U.S. patent application number 11/748792 was filed with the patent office on 2008-02-28 for power delivery control and balancing between multiple loads.
This patent application is currently assigned to HUETTINGER ELEKTRONIK GMBH + CO. KG. Invention is credited to Dieter Meier, Alfred Trusch, Peter Wiedemuth, Gerhard Zaehringer.
Application Number | 20080048498 11/748792 |
Document ID | / |
Family ID | 32747881 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080048498 |
Kind Code |
A1 |
Wiedemuth; Peter ; et
al. |
February 28, 2008 |
Power Delivery Control and Balancing Between Multiple Loads
Abstract
A plasma process machine includes at least two electrodes
disposed in a processing chamber and in contact with targets, an
alternating current source connected to supply power to the
electrodes, and a power delivery controller adapted to control
power delivered by the alternating current source to the
electrodes. The power delivery controller is configured to
determine a control value from a comparison between actual power
delivery as detected by a detector and a desired power delivery,
and to adjust power delivery based on the control.
Inventors: |
Wiedemuth; Peter;
(Herbolzheim, DE) ; Trusch; Alfred; (Breisach,
DE) ; Meier; Dieter; (Breisach, DE) ;
Zaehringer; Gerhard; (Freiburg, DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
HUETTINGER ELEKTRONIK GMBH + CO.
KG
Freiburg
DE
|
Family ID: |
32747881 |
Appl. No.: |
11/748792 |
Filed: |
May 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11203433 |
Aug 15, 2005 |
|
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11748792 |
May 15, 2007 |
|
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PCT/EP04/01293 |
Feb 12, 2004 |
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11203433 |
Aug 15, 2005 |
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Current U.S.
Class: |
307/31 |
Current CPC
Class: |
G05F 1/12 20130101; H01J
37/32431 20130101 |
Class at
Publication: |
307/031 |
International
Class: |
H02J 3/00 20060101
H02J003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2003 |
DE |
DE 103 06 347.1 |
Claims
1. (canceled)
2. A power supply comprising: an alternating current source; and a
power delivery control unit adapted to control the power delivered
by the alternating current source into at least two electrical
loads, the power delivery control unit comprising: a control member
that determines a control value from a comparison between actual
power delivery as detected by a detector and a desired power
delivery; and an adjusting member adapted to be inserted between
the alternating current source and at least one load; and an arc
management circuit that generates a control value to which the
adjusting member is responsive.
3. The power supply of claim 2, wherein the loads comprise
electrodes of a plasma processing device.
4. The power supply of claim 2, wherein the alternating current
source has a bridge circuit.
5. The power supply of claim 2, wherein the alternating current
source comprises an output transformer at the output of which an
alternating voltage is present, which is galvanically isolated from
ground with respect to power and consists only of an alternating
portion.
6. The power supply of claim 5, wherein the output transformer has
a resonant circuit on its primary side.
7. The power supply of claim 2, wherein the adjusting member
comprises at least one controllable DC voltage source.
8. The power supply of claim 2, wherein the adjusting member
comprises at least one controllable ohmic load.
9. The power supply of claim 8, wherein the adjusting member
comprises two controllable ohmic loads, separated via
oppositely-directed diodes.
10. The power supply of claim 8, wherein the ohmic loads comprise
controllable semi-conductors.
11. The power supply of claim 2, wherein the adjusting member
comprises two impedances that are inductively controllable and
separated via oppositely-directed diodes.
12. The power supply of claim 2, wherein the adjusting member
comprises a transformer whose primary winding is adapted to be
inserted in a connecting lead between the alternating current
source and one of the loads, and at whose secondary winding is
provided a switching device controlled by driving signals generated
from the control value by a driving circuit.
13. The power supply of claim 2, wherein the detector comprises a
measuring device for power-dependent values.
14. The power supply of claim 2, wherein the alternating current
source comprises a resonant circuit disposed downstream of the
bridge circuit.
