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Point of load sine amplitude converters and methods Number:7,145,786 from the United States Patent and Trademark Office (PTO) owispatent

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Title: Point of load sine amplitude converters and methods

Abstract: In a preferred embodiment, a Sine Amplitude Converter ("SAC") method and apparatus for VTMs converts a DC input voltage to a DC output voltage using a fixed transformation ratio at a frequency locked to a resonance. The SAC uses a resonant circuit including a transformer and complementary primary switches operating with balanced switching and a high power conversion duty cycle (e.g., above 94%) to perform high frequency, low noise, single stage power processing. The resonant circuit may have a low Q while enhancing conversion efficiency. Common-mode noise may be effectively reduced using symmetrical resonant power trains.In a preferred embodiment, a low profile (<0.16 inch high), low permeability "dog's bones" core structure, integrated with multi-layer PCB windings to complete SAC transformers, gives rise to a VTM manufacturing platform with greater than 400 Watts/cubic-inch power density and 95% efficiency, converting 100 150 Watts at the point of load. Capable of low manufacturing costs, this enabling technology supports flexible, molded packages for VTMs, which are characteristic of large IC's or "System In a Package" ("SIP") devices, as distinct from the standard "bricks" characteristic of the DC-DC converters, the workhorses of vintage Distributed Power Architecture ("DPA").

Patent Number: 7,145,786 Issued on 12/05/2006 to Vinciarelli


Inventors: Vinciarelli; Patrizio (Boston, MA)
Assignee: VLT, Inc. (Sunnyvale, CA)
Appl. No.: 11/181,957
Filed: July 14, 2005


Related U.S. Patent Documents

Application NumberFiling DatePatent NumberIssue Date
10443573May., 20036975098
10264327Oct., 20026930893
10066418Jan., 2002

Current U.S. Class: 363/17 ; 363/98
Current International Class: H02M 3/335 (20060101)
Field of Search: 363/17,98,132


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Primary Examiner: Sterrett; Jeffrey
Attorney, Agent or Firm: Fish & Richardson P.C.

Parent Case Text



This application is a divisional of U.S. application Ser. No. 10/443,573, filed May 22, 2003 now U.S. Pat. No. 6,975,098 (incorporated herein by reference) which is a continuation-in-part of U.S. application Ser. No. 10/264,327, filed Oct. 1, 2002 now U.S. Pat. No. 6,930,893 (incorporated herein by reference) which is a continuation-in-part of U.S. application Ser. No. 10/066,418, filed Jan. 31, 2002 (now abandoned).
Claims



What is claimed is:

1. A method of converting power from an input source for delivery to a load, where the load may vary over a normal operating range, comprising: providing a transformer; forming a resonant circuit including the transformer and having a characteristic resonant frequency and period; providing output circuitry connected to the transformer for delivering a rectified output voltage to the load; providing a first pair of primary switches connected in series and a second pair of primary switches connected in series, the first and second pairs connected to drive the resonant circuit; and providing a switch controller to operate the first and second pair of primary switches in opposition of phase in a series of converter operating cycles at resonance or frequency modulated near resonance; and arranging the resonant circuit and primary switches symmetrically to reduce common-mode noise.

2. The method of claim 1 wherein: the transformer comprises first and second primary windings; and the first pair and second pair of primary switches drive the first and second primary windings in opposition of phase.

3. The method of claim 2 wherein the first and second pair and the first and second primary windings form two half-bridges driven in opposition of phase.

4. The method of claim 1 wherein the primary switches form a full-bridge circuit to drive the transformer; the transformer comprises two primary windings; and the resonant circuit comprises a resonant capacitor connected in series with and between the two primary windings.

5. The method of claim 1 wherein the primary switches form a full-bridge circuit to drive the transformer; the resonant circuit comprises first and second resonant capacitors; and the transformer comprises a primary winding connected in series with and between the first and second resonant capacitors.

6. The method of claim 5 wherein the primary winding comprises a plurality of series connected primary windings.

7. A method of converting power from an input source for delivery to a load, where the load may vary over a normal operating range, comprising: providing a transformer; forming a resonant circuit including the transformer and having a characteristic resonant frequency and period and having a Q less than 13; providing output circuitry connected to the transformer for delivering a rectified output voltage to the load; providing a primary switch connected to drive the resonant circuit; providing a switch controller to operate the primary switch in a series of converter operating cycles; and providing a conversion efficiency from the source to the load having a peak greater than 90% within the normal operating range.
Description



TECHNICAL FIELD

This invention relates to the field of electrical power conversion and more particularly to distributed electronic power conversion systems.

