U.S. patent application number 10/209034 was filed with the patent office on 2004-02-05 for ripple cancellation circuit for ultra-low-noise power supplies.
Invention is credited to Schutten, Michael Joseph, Steigerwald, Robert Louis.
Application Number | 20040022077 10/209034 |
Document ID | / |
Family ID | 31186948 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040022077 |
Kind Code |
A1 |
Steigerwald, Robert Louis ;
et al. |
February 5, 2004 |
RIPPLE CANCELLATION CIRCUIT FOR ULTRA-LOW-NOISE POWER SUPPLIES
Abstract
A low-ripple power supply includes a storage capacitor coupled
across load terminals, and an inductor connected to a source of
voltage including a varying or pulsatory component and a direct
component, for causing a flow of current to said capacitor through
the inductor. The varying component of the inductor current flowing
in the capacitor results in ripple across the load. A winding is
coupled to the inductor for generating a surrogate of the varying
inductor current. The surrogate current is added to the inductor
current to cancel or reduce the magnitude of the varying current
component. This cancellation effectively reduces the varying
current component flowing in the storage capacitor, which in turn
reduces the ripple appearing across the load terminals.
Inventors: |
Steigerwald, Robert Louis;
(Burnt Hills, NY) ; Schutten, Michael Joseph;
(Rotterdam, NY) |
Correspondence
Address: |
DUANE MORRIS LLP
100 COLLEGE ROAD WEST, SUITE 100
PRINCETON
NJ
08540-6604
US
|
Family ID: |
31186948 |
Appl. No.: |
10/209034 |
Filed: |
July 31, 2002 |
Current U.S.
Class: |
363/39 |
Current CPC
Class: |
H02J 1/02 20130101; H02M
3/337 20130101; H02M 1/14 20130101; H02M 3/33573 20210501; H02M
3/156 20130101 |
Class at
Publication: |
363/39 |
International
Class: |
H02J 001/02 |
Claims
What is claimed is:
1. A power supply, comprising: a pair of load terminals; a storage
capacitor coupled across said pair of load terminals; first
inductance means coupled to said storage capacitor to thereby form
a combined circuit; a source of voltage, which voltage includes a
direct voltage component and a time-varying voltage component, said
source of voltage being coupled to said combined circuit for
producing a flow of current therethrough, which flow of current
results in division of said direct voltage component and said
time-varying voltage component between at least said first
inductance means and said storage capacitor, whereby that portion
of said time-varying voltage component appearing across said first
inductance means tends to cause a time-varying current flow through
said first inductance means and said storage capacitor;
magnetically coupled inductive means responsive to said
time-varying voltage component appearing across said inductance
means, for generating a second time-varying current component in
response thereto, which second time-varying current component is
similar to said-time-varying current flow through said first
inductance means; and combining means coupled to said combined
circuit and to said magnetically coupled inductive means, for
combining said second time-varying current component with at least
said time-varying current flow in such a manner as to tend to
oppose said time-varying current flow.
2. A power supply according to claim 1, wherein said source of
voltage includes a switch which recurrently applies a direct
voltage to said combined circuit, and applies a reference potential
across said combined circuit during those intervals in which said
direct voltage is not applied, whereby said time-varying component
is a rectangular wave.
3. A power supply according to claim 1, wherein said magnetically
coupled inductive means comprises an inductive winding magnetically
coupled to said first inductive means, whereby said second
time-varying current component is directly generated.
4. A power supply according to claim 1, wherein said magnetically
coupled inductive means comprises: a transformer including a
primary winding coupled across said first inductance means, and
also including a secondary winding across which a secondary voltage
is generated in response to said time-varying voltage component
appearing across said first inductance means; and an inductor
coupled in series with said secondary winding of said transformer,
for producing said second time-varying current component in
response to said secondary voltage.
5. A power supply according to claim 1, wherein said combining
means comprises a direct-voltage blocking capacitor.
6. A power supply according to claim 1, wherein said source of
voltage comprises: a phase-shifted full-wave switched bridge
circuit including first and second tap points across which an
alternating voltage is generated; a transformer including a primary
winding connected to said first and second tap points and also
including a secondary winding across which a varying voltage is
generated in response to said alternating voltage; and rectifying
means coupled to said secondary winding for converting said varying
voltage into a varying direct voltage.
7. A power supply according to claim 1, wherein said first
inductance means and said magnetically coupled inductive means
responsive to said time-varying voltage component appearing across
said inductance means, for generating a second time-varying current
component in response thereto, comprises a unitary arrangement,
said unitary arrangement comprising: a magnetic core including
first and second spaced-apart magnetic paths through which magnetic
flux flows, said first inductance means including a conductor
winding about said first magnetic path and said magnetically
coupled inductive means comprising a conductor winding about said
second magnetic path.
8. A power supply according to claim 7, wherein said magnetic core
is in the form of two half-cores, each having a cross-sectional
shape in the general form of the letter "U," and spaced apart by a
pair of gaps located at the distal ends of said legs, and wherein
said first magnetic path comprises one leg of each of said halves
together with one of said gaps, and said second magnetic path
comprises another leg of each of said halves together with another
of said gaps.
