U.S. patent application number 16/718680 was filed with the patent office on 2021-05-27 for dual-mode active clamp flyback converter.
The applicant listed for this patent is ASIAN POWER DEVICES INC.. Invention is credited to Tsung-Liang HUNG, Yeu-Torng YAU.
Application Number | 20210159802 16/718680 |
Document ID | / |
Family ID | 1000005579973 |
Filed Date | 2021-05-27 |
View All Diagrams
United States Patent
Application |
20210159802 |
Kind Code |
A1 |
YAU; Yeu-Torng ; et
al. |
May 27, 2021 |
DUAL-MODE ACTIVE CLAMP FLYBACK CONVERTER
Abstract
A dual-mode active clamp flyback converter includes a
transformer circuit, a clamping energy storage circuit, and a main
switch circuit. The transformer circuit is coupled to a load, and
the transformer circuit includes an auxiliary winding. The clamping
energy storage circuit is coupled to the transformer circuit. If
the load as a heavy loading, the clamping energy storage circuit is
turned on. If the load as a light loading, the clamping energy
storage circuit is turned off. The main switch circuit is coupled
to the transformer circuit. When the main switch circuit is turned
on, the auxiliary winding releases energy to a primary-side winding
of the transformer circuit.
Inventors: |
YAU; Yeu-Torng; (Taoyuan
City, TW) ; HUNG; Tsung-Liang; (Taoyuan City,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASIAN POWER DEVICES INC. |
Taoyuan City |
|
TW |
|
|
Family ID: |
1000005579973 |
Appl. No.: |
16/718680 |
Filed: |
December 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 1/0048 20210501;
H02M 1/083 20130101; H02M 3/33569 20130101; H02M 3/33507
20130101 |
International
Class: |
H02M 3/335 20060101
H02M003/335; H02M 1/08 20060101 H02M001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2019 |
TW |
108142639 |
Claims
1. A dual-mode active clamp flyback converter comprising: a
transformer circuit coupled to a load, and the transformer circuit
including an auxiliary winding, a clamping energy storage circuit
coupled to the transformer circuit, if the load as a heavy loading,
the clamping energy storage circuit configured to turn on, and if
the load as a light loading, the clamping energy storage circuit
configured to turn off, and a main switch circuit coupled to the
transformer circuit, when the main switch circuit configured to
turn on, the auxiliary winding configured to release energy to a
primary-side winding of the transformer circuit, wherein, after the
clamping energy storage circuit is configured to turn on and then
turn off, the main switch circuit is configured to enter a
zero-voltage switching mode, wherein, the transformer circuit
further includes a secondary-side winding coupled to the load, the
primary-side winding is coupled in parallel to a magnetizing
inductance of the transformer circuit, and is coupled to an input
voltage through a leakage inductance of the transformer circuit,
wherein, the clamping energy storage circuit includes an auxiliary
switch, a clamping capacitor, and a diode that are coupled to each
other, the auxiliary switch is coupled to the input voltage and the
leakage inductance, the clamping capacitor is coupled to the
magnetizing inductance, the primary-side winding, and the main
switch circuit, and the diode is coupled to the auxiliary
winding.
2. The dual-mode active clamp flyback converter in claim 1, wherein
under a condition that inputting a fixed voltage to the transformer
circuit, a turning point of a conversion efficiency obtained
according to a conversion efficiency ratio of the load coupled to
the transformer circuit, when a value of an actual output power is
less than a value of an output power corresponding to the turning
point of the conversion efficiency, the load as the light loading,
when the value of the actual output power is greater than the value
of the output power corresponding to the turning point of the
conversion efficiency, the load as the heavy loading.
3-4. (canceled)
5. The dual-mode active clamp flyback converter in claim 1, wherein
the main switch circuit includes a main switch, one end of the main
switch is coupled to the primary-side winding, the magnetizing
inductance, and the clamping capacitor, the other end of the main
switch is coupled to the auxiliary winding and the input
voltage.