BACKGROUND

DC-DC converters transfer power from a DC electrical input source to a load by transferring buckets of energy between windings of an isolation transformer. The DC output voltage delivered to the load is controlled by adjusting the timing of internal power switching elements (e.g., by controlling the converter switching frequency and/or the switch duty cycle and/or the phase of switches). As defined herein, the functions of a "DC-DC converter" comprise: a) isolation between the input source and the load; b) conversion of an input voltage to an output voltage; and c) regulation of the output voltage. DC-DC converters may be viewed as a subset of a broad class of switching power converters, referred to as "switching regulators," which convert power from an input source to a load by processing energy through intermediate storage in reactive elements. As defined herein, the functions of a "Switching Regulator" comprise: a) conversion of an input voltage to an output voltage, and b) regulation of the output voltage. If the required output voltage is essentially a positive or negative integer (or rational) multiple of the input voltage, the conversion function may also be efficiently performed by a capacitive "Charge Pump," which transfers energy by adding and subtracting charge from capacitors.

The introduction of commercial DC-DC converters capable of efficiently switching at high frequencies (e.g., 1 MHz) has brought about significant miniaturization of the DC-DC converter function. The reduction in switching losses made possible by the invention, in the early 1980's, of zero current switching ("ZCS") and zero voltage switching ("ZVS") power conversion topologies, led to an increase in converter operating frequency that translated into a commensurate breakthrough in power density. The power density of DC-DC converters jumped from about 1 Watt/cubic inch to over 20 Watts/cubic inch. The reduction of DC-DC converter volume per unit of power delivered, and the corresponding reduction in DC-DC converter weight, created many new opportunities for the deployment of DC-DC converters and enabled the development of more advanced power systems and power system architectures for electronic products and systems. These products and systems have also benefited from advances in power density and efficiency of commercial Switching Regulators and Charge Pumps.

High frequency DC-DC converters have been packaged to provide flexibility in mechanical mounting and thermal management. A typical DC-DC converter (FIG. 1) is an enclosed assembly 10 comprising a metal surface 12 for extracting heat and connection pins 13 for connecting the converter to the source and the load. Contemporary DC-DC converters, commercially available from many vendors, offer power densities up to 100 Watts per cubic inch and the height of the overall assembly, exclusive of the pins, is typically 0.5 inch.

It is known that there is a tradeoff between DC-DC converter operating efficiency and power density on the one hand, and the range of input voltages over which the converter is designed to operate on the other. Narrower input voltage operating ranges may allow for more efficient converters and higher power densities. It is also known that, for a given level of power delivery, the efficiency of a power converter typically decreases with decreasing output voltage. For example, a converter delivering 2V at 100 Amperes (100 Watts) will typically exhibit higher losses than a converter delivering 5V at 20 Amperes (100 Watts).

Certain electronic systems contain a multiplicity of subsystems on printed circuit boards ("PCBs"), closely spaced and interconnected within an enclosure or rack, each PCB requiring a complement of voltages suitably adapted to the unique power requirements of the circuitry on the PCB. Prior to the availability of high density and low profile (0.5 inch tall) DC-DC converters, most such systems relied on a "centralized power architecture" ("CPA"). In the CPA architecture, the various well-regulated voltages required by the PCBs (e.g., 2V, 5V, 12V) are generated in a centralized power supply and bussed around the system for delivery to each of the PCB subassemblies. With the CPA architecture, high currents at relatively low voltages need to be delivered over substantial distances and the management of power losses and voltage drops throughout the system is difficult and costly. The advent of high-density DC-DC converters enabled a migration from the CPA to a "distributed power architecture" ("DPA"). In the DPA architecture, these problems are overcome by bussing a relatively higher, less well-regulated, voltage around the system (e.g., 300V, 48V, 24V) to provide input power to DC-DC converters on the PCBs, which perform the functions of isolation, voltage conversion and regulation at the point-of-load. In addition to simplifying power distribution, the DPA provides system design flexibility, since each subsystem can be provided with DC-DC converters which deliver whatever voltages are needed without requiring modifications to a centralized power supply or distribution system. System design flexibility is further enhanced by the availability of high density Switching Regulators and Charge Pumps.