15. The power supply of claim 2, wherein the alternating current
source comprises an additional output transformer.
16. The power supply of claim 15, wherein the output transformer is
an air transformer.
17. The power supply of claim 2, wherein the alternating current
source generates an alternating current of a frequency of between
about 1 kHz and 1 MHz.
18. The power supply of claim 17, wherein the frequency is between
about 50 kHz and 500 kHz.
Description
CLAIM FOR PRIORITY
[0001] The present application is a continuation of U.S.
application Ser. No. 11/203,433, filed Aug. 15, 2005, which is a
continuation of International Application No. PCT/EP2004/001293,
filed Feb. 12, 2004, which claims priority from German Application
No. 103 06 347.1, filed Feb. 15, 2003. The contents of the prior
applications are incorporated herein in their entirety by
reference.
TECHNICAL FIELD
[0002] The invention relates to the delivery of power provided by
an alternating current source to multiple loads.
BACKGROUND
[0003] In a plasma process, electrical loads designed as electrodes
are positioned in a plasma chamber. To stimulate the plasma
process, the electrodes are connected to the alternating voltage of
a power supply. The electrodes are in contact with so-called
targets. The targets consist of a base material on the electrodes
e.g., a coating. In a plasma coating process of this type, this
base material can be removed from the targets. The targets of such
arrangements are usually similar, i.e., they consist of the same
material, have substantially the same size and the same
construction and are therefore usually supplied with substantially
the same power. In the plasma process, the targets are ablated at
substantially the same speed. However, slight differences cannot be
eliminated. The targets may initially be asymmetrical or become
asymmetrical because of ablation during the plasma process. These
asymmetrics can cause differences in the impedances and burning
voltages of the targets. These differences result in different
power delivery and different wear periods. This effect can cause
one target, which has been worn to a larger extent, to consume more
power than other targets, and therefore burn even more quickly. The
final result of this effect is that one target is completely burnt
while others still have sufficient material. This behavior is
highly undesired. Although this problem has been known for a long
time, there has been no remedy so far.
[0004] It is therefore desirable to provide a method for
influencing the power delivery into the electrical loads, and an
associated device.
[0005] Plasma processes do not always run completely continuously.
Impurities, temporally and locally limited charging or other
instabilities in the chamber can produce spark-overs in the plasma,
so-called arcs, at irregular intervals. These arcs can entail
undesired consequences in many cases, such as, e.g., rapid current
increase and voltage drops. This can disturb the plasma process,
with the consequence of undesired result for target and plasma
process. For this purpose, so-called arc management circuits are
provided for plasma process power supplies. They stop undesired
power delivery in case of such an arc. Upon detection of such an
arc, the current supply is generally switched off as quickly as
possible or after a defined time period. It is thereby often
important to interrupt the power delivery into the plasma process
as quickly as possible to protect the power supply, the targets and
the objects to be coated.
SUMMARY
[0006] Various aspects of the invention feature a method for
delivering power from an alternating current source to at least two
electrical loads by detecting the actual power delivery to the
loads, and then comparing the detected actual power delivery with a
given desired power delivery, and adjusting the power delivery when
the detected and desired power deliveries differ.
[0007] The adjustment is preferably effected by delivering or
removing power from/to the alternating current source and at least
one of the loads. This process ensures that the power delivery is
based on a measurement of the delivered actual power. The disclosed
method permits control of the power delivered to the electrodes
independently of the type of alternating current source in a plasma
process such that it corresponds to a predetermined power delivery.
Adjustment may alternatively be effected by changing the control of
the alternating current source in such a manner that the actual
power delivery equals the desired power delivery.
[0008] In a plasma process, each connection of the alternating
voltage source can be connected to at least one electrode. In this
case, the electrodes are the electrical loads to which the power is
delivered.