9. A power supply according to claim 7, wherein said magnetic core
is in the form of one of an E or pot core in two halves having
legs, each having a cross-section in the general shape of the
letter "E," which halves fit together with a gap between the center
legs of said halves, and wherein said first magnetic path includes
said center leg of one of said halves of said core, and said second
magnetic path includes said center leg-of the other one of said
halves of said core.
10. A power supply according to claim 7, wherein said magnetic core
is in the form of an E core in two halves, each of which halves has
a cross-section defining three legs and a base in the general shape
of the letter "E," which halves fit together with a first gap
between the center legs of said halves and a second gap between one
pair of outer legs, and wherein said first magnetic path includes
said one pair of outer legs of said halves of said core and said
second gap, and said second magnetic path includes the other of
said outer legs of said halves of said core and no gap.
11. A method for generating a direct voltage across load terminals,
said method comprising the steps of: integrating first current
applied to a storage capacitor connected across the load terminals:
applying to an inductor a voltage including a direct component and
a varying component, to thereby generate said first current,
whereby said varying component of said first current, when
integrated by said storage capacitor, produces unwanted variations
in the load voltage; applying said voltage including a direct
component and a varying component to a second inductive
arrangement, for thereby producing a current surrogate including a
varying component corresponding to said varying current component
and lacking a component corresponding to said direct component; and
coupling said current surrogate to said capacitor in such a manner
that said current surrogate reduces the amplitude of said varying
component of said first current.
12. A method according to claim 11, wherein said step of applying
said voltage including a direct component and a varying component
to a second inductive arrangement, for thereby producing a current
surrogate including a varying component corresponding to said
varying current component and lacking a component corresponding to
said direct component, includes the further step of: applying said
voltage including a direct component and a varying component to the
primary winding of a transformer, and taking from a secondary
winding of said transformer a secondary voltage; and applying said
secondary voltage to second inductor, to produce said current
surrogate including a varying component corresponding to said
varying current component and lacking a component corresponding to
said direct component.
13. A method according to claim 11, wherein said step of applying
said voltage including a direct component and a varying component
to a second inductive arrangement, for thereby producing a current
surrogate including a varying component corresponding to said
varying current component and lacking a component corresponding to
said direct component, includes the further step of: applying said
voltage including a direct component and a varying component to a
first inductive winding of a loosely coupled winding arrangement,
and taking from a second winding of said loosely coupled winding
arrangement said current surrogate including a varying component
corresponding to said varying current component and lacking a
component corresponding to said direct component.
14. A power supply, comprising: a source of voltage defining first
and second terminals: a controlled switch including a first
electrode coupled to said first terminal of said source of voltage
and defining a second electrode, for recurrently coupling said
voltage to said second electrode of said controlled switch;
unidirectional current conducting means connected to said second
electrode of said controlled switch and to said second terminal of
said source of voltage, poled for nonconduction when said voltage
is coupled to said second electrode of said controlled switch; a
storage capacitor including a first electrode connected to said
second terminal of said source of voltage and also including a
second electrode common with a load terminal, for integrating
current applied thereto for generating a load voltage; an inductor
connected to said second electrode of said controlled switch and to
said second electrode of said storage capacitor, for generating an
inductor current in response to the voltage at said second
electrode of said controlled switch, which inductor current
includes direct and varying current components; a transformer
including a secondary winding and also including a primary winding
coupled across said inductor, for producing a voltage at said
secondary winding related to the voltage across said inductor; a
second inductive arrangement coupled to said secondary winding of
said transformer, for producing a current surrogate having
properties similar to said varying component of said inductor
current; and a combining arrangement including a blocking capacitor
coupled to said second inductive arrangement and to said storage
capacitor, for adding said current surrogate to said inductor
current flowing to said storage capacitor, in a manner such as to
tend to cancel said time-varying component of said inductor
current.
15. A power supply, comprising: a source of voltage defining first
and second terminals: a controlled switch including a first
electrode coupled to said first terminal of said source of voltage
and defining a second electrode, for recurrently coupling said
voltage to said second electrode of said controlled switch;
unidirectional current conducting means connected to said second
electrode of said controlled switch and to said second terminal of
said source of voltage, poled for nonconduction when said voltage
is coupled to said second electrode of said controlled switch; a
storage capacitor including a first electrode connected to said
second terminal of said source of voltage and also including a
second electrode common with a load terminal, for integrating
current applied thereto for generating a load voltage; an inductor
connected to said second electrode of said controlled switch and to
said second electrode of said storage capacitor, for generating an
inductor current in response to the voltage at said second
electrode of said controlled switch, which inductor current
includes direct and varying current components; an inductive second
winding loosely coupled to said inductor, said inductive second
winding producing a current surrogate having properties similar to
said varying component of said inductor current; and a combining
arrangement including a blocking capacitor coupled to said second
inductive winding and to said storage capacitor, for adding said
current surrogate to said inductor current flowing to said storage
capacitor, in a manner such as to tend to cancel said varying
component of said inductor current.
Description
FIELD OF THE INVENTION
[0001] This invention relates to direct-voltage power supplies, and
more particularly to low-noise or low-ripple power supplies.