The DPA architecture is discussed in Tabisz et al, "Present and Future of Distributed Power Systems," APEC '92 Conference Proceedings, 1992, pp. 11 18; in Mweene et al, A High-Efficiency 1.5 kW, 390 50V Half-Bridge Converter Operated at 100% Duty Ratio," APEC '92 Conference Proceedings, 1992, pp. 723 730; in Choi et al, "Dynamics and Control of DC-to-DC Converters Driving Other Converters Downstream," IEEE Transactions on Circuits and Systems--I: Fundamental Theory and Applications, October 1999, pp. 1240 1248; and in Lee et al, "Topologies and Design Considerations for Distributed Power System Applications," Proceedings of the IEEE, June 2001, pp. 939 950.

Non-resonant full-bridge, half-bridge, and push-pull DC-to-DC transformer topologies are known. See e.g. Severns and Bloom, "Modern DC-to-DC Switchmode Power Conversion Circuits," ISBN 0-442-21396-4, pp. 78 111. Series, parallel, and other resonant forms of switching power converters are also known. See e.g., Steigerwald, "A Comparison of Half-Bridge Resonant Converter Topologies," IEEE Transactions on Power Electronics, Vol. 2, No. 2, April 1988. Variable frequency, series resonant, half-bridge converters for operation from an input voltage source are described in Baker, "High Frequency Power Conversion With FET-Controlled Resonant Charge Transfer," PCI Proceedings, April 1983, and in Nerone, U.S. Pat. No. 4,648,017. Half-bridge, single-stage, ZVS, multi-resonant, variable frequency converters, which operate from an input voltage source are shown in Tabisz et al, U.S. Pat. No. 4,841,220 and Tabisz et al, U.S. Pat. No. 4,860,184. A variable frequency, full-bridge, resonant converter, in which an inductor is interposed between the input source and the resonant converter is described in Divan, "Design Considerations for Very High Frequency Resonant Mode DC/DC Converters," IEEE Transactions on Power Electronics, Vol. PE-2, No. 1, January, 1987. A variable frequency, ZVS, half-bridge LLC series resonant converter is described in Bo Yang et al, "LLC Resonant Converter for Front End DC-DC Conversion," CPES Seminar 2001, Blacksburg, Va., April 2001. Analysis and simulation of a "Low Q" half-bridge series resonant converter, wherein the term "Low Q" refers to operation at light load, is described in Bo Yang et al, "Low Q Characteristic of Series Resonant Converter and Its Application," CPES Seminar 2001, Blacksburg, Va., April 2001.

Fixed-frequency half-bridge and full-bridge resonant converters are also known in which output voltage control is achieved by controlling the relative timing of switches. A half-bridge, single-stage, ZVS, multi-resonant, fixed-frequency converter that operates from an input voltage source is shown in Jovanovic et al, U.S. Pat. No. 4,931,716. A full-bridge, single-stage, ZVS, resonant, fixed-frequency converter that operates from an input voltage source is shown in Henze et al, U.S. Pat. No. 4,855,888.

A full-bridge, single-stage, ZCS, series-resonant, fixed-frequency converter, operating at a frequency equal to the characteristic resonant frequency of the converter, is shown in Palz, "Stromversorgung von Satelliten--Wanderfeldrohren hoher Leistung" ("Power Supply for Satellites--High Capacity Traveling-Wave Tubes"), Siemens Zeitschrift, Vol. 48, 1974, pp. 840 846. Half and full-bridge, single-stage, ZVS, resonant, converters, for powering fluorescent tubes are shown in Nalbant, U.S. Pat. No. 5,615,093.

A DC-to-DC Transformer offered for sale by SynQor, Hudson, Mass., USA, called a "BusQor.TM. Bus Converter," that converts a regulated 48VDC input to a 12 VDC output at a power level of 240 Watts and that can be paralleled with other similar converters for increased output power delivery, and that is packaged in a quarter brick format, is described in data sheet "Preliminary Tech Spec, Narrow Input, Isolated DC/DC Bus Converter," SynQor Document No. 005-2BQ512J, Rev. 7, August, 2002.

The art of resonant power conversion, including operation below or above resonant frequency, utilizing either ZCS or ZVS control techniques and allowing the resonant cycle to be either completed or purposely interrupted, is summarized in Chapter 19 of Erickson and Maksimovic, "Fundamentals of Power Electronics," 2nd Edition, Kluwer Academic Publishers, 2001.

