U.S. patent number RE40,072 [Application Number 11/062,350] was granted by the patent office on 2008-02-19 for loss and noise reduction in power converters.
This patent grant is currently assigned to VLT Corporation. Invention is credited to Jay Prager, Patrizio Vinciarelli.
United States Patent |
RE40,072 |
Prager , et al. |
February 19, 2008 |
Loss and noise reduction in power converters
Abstract
An apparatus includes (a) switching power conversion circuitry
including an inductive element connected to deliver energy via a
unidirectional conducting device from an input source to a load
during a succession of power conversion cycles, and circuit
capacitance that can resonate with the inductive element during a
portion of the power conversion cycles to cause a parasitic
oscillation, and (b) clamp circuitry connected to trap energy in
the inductive element and reduce the parasitic oscillation.
Inventors: |
Prager; Jay (Groton, MA),
Vinciarelli; Patrizio (Boston, MA) |
Assignee: |
VLT Corporation (San Antonio,
TX)
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Family
ID: |
25267708 |
Appl.
No.: |
11/062,350 |
Filed: |
February 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09834750 |
Apr 13, 2001 |
06522108 |
Feb 18, 2003 |
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Current U.S.
Class: |
323/222 |
Current CPC
Class: |
H02M
3/155 (20130101); H02M 3/33569 (20130101); H02M
1/34 (20130101); H02M 3/33576 (20130101); Y02B
70/10 (20130101); H02M 1/342 (20210501) |
Current International
Class: |
G05F
1/56 (20060101) |
Field of
Search: |
;323/220,222,282
;363/39,50,59,60 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2218055 |
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Oct 1973 |
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DE |
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2756799 |
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Jun 1978 |
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DE |
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2756773 |
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Jul 1978 |
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DE |
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6-36384 |
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May 1994 |
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JP |
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11-127575 |
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May 1999 |
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JP |
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Other References
EPO Communication, Mar. 3, 2005 Rejection. cited by other .
JPO Communication, Mar. 15, 2005 Allowance. cited by other .
EPO Communication, Aug. 18, 2005, Reversal of Rejection of Mar. 3,
2005. cited by other .
EPO Communication, Jan. 13, 2006, Allowance including claim
amendments (pp. 17, 19). cited by other .
Maruhashi et al., "A High Power Switching Regulator System Driven
By High-Frequency Resonant Thyristor Chopper Circuit," Memoirs of
the Faculty of Engineering, Kobe University, No. 22, pp. 99-111,
Mar. 1976. cited by other.
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Primary Examiner: Berhane; Adolf
Attorney, Agent or Firm: Fish & Richardson P.C.
Claims
What is claimed is:
1. Apparatus comprising.Iadd.:.Iaddend. switching power conversion
apparatus for converting power from an input source for delivery to
a load comprising an inductive element connected to deliver energy
via a unidirectional conducting device from said input source to
said load during a succession of power conversion cycles, circuit
capacitance which can resonate with said inductive element during a
potion of said power conversion cycle to cause a parasitic
oscillation unrelated to the power conversion process, and clamp
circuitry configured to trap energy in the inductive element and
prevent said parasitic oscillation.
2. The apparatus of claim 1 wherein said power conversion apparatus
.[.is.]. .Iadd.comprises .Iaddend.a unipolar, non-isolated boost
converter comprising a shunt switch.
3. The apparatus of claim 2 in which the shunt switch is controlled
to cause the power conversion to occur in a discontinuous mode.
4. The apparatus of claim 1 in which the clamp circuitry is
configured to trap the energy in the inductor in a manner that is
essentially non-dissipative.
5. The apparatus of claim 1 in which the clamp circuitry comprises
elements configured to trap the energy by short-circuiting the
inductor during a controlled time period.
6. The apparatus of claim 1 in which the inductive element
comprises a choke.
7. The apparatus of claim 1 in which the inductive element
comprises a transformer.