BACKGROUND OF THE INVENTION
[0002] Much of the advance in standard of living over the past
twenty or so years results from the use of advanced communications,
data processing, and environmental sensing techniques. The devices
used in such communications, processing, and sensing generally
become more useful as their sizes are decreased, such that more of
them can be used. For example, computers and cellular phones
require ever-smaller elements, and become more capable as the
number of devices which can be accommodated increases. Similarly,
lightweight and reliable sensors can be used in large numbers in
vehicles to aid in control and, in the case of spacecraft and
military vehicles, to aid in carrying out their missions.
[0003] Most modern semiconductor devices, and other devices
important for the above purposes, are generally energized or biased
by direct voltages. As devices have become smaller, their powering
requirements also advantageously decrease. Unfortunately, a
concomitant of low power requirements is often sensitivity to
unintended noise or fluctuations in the applied power. It is easy
to understand that extremely small transistors, which ordinarily
operate at two or three volts, could be destroyed by application of
tens of volts. It is less apparent but true that small-percentage
variations or noise on the applied powering voltage may result in
degradation of the operating characteristics of semiconductor and
other devices and the circuits in which they operate, which may
adversely affect the performance. It is a commonplace that
conventional radio and television receivers will respond to noise
on or sudden changes in their supply voltages with aural or visual
distortions, or both.
[0004] In general, electronic equipments require direct voltages
for their power sources. There are two general sources of
electrical energy which can be used to provide the power, and these
two sources are batteries, which provide direct voltage, and power
mains of an alternating voltage. When power mains are the source of
electrical energy, it is common to rectify the alternating voltage
to achieve a direct voltage. The power mains are used to drive
machine motors in addition to electronic equipment, so the mains
voltages tend to be higher than the voltages required for
electronic equipment, and rectified voltages also tend to be higher
than desired or usable. In the past, transformers have been used to
convert the mains power to voltages more compatible with electronic
equipment. However, transformers operating at 60 Hz tend to be much
larger than is desirable in modern miniaturized equipment. It might
be thought that there are no problems with the powering of
electronic equipment from batteries, which directly provide direct
voltage. However, batteries have the same general problem as that
of mains powering, namely that available direct voltage does not
necessarily correspond with the desired operating voltage. One
modern technique for producing voltages for powering electronic
equipment is that of use of a switching power supply or switching
converter, which changes a direct source voltage to a different
direct voltage.
[0005] A switching power converter can operate from a direct
voltage derived from the power mains or from a battery, and can
either increase or decrease the output voltage relative to the
input voltage. These switching power converters take many different
forms, some examples of which include those described in U.S. Pat.
No. 4,163,926 issued Aug. 7, 1979 in the name of Willis; U.S. Pat.
No. 4,190,791, issued Feb. 26, 1980 in the name of Hicks; U.S. Pat.
No. 4,298,892 issued Nov. 3, 1981 in the name of Scott; U.S. Pat.
No. 4,761,722 issued Aug. 2, 1988 in the name of Pruitt; and U.S.
Pat. No. 5,602,464 issued Feb. 11, 1997 in the name of Linkowski et
al.
SUMMARY OF THE INVENTION
[0006] A power supply according to an aspect of the invention
powers a load. A storage capacitor is coupled across the load. A
first inductance arrangement is coupled to the storage capacitor,
which is coupled across the load, to thereby form a combined
circuit. A source of voltage produces a direct voltage component
and a time-varying voltage component. The source of voltage is
coupled to the combined circuit for producing a flow of current
therethrough, which flow of current results in division of the
direct voltage component and the time-varying voltage component
between at least the first inductance arrangement and the storage
capacitor coupled across the load, whereby that portion of the
time-varying voltage component appearing across the first
inductance arrangement tends to cause a time-varying current flow
through the first inductance arrangement. A magnetically coupled
inductive arrangement is responsive to the time-varying voltage
component appearing across the inductance arrangement, for
generating a second time-varying current component in response to
the time-varying voltage. The second time-varying current component
is similar to the time-varying current flow through the first
inductance arrangement. A combining arrangement is coupled to the
combined circuit and to the magnetically coupled inductive
arrangement, for combining the second time-varying current
component with at least the time-varying current flow in such a
manner as to tend to oppose the time-varying current flow.
[0007] In one embodiment, the source of voltage includes a switch
which recurrently applies a raw direct voltage to the combined
circuit, and applies a reference potential across the combined
circuit during those intervals in which the raw direct voltage is
not applied, whereby the time-varying component is a rectangular
wave.
[0008] In another embodiment, of the power supply, the source of
voltage comprises a phase-shifted full-wave switched bridge circuit
including first and second tap points across which an alternating
voltage is generated, and a transformer including a primary winding
connected to the first and second tap points. The transformer also
includes a secondary winding across which a varying voltage is
generated in response to the alternating voltage. The source of
voltage also includes a rectifying arrangement coupled to the
secondary winding for converting the varying voltage into a varying
or pulsating direct voltage.
[0009] In one version of a power supply according to an aspect of
the invention, the magnetically coupled inductive arrangement
comprises an inductive winding magnetically coupled to the first
inductive arrangement, whereby the second time-varying current
component is directly generated. In another version of a power
supply according to this aspect of the invention, the magnetically
coupled inductive arrangement comprises a transformer including a
primary winding coupled across the first inductance arrangement,
and also including a secondary winding across which a secondary
voltage is generated in response to the time-varying voltage
component appearing across the first inductance arrangement. An
inductor or other inductance means is coupled in series with the
secondary winding of the transformer, for producing the second
time-varying current component in response to the secondary
voltage.