[0009] By "alternating current source" we mean a power source
having an alternating voltage and an alternating current at its
output. It many be a poser source with current source or voltage
source characteristics or other characteristics, and the voltage
and current may be of any form and even contain a DC portion. In
particular, we mean to include alternating current sources that
provide at their outputs only AC portions and no DC portions, due
to galvanic isolation. Control of the alternating current source
can be utilized also for such alternating current sources without
DC portions to adjust the actual power delivery to the desired
power delivery.
[0010] The predetermined desired power delivery may thereby be
symmetric or asymmetric. Depending on whether a symmetric or
asymmetric desired power delivery is predetermined, the power
delivered by the alternating current source is preferably
controlled in such a manner that the actual power delivery to the
loads corresponds to the desired power delivery. To ensure that the
targets have identical wear times, the predetermined desired power
delivery makes sense, e.g., to counteract already effected
irregular wear or to ablate targets of different materials or
structures in the desired manner.
[0011] In a particular embodiment, the actual power delivery is
detected by determining power-dependent values for each load, which
may be effected in the most different ways. A power-dependent value
could, e.g., be the temperature at an electrode or the radiation
emitted by the plasma at an electrode. To determine the
power-dependent values, the current and voltage at the loads are
usually measured.
[0012] In a plasma process comprising two electrodes each being
connected to a connection of the alternating current source, the
average effective power to each electrode corresponds substantially
to the current in the direction of the electrode, multiplied by the
voltage measured between ground and the electrode.
[0013] In an advantageous method variant, the frequency of the
alternating current source is between 1 kHz and 1 Mhz, in
particular, between 50 kHz and 500 kHz.
[0014] Another aspect of the invention features a power delivery
control unit including a control member and an adjusting member.
The control member determines a control value from a comparison
between the actual power delivery detected by a detecting device
and a given desired power delivery. The adjusting member can be
looped in between the alternating current source and at least one
electrical load and adjust the power delivery on the basis of the
control value. "Looping in" thereby means that the adjusting member
is connected in series with the alternating current source. Bu
inserting the adjusting member into a connecting line between the
alternating current source and the electrical load, this device
offers versatile application and can also be retrofitted to
existing systems. Several connecting lines can be combined into one
multi-conductor connecting line.
[0015] Various aspects of the invention can advantageously provide
the detection of the actual power delivery to the loads, thereby
permitting control of the power delivery. The loads may each be
designed as at least one electrode in a plasma process. For an
alternating current source with two connections, each electrode may
be connected to a respective connection of the alternating current
source. It is also possible to connect several electrodes to one
connection. The power delivery control unit can thereby influence
the wear times of the individual targets connected to the
electrodes.
[0016] The adjusting member may include a controllable DC voltage
source. This is one possibility of influencing the power delivery
to the electrodes, which can be realized in a particularly simple
manners. Both positive and negative voltages may be set at the
direct voltage source, depending on which load is to be delivered
with power. The direct voltage source may have any design, e.g.,
even two direct voltage sources which are connected in opposite
polarity and can each individually output only a positive voltage,
and are alternately connected depending on the voltage polarity
required.
[0017] In another embodiment, the adjusting member includes at
least one controllable ohmic load. The power delivery is thereby
influenced by removing power from at least one of the loads. If, in
a plasma process with one electrode being connected to each
connection of the alternating current source, the power delivery
into the electrode is determined by the current in the direction of
the electrode and the voltage of the electrode to ground, the power
removal can be controlled by one single, looped-in ohmic load in
that the ohmic load is controlled in time with the frequency of the
alternating current source to always have a higher ohmic value in
one current direction than in the other current direction. This
requires complex and precise driving of the ohmic load. In one
configuration the driving of ohmic loads is less complex, wherein
two ohmic loads are looped-in through diodes which are connected in
opposite orientation, such that each ohmic load is associated with
a current direction.
[0018] In some configurations, the ohmic loads include controllable
semi-conductors, such as so-called insulated gate bipolar
transistors (IGBTs). With corresponding switching, these elements
can generate ohmic loads in a very simple manner, which are
controlled by the control value via a driving circuit
embodiment.
