The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "The field of the invention generally relates to power supplies and, more specifically, to a versatile DC output power supply.
"There are two main classes of power supply or converter: (1) AC to DC, and (2) DC to DC. An AC to DC power supply generally converts AC line voltage as its input to a DC output voltage and is found, for example, in applications such as home audio amplifiers. It can generally be implemented as either a linear or switching power supply. A DC to DC power supply converts from one existing DC voltage to another, for example from a battery, to another higher or lower voltage level. It is typically implemented with a switching power supply. For general use, DC to DC power supplies convert voltages and also provide isolation between input and output.
"Common components of a conventional power supply include a transformer, rectifier, and smoothing/storage capacitors. Additional components commonly utilized in a switching power supply include a control IC chip, power transistors, filtering and screening to prevent electro-magnetic interference (EMI). The demand for ever smaller equipment has led to a preponderance of switching power supplies.
"Conventional linear power supplies, used for instance in home audio amplifiers, use a large, heavy, expensive transformer to convert a low frequency, high-voltage AC line supply to a lower voltage suitable for the amplifier or other application. The high-voltage AC line supply is first dropped down to a lower AC voltage, and then the lower AC voltage waveform is rectified to DC. However, the rectified voltage is discontinuous and so large storage capacitors are needed in order to provide a smooth voltage for the amplifier. Even so, the DC supply still has an appreciable irregularity (the ripple voltage) superimposed upon the DC which can manifest as an audible hum and buzz at the amplifier output unless considerable care is taken with the amplifier design and layout.
"While the design of such a power supply is relatively simple and the EMI emissions relatively low, the transformer is large, heavy and very expensive. The storage capacitors are also large and expensive. Thus the overall bulk of this power supply approach precludes its use on lightweight, low profile designs. The power losses in the power supply are relatively low, with an overall efficiency generally found in the 85-90% range.
"An alternative to using linear power supplies is to employ a switched-mode power conversion technique. In this technique, the line voltage is first of all rectified and smoothed at full line voltage. This allows the storage capacitor to be smaller as compared to the linear power supply, and also less expensive. The resulting high voltage DC signal is then converted to a lower voltage by chopping it at a very high frequency--several tens of kHz typically--to produce an AC output signal which is transformed down to a lower voltage through a small transformer. Because the operating frequency is much higher than with a linear power supply, the transformer can be much smaller than in a conventional linear power supply. However, the AC signal on the output side of the transformer again has to be rectified to obtain DC and must still be smoothed with storage capacitors, albeit smaller ones than in a linear power supply. An example of such a power supply is an external power supply generally used to power a laptop computer.
"One penalty to be paid in this approach is that, in order to retain efficiency, the chopping of the DC produces high frequency AC with a discontinuous, square waveshape. Such a waveshape generates high levels of very high frequencies which radiate to cause radio frequency interference (EMI). Careful design, layout and screening are required to reduce these emissions to an acceptable limit. The switching frequency components also need to be removed or isolated from the input and output lines, requiring extra magnetic components that add to the cost and bulk of the supply. The efficiency, although theoretically capable of being very high, typically lies in the 80-90% range. Overall, the size and weight of the switched-mode power supply can be reduced considerably compared to a conventional linear power supply and the basic component cost can also be lower. However, the complexities inherent in the design of a switching power supply can add considerably to the design and certification costs and result in a time to market of many months.
"In sum, linear power supplies tend to be larger in size and profile, relatively costly, and heavy. They are advantageous in terms of efficiency and low EMI. Switching power supplies tend to be smaller and weigh less. Due to higher frequency operation, the transformers and capacitors of a switching power supply tend to be smaller than with a linear power supply. However, switching power supplies can be less efficient than linear power supplies, and produce significantly more EMI which requires careful filtering and screening. Switching power supplies are also more complex, needing control circuitry and power switching devices. They take longer to design and are generally more expensive than linear power supplies. The trend is towards ever smaller power supplies, requiring higher frequency operation and hence more potential issues relating to EMI.
"Larger power supplies may utilize three-phase power generation, which is an alternative power supply technique to the ones thus far described. In a three-phase system, three power lines carry three alternating currents of the same frequency but different phases, which reach their instantaneous peak values at different times. The current waveforms are offset by 120 degrees from one another (that is, each current is offset by one-third of a cycle from the other two waveforms). This staggering of waveforms allows energy to be continuously provided to the load(s), with a reduced but nonetheless substantial ripple. As a result, a constant amount of power is transferred over each cycle of the current. Transformers may be used to step-up or step-down the voltage levels at various points in a three-phase power network. A three-phase rectifier bridge commonly includes six diodes, with two diodes used for each branch of the three-phases.
"While three-phase power supply systems have some benefits, they are also subject to certain drawbacks or limitations. For example, a minimum of three conductors or power lines is generally required, as well as three sets of circuitry for level-shifting (with transformers) and rectifying each branch. Also, while ripple is reduced over a single-phase power supply, the ripple is still substantial and in general requires storage capacitors to bring down to an acceptable level.