8. The apparatus of claim 5 in which the elements comprise a second
switch connected effectively in parallel with the inductor.
9. The apparatus of claim 8 in which the second switch is connected
directly in parallel with the inductor.
10. The apparatus of claim 8 in which the second switch is
inductively coupled in parallel with the inductor.
11. The apparatus of claim 8 in which the second switch comprises a
field effect transistor in series with a diode.
12. The apparatus of claim 8 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a unipolar,
non-isolated boost converter comprising a shunt switch and a switch
controller, said switch controller controlling the timing of a
power delivery period during which said shunt switch is open and a
shunt period during which the shunt switch is closed.
13. The apparatus of claim 12 in which the shunt switch is
controlled to cause the power conversion to occur in a
discontinuous mode.
14. The apparatus of claim 12 in which the second switch is opened
for a period before the shunt switch is closed in order to
discharge parasitic capacitances in the apparatus.
15. The apparatus of claim 1 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a unipolar, isolated,
single-ended forward converter.
16. The apparatus of claim 15 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a buck converter.
17. The apparatus of claim 15 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a flyback
converter.
18. The apparatus of claim 15 wherein said single-ended forward
converter .[.is.]. .Iadd.comprises .Iaddend.a zero-current
switching converter.
19. The apparatus of claim 15 wherein said single-ended forward
converter .[.is.]. .Iadd.comprises .Iaddend.a PWM converter.
20. The apparatus of claim 1 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a bipolar,
non-isolated, boost converter.
21. The apparatus of claim 1 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a bipolar, non-isolated
boost converter.
22. The apparatus of claim 1 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a bipolar, non-isolated
buck converter.
23. The apparatus of claim 1 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a bipolar, non-isolated
boost converter.
24. The apparatus of claim 1 wherein said power conversion
apparatus .[.is.]. .Iadd.comprises .Iaddend.a bipolar, isolated
buck converter.
25. In a power converter which converts power from an input source
for delivery to a load during a succession of power conversion
cycles and which comprises an inductive element connected to
deliver power via a unidirectional conducting device from said
input source to said load and a circuit capacitance which can
resonate with said inductive element during a portion of said power
conversion cycle to cause a parasitic oscillation unrelated to the
power conversion process, a method for preventing said parasitic
oscillations comprising providing clamp circuitry for trapping
energy in the inductive element during a portion of the power
conversion cycle.
26. The method of claim 25 also including releasing the energy from
the inductor essentially non-dissipatively.
27. The method of claim 17 wherein the trapping of energy comprises
short-circuiting the inductive element during a controlled time
period.
28. The method of claim 27 in which the short-circuiting is done by
a second switch connected effectively in parallel with the
inductive element.
29. The apparatus of claim 28 also including opening the second
switch for a portion of the power conversion cycle in order to
discharge parasitic capacitances.
.Iadd.30. Apparatus comprising switching power conversion apparatus
for converting power from an input source for delivery to a load
comprising an inductive element connected to deliver energy from
said input source to said load during a succession of power
conversion cycles, clamp circuitry configured to hold energy in the
inductive element, and control circuitry configured to regulate the
on and off periods of the clamp circuitry such that the clamp
circuitry is configured to carry a reverse current flowing in the
inductor and is turned off at a time when a remaining current is
flowing in the inductor, wherein the remaining current has a level
that is at least a substantial portion of a peak value of the
reverse current. .Iaddend.
.Iadd.31. The apparatus of claim 30 wherein the remaining current
is used to charge or discharge parasitic capacitances.
.Iaddend.
.Iadd.32. A method comprising: providing power conversion circuitry
having an inductive element connected to deliver power from an
input source to a load during a succession of power conversion
cycles; providing clamp circuitry for holding energy in the
inductive element during a portion of the power conversion cycle;
providing control circuitry for controlling the on and off times of
the clamp circuitry, configuring the on and off times of the clamp
circuitry to hold energy in the inductive element during the on
time of the clamp and to release a substantial portion of the held
energy during the off time of the clamp. .Iaddend.