[0019] In another embodiment, the adjusting member includes two
impedances which can be inductively controlled and are separated
via oppositely-oriented diodes. They, too, are controlled to remove
power to adjust the actual power delivery to the desired power
delivery.
[0020] In yet another embodiment, the adjusting member includes a
transformer whose primary winding can be looped-in in a connecting
line between alternating current source and load, and at whose
secondary winding is provided a switching device with
semi-conductor components which can be adjusted by the control
value. These are also controlled in such a manner that power is
removed to adjust the actual power delivery to the desired power
delivery.
[0021] Further embodiments of the adjusting member for delivering
and removing power are feasible, as well as a combination of the
above-mentioned embodiments for, e.g., delivering and also removing
power.
[0022] In a further embodiment, the detecting device is designed as
a measuring device for power-dependent values, which can be
effected in different ways. One possible measuring device consists
of means for measuring the voltage at each electrical load, such as
the voltage from load to ground, a further means for measuring the
current into the loads, and a multiplying member that determines
the power for each load from the measured voltage and the measured
current. There are other ways to determine a power-dependent
values, such as by providing a temperature measuring device on each
load.
[0023] Another aspect of the invention features a power supply
comprising a power delivery control unit and alternating current
source as described above. When the alternating current source and
power delivery control unit are combined in one unit, the same
current and voltage measuring means can be utilized to control the
alternating current source and also for the power delivery
unit.
[0024] In one embodiment, the alternating current source includes
an output transformer at the output of which an alternating voltage
is present that is galvanically isolated from ground with regard to
power, has only an AC portion and no DC portion, and is connected
to the loads via connecting leads. The arrangement including the
output transformer is advantageous in that the alternating voltages
can be adjusted at the output of the power supply through changing
the winding number of the output transformer to the requirements of
the loads. Identical power supplies can be provided for different
application ranges except for the output transformers. The output
transformers can have a very similar design. "Galvanically isolated
from ground with regard to power" means that the ground of the
alternating current source and the alternating voltage have no
galvanic connection outside of the plasma chamber via which a
considerable amount of the power flows. A "galvanic isolation from
ground with regard to power" is obtained even if a high-ohmic
connection between alternating voltage at the output of the power
supply to ground is provided, e.g., for voltage measurement or
discharge of charges from the electrodes, or if there is a
conducting connection between electrodes and ground within the
plasma chamber. Various aspects of the invention offer now the
possibility to control the power delivery to the loads even for
existing power supplies that previously provided no possibility to
divide the power onto the electrodes.
[0025] In a further development, the power supply has an
oscillating circuit on the primary side of the output transformer,
which is usually operated close to resonance, a so-called resonant
circuit. Alternating current sources of this type have an excellent
efficiency. Primary inductances from the output transformer can be
utilized as inductances for this resonant circuit.
[0026] In one embodiment, the power supply includes an arc
management circuit that generates a further control value that acts
on the adjusting member. The arc management circuit is preferable
connected to the adjusting member, and the power is always removed
via the adjusting member in case of an arc if the management
circuit stops the power delivery to the electrodes. The control
value generated by the arc management circuit has priority to the
control value generated by the control member.
[0027] Another aspect of the invention features a power supply with
a control member determining a control value through a comparison
of the actual power delivery detected by a detecting device and a
given desired power delivery, and an alternating current source
driven by a control means. The control means drives the alternating
current source on the basis of the control value transmitted by the
control member in such a manner that the properties of the
alternating current are changed such that the actual power delivery
into the loads is equal to the desired power delivery.
[0028] The alternating current source may be, e.g., a bridge
circuit with a downstream resonant circuit. The bridge circuit is
supplied with a DC current. Symmetric driving of the bridge circuit
produces a symmetric alternating current and a symmetric AC voltage
which can be transmitted, such as via an output transformer. The
output transformer may be part of a resonant circuit.