[0010] A power supply according to an aspect of the invention, in
which the first inductance means and the magnetically coupled
inductive means responsive to the time-varying voltage component
appearing across the inductance means, for generating a second
time-varying current component in response thereto, comprises a
unitary arrangement, and the unitary arrangement comprises a
magnetic core with first and second spaced-apart magnetic paths
through which magnetic flux flows. The first inductance means
includes a conductor winding about the first magnetic path, and the
magnetically coupled inductive means comprising a conductor winding
about the second magnetic path. In a first variant of this
arrangement, the magnetic core is in the form of two half-cores,
each having a cross-sectional shape in the general form of the
letter "U," spaced apart by a pair of gaps located at the distal
ends of the legs, and the first magnetic path comprises one leg of
each of the halves together with one of the gaps, and the second
magnetic path comprises another leg of each of the halves together
with another of the gaps. In a second variant of this arrangement,
the magnetic core is in the form of one of an E or pot core in two
halves having legs, where each half has a cross-section in the
general shape of the letter "E," which halves fit together with a
gap between the center legs of the halves. In this second variant,
the first magnetic path includes the center leg of one of the
halves of the core, and the second magnetic path includes the
center leg of the other one of the halves of the core. In a third
variant, the magnetic core is in the form of an E core in two
halves, each of which halves has a cross-section defining three
legs and a base in the general shape of the letter "E," which
halves fit together with a first gap between the center legs of the
halves and a second gap between one pair of outer legs. In this
third variant, the first magnetic path includes the one pair of
outer legs of the halves of the core and the second gap, and the
second magnetic path includes the other of the outer legs of the
halves of the core and no gap.
[0011] In yet another hypostasis of the invention, the combining
arrangement comprises a direct-voltage blocking capacitor. This
blocking capacitor may be placed in series with the inductive
winding of the one embodiment or in series with the secondary
winding and inductor of the other embodiment.
BRIEF DESCRIPTION OF THE DRAWING
[0012] FIG. 1 is a simplified schematic diagram of a switching buck
voltage regulator with current ripple cancellation according to an
aspect of the invention;
[0013] FIGS. 2a. 2b. and 2c are amplitude-time plots of voltages
and currents which occur in the regulator of FIG. 1 during
operation;
[0014] FIG. 3 is a simplified schematic diagram of an alternate
embodiment of a regulator according to an aspect of the
invention;
[0015] FIG. 4 is a semipictorial representation of the arrangement
of transformer T1 and inductor L2 used in the arrangement of FIG.
1;
[0016] FIG. 5 illustrates one possible arrangement of loosely
coupled inductors of FIG. 3;
[0017] FIG. 6 is a semipictorial representation of an E core or pot
core arranged to produce an inductive arrangement for use in FIG.
3;
[0018] FIG. 7 is an arrangement similar to that of FIG. 5, except
in that an additional flux path with an air gap is provided through
the center of the core; and
[0019] FIG. 8 is a simplified schematic diagram illustrating
another aspect of the invention.
DESCRIPTION OF THE INVENTION
[0020] In FIG. 1, an unregulated or "raw" direct voltage Vin is
applied from a source (not illustrated) to regulator or power
supply 10 input terminals 12.sub.1 and 12.sub.2. A controllable
switch illustrated as a field-effect transistor (FET) Q1 is
controlled, by means which are not illustrated but which are well
known in the art, to switch in a recurrent manner. The switching
may be periodic or aperiodic, but the effect is to recurrently
apply the Vin voltage "across" terminals 14.sub.1 and 14.sub.2, as
illustrated by plot v1(t) of FIG. 2a in the intervals t0 to t1, t0'
to t1', and t0" to t1". Those skilled in the art will understand
that the words "across" and "between" as used in electrical
contexts have no particular physical meaning as might be ascribed
in a mechanical or common context.
[0021] As illustrated in FIG. 1, power supply 10 includes an
inductor or inductive arrangement 16 connected in "series" with an
output filter capacitor Cout, and the resulting series combination
or combined circuit is connected across terminals 14.sub.1 and
14.sub.2 for receiving the varying or pulsatory voltage v1(t).
Under the impetus of each voltage pulse in the intervals t0 to t1,
t0' to t1', and t0" to t1" of FIG. 2a, electrical current through
inductor L1 increases, as illustrated in the relevant intervals by
plot (I.sub.L1+I.sub.N1) in FIG. 2b. In this context, I.sub.L1
represents the magnetizing or inductive current component flowing
in inductor L1. The increasing current flow through the inductor L1
in the intervals t0 to t1, t0' to t1', and t0" to t1" of FIG. 2a
flows as current I.sub.0 through output filter capacitor Cout.
Since output capacitor Cout is relatively large, its ac voltage is
small and most time varying currents flow therethrough. As known to
those skilled in the art, the flow of increasing current results,
in general, in an increasing output voltage Vout across output
filter capacitor Cout, although the current drawn by the load,
represented by resistor R.sub.L in FIG. 1, may under some
conditions exceed the inductor current, thereby resulting in a net
reduction of Vout. The voltage across output filter capacitor Cout
is the voltage available to supply the load represented by resistor
R.sub.L.