6. The dual-mode active clamp flyback converter in claim 5, wherein
when the auxiliary switch is configured to turn off and the main
switch is configured to turn on, the input voltage, the leakage
inductance, the primary-side winding, and the main switch
constitute a first loop, the input voltage, the leakage inductance,
the primary-side winding, the clamping capacitor, the diode and the
auxiliary winding constitute a second loop, if the clamping
capacitor has temporarily stored energy from the leakage
inductance, the clamping capacitor, the main switch, the auxiliary
winding, and the diode constitute a third loop; in the first loop,
the leakage inductance is configured to perform energy storage, and
the magnetizing inductance is configured to perform magnetization;
in the second loop, the magnetizing inductance is configured to
perform magnetization; in the third loop, the clamping capacitor is
configured to release energy to the primary-side winding through
the auxiliary winding, when the auxiliary switch and the main
switch are configured to turn off, the leakage inductance, the
primary-side winding, the clamping capacitor, and a body diode
parasitic to the auxiliary switch constitute a fourth loop, in the
fourth loop, the leakage inductance is configured to perform energy
release, and the magnetizing inductance is configured to perform
demagnetization.
7. The dual-mode active clamp flyback converter in claim 6, wherein
if the load as the heavy loading, after the fourth loop is
constituted, the auxiliary switch is turned on and the main switch
is turned off, the leakage inductance, the primary-side winding,
the clamping capacitor, and the auxiliary switch constitute a fifth
loop, in the fifth loop, the leakage inductance is configured to
perform energy storage, and the magnetizing inductance is
configured to perform demagnetization.
8. The dual-mode active clamp flyback converter in claim 7, wherein
if the load as the heavy loading, after the fifth loop is
constituted, the auxiliary switch and the main switch are turned
off, the input voltage, the leakage inductance, the primary-side
winding, and a body diode parasitic to the main switch constitute a
sixth loop, in the sixth loop, the leakage inductance is configured
to perform energy release.
9. The dual-mode active clamp flyback converter in claim 8, wherein
if the load as the heavy loading, after the sixth loop is
constituted, the auxiliary switch is turned off and the main switch
is turned on, and then the second loop and the third loop are
constituted.
10. The dual-mode active clamp flyback converter in claim 6,
wherein if the load as the light loading, after the fourth loop is
constituted, the auxiliary switch and the main switch are turned
off, and then the first loop and the third loop are constituted.
Description
BACKGROUND
Technical Field
[0001] The present disclosure relates to an active clamp flyback
converter, and more particularly to a dual-mode active clamp
flyback converter that can automatically switch operating modes to
optimize conversion efficiency for heavy loading or light
loading.
Description of Related Art
[0002] The statements in this section merely provide background
information related to the present disclosure and do not
necessarily constitute prior art.
[0003] Conventional flyback converters are widely used in power
conversion systems suitable for low-to-medium-power because of
their circuit has simple architecture. The flyback converters have
advantages of electrical isolation and output voltage adjustable by
ratio of winding. There is a leakage inductance in the transformer.
When a switch is turned on and the magnetized inductance of
primary-side store energy, the leakage inductance will also be
stored energy. When the switch is turned off and the magnetizing
inductance starts to release energy to secondary-side, if no
release path for stored energy of the leakage inductance, the
leakage inductance may release energy to a capacitor of the switch,
which will cause the output voltage to rise sharply and may appear
a high voltage spike, and which will cause damage to the switch. In
recent years, in order to solve the above problems, a technology of
active clamping has been proposed successively.
[0004] However, a conventional active clamp flyback (ACF)
converters has higher conversion efficiency when that operates
under a condition with low voltage and heavy loading. But when the
conventional ACF converter is operated at high voltage and light
load, the conversion efficiency is significantly lower than that of
a passive lossless shock absorber flyback converter. Furthermore,
although the conventional flyback converter with leakage inductance
energy recovery winding has higher conversion efficiency when that
operates under a condition with high voltage and light loading, but
the conversion efficiency is significantly lower than that of the
ACF converter when operating under a condition with low voltage and
heavy loading.
[0005] Therefore, how to design a dual-mode active clamp flyback
converter to solve the technical problems above is an important
subject studied by the inventors and proposed in the present
disclosure. In particular, solving the technical problem that it is
difficult to improve the conversion efficiency.
