Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2002-08-08
2004-09-07
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
C323S259000, C323S282000, C323S235000
Reexamination Certificate
active
06788033
ABSTRACT:
BACKGROUND
This description relates to buck-boost DC—DC switching power conversion, e.g., in converters for which the input operating voltage delivered to the converter may span a range of values extending below and above the magnitude of the DC voltage delivered at the output of the converter.
Electrical and electronic equipment and systems often require conversion of an input voltage to an output voltage, which may be higher or lower than or approximately the same as the input voltage. For example, in stationary or portable systems powered by a DC battery it is often necessary to maintain constancy of output voltages independently of the state of charge and voltage of the battery. As another example, in systems utilizing the new power distribution architecture described in Vinciarelli, U.S. patent application Ser. No. 10/006481, “Factorized Power Architecture with Point of Load Sine Amplitude Converters”, filed Jan. 31, 2002 (the '481 Application) and incorporated in its entirety by reference, it may be necessary to pre-regulate the “factorized bus voltage” delivered by a pre-regulator module (or “PRM”, as that term is used in the '481 application) to point-of-load voltage transformation modules (or “VTMs”, as that term is defined in the '481 application) by stepping up or down voltage from an input source. As another example, in systems powered from an AC voltage source it is often necessary to draw power from the AC source with near unity power factor while delivering power at a DC output voltage which may be higher or lower than the instantaneous voltage of the AC line. In general, it would be desirable to flexibly achieve the appropriate step up or step down of a voltage with high conversion efficiency, high power density, and low noise.
Buck-boost converters are known in the art. The buck-boost converter
10
, shown in
FIG. 1A
, for example, is described in Severns and Bloom, “Modern DC-to-DC Switchmode Power Conversion Circuits,” 1985, ISBN 0-442-21396-4, pp. 156-157. In the converter of
FIG. 1A
the switches
2
,
3
are operated synchronously: switch
2
is in position “A” when switch
3
is in position “A” and vice versa. Energy delivered from the input source
6
is stored in inductor
4
when switch
2
and
3
are in the “A” position and energy is delivered from the inductor to the load
5
when switch
2
and
3
are in the “B” position. As also explained in Severns and Bloom, ibid., pp. 157-158, the converter of
FIG. 1A
may be reduced to a single switch buck-boost converter
12
of
FIG. 1B
, in which the output voltage, Vo, has a polarity inversion relative to the input source.
In both cases, owing to substantial losses in the inductor and switching elements, the converter architectures of FIG.
1
A and
FIG. 1B
are inefficient relative to other architectures, such as a buck converter or a boost converter which are only capable of, respectively, step-down or step-up of an input voltage. In fact, it has been tempting to conclude that the ability to provide both step-down and step-up of voltage within the same converter comes at a price in terms of reduced efficiency and power density.
This expectation has not been altered by more recent developments. A buck-boost converter incorporating four switches is described in an October 2001 datasheet for the LTC3440 “Micropower Synchronous Buck-Boost DC/DC Converter” integrated circuit manufactured by Linear Technology Corporation, Milpitas, Calif., U.S.A. A simplified schematic of the converter circuit
14
is shown in FIG.
2
. In the Figure the converter operates in a continuous conduction (i.e., the current in the inductor
23
, I
L
is nonzero throughout the entire operating cycle). A switch controller
19
operates the four MOSFET switches
11
,
13
,
15
,
17
in one of three modes: (1) in a buck mode, with switch
15
always closed and switch
17
always open, when the magnitude, Vin, of the input voltage source
6
is within a range of values which are greater than the voltage, Vo, delivered to the load; (2) in a boost mode, with switch
11
always closed and switch
13
always open, when the magnitude, Vin, of the input voltage source is within a range of values which are less the voltage, Vo; and (3) in a buck-boost mode, with a first pair of switches,
11
and
13
, “phasing in” to achieve a minimum duty cycle for switch
13
, as a second pair of switches,
15
and
17
, “phases out” to reduce to zero the duty cycle of switch
17
, as the magnitude, Vin, of the input voltage source traverses a range of values which bracket the value Vo. As such, this “buck-boost” architecture merely bridges a transition from the boost architecture to the buck architecture, while incurring increased losses and an intermediate reduction of efficiency relative to boost and buck modes that it is bridging. Owing to continuous conduction in the inductor, in each of the three modes referenced above switching losses occur when certain switching elements are turned ON to carry current without the voltage across the switching element being reduced prior to turn ON. Even at light load, where continuous conduction cannot be maintained with a finite value of inductor
23
, a lossy damper circuit, comprising switch
16
and “anti-ring” resistor
18
, is included to dissipate energy stored in the parasitic capacitances of the inductor and the switches.
Clamp circuitry for preventing oscillatory noise in switching power converters by using a switch to trap energy in an inductive element and release it to reduce switching losses is described in Vinciarelli et al, U.S. patent application Ser. No. 09/834,750, “Loss and Noise Reduction in Power Converters”, Apr. 13, 2001 (the “'750 Application”), assigned to the same assignee as this application and incorporated in its entirety by reference.
SUMMARY
In general, in one aspect, the invention features apparatus to operate at a power level within a range of power levels that includes a rated maximum power level of the apparatus. The apparatus includes circuit elements to deliver power at an output voltage to a load from a source at an input voltage using an inductor selectively connected between the source and the load during a power conversion cycle. The inductor conducts a current having an average positive value during the power conversion cycle. A first switching device is interposed between the source and a first terminal of the inductor. A second switching device is interposed between a second terminal of the inductor and the load, and a switch controller to turn ON the first switching device during a time interval within the power conversion cycle during which the current is negative.
Implementations of the invention may include one or more of the following features. The input voltage is within a range of input voltages that is less than the output voltage. The input voltage is within a range of input voltages that is greater than the output voltage. The input voltage is within a range of input voltages that includes the output voltage. The first switching device is turned ON at a time when the voltage across the first switching device is less than the input voltage. The first switching device is turned ON at a time when the voltage across the first switching device is essentially zero. The apparatus of claim also includes a third switching device interposed between ground and the first terminal of the inductor, the switch controller controlling the opening and closing of the third switching device. The third switching device is turned ON at a time when the voltage across the third switching device is less than the input voltage. The second switching device comprises a rectifier. The second switching device is turned ON at a time when the voltage across the second switching device is less than the output voltage. The apparatus also includes a fourth switching device interposed between ground and the second terminal of the inductor, the switch controller controlling the opening and closing of the fourth switching device. The fourth switching device is turned ON at a tim
Fish & Richardson P.C.
Han Jessica
VLT, Inc.
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