Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-05-23
2004-02-24
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S048000
Reexamination Certificate
active
06697265
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to power conversion apparatus utilizing resonant dc converter topology for dc power supplies, and more particularly, to dc power supplies utilizing resonant dc converter topologies that provide a wide load range at full power for application to plasma processing.
2. Brief Description of the Prior Art
DC power supplies have found wide spread use in plasma processing applications such as plasma sputter deposition of thin films. It is advantageous if the power supply is able to deliver maximum power to the plasma over as wide a range of plasma load impedances as possible. U.S. Pat. No. 5,535,906 issued to Geoffrey N. Drummond assigned to the assignee of the instant application that teaches a multiphase L-C-C resonant power supply for plasma loads. A simplified schematic diagram of a converter following the teachings of U.S. Pat. No. 5,535,906 is shown in FIG.
6
. This type of power supply can typically deliver full-power over about a 4:1 range of load impedances, but the range of load impedances that may be presented by plasma loads at given power level may be much greater. Consequently, several models of a power supply may be required to accommodate the range of plasma load impedances. There has been a long-felt need for a power supply which can provide full power over a broad range of load impedances to consolidate the number of power supply models that are required to operate various plasma loads.
The full-power output impedance range of a power supply is primarily determined by losses in the components. The losses in a resonant power supply for a given output power level and a given dc supply voltage are inversely related to the power factor seen by the inverter switches. In
FIG. 6
, switches
96
,
98
,
100
,
103
,
104
and
106
represent electronic switches such as field-effect transistors (FETs). Each switch may also include diodes connected to prevent current from flowing in the body diodes of the FETs. The power factor seen by the inverter switches may be defined as the cosine of the phase angle between the fundamental component of the square-wave voltage produced by a pair of switches (e.g.
96
and
98
), and the fundamental component of the current flowing out of the node where the switches are connected to each other (e.g. the current through capacitor
108
.)
There is an optimal load resistance for which the power factor is closest to unity. The power factor is reduced as the load resistance varies from the optimal value. This effect is plotted in
FIG. 9
for an implementation of the prior-art power supply of
FIG. 6
, and also for embodiments of the present invention. Modifying a power supply circuit so that the range of load impedances for which the inverter power factor is relatively high is broadened increases the full-power impedance range of the power supply.
U.S. Pat. No. 5,874,788 issued to Thomas McCartney teaches the use of a rectifier circuit at input of ac-dc power supplies that can be switched between normal and voltage-doubling modes in order to broaden the range of ac mains voltages for which the power supply can properly operate. A pair of series-connected capacitors
76
and
78
are connected between dc output terminals
80
and
82
of a bridge rectifier consisting of diodes
66
,
68
,
70
and
72
, as illustrated in FIG.
3
. Switch
74
allows the circuit to be adapted to differing ac input voltages applied between ac input terminals
62
and
64
. When switch
74
is open, the dc voltage between output terminals
80
and
82
is approximately equal to the amplitude (peak value) of the ac mains voltage. Closing switch
74
approximately doubles the dc voltage between output terminals
80
and
82
. Switch
74
is closed for a 120 volt ac input voltage and open for 240 volts ac. Consequently, the voltage between the dc output terminals remains relatively constant for both 120 volt and 240 volt ac mains voltages. The values of capacitors
76
and
78
are selected to be large enough so that the voltage-doubling function is achieved over the intended range of load resistances.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a resonant dc power supply that has a wide output impedance range. It is also an object of this invention to provide a wide range dc power supply that utilizes passive networks with a minimum number of parts and has low cost. In furtherance of these objects, there is provided a novel dc power supply design that utilizes a capacitive network that modifies the output range of conventional converter topologies wherein load impedance, converter frequency and output interactions provide high inverter power factors and low circuit losses over load impedance ranges as high as 64:1. Selectively doubling the output voltage electronically with capacitors for high impedance loads or halving it electronically for low impedance loads with an inductive choke can extend the full power load impedance range of a power supply as taught herein.
Both single-phase and multiphase circuits are taught that place capacitors in parallel with rectifying diodes wherein the capacitors have little effect for low values of load resistance.
REFERENCES:
patent: 3911324 (1975-10-01), Bishop
patent: 4555751 (1985-11-01), Koga et al.
patent: 4686619 (1987-08-01), Edwards
patent: 4831508 (1989-05-01), Hunter
patent: 4855890 (1989-08-01), Kammiller
patent: 5422804 (1995-06-01), Clark
patent: 5535906 (1996-07-01), Drummond
patent: 5874788 (1999-02-01), McCartney
patent: 6212083 (2001-04-01), Sakakibara
Drummond Geoffrey N.
Hesterman Bryce L.
Advanced Energy Industries Inc.
Hudson, Jr. Benjamin
Sterrett Jeffrey
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