[0029] If the bridge circuit is asymmetrically driven, the
switching elements of the bridge circuit are driven with an
asymmetric pulse-duty factor which can reduce, e.g., the duration
of the positive half-wave and extend the duration of the negative
half-wave of the AC voltage. If the amplitude of the shortened
half-wave is correspondingly larger than that of the extended
half-wave, a signal without DC portions is obtained which can be
transmitted to the output of the alternating current source via the
output transformer. An asymmetrical signal of this type generates
asymmetric load distribution to the loads (targets) as shown
through measurements on plasma processes. This asymmetry of the
load distribution can be controlled through asymmetric control of
the alternating current source. The actual power delivery can
thereby be adjusted to the desired power delivery for symmetrical
and asymmetrical desired power deliveries.
[0030] Asymmetrical driving of this type generates large currents
in the output transformer which can lead to saturation of the core
material in conventional transformers with iron or ferrite cores,
as described in U.S. Pat. No. 6,532,161, for example. An air
transformer has no iron or ferrite core and therefore cannot
saturate. For this reason, an air transformer is preferably
used.
[0031] Another aspect of the invention features a plasma process
machine having at least two electrodes disposed in a processing
chamber and in contact with targets; an alternating current source
connected to supply power to the electrodes; and a power delivery
controller adapted to control power delivered by the alternating
current source to the electrodes. The power delivery controller is
configured to determine a control value from a comparison between
actual power delivery as detected by a detector and a desired power
delivery, and to adjust power delivery based on the control
value.
[0032] Further features and advantages of the invention can be
extracted from the following description of embodiments of the
invention, the figures of the drawing showing details which are
essential to the invention and from the claims. The individual
features can be realized either individually or collectively in
arbitrary combination in a variant of the invention.
DESCRIPTION OF DRAWINGS
[0033] FIG. 1 is a schematic diagram of a power delivery control
unit, an alternating current source, and a plasma chamber.
[0034] FIG. 2 is a schematic diagram of a power supply that
combines an alternating current source, a power delivery control
unit and an arc management circuit, and a plasma chamber.
[0035] FIG. 3 is a schematic diagram of an alternating current
source with an output transformer and a resonant circuit.
[0036] FIG. 4 is a schematic diagram of an adjusting member with
controlled direct voltage sources.
[0037] FIG. 5 is a schematic diagram of an adjusting member with
two ohmic loads.
[0038] FIG. 6 is a schematic diagram of an adjusting member with
two controllable impedances.
[0039] FIG. 7 is a schematic diagram of an adjusting member with a
transformer that can be short-circuited on the secondary side.
[0040] FIG. 8 is a schematic diagram of an adjusting member with a
transformer that can also be short-circuited on the secondary
side.
[0041] FIG. 9 is a schematic diagram of a power supply with an
alternating current source that can be driven.
[0042] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0043] FIG. 1 shows a schematic representation of a power delivery
control unit 1 together with an alternating current source 2 and a
plasma chamber 3. The alternating current source 2 is connected via
two connecting leads 10a and 10b to two electrical loads, which are
designed as electrodes 4a and 4b and are positioned in the plasma
chamber 3. The power delivery control unit 1 includes three
components: an adjusting member 5, a control member 6, and a
measured value detecting member 7. The adjusting member 5 is
looped-in in the connecting lead 10b. It receives a control value
from the control member 6 via the connection 11. The voltage at the
nodes 9a and 9b on the connecting leads 10a and 10b is measured and
processed into one voltage signal each. An ammeter 8 measures the
current in the connecting lead 10b and processes it into a current
measuring signal. The measured value detecting member 7, the
ammeter 8, and the voltage measurement on the nodes 9a and 9b
together form a detecting device for detecting the actual power
delivery into the loads. The measured value detecting member 7
detects one power signal each from these measured signals, which
corresponds to the effective power delivered to the electrodes 4a
and 4b. The power in the electrode 4a consists substantially of the
voltage measured on the electrode 4a or on the node 9a, multiplied
by the current in the direction of this electrode. The power in the
electrode 4b also consists substantially of the voltage measured on
the electrode 4b or on the node 9b, multiplied by the current in
the direction of this electrode. The current measured by the
ammeter 8 can be divided into a positive and a negative portion.