Cascaded converters, in which a first converter is controlled to generate a voltage or current, which serves as the source of input power for a DC-to-DC transformer stage, are known. A discussion of canonical forms of cascaded converters is given in Severns and Bloom, ibid, at, e.g., pp. 114 117, 136 139. Baker, ibid, discusses the use of a voltage pre-regulator cascaded with a half-bridge, resonant, variable-frequency converter. Jones, U.S. Pat. No. 4,533,986 shows a continuous-mode PWM boost converter cascaded with both PWM converters and FM resonant half-bridge converters for improving holdup time and improving the power factor presented to an AC input source. A zero-voltage transition, current-fed, full-bridge PWM converter, comprising a PWM boost converter delivering a controlled current to a PWM, full-bridge converter, is shown in Hua et al, "Novel Zero-Voltage Transition PWM Converters," IEEE Transactions on Power Electronics, Vol. 9, No. 2, March, 1994, p. 605. Stuart, U.S. Pat. No. 4,853,832, shows a full-bridge series-resonant converter cascaded with a series-resonant DC-to-DC transformer stage for providing AC bus power to distributed rectified loads. A half-bridge PWM DC-to-DC transformer stage for use in providing input power to point-of-load DC--DC converters in a DPA is described in Mweene et al, ibid. Schlecht, U.S. Pat. Nos. 5,999,417 and 6,222,742 shows DC-DC converters which incorporate a DC-to-DC transformer stage cascaded with a switching regulator. Vinciarelli, "Buck-Boost DC-DC Switching Power Conversion," U.S. patent application Ser. No. 10/214,859, filed Aug. 8, 2002, assigned to the same assignee as this application and incorporated by reference, discloses a new, high efficiency, ZVS buck-boost converter topology and shows a front-end converter comprising the disclosed topology cascaded with a DC-DC converter and a DC-to-DC transformer.

A power distribution architecture proposed by Intel Corporation, Santa Clara, Calif., USA, called NPSA ("New Power Supply Architecture"), is described by Colson in "Intel Platform Solutions," Issue 23, September, 1999, and by Reynolds in "Intel Development Forum Highlights: Fall 1999," published by Gartner, Dataquest, November, 1999. NPSA comprises a front-end converter which generates a 30 VAC, 1 MHz, distribution bus for delivery to regulating AC-DC converters located near distributed loads. A power distribution architecture comprising a front-end converter which generates a 12 VDC distribution bus for use by point-of-load isolated and non-isolated converters is described briefly in "Tiny Titans: Choose `Em and Use `Em With Care," EDN magazine, May 2, 2002, p. 48. A power distribution architecture comprising a front-end isolated bus converter which generates an unregulated 12 VDC distribution bus for use by point-of-load non-isolated regulating DC-DC converters is described in "Distributed Power Moves To Intermediate Voltage Bus," Electronic Design magazine, Sep. 16, 2002, p. 55.

The accepted approach for delivering power to future generation microprocessors revolves around power conversion topologies and control techniques that support high-bandwidth performance under closed-loop control. The strategy is to keep the voltage at the microprocessor within an allowable range under rapid transitions in the current drawn by the microprocessor by: a) providing adequate bypass capacitance at the point-of-load to absorb the rate of change of current within a time scale shorter than the response time of the upstream power converter and b) providing a converter having a very fast closed loop response to limit the amount of point-of-load capacitance that is needed.

This approach relies upon the "multiphase buck topology" employing N buck converters operating in parallel, locked at the highest practical frequency and "interleaved" by a phase equal to 360/N. Interleaving provides faster transient response by allowing a reduction in the value of the inductance in series with the output of each buck stage (thus increasing the slew rate of current) and by allowing sampling of the output error voltage at N times the base frequency (thus extending the Nyquist limit for closed loop stability to a fraction of the multiplied frequency as opposed to the base frequency). As the microprocessor current and current rate of change keeps growing with every generation of microprocessor, more and more phases are added to keep up with it. And control methods to extract the most in terms of close loop bandwidth are being developed.

An example of this microprocessor power paradigm (using double-edge modulation to extract closed-loop bandwidth in the 1.5 MHz range from a system consisting of 8 interleaved buck converters each operating at 1 MHz) is discussed in "New Control Method Boosts Multiphase Bandwidth," Paul Harriman, Power Electronics, January 2003, pp. 36 45.