.Iadd.33. The method of claim 32 wherein the release of the held
energy is used to charge or discharge parasitic capacitances.
.Iaddend.
.Iadd.34. A method comprising: providing power conversion circuitry
having an inductive element connected to deliver power from an
input source to a load during a succession of power conversion
cycles; providing clamp circuitry for conducting a current flowing
in the inductive element during a portion of the power conversion
cycle; providing control circuitry for controlling the on and off
times of the clamp circuitry; configuring the on and off times of
the clamp circuitry to carry a reverse current flowing in the
inductor and to turn off the clamp circuitry before the reverse
current flowing in the inductor decays essentially to zero.
.Iaddend.
.Iadd.35. The method of claim 34 wherein the reverse current
flowing in the inductor is used to charge or discharge parasitic
capacitances during the off time of the clamp. .Iaddend.
Description
BACKGROUND
This invention relates to reducing energy loss and noise in power
converters.
As shown in FIGS. 1 and 2, in a typical PWM non-isolated DC-to-DC
shunt boost converter 20 operated in a discontinuous mode, for
example, power is processed in each of a succession of power
conversion cycles 10. During a power delivery period 12 of each
power conversion cycle 10, while a switch 22 is open, power
received at an input voltage Vin from a unipolar input voltage
source 26 is passed forward as a current that flows from an input
inductor 21 through a diode 24 to a unipolar load (not shown) at a
voltage Vout. Vout is higher than the input voltage, Vin.
FIGS. 2A and 2B show waveforms for an ideal converter in which
there are no parasitic capacitances or inductances and in which the
diode 24 has zero reverse recovery time. During the power delivery
period 12, the current in the inductor falls linearly and reaches a
value of zero at time tcross. At tcross, the ideal diode
immediately switches off, preventing current from flowing back from
the load towards the input source, and the current in the inductor
remains at zero until the switch 22 is closed again at the next
time ts1off. Thus, no energy is stored in the inductor 21 between
times tcross and ts1on.
During another, shunt period 14 of each cycle, while switch 22 is
closed, the voltage at the left side of the diode (node 23) is
grounded, and no current flows in the diode. Instead, a shunt
current (Is) is conducted from the source 26 into the inductor 21
via the closed switch 22. In a circuit with ideal components, the
current in the inductor would begin at zero and rise linearly to
time ts1off, when switch 22 is turned off to start another power
delivery period 12.
In a non-ideal converter, in which there are parasitic circuit
capacitances and the diode is non-ideal (e.g., for a bipolar diode
there will be a reverse recovery period and for a Schottky diode
there will be diode capacitance), an oscillatory ringing will occur
after tcross.
In one example, waveforms for a non-ideal converter of the kind
shown in FIG. 1 are shown in FIGS. 2C and 2D. Because of the
reverse recovery characteristic of the diode, the diode does not
block reverse current flow at time tcross. Instead, current flows
in the reverse direction through the diode 24 and back into the
inductor 21 during a period 18. At time tdoff, the diode snaps
fully off and the flow of reverse current in the diode goes to
zero.
Because of the reverse flow of current in the diode during the
diode recovery period, energy has been stored in the inductor as of
the off time tdoff (the "recovery energy"). In addition, parasitic
circuit capacitances (e.g., the parasitic capacitances of the
switch 22, the diode 24, and the inductor 24, not shown) also store
energy as of time tdoff (e.g., the parasitic capacitance of switch
22 will be charged to a voltage approximately equal to Vout).
After time tdoff, energy is exchanged between the inductor and
parasitic capacitances in the circuit. As shown in FIGS. 2C and 2D,
the energy exchange causes oscillatory ringing noise in the
circuit. Furthermore, the presence of oscillatory current will
generally result in energy being dissipated wastefully in the
circuit at the start of the next shunt period when the switch is
closed at time ts1on. The energy loss can amount to several percent
of the total energy processed during a cycle.