The positive portion of the current, multiplied by the voltage
measured on the node 9a, shows the effective power delivered to the
electrode 4a. The negative portion of the current, multiplied by
the voltage measured on the node 9b, gives the effective power
delivered to the electrode 4b. One multiplying member therefore
calculates one power signal for each electrode from the current
measuring signal portions and the voltage measuring signals. The
actual power delivery into the electrodes is determined from the
two power signals. It is transmitted to the control member 6 via a
connection 12. The control member 6 compares the actual power
delivery with an internal desired power delivery. If it is
symmetrical, the control member 6 adjusts the control value such
that both electrodes are delivered with the same power. The
adjusting member 5 may deliver or remove power in any current
direction. This is explained in more detail below.
[0044] FIG. 2 shows a power supply 20 that includes the alternating
voltage source 1 and the power delivery control unit 1 in
accordance with FIG. 1, and an additional arc management circuit
23. The arc management circuit 23 determines the current with the
ammeter 21 and the voltage at the nodes 22a and 22b, thereby
permitting detection of an arc by the arc management circuit 23.
The arc management circuit 23 controls the alternating current
source 2 via the connection 25 and the adjusting member 5 via the
connection 24. In this manner, the remaining power can be removed
via the adjusting member 5 if the arc management circuit interrupts
the power delivery to the loads (e.g., electrodes 4a and 4b)l.
[0045] FIG. 3 shows a particular embodiment of an alternating
current source 2 that can be provided in the control unit 1 of the
power supply 20. The alternating current source 2 includes an
output transformer with a primary winding 31a and a secondary
winding 31b and an oscillating circuit capacitor 32. The
alternating voltage of such an alternating current source has no DC
portion at its outputs. The capacitance 32 and the primary
inductance of the transformer (31a and 31b) together produce an
oscillating circuit that is operated close to resonance. With such
an alternating current source, the output voltages and output
currents can be ideally adjusted to the requirements of the loads
by tuning the secondary winding 31b of the transformer. Thus,
different loads require only a different transformer, rather than a
completely new current supply. The resonant circuit ensures high
efficiency of the current supply.
[0046] FIGS. 4-7 show examples of the adjusting member 5 shown in
FIG. 1. The adjusting member 5 is looped-in in each case in the
connecting lead 10b between alternating current source 2 and plasma
chamber 3.
[0047] In FIG. 4, the adjusting member 40 is looped-in into the
connecting lead 10b at the connection 47 and 48 and receives the
control value via the connection 42, and converts it into a driving
signal 46 in a driving circuit embodiment 41 for two
oppositely-directed, adjustable direct current supplies 45a and
45b. A switch 43 is driven by a further driving signal 44 that is
also generated by the driving circuit embodiment 41. The switch 43
connects one of direct current supplies 45a and 45b having the
desired polarity to deliver power. It is also possible to provide a
direct current supply with advice for reversing the polarity or a
direct current supply with two output polarities instead of the two
switchable direct current supplies.
[0048] In FIG. 5 the adjusting member 50 is looped-in into the
connecting lead 10b at the connections 57 and 58. It receives the
control value via the connection 52, which it converts into driving
signals 54a and 54b for two insulated gate bipolar transistors
("IGBTs") 56a and 56b in a driving circuit embodiment 51. The IGBTs
are connected to oppositely-directed diodes 55a and 55b in such a
manner that always one IGBT 56a and 56b carries the current for one
direction. The IGBTs 56a and 56b are driven in such a manner that
they represent ohmic loads in the conducting direction, in this
manner permitting independent control of each current direction.