[0022] There are many ways to view the effects of the pulsating or
varying supply voltage v1(t) applied across the series combination
of inductor L1 and output filter capacitor Cout. The applied
voltage v1(t) may be viewed as consisting of a direct voltage
component with a pulsatory voltage component superposed thereon.
The inductor and capacitor may be viewed as a voltage divider, in
which case the direct voltage component of v1(t) may be viewed as
being developed solely across the output filter capacitor, as in
steady-state operation the inductor L1 cannot develop or withstand
a direct voltage. In this voltage divider view, the alternating
component of the applied voltage v1(t) may be viewed as appearing
across the inductance of inductor L1, assuming that output filter
capacitor Cout has zero impedance. However, filter capacitors do
not have zero impedance, so some portion of the applied pulsatory
or varying component of the applied voltage v1(t) will appear
across output filter capacitor Cout. This portion of the pulsatory
voltage is then an undesired ripple which is manifest across the
load R.sub.L. In an alternative view, that portion of the pulsatory
or varying applied voltage v1(t) which is applied to or across
inductor L1 results in a varying current flow in the inductor,
which current also flows mostly through the internal impedance of
output filter capacitor Cout, and thereby generates an undesired
ripple voltage which appears across the load R.sub.L.
[0023] However the mechanism which generates the ripple across the
output filter capacitor is viewed, the ripple is undesirable.
According to an aspect of the invention, an additional current is
generated, which ideally is equal in magnitude and opposite in
phase to the alternating component of the current through the
inductor L1, and this additional current is supplied to output
filter capacitor Cout together with the inductor L1 current, in a
phase or polarity which cancels or offsets the alternating
component of current. In effect, the output filter capacitor "sees"
only a direct current flow because the time-varying currents in
inductor L1, winding N1 and auxiliary inductor L2 add to zero.
Since no alternating current component flows through the internal
impedance of output filter capacitor Cout, no ripple voltage can be
generated across the capacitor. Of course, nothing is perfect, so
there will necessarily always be some difference between the
compensating ripple current and the ripple current actually flowing
in the inductor L1 and output filter capacitor Cout which will
prevent total cancellation, but significant ripple current
reduction should result.
[0024] In FIG. 1, a diode D1 has its cathode connected to terminal
14.sub.1 and its anode connected to terminal 14.sub.2. Those
skilled in the art recognize this as a "freewheeling" diode, which
is maintained in a nonconductive condition during those intervals
in which the raw supply voltage is coupled through switching
transistor Q1, corresponding to intervals t0 to t1, t0' to t1', and
t0" to t1" of FIG. 2a. During those intervals when switching
transistor Q1 is nonconductive, the energy stored in inductor L1
tends to cause current to continue to flow in the path including
Cout and D1, with the result that D1 becomes forward-biased and
allows the inductive current to continue flowing in the intervals
t1 to t0', t1' to t0", and after t1". When diode D1 is conductive,
its voltage drop is small, and may be viewed as being zero for
purposes of this analysis. Since the energy stored in inductor L1
is the motive force for the current I.sub.L1, the current during
intervals t1 to t0', t1' to t0", and after t1', the magnitude of
the current decreases, as illustrated in FIG. 2b. Thus, the current
flow through inductor L1 includes a varying component which
increases during those intervals in which voltage is applied by v1
being positive, and which decreases during those intervals in which
diode D1 conducts and a voltage of opposite polarity is applied to
inductor L1 by output capacitor Cout.
[0025] In FIG. 1, a transformer T1 includes a primary winding
designated N1 and a secondary winding designated N2, poled as
indicated by the standard dot notation. The primary winding N1 is
connected across inductor L1, so that transformer T1 is energized
by that varying component of the applied voltage appearing across
inductor L1, which in most cases will be the principal portion of
the varying component of the applied voltage. The varying component
of voltage applied to primary winding N1 of transformer T1
transforms to the secondary N2 side of the transformer. The voltage
applied to primary winding N1 of Transformer T1 may be viewed as
being similar to the pulsatory or varying component of the voltage
applied to terminals 14.sub.1 and 14.sub.2, so the voltage across
secondary winding N2 may be viewed as a surrogate for the varying
component of the applied voltage v.sub.1, except for that minor
portion appearing across output filter capacitor Cout. The dotted
end of secondary winding N2 is connected to terminal 142. The
voltage appearing across the secondary winding N2, which is a
surrogate for the applied varying voltage component, is applied to
a second inductor or inductance arrangement L2, which generates a
current which is a surrogate for the varying component of current
through inductor L1. Those skilled in the art will know how to
select the parameters of transformer T1 and inductor L2 so as to
cause the surrogate varying current to substantially equal the
varying current component in inductor L2 plus the current in the
primary of transformer T1.
[0026] A solution for selecting L2 when N2 and N1 are given is 1 L
2 = L 1 ( N2 N1 ) ( 1 - N2 N1 ) . 1
[0027] where L1, L2, N1, and N2 all have real, positive values.