SUMMARY
In general, in one aspect, the invention features apparatus that
includes (a) switching power conversion circuitry including an
inductive element connected to deliver energy via a unidirectional
conducting device from an input source to a load during a
succession of power conversion cycles, and circuit capacitance that
can resonate with the inductive element during a portion of the
power conversion cycles to cause a parasitic oscillation, and (b)
clamp circuitry connected to trap energy in the inductive element
and reduce the parasitic oscillation.
Implementations of the invention may include one or more of the
following. The power conversion circuitry comprises a unipolar,
non-isolated boost converter comprising a shunt switch. The power
conversion circuitry is operated in a discontinuous mode. The clamp
circuitry is configured to trap the energy in the inductor in a
manner that is essentially non-dissipative. The clamp circuitry
comprises elements configured to trap the energy by
short-circuiting the inductor during a controlled time period. The
inductive element comprises a choke or a transformer. The elements
comprise a second switch connected effectively in parallel with the
inductor. The second switch is connected directly in parallel with
the inductor or is inductively coupled in parallel with the
inductor. The second switch comprises a field effect transistor in
series with a diode.
The power conversion circuitry comprises a unipolar, non-isolated
boost converter comprising a shunt switch and a switch controller,
the switch controller being configured to control the timing of a
power delivery period during which the shunt switch is open and a
shunt period during which the shunt switch is closed.
The shunt switch is controlled to cause the power conversion to
occur in a discontinuous mode. The second switch is opened for a
period before the shunt switch is closed in order to discharge
parasitic capacitances in the apparatus. The power conversion
circuitry comprises at least one of a unipolar, isolated,
single-ended forward converter, a buck converter, a flyback
converter, a zero-current switching converter, a PWM converter, a
bipolar, non-isolated, boost converter, a bipolar, non-isolated
boost converter, a bipolar, non-isolated buck converter, a bipolar,
isolated boost converter, or a bipolar, isolated buck
converter.
In general, in another aspect, the invention features, a method
that reduces parasitic oscillations by trapping energy in the
inductive element during a portion of the power conversion
cycles.
Implementations of the invention include releasing the energy from
the inductor essentially non-dissipatively. The energy is trapped
by short-circuiting the inductive element during a controlled time
period. The short-circuiting is done by a second switch connected
effectively in parallel with the inductive element. The second
switch is opened for a portion of the power conversion cycle in
order to discharge parasitic capacitances. The invention reduces
undesirable ringing noise generated in a power converted by
oscillatory transfer of energy between inductive and capacitive
elements in the converter and recycles this energy to reduce or
eliminate the dissipative loss of energy associated with turn-on of
a switching element in the converter.
Other advantages and features will become apparent from the
following description and from the claims.
DESCRIPTION
FIG. 1 shows a power conversion circuit.
FIGS. 2A-2D shows timing diagrams.
FIGS. 3, 5 and 6 show power conversion circuits with recovery
switches.
FIG. 4 shows a timing diagram.
FIG. 7 shows a PWM, unipolar, isolated buck converter comprising a
clamp circuit.
FIGS. 8A and 8B show waveforms for the converter of FIG. 7.
FIGS. 9A, 9B, 9C, and 9D show isolated, single-ended converters
which comprise a clamp circuit.
With reference to FIGS. 1, 2C and 2D, at time tdoff the parasitic
capacitance across the switch 22 is charged to a voltage
(approximately equal to Vout) which is greater than Vin and a
current flows in L1 owing to the reverse recovery of the diode
24.
After tdoff, with the switch 22 open and the diode non-conductive,
energy stored in the resonant circuit formed by the circuit
parasitic capacitances and inductor L1 causes oscillatory ringing
in Iin and Vs. This oscillation (referred to herein as "parasitic
oscillation" or simply "noise") is unrelated to the power
conversion process, and may require that noise filtering components
be added to the converter (not shown). In addition, closure of the
switch 22 after tdoff will result in a wasteful loss of some or all
of this energy ("switching loss").