Since the power into respectively one of the two electrodes depends
directly on the current in the direction of this electrode,
independent control of the power in each electrode is possible.
[0049] In FIG. 6 the adjusting member 60 is looped-in into the
connecting lead 10b at connections 67 and 68. It receives the
control value via the connection 62 and converts it into driving
circuits 65 and 66 in a driving circuit embodiment 61 for two
inductively controllable impedance 64a and 64b which are connected
to oppositely-directed diodes 63a and 63b in such a manner that
always one impedance carries the current for one direction with the
consequence that a high direct current portion in the saturated
state and represent only a small resistance to the passing current.
The impedances 64a and 64b can be inductively pre-magnetized via
the circuits 65 and 66 such that they can be independently
desaturated in a controlled manner, thereby representing a higher
resistance to the passing current, permitting again separate
adjustment of the power delivery for each current direction.
[0050] In FIG. 7, the adjusting ember 70 is looped-in into the
connecting lead 10b at connections 77 and 78. It receives the
control value via the connection 72, which it converts into driving
signals 79a and 79b for two oppositely-directed IGBTs 73 and 74 in
a driving circuit embodiment 71. A transformer with a primary
winding 75a is connected between the connections 77 and 78. The
secondary winding 75b is short-circuited by the IGBTs 73, 74 in the
normal case. Depending on the current direction in which the power
is removed, either the IGBT 73 is brought into a high-ohmic state
via the driving signal 79a or the IGBT 74 is brought into a
high-ohmic state via the driving signal 79b. This permits again
separate adjustment of the power delivery for each current
direction.
[0051] In FIG. 8, the adjusting member 80 is looped-in into the
connecting lead 10b at the connections 87 and 88. It receives the
control value via the connection 82, which it converts into driving
signals 86a or 86b in a driving circuit 81 for two IGBTs 84a and
84b connected at a network node 89. A transformer with a primary
winding 85a is connected between the connections 87 and 88. The
secondary winding 85b is short-circuited in the normal case in a
similar manner as in FIG. 7. In this case, the current flows
additionally via the diodes 83a and 83b, which may be parasitic
diodes in the IGBTs 84a and 84b or external diodes. The IGBTs 84a
and 84b can be brought into a high-ohmic state individually and
independently of each other through the driving signals 86a and
86b, which permits separate adjustment of the power delivery for
each current direction.
[0052] FIG. 9 shows a power supply 20 that includes the alternating
current source 2 that is supplied with a direct current, a control
member 6 and a measured value detecting member 7. The control
member 6 is connected to a control means 90 that controls the
bridge circuit 91. A resonant circuit 92 is connected to the bridge
circuit 91, wherein the output transformer 31 represents part of
the resonant circuit 92. The power-dependent actual values detected
in the measured value detecting member 7, which is part of a
detecting device, are compared in the control member 6 with the
desired values. The control member 6 determines therefrom a control
value that is passed on to the control means 90. The control means
90 controls the switching on and off times, i.e., the pulse-duty
factor, of the individual switches of the bridge circuit 91 in such
a manner that the detected actual power values are identical to the
given desired values. The resonant circuit 92 forms the output
voltage of the bridge circuit 91 into a signal which is similar to
a sinusoidal shape, but which may be asymmetrical. No DC portions
are transmitted by the transformer 31. The power delivery into the
loads 4a and 4b may nevertheless be different and be adjusted
through driving of the switches of the bridge circuit 91 with a
certain pulse-duty factor predetermined by the control means. The
pulse-duty factor may be different and asymmetrical for each switch
or switch pair, i.e., the switching on and off times may have
different lengths. The actual power delivery into the loads can
thereby be adjusted to the predetermined desired power
delivery.
[0053] A number of implementations have been described.
Nevertheless, it will be understood that various modifications may
be made. Accordingly, other embodiments are within the scope of the
following claims.
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