[0028] The three currents are combined by coupling the "output"
ends of inductors L1 and L2 together with transformer primary
winding N1 at a junction point 18 corresponding to the juncture of
"serially` connected inductor L1 and output filter capacitor Cout.
In order to avoid the application of direct voltage from junction
point 18 to the serial combination of inductor L2 and secondary
winding N2, which might result in the flow of excess current to
ground, a direct voltage blocking capacitor Cb is placed in the
serial connection. As illustrated, blocking capacitor Cb is placed
between inductor L2 and tap point 18, but Cb could also be placed
between N2 and L2, or alternatively between N2 and ground or
connection 142.
[0029] In operation of the arrangement of FIG. 1, the switching of
Q1 produces a pulsatory or varying voltage v1(t) as described in
conjunction with FIG. 2a, with the result that a total current
(I.sub.L1+I.sub.N1) flows as illustrated in FIG. 2b, with the
I.sub.L1 component of current flowing through inductor L1, and with
the I.sub.N1 component flowing through the primary winding N1 of
transformer T1. The flow of primary current i.sub.N1 of FIG. 2c in
transformer T1 results in a flow of varying current i.sub.L2
through secondary winding N2 and through inductor L2. Comparing
current (I.sub.L1+I.sub.N1) of FIG. 2b with current i.sub.L2 of
FIG. 2c shows that they are about equal in magnitude and of
opposite phase or polarity, so that the result of their addition at
tap point 18 is cancellation of the time-varying component of
current. With no varying component of current flowing through
output filter capacitor Cout, no ripple voltage is generated
thereacross which can appear across the load being energized.
[0030] FIG. 3 is a simplified schematic diagram of an alternate
embodiment of an aspect of the invention. Elements of FIG. 3
corresponding to those of FIG. 1 are designated by like reference
alphanumerics. Generally, the arrangement of FIG. 3 substitutes
loosely coupled windings for first inductor L1, transformer T1, and
second inductor L2. In the arrangement of L1 of FIG. 3, N1
represents an inductive winding having an inductance equivalent to
the inductance of winding L1 of FIG. 1. Winding N2 of FIG. 3 is
magnetically coupled to winding N1, to thereby produce a resulting
voltage in winding N2. However, winding N2 of FIG. 3 is also
inductive, at least in part by virtue of its loose coupling to
winding N1, and therefore also inherently includes the inductive
property which is provided in the arrangement of FIG. 1 by separate
inductor L2. Thus, the arrangement of FIG. 3 operates essentially
identically to the arrangement of FIG. 1.
[0031] FIG. 4 is a semipictorial representation of the arrangement
of transformer T1 and inductor L2 used in the arrangement of FIG.
1. In FIG. 4, the core is represented by two C sections or halves
410a, 410b defining a gap 412 between legs 410a1 and 410b1. Winding
N1 is wound onto one leg of the core, and winding N2 is wound over
winding N1, thereby providing substantial magnetic coupling.
Inductor L2 is illustrated as a separate winding on a toroidal
magnetic core. Capacitor Cb is also shown. By contrast, FIG. 5
illustrates the arrangement of loosely coupled inductors of FIG. 3.
In FIG. 5, the core 501 is illustrated as two halves 410a and 410b
defining a gap 412.sub.1 between legs 410a1 and 410b1 and a
corresponding gap 412.sub.2 between legs 410a2 and 410b2. Winding
N1, corresponding to the main inductor L1, is illustrated as being
wound on the left leg 410a2, 410b2 of the core, and winding N2 is
illustrated as being wound on the right leg 410a1, 410b1 of the
core. The magnetic coupling between windings N1 and N2 is reduced
relative to that of the arrangement of FIG. 4, and the uncoupled
inductance of each winding is greater. As illustrated in FIG. 5,
capacitor Cb is connected directly to winding N2.
[0032] FIG. 6 is a semipictorial representation of the use of an E
core or a pot core (seen in cross-section) designated 601 to
produce an inductive arrangement for use in the arrangement of FIG.
3. In FIG. 6, the coupling between windings N1 and N2 is reduced
relative to what it might otherwise be by the spatial separation of
the windings. The core 601 is in the form of two halves 601a, 601b,
each of which has the general shape of the letter "E," with upper
half 601a having outer legs 601a1 and 601a2, and a center leg 610a,
and with lower half 601b having outer legs 601b1 and 601b2 and a
center leg 610b. The gap 612 between center legs 610a and 610b in
the central portion of the core is set to give the correct value of
inductance L1. FIG. 7 is an arrangement 700 generally similar to
that of FIG. 5, except in that an additional flux path 710a, 710b
with an air gap 712 is provided through the center of the core 701.
Winding N2 is wound on legs 701a2, 701b2. The additional flux path
710a, 710b, 712 can be used to affect or decrease the coupling
between windings N1 and N2 in a manner controlled by the dimension
of the air gap, thus increasing the effective value of the
equivalent L2. Such a magnetic shunt insures that, for most
applications, the correct value of L1 can be obtained by
controlling the air gap 714 on the left leg 701a1, 701b1 while the
correct value of L2 can be obtained by shunting coupling flux
through the center leg under control of its air gap, while still
maintaining the correct turns ratio L1/L2.