A series resonant converter in which ZVS is accomplished by exploiting the flow of magnetizing current in a transformer, or in an inductor connected in parallel with the primary winding of a transformer, is described in Ferreira, U.S. Pat. No. 5,448,467.

Low-loss gate drivers for driving capacitive gate terminals of power switching devices are described in Yao et al, "A Novel Resonant Gate Driver for High Frequency Synchronous Buck Converters," IEEE Transactions on Power Electronics, Vol. 17, No. 2, March 2002 and in Fisher et al, U.S. Pat. No. 5,179,512, in Steigerwald, U.S. Pat. No. 5,514,921 and Schlecht, ibid.

A variety of isolated power conversion topologies are compared for use as voltage regulator modules ("VRM") in Ye et al, "Investigation of Topology Candidates for 48V VRM," 2002 APEC Conference. Projected trends in performance requirements for VRMs and a proposed technology roadmap for achieving those requirements are summarized in Stanford, "New Processors Will Require New Powering Technologies," Power Electronics Technology magazine, February 2002.

Modulating the channel resistance of a MOSFET synchronous rectifier switch as a means of regulating an output voltage of a switching power converter is described in Mullett et al, U.S. Pat. No. 6,330,169 B2.

SUMMARY

In general, an aspect features an apparatus for converting power from an input source to a load, including a circuit board having a plurality of conductive layers, a transformer having a permeable core comprising a plurality of core elements, each core element passing through a hole in the circuit board, and primary and secondary windings formed by respective patterns on a plurality of conductive layers of the circuit board and around a plurality of core elements. A series resonant circuit includes the transformer and has a characteristic resonant frequency. Two or more primary switches are connected to drive the resonant circuit and output circuitry is connected to the transformer for delivering a rectified output voltage.

Implementations of the apparatus may include one or more of the following features. The core element may include a core piece and an end piece. The core piece may have a portion for passing through the hole in the circuit board. The portion of the core piece may be cylindrical and the hole may be a circular hole. The transformer may be a "dog's bones" transformer and the orientation of windings associated with neighboring dog's bones may be poled in opposite directions. The effective permeability of the permeable core may be less than 100. The effective permeability of the permeable core may be less than 50. The circuit board, the transformer, the primary switches, the resonant circuit and the output circuitry may be over molded to form an integrated circuit sized package having a height less than 0.28 inch. The characteristic resonant frequency may be greater than 500 kHz and the power density may be greater than 200 Watts/cubic-inch.

In general, another aspect features a method of converting power from an input source for delivery to a load, where the load may vary over a normal operating range, including providing a transformer, forming a resonant circuit including the transformer and having a characteristic resonant frequency and period, providing output circuitry connected to the transformer for delivering a rectified output voltage to the load, providing a first pair of primary switches connected in series and a second pair of primary switches connected in series, the first and second pairs connected to drive the resonant circuit, providing a switch controller to operate the first and second pair of primary switches out of phase in a series of converter operating cycles, and arranging the resonant circuit and primary switches symmetrically to reduce common-mode noise.

Implementations of the method may include one or more of the following features. The transformer may have first and second primary windings and the first pair and second pair of primary switches may drive the first and second primary windings out of phase. The first and second pair and the first and second primary windings may form two half-bridges driven out of phase. The primary switches may form a full-bridge circuit to drive the transformer, the transformer may have two primary windings, and the resonant circuit may have a resonant capacitor connected in series with and between the two primary windings. The primary switches may form a full-bridge circuit to drive the transformer, the resonant circuit may have first and second resonant capacitors, and the transformer may have a primary winding connected in series with and between the first and second resonant capacitors. The primary winding may include a plurality of series connected primary windings.

In general, another aspect features a method of converting power from an input source for delivery to a load, where the load may vary over a normal operating range. The method includes providing a transformer, forming a resonant circuit including the transformer and having a characteristic resonant frequency and period and having a Q less than 13, providing output circuitry connected to the transformer for delivering a rectified output voltage to the load, providing a primary switch connected to drive the resonant circuit, providing a switch controller to operate the primary switch in a series of converter operating cycles, and providing a conversion efficiency having a peak greater than 90% from source to load within the normal operating range.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a DC-DC power converter.