By providing mechanisms for clamping the circuit voltages, the
noise can be reduced or eliminated, and the stored energy can be
trapped in an inductor and then released essentially losslessly
back to the circuit. Generally, the capturing and later release of
the energy is achieved by effectively shorting and then un-shorting
the two ends of an inductor at controlled times.
As shown in FIG. 3, in one implementation, a unipolar,
non-isolated, discontinuous boost converter circuit 28 includes a
series circuit, comprising a recovery switch Rs 30 and a diode 32,
that is connected across the ends of the inductor 34, and a
controller 36 that regulates the on and off periods of both the
recovery switch 30 and the shunt switch 22.
The recovery switch 30 is turned on and off in the following cycle.
The switch may be turned on any time during the power delivery
period 12 when the voltage across the inductor, VB (FIG. 3), is
negative, because this will result in diode 32 being reverse
biased. During the reverse recovery period, the diode 32 prevents
the current that is flowing backward from the diode 38 from flowing
in recovery switch 30. Instead, the reverse recovery energy is
stored in the inductor.
After the diode snaps off, the energy stored in circuit parasitic
capacitances will be exchanged with the inductor and the voltage,
Vs, across shunt switch 22 will ring down. When the input voltage
Vs rings down to the input voltage, Vin, the voltage VB will equal
zero, the recovery diode 32 will conduct and the recovery switch 30
and the diode 32 will short the ends of the inductor 34. In that
state, the inductor 34 cannot exchange energy with any other
circuit components. Therefore, the energy is "trapped" in the
inductor and ringing in the main circuit is essentially
eliminated.
Later, prior to the shunt switch being closed to start the shunt
period, the recovery switch is opened. Because the current trapped
in the inductor flows in the direction back toward the input
source, opening the recovery switch 30 will result in an
essentially lossless charging and discharging of parasitic circuit
capacitances and a reduction in the voltage, Vs, across the shunt
switch. By providing for a reduction in shunt switch voltage, Vs,
the loss in the shunt switch associated with discharging of
parasitics ("turn-on loss") can be reduced or, in certain cases,
essentially eliminated.
As shown in FIG. 4, the delay between the opening of the recovery
switch 30 and the closing of the shunt switch 22 may be adjusted so
that the closure of the shunt switch corresponds in time to
approximately the time of occurrence of the first minimum in the
voltage Vs following the opening of the recovery switch at time
trsoff (the dashed line in the Figure shows how the voltage Vs
would continue to oscillate after ts1on if the shunt switch 22 were
not turned on at that time). In case where the voltage rings all
the way down to zero (not shown in the Figure) the turn-on loss in
the shunt switch can be essentially eliminated. Since capacitance
energy is proportional to the square of the voltage, however, any
amount of voltage reduction is important.
As shown in FIG. 5, in another approach, instead of wiring the
recovery switch and diode directly across the inductor, a recovery
switch 50 and a diode 52 are connected in series with a secondary
winding 54 that is transformer-coupled to the inductor. The series
circuit is connected to the ground side of the circuit for
convenience in controlling the switch. The control switch may be
implemented as a MOSFET in series with a diode. Turn-on losses will
occur as a result of the body capacitor of the switch 50, but they
are relatively small because the switch die is relatively
small.
As shown in FIG. 6, in another implementation, a bipolar
discontinuous boost converter 60 operating from a bipolar input
source, Vac, uses the transformer-coupled switching technique of
FIG. 5, but includes two recovery switches 62, 64 connected to
respective ends of the winding 66. One of the recovery switches is
always on for one polarity of input source Vac, and the other
recovery switch is turned on and off using the same strategy as in
FIG. 5. The scenario is reversed when the polarity of the input
source reverses.
Care must be taken not to have the shunt switch and the recovery
switch on at the same time, which would short-circuit the
source.
The energy-trapping technique may be applied to any power
converter, isolated or non-isolated, PWM or resonant, in which
energy storage in inductive and capacitive circuit elements results
in parasitic oscillations within the converter.