[0033] Those skilled in the art will recognize that the
arrangements of FIGS. 5, 6, and 7 provide for loosely coupled
windings which will exhibit more uncoupled inductance than the
N1/N2 windings of FIG. 4. Consequently, the arrangements of FIGS.
5, 6, and 7 can provide performance equivalent to that of FIG.
4.
[0034] FIG. 8 is a simplified schematic diagram illustrating
another aspect of the invention. In the arrangement of FIG. 8, the
voltage applied to the inductor-capacitor "series" circuit does not
come directly from a controllable switch as in FIGS. 1 and 3, but
rather comes by way of a rectifier arrangement. In FIG. 8, 810
represents a full-wave bridge circuit including plural controllable
switches. As known to those skilled in the art, these switches can
be operated in a number of modes. For definiteness, the switches of
FIG. 8 are operated by a controller (not illustrated) in a
phase-shifted mode, in which the switches are rendered conductive
in a manner such as to minimize the voltages across the switches
during at least one of turn-on and turn-off. The result of these
operations is to produce an alternating voltage across a primary
winding N1 of a transformer 812. The alternating voltage applied to
primary winding N1 of transformer 812 causes an alternating voltage
to be generated across the secondary winding, illustrated as
separate windings N2.sub.a and N2.sub.b, with a tap point 814
therebetween. A pair of diodes or rectifiers R1 and R2 are
illustrated in FIG. 8, with their anodes connected to the ends of
secondary windings N2.sub.a and N2.sub.b, respectively, which are
remote from tap 814. The cathodes of rectifiers R1 and R2 are
connected together and to an inductive winding L1. Inductive
winding L1 is connected in "series" with an output filter capacitor
Cout, as in FIG. 3. An inductive winding L2 is loosely coupled to
winding L1 as described in conjunction with FIG. 3, and is
connected to reference tap 814 and by way of a blocking capacitor
Cb to a junction point 818. With the described arrangement, a
voltage having both direct and varying components appears between
reference tap 814 and input terminal 814.sub.1. The alternating
voltage is manifest across the series combination of L1 and Cout,
as described in conjunction with FIGS. 1 and 3, and the arrangement
of winding L2 coupled to point 818 tends to cancel the alternating
or varying current components in inductor L2. This, in turn,
reduces the magnitude of the alternating current components flowing
in capacitor Cout, with consequent reduction in the voltage ripple
or noise appearing at the load terminals 20.sub.1 and 20.sub.2.
[0035] It should be emphasized that the arrangement for
cancellation of alternating current components may be used in the
case in which an alternating sine wave is rectified to produce
"pulsating direct voltage," corresponding-to a sequence of
unidirectional half-sine-waves. In general, any alternating voltage
waveshape that generates an ac current in inductor L1 can be
cancelled using the invention.
[0036] Thus, speaking very generally, a low-ripple power supply
includes a storage capacitor coupled across load terminals, and an
inductor connected to a source of voltage including a varying or
pulsatory component and a direct component, for causing a flow of
current to said capacitor through the inductor. The varying
component of the inductor current flowing in the capacitor results
in ripple across the load. A winding is coupled to the inductor for
generating a surrogate of the varying inductor current. The
surrogate current is added to the inductor current to cancel or
reduce the magnitude of the varying current component. This
cancellation effectively reduces the varying current component
flowing in the storage capacitor, which in turn reduces the ripple
appearing across the load terminals.
[0037] More particularly, a power supply (10) according to an
aspect of the invention is capable of powering a load (R.sub.L)
coupled to load terminals (20.sub.1, 20.sub.2). A storage capacitor
(Cout) is coupled across the load (R.sub.L) terminals (20.sub.1,
20.sub.2). A first inductance arrangement (L1) is coupled to the
storage capacitor (Cout), which is coupled across the load
(R.sub.L) terminals (20.sub.1, 20.sub.2), to thereby form a
combined circuit (L1, Cout). A source of voltage (Vin, Q1, D1)
produces a direct voltage component and a time-varying voltage
component. The source of voltage (Vin, Q1, D1) is coupled to the
combined circuit (L1, Cout) for producing a flow of current
therethrough, which flow of current results in division of the
direct voltage component and the time-varying voltage component
between at least the first inductance arrangement (L1) and the
storage capacitor (Cout) coupled across the load (R.sub.L)
terminals (20.sub.1, 20.sub.2), whereby that portion of the
time-varying voltage component appearing across the first
inductance arrangement (L1) tends to cause a time-varying current
(i.sub.L1) flow through the first inductance arrangement (L1). A
magnetically coupled inductive arrangement (T1, L2; 310) is
responsive to the time-varying voltage component appearing across
the inductance arrangement (L1), for generating a second
time-varying current component (i.sub.L2) in response to the
time-varying voltage. The second time-varying current component
(i.sub.L2) is similar to the time-varying current flow (i.sub.L1)
through the first inductance arrangement (L1). A third time-varying
current component (i.sub.N1) proportional to i.sub.L2 flows in the
primary of the transformer. A combining arrangement (Cb, 18; Cb,
818) is coupled to the combined circuit (L1, Cout) and to the
magnetically coupled inductive arrangement (T1, L2; 310), for
combining the second time-varying current component (i.sub.L2) with
at least the time-varying current flow (i.sub.L1) in such a manner
as to tend to oppose the time-varying current flow. This may be
viewed as a combining of the second time-varying current component
(i.sub.L2) and the third time-varying current (i.sub.N1) with the
time-varying current flow (i.sub.L1) in such a manner as to tend to
oppose the time-varying current flow.