FIGS. 2A and 2B show block diagrams of prior art distributed power architectures.

FIGS. 3A and 3B show block diagrams of examples of the factorized power architecture.

FIG. 4A shows a perspective view of a printed circuit board assembly with a point-of-load DC-DC converter.

FIG. 4B shows a perspective view of a printed circuit board assembly with a point-of-load voltage transformation module.

FIG. 4C shows a perspective view of a printed circuit board assembly with a power regulation module and a point-of-load voltage transformation module.

FIG. 5A shows an end view of printed circuit board assemblies incorporating DC-DC converters mounted side-by-side.

FIG. 5B shows an end view of printed circuit board assemblies incorporating point-of-load voltage transformation modules mounted side-by-side.

FIG. 6 shows a block diagram of another example of the factorized power architecture.

FIG. 7 shows a block diagram of another example of the factorized power architecture.

FIGS. 8A through 8C show block diagrams of multiple-output power regulators for use in the factorized power architecture.

FIG. 9 shows a schematic of a sine amplitude topology for use in a voltage transformation module.

FIGS. 10A through 10H show waveforms for the topology of FIG. 9.

FIG. 11 shows a MOSFET equivalent circuit model.

FIG. 12 shows a schematic of an alternate sine amplitude converter topology for use in a voltage transformation module.

FIG. 13 shows a schematic of an alternate sine amplitude converter topology for use in a voltage transformation module.

FIG. 14 shows a schematic of an alternate sine amplitude converter topology for use in a voltage transformation module.

FIG. 15A shows a schematic of circuitry using a single secondary winding with full-wave bridge-rectification for use with a sine amplitude topology.

FIGS. 15B and 15C show alternate embodiments of output rectification circuitry with synchronous rectifiers for use in a sine amplitude converter topology.

FIG. 16 shows a block diagram of a power regulator for use with an AC input source.

FIG. 17 shows a block diagram of a power regulator for use with a DC input source.

FIG. 18 is a block diagram of remote feedback by way of the Power Regulator within the factorized power architecture.

FIG. 19 is a block diagram of remote feedback by way of a PRM within the factorized power architecture.

FIG. 20 is a block diagram of remote feedback by way of a power regulator or PRM from a point-of-load feedback controller.

FIG. 21 shows a partial schematic of alternate circuitry for a sine amplitude converter topology for use in a dual output voltage transformation module.

FIG. 22 shows a schematic of an automatic switch controller.

FIGS. 23A 23D show waveforms for the automatic switch controller of FIG. 22.

FIG. 24 shows a schematic of circuitry for generating a control signal V.sub.s for use with a switch controller in a voltage transformation module.

FIG. 25 shows a schematic of circuitry for current limiting in a sine amplitude converter topology.

FIG. 26 shows a schematic of an equivalent circuit of a sine amplitude converter topology during clamping.

FIGS. 27A and 27B show waveforms for the sine amplitude converter topology of FIG. 25 during clamping.

FIG. 28 shows a schematic of damping circuitry for use in a sine amplitude converter topology.

FIG. 29A shows a block diagram of a buck regulated sine amplitude DC-DC converter.

FIG. 29B shows a block diagram of a boost regulated sine amplitude DC-DC converter.

FIG. 29C shows a block diagram of a buck-boost regulated sine amplitude DC-DC converter.

FIG. 30 shows a block diagram of a bootstrap regulated sine amplitude DC-DC converter.

FIG. 31 is a block diagram of a power-sharing array of VTMs with optional remote feedback to a power regulator or PRM from a point-of-load feedback controller.

FIG. 32 shows a cross section of a transformer structure.

FIG. 33 shows a schematic block diagram of a transformer using the structure of FIG. 32.

FIGS. 34A and 34B show top and bottom perspective views of a sine amplitude converter using the transformer structure of FIG. 32.

FIG. 35 shows a schematic of a SAC converter 302 including a low-loss, common-source gate-drive circuit.

FIGS. 36A 36C show waveforms for the converter of FIG. 35.

FIGS. 37A 37H show waveforms for the converter of FIG. 35.

FIG. 38 shows an equivalent circuit of a switch for use in the gate drive circuit of the converter of FIG. 35.

FIGS. 39A and 39B show alternative embodiments of switches using discrete components.

FIGS. 40A and 40B show perspective views of an embodiment of the converter of FIG. 35.

