ground terminal.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
The invention may provide a novel capacitor divider based offline AC/DC converter with a second stage switch mode power converter, in which a capacitor divider may be used as the input stage to step down the voltage from an external power source. This may be followed by a rectifier and a second stage that may include a switch mode power supply. The invention may find application in the area of aircraft electrical systems for supplying low power, low voltage control circuits. The invention may also find applications in areas in which compact circuits may be required due to limitations of size and weight.
The capacitor divider used in the invention may be composed of low capacitance parts that reduce the requirement for a high value capacitor having a comparatively large size when compared to other circuit components. The invention may provide additional benefits of intrinsic current limiting, intrinsic voltage limiting, and very little input current spikes. These intrinsic benefits may also promote relatively simple control requirements for the switch mode power supply in the second stage of the power converter. Conventional current mode control may not be required. Simple hysteresis control may be applied without additional protection of the circuit from over voltage or over current conditions. This may tend to reduce parts count without compromising the reliability of the circuit.
The first stage of the inventive electrical circuit may be a capacitor divider that does not require the bulky capacitor used in a conventional switch mode AC/DC converter. This may be followed by a rectifier of standard design well known in the prior art, followed by a second stage that may be a simplified switch mode power supply. The second stage may eliminate the line frequency transformer used in conventional linear power supplies. As a result, the power converter provided by the invention may achieve smaller size and less parts count compared to other power converters found in the prior art. Furthermore, the invention may accommodate voltage sources having variable frequency and variable voltage. Frequency ranges typically encountered by the invention in aircraft power systems may be from about 360 Hz to about 800 Hz. Voltage ranges may be from about 90 v. to about 180 v. Thus, the invention can be advantageously employed in situations in which either the frequency, the voltage, or both may vary, to provide a stable DC voltage to a load.
Turning now to the description of the novel circuit and with reference first to
Note that capacitor 301 may be the only a high voltage component. Since capacitor 301 is in series with the remainder of the circuit 300, then any short circuit in the remainder of the circuit will not result in a high current being drawn from the voltage source 304. The capacity of capacitor 301 may be selected so that under all conditions capacitor 301 may provide the current required by the low power, low voltage control circuit connected as the load across the output power terminal 308 and output ground terminal 309 of the circuit 300. For a low power avionics application, the physical size of capacitor 301 may be fairly small, such as by way of example and not of limitation, an SMT 1206 capacitor manufactured by Panasonic, which is constructed as a stacked dielectric film capacitor with internal electrodes, having a maximum capacity of 1 μF and a physical size in millimeters measuring 3.2×1.6×1.4. Capacitor 302 may establish the maximum voltage limit for the low voltage side circuit. The presence of capacitor 302 may ensure that no over-voltage occurs in the DC output terminals 308.
Rectifier 303 may be of any typical construction generally found in the art, without departing from the scope of the invention. Rectifier 303 may rectify the low AC voltage dropped across capacitor 302. Capacitor 305 may function as a smoothing capacitor that makes the unregulated DC voltage ready for the second stage 306 circuit to process. The choice of configuration for the second stage 306 may depend upon the particular application and may be chosen without departing from the scope of the invention.
Referring now to
The circuit 600 shown in
Referring now to
The input stage of the circuit provided by the invention may be a capacitor divider, so the overall impedance presented by the inventive circuit may be capacitive in nature. In many cases, the capacitive impedance may provide reactive compensation to the system. However, this is not always preferred. It may be desirable to additionally cut the reactive current within the circuit. The circuit 900 shown in
Referring now to
Thus, it may be seen that a novel capacitor divider based offline AC/DC converter has been provided and described herein. It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
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