[0038] In one embodiment, the source of voltage (Vin, Q1, D1, 810,
812, R1, R2) includes a switch (Q1; 810, 812, R1, R2) which
recurrently applies a raw direct voltage to the combined circuit
(L1, Cout), and applies a reference potential (diode drop, for
example) across the combined circuit (L1, Cout) during those
intervals in which the raw direct voltage is not applied, whereby
the time-varying component is a rectangular wave.
[0039] In another embodiment, of the power supply (10), the source
of voltage (Vin, Q1, D1, 810, 812, R1, R2) comprises a
phase-shifted full-wave switched bridge circuit (810) including
first (811.sub.1) and second (811.sub.2) tap points across which an
alternating voltage is generated, and a transformer (812) including
a primary winding (N1) connected to the first (811.sub.1) and
second (811.sub.2) tap points. The transformer (812) also includes
a secondary winding (N2.sub.a, N2.sub.b) across which a varying
voltage is generated in response to the alternating voltage. The
source of voltage (Vin, Q1, D1, 810, 812, R1, R2) also includes a
rectifying arrangement (R1, R2) coupled to the secondary winding
(N2.sub.a, N2.sub.b) for converting the varying voltage into a
varying or pulsating direct voltage.
[0040] In one version of a power supply (10) according to an aspect
of the invention, the magnetically coupled inductive arrangement
(T1, L2; 310) comprises an inductive winding (L2) magnetically
coupled to the first inductive arrangement (L1), whereby the second
time-varying current component is directly generated. In another
version of a power supply (10) according to this aspect of the
invention, the magnetically coupled inductive arrangement comprises
a transformer (T1) including a primary winding (N1) coupled across
the first inductance arrangement (L1), and also including a
secondary winding (N2) across which a secondary voltage is
generated in response to the time-varying voltage component
appearing across the first inductance arrangement (L1). An inductor
(L2) or other inductance means is coupled in series with the
secondary winding (N2) of the transformer (T1), for producing the
second time-varying current component in response to the secondary
voltage.
[0041] A power supply according to an aspect of the invention, in
which (a) the first inductance means and (b) the magnetically
coupled inductive means responsive to the time-varying voltage
component appearing across the inductance means, for generating a
second time-varying current component in response thereto,
comprises a unitary magnetic arrangement (500, 600, 700). This
unitary magnetic arrangement (500, 600, 700) comprises a magnetic
core (501, 601, 701) with first and second spaced-apart magnetic
paths through which magnetic flux flows. The first inductance means
includes a conductor winding about the first magnetic path, and the
magnetically coupled inductive means comprising a conductor winding
about the second magnetic path. In a first variant of this
arrangement, the magnetic core (500) is in the form of two
half-cores (410a, 410b), each having a cross-sectional shape in the
general form of the letter "U," spaced apart by a pair of gaps
(412.sub.1, 412.sub.2) located at the distal ends of the legs, and
the first magnetic path comprises one leg (410a2, 410b2) of each of
the halves (410a, 410b) together with one of the gaps (412.sub.2),
and the second magnetic path comprises another leg (410a1, 410b1)
of each of the halves (410a, 410b) together with another of the
gaps (412.sub.1). In a second variant of this arrangement, the
magnetic core (600) is in the form of one of an E or pot core in
two halves (601a, 601b) having legs (601a1, 601a2, 610a, 601b1,
601b2, 610b), where each half (601a, 601b) has a cross-section in
the general shape of the letter "E," which halves (601a, 601b) fit
together with a gap (612) between the center legs (610a, 610b) of
the halves (601a, 601b). In this second variant, the first magnetic
path includes the center leg (610a) of one of the halves (601a) of
the core (601), and the second magnetic path includes the center
leg (610b) of the other one (601b) of the halves of the core (601).
In a third variant, the magnetic core (701) is in the form of an E
core in two halves (701a, 701b), each of which halves (701a, 701b)
has a cross-section defining three legs (701a1, 701a2, 710a, 701b1,
701b2, 710b) and a base (701ab, 701bb) in the general shape of the
letter "E," which halves (701a, 701b) fit together with a first gap
(712) between the center legs (710a, 710b) of the halves (701a,
701b) and a second gap (714) between one pair (701a1, 701b1) of
outer legs. In this third variant, the first magnetic path includes
the one pair of outer legs (701a1, 701b1) of the halves (701a,
701b) of the core and the second gap (714), and the second magnetic
path includes the other ones (701a2, 701b2) of the outer legs of
the halves (701a, 701b) of the core (701) and no gap.
[0042] In yet another hypostasis of the invention, the combining
arrangement comprises a direct-voltage blocking capacitor (Cb).
This blocking capacitor (Cb) may be placed in series with the
inductive winding (N2) of the one embodiment or in series with the
secondary winding (N2) and inductor (L2) of the other
embodiment.
* * * * *