FIG. 41 shows a schematic of portion of a converter of the kind illustrated in FIGS. 9 and 35 with inter-winding parasitic capacitances.

FIG. 42 shows a schematic of an alternative embodiment of a portion of the converter for reducing the effects of the inter-winding parasitic capacitances.

FIG. 43 shows a partial schematic of the low-loss, common-source gate-drive circuitry of the converter of FIG. 35.

FIG. 44 shows a schematic of an alternative low-loss, common-source gate-drive circuit.

FIG. 45 shows a schematic of another alternative low-loss, common-source gate-drive circuit.

FIGS. 46A, 46B, 46C show schematics of alternative full-bridge embodiments of a portion of the converter for reducing the effects of inter-winding parasitic capacitances.

FIGS. 47A and 47B show, respectively, a schematic and waveform for an isolated gate driver circuit having a bipolar gate control waveform.

FIGS. 48A, 48B and 48C show, respectively, a schematic and waveforms for an isolated gate driver circuit according to the invention having a unipolar gate control waveform.

FIG. 49 shows another embodiment of the gate driver circuit of FIG. 48A for use with complementary MOSFET switches.

FIG. 50 shows another embodiment of the gate driver circuit of FIG. 49.

FIG. 51 shows a partial schematic of a SAC comprising output voltage regulation circuitry according to the invention.

FIG. 52 shows a partial schematic of a SAC comprising current limit circuitry according to the invention.

FIG. 53 shows an integrated power MOSFET.

FIG. 54 shows a gate driver of the kind shown in FIG. 49 using integrated power MOSFET devices of the kind shown in FIG. 53.

FIGS. 55A and 55B show a DC-DC converter.

FIG. 56 shows a switching power converter feeding a load.

FIGS. 57A 57D show waveforms for the circuit of FIG. 56.

FIG. 58 shows an FPA adapted to supply a microprocessor load.

FIGS. 59A, 59B, and 59C show circuit models of a bi-directional VTM.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A system 20 using the prior art distributed power architecture is shown in FIG. 2A. In the system, a front-end power processor 22 accepts power from an input source 24 and converts it into a bus voltage, V.sub.bus, which is distributed over a distance via a distribution bus 26 to a number of separate electronic circuit subassembly PCBs 28a, 28b, 28c . . . 28n, each of which incorporates one or more DC-DC converters, e.g., DC-DC converters 30a . . . 30i. The bus voltage, V.sub.bus, is delivered to the inputs of the DC-DC converters 30a . . . 30i and each DC-DC converter delivers regulated output voltages (e.g., voltages V.sub.1 to V.sub.7) for use by circuitry on the subassembly (not shown). Given that DC-DC converters provide a regulation function which enables them to operate over a range of input voltages, the voltage V.sub.bus will typically be an unregulated voltage or one which is regulated, but whose value does not control the output voltages (i.e., voltages V.sub.1 to V.sub.7) required by the system.

Another prior art DPA system is shown in FIG. 2B. In the system, an isolated front-end power processor 29 accepts power from an input source 24 and converts it into a bus voltage, V.sub.bus, which is distributed over a distance via a distribution bus 26 to a number of separate electronic circuit subassembly PCBs 25a, 25b . . . 25n, each of which incorporates one or more non-isolated switching regulators, e.g., switching regulators 31a . . . 31e. The bus voltage, V.sub.bus, is delivered to the inputs of the switching regulators 31a . . . 31e and each switching regulator delivers a regulated output voltage (e.g., voltages V.sub.1 to V.sub.3) for use by circuitry on the subassembly (not shown). In such a system, the non-isolated switching regulators are sometimes referred to as VRMs ("Voltage Regulator Modules") and one such VRM may be dedicated to power a single integrated circuit device. Given that switching regulators, or VRMs, provide a regulation function which enables them to operate over a range of input voltages, the voltage V.sub.bus will typically be an unregulated voltage or one which is regulated, but whose value does not control the output voltages (i.e., voltages V.sub.1 to V.sub.3) required by the system.

In cases in which the input source is an AC utility source, the front-end power processor 22 or the isolated power processor 29 will comprise rectification circuitry for converting the bipolar AC input voltage and current into unipolar form and may also comprise power-factor-correcting circuitry (neither of which are shown in the Figures).