FIG. 7, for example, shows a PWM, unipolar, isolated buck converter
70 comprising a clamp circuit 76. In such a converter, the voltage
delivered by the input source 72, Vin, is higher than the DC output
voltage, Vout, delivered to the load 81. In a first part of a
converter operating cycle, the switch 74 is closed and energy is
delivered to the load from the input source 72 via the output
inductor 82. In a second part of a converter operating cycle, the
switch is open and energy stored in the inductor 82 flows as output
current, Io, to the load via the diode 75. For load values above
some lower limit, the output current, Io, flows continuously in the
output inductor Lout 82. Below that lower limit, however, the
instantaneous current in the output inductor 82 drops to zero and
attempts to reverse. Under these circumstances the diode will block
and, in the absence of the clamp circuit 76, an oscillation will
begin as energy is transferred back and forth between the inductor
82 and circuit parasitic capacitances (e.g., the parasitic
capacitances of the switch 74, the diode 75, the inductor 82 and
the clamp circuit 76, not shown). Waveforms for the converter of
FIG. 7, with the clamp circuit, are shown in FIGS. 8A and 8B.
In FIGS. 8A and 8B, the switch 74 is on at time t=0, the voltage VD
is approximately equal to Vin, and the current Io is increasing
owing to the polarity of the voltage impressed across Lout. At time
tsoff, switch 74 turns off and the voltage VD drops to essentially
zero volts as the parasitic capacitances across the diode 75 are
discharged and the diode conducts. The clamp switch 78 may be
turned on any time after the voltage VD drops below Vout.
At time tcross the current Io declines to zero and attempts to
reverse. After the diode 75 ceases conducting, the voltage VD rings
up until the clamp diode 80 begins to conduct at time tc, when the
voltage VD is approximately equal to Vout. Between times tc and
tcoff the clamp circuit clamps the inductor and prevents parasitic
oscillations. At time tcoff, the clamp switch is opened and the
voltage VD rings up toward Vin. At time tson the switch 74 is
closed, initiating another converter operating cycle. A switch
controller 77 controls the relative timing of the two switches 74,
78. As for the timing discussed in FIG. 4, the delay between the
opening of the clamp switch 78 and the closing of the switch 74 is
adjusted so that the closure of switch 74 corresponds in time to
approximately the time of occurrence of the first maximum in the
voltage Vs following the opening of the clamp switch 78. This
minimizes or eliminates the switching loss associated with closure
of switch 74.
The transformer coupled clamp circuit of FIG. 5 may be used in the
converter of FIG. 7.
Other embodiments are within the scope of the following claims.
For example, the technique may be applied to any switching power
converter in which there is a time period during which undesired
oscillations occur as a result of energy being transferred back and
forth between unclamped inductive and capacitive energy storing
elements.
For example, FIGS. 9A through 9D show isolated, single-ended
converters which comprise a clamp circuit 76 according to the
invention. FIG. 9A is a unipolar, single-ended, forward PWM
converter; FIG. 9B is a unipolar, single-ended, zero-current
switching forward converter (as described in U.S. Pat. No.
4,415,959, incorporated by reference); FIG. 9C is a unipolar,
single-ended, flyback converter with a clamp circuit 76 connected
to the primary winding 105 of the flyback transformer; and FIG. 9D
is a unipolar, single-ended, flyback converter with a clamp circuit
76 connected to the secondary winding 104 of the flyback
transformer.
The clamp circuit may be modified to be of the magnetically coupled
kind shown in FIG. 5, above. Other topologies to which the
technique may be applied include resonant and quasi-resonant
non-isolated, boost, buck and buck-boost converters. By use of
bipolar clamp circuitry of FIG. 6, or equivalent circuitry, the
technique may be applied to bipolar equivalents of unipolar PWM,
resonant and quasi-resonant non-isolated, boost, buck and
buck-boost converters.
* * * * *