"A need exists for a power supply or converter that can be made small, lightweight and reasonably inexpensive, with minimal EMI. A need further exists for such a power supply that avoids the complexities and complications of a switching power supply. A further need exists for a power supply that can reduce the need for large components and thus be made small in size and profile and lightweight."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "In one aspect, a power supply is provided in which one or more input waveforms are shaped or otherwise selected so that the output waveform requires minimal smoothing for generation of a DC output waveform.
"According to one or more embodiments, a power supply is provided having one or more input waveforms are shaped or otherwise selected prior to being provided to an isolating transformer. The nature of the input waveforms is shaped or selected so that the transformed waveform requires no or minimal smoothing for generation of a DC output waveform.
"The power supply may comprise a waveform generator, a level conversion stage for stepping the voltage level up (or down), a rectification stage, and a signal combiner. The waveform generator may generate complementary waveforms, such that after each of the complementary waveforms is rectified and combined their sum will be constant, thus requiring no or minimal smoothing for generation of a DC output waveform.
"In one embodiment, a DC output power supply comprises a waveform generator, at least one transformer, a rectification stage, and a signal combiner. The waveform generator may generate complementary waveforms, such that after each of the complementary waveforms is rectified and combined their sum will be constant. The complementary waveforms are preferably identical but are 90-degrees out of phase from one another, although in other embodiments the waveforms may have a different relationship. The complementary waveforms are applied to a pair of transformers or a single transformer with separate windings. The outputs of the transformers are provided to the rectification stage, which outputs a pair of rectified signals. The rectified signals have the property that when added together, their sum is constant. The rectified signals are provided to the signal combiner, which sums the signals and produces a constant DC output signal.
"In certain embodiments, the output voltage is monitored and fed back to the input side of the power supply, which adjusts the amplitude or other characteristics of the complementary waveform signals prior to being applied to the transformer(s).
"In other embodiments, a switched-capacitor technique is used to adjust (e.g., step up) the voltage level of the complementary waveforms, instead of transformer(s). In other respects, the power supply operates in a similar fashion.
"Embodiments as described herein may result in one or more advantages, including being smaller, lighter, thinner and/or less expensive than a conventional power supply, with fewer large components, while retaining high efficiency. The power supply can be designed so as to produce minimal or insignificant EMI. Because the power supply can be simpler to design and manufacture, it can be brought to market more quickly, thus resulting in a faster product design cycle.
"Further embodiments, alternatives and variations are also described herein or illustrated in the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 is a conceptual block diagram of a DC output power supply as disclosed herein, using one or more transformers for signal level conversion.
"FIG. 2 is a set of waveform diagrams illustrating operation of the power supply shown in FIG. 1, in accordance with one example.
"FIG. 3 is a set of waveform diagrams illustrating operation of the power supply shown in FIG. 1, in accordance with another example.
"FIG. 4 is a block diagram showing components of an embodiment of a voltage-controlled DC output power supply as disclosed in accordance with the conceptual block diagram of FIG. 1.
"FIG. 5 is a block diagram showing components of an embodiment of a current-controlled DC output power supply as disclosed in accordance with the conceptual block diagram of FIG. 1.
"FIG. 6 is a block diagram illustrating one example of a signal generator as may be used in connection with various embodiments as disclosed herein.
"FIG. 7 is a schematic diagram showing an embodiment of a power supply using a similar technique to FIG. 1, but implemented with switched capacitor circuits.
"FIG. 8 is a conceptual block diagram of a DC output power supply as disclosed herein.
"FIG. 9 is a block diagram illustrating a second example of a signal generator as may be used in connection with various embodiments as disclosed herein.
"FIG. 10 is a waveform diagram illustrating an example of a pair of frequency modulated signals as may be output by a signal generator.
"FIGS. 11A and 11B are schematic diagrams of a portion of a DC power supply operating in accordance with the principles of FIG. 1, using different input waveforms in each case.
"FIG. 12 is a schematic diagram of a portion of a DC power supply having amplifiers configured as integrators.
"FIG. 13 is a diagram of waveforms as may be used in connection with a DC power supply having transconductance amplifiers with an integrator characteristic.
"FIG. 14 is a schematic diagram of a portion of a DC power supply employing feedforward techniques to linearize the power amplifiers.
"FIG. 15 is a schematic diagram of a portion of a DC power supply employing both feedforward and feedback techniques.
"FIG. 16 is a schematic diagram of another embodiment of a DC power supply employing both feedforward and feedback techniques.
"FIG. 17 is a schematic diagram of an embodiment using switched capacitor circuits to form a multi-stage power converter.
"FIG. 18 is a schematic diagram showing a switched capacitor power supply having a combination of positive and inverting boosters circuits."
For additional information on this patent application, see: Jones, Owen; Fincham, Lawrence R. Power Converter with Low Ripple Output. Filed
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