Compared to the CPA architecture, the benefits of the DPA architecture of FIGS. 2A and 2B include distribution bus simplicity; flexibility in providing many different load voltages without modifying the underlying power distribution scheme or bus voltage V.sub.bus (i.e., by simply providing DC-DC converters with the appropriate output voltages); and minimization of interactions between regulated output voltages owing to variations in loads, bus voltage, distribution bus impedance and related factors.

There are, however, drawbacks to the DPA architecture. In the system of FIG. 2A, for example, incorporation of isolated DC-DC converters onto subassemblies uses up valuable board space; the height of the converters above the subassembly PCB sets a lower limit on spacing between subassemblies and interferes with the flow of cooling air over nearby components; and the DC-DC converters themselves dissipate heat which affects the temperature of nearby components and which must be removed from the region of the subassemblies. Furthermore, if a single DC-DC converter cannot provide adequate power or fault-tolerance for a particular output voltage, multiple DC-DC converters will need to be paralleled, creating additional complexity owing to the need to connect remote sense leads from each paralleled converter to a single, common, point and the need for additional circuitry within each paralleled converter to force power sharing among the units.

These drawbacks are compounded by trends toward higher circuit and systems densities and toward lower system voltages (e.g., to 2V, 1V and below) and the attendant relatively poorer efficiency, and higher dissipation, of the DC-DC converters needed to supply them. While the VRMs of FIG. 2B may have higher power density and efficiency than DC-DC converters, they can create ground-loop problems, owing to their lack of isolation, and they have limited voltage step-down capability (e.g., it is difficult to efficiently generate 1 Volt using a non-isolated VRM when operating from a 48 Volt bus). In either case, a significant compromise in point-of-load power density and efficiency results from the DPA system requirement that DC-DC converters and switching regulators be capable of handling arbitrary voltage transformation ratios and provide regulation over a wide range of input voltages. This architectural requirement forces imbalances in the duty cycles (as defined below) of switching elements and reduced transformer utilization in single stage DC-DC converters, limiting their power density and efficiency.

A system 36 using a new power distribution architecture, called "Factorized Power Architecture" ("FPA"), is shown in FIG. 3A. In the system 36, a front-end power regulator 38 at a first location accepts power from an input source 46 and converts it into a controlled bus voltage at its output, V.sub.f, which is distributed over a distance via a "factorized" distribution bus 40 to a remotely located Voltage Transformation Module ("VTM") 44. The VTM comprises an isolation transformer (not shown) and transforms the voltage V.sub.f into a voltage V.sub.out, for delivery to a load 41. Unlike the DC-DC converters 30 in the DPA of FIG. 2, a VTM in the FPA system may be designed to operate over a tailored, narrow range of input voltages enabling numerous efficiency and power density enhancing features to be deployed. In the preferred VTM architecture discussed in greater detail below, primary and secondary switching elements may be coupled to the primary and secondary windings of the VTM transformer to perform single stage power processing. The VTM may use balanced switching duty cycles in which each primary switching element of a complementary pair is on for essentially the same amount of time as its complement and each secondary switching element of a complementary pair is ON for essentially the same amount of time as its complement. Additionally, the VTM may operate at greater than 90 percent power conversion duty cycle (as defined below) which is indicative of the fraction of each converter operating cycle during which switches in the converter are enabled (as defined below) and power is being transferred from a primary to a secondary of the VTM transformer. The combination of balanced duty cycles and high power conversion duty cycles, coupled with a short converter operating period, may provide higher power conversion density, efficiency and ease of input/output filtering.

The VTM delivers a DC output voltage, V.sub.out, which is a fixed fraction of the voltage, V.sub.in, (nominally V.sub.f) delivered to its input. The voltage transformation ratio or voltage gain of the VTM (which may be defined as the ratio, K=V.sub.out/V.sub.in, of its output voltage to its input voltage at a load current) is fixed by design, e.g. by the VTM converter topology, its timing architecture and the turns ratio of the transformer included within it. In certain practical implementations without a feedback loop, using non-idealized components, the effective output resistance of the VTM will cause some droop in output voltage as a function of load current as discussed further below. In a typical FPA application, the VTM 44 is placed on a subassembly 42, so that it is close within the subassembly to the load 41 which it powers, and the voltage V.sub.out is lower than the voltage V.sub.f so that power loss and voltage drop in the factorized bus 40 are minimized.

Owing to their fixed gain and effective output


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