SUMMARY
[0006] The purpose of the present disclosure is to provide a
dual-mode active clamp flyback converter, which can automatically
switch operating modes for optimized efficiency in response to
heavy loading or light loading to solve the technical problem that
it is difficult to improve the conversion efficiency, and achieve
the purpose of convenient operation, improve conversion efficiency
and save power consumption costs.
[0007] In order to achieve the purpose above-mentioned, the
dual-mode active clamp flyback converter includes a transformer
circuit, a clamping energy storage circuit and a main switch
circuit. The transformer circuit is coupled to a load, and the
transformer circuit including an auxiliary winding. The clamping
energy storage circuit is coupled to the transformer circuit, if
the load as a heavy loading, the clamping energy storage circuit
turns on, and if the load as a light loading, the clamping energy
storage circuit turns off. The main switch circuit is coupled to
the transformer circuit, when the main switch circuit turns on, the
auxiliary winding releases energy to a primary-side winding of the
transformer circuit. After the clamping energy storage circuit
turns on and then turns off, the main switch circuit enters a
zero-voltage switching mode.
[0008] Further, under a condition that inputting a fixed voltage to
the transformer circuit, a turning point of a conversion efficiency
obtained according to a conversion efficiency ratio of the load
coupled to the transformer circuit, when a value of an actual
output power is less than a value of an output power corresponding
to the turning point of the conversion efficiency, the load as the
light loading, when the value of the actual output power is greater
than the value of the output power corresponding to the turning
point of the conversion efficiency, the load as the heavy
loading.
[0009] Further, the transformer circuit further includes a
secondary-side winding coupled to the load, the primary-side
winding is coupled in parallel to a magnetizing inductance of the
transformer circuit, and coupled to an input voltage through a
leakage inductance of the transformer circuit.
[0010] Further, the clamping energy storage circuit includes an
auxiliary switch, a clamping capacitor, and a diode that are
coupled to each other, the auxiliary switch is coupled to the input
voltage and the leakage inductance, the clamping capacitor is
coupled to the magnetizing inductance, the primary-side winding,
and the main switch circuit, and the diode is coupled to the
auxiliary winding.
[0011] Further, the main switch circuit includes a main switch, one
end of the main switch is coupled to the primary-side winding, the
magnetizing inductance, and the clamping capacitor, the other end
of the main switch is coupled to the auxiliary winding and the
input voltage.
[0012] Further, when the auxiliary switch turns off and the main
switch turns on, the input voltage, the leakage inductance, the
primary-side winding, and the main switch constitute a first loop,
the input voltage, the leakage inductance, the primary-side
winding, the clamping capacitor, the diode and the auxiliary
winding constitute a second loop, if the clamping capacitor has
temporarily stored energy from the leakage inductance, the clamping
capacitor, the main switch, the auxiliary winding, and the diode
constitute a third loop; in the first loop, the leakage inductance
performs energy storage, and the magnetizing inductance performs
magnetization; in the second loop, the magnetizing inductance
performs magnetization; in the third loop, the clamping capacitor
releases energy to the primary-side winding through the auxiliary
winding.
[0013] Further, when the auxiliary switch and the main switch turn
off, the leakage inductance, the primary-side winding, the clamping
capacitor, and a body diode parasitic to the auxiliary switch
constitute a fourth loop, in the fourth loop, the leakage
inductance performs energy release, and the magnetizing inductance
performs demagnetization.
[0014] Further, if the load as the heavy loading, after the fourth
loop is constituted, the auxiliary switch is turned on and the main
switch is turned off, the leakage inductance, the primary-side
winding, the clamping capacitor, and the auxiliary switch
constitute a fifth loop, in the fifth loop, the leakage inductance
performs energy storage, and the magnetizing inductance performs
demagnetization.
[0015] Further, if the load as the heavy loading, after the fifth
loop is constituted, the auxiliary switch and the main switch are
turned off, the input voltage, the leakage inductance, the
primary-side winding, and a body diode parasitic to the main switch
constitute a sixth loop, in the sixth loop, the leakage inductance
performs energy release.
[0016] Further, if the load as the heavy loading, after the sixth
loop is constituted, the auxiliary switch is turned off and the
main switch is turned on, and then the second loop and the third
loop are constituted.
[0017] Further, if the load as the light loading, after the fourth
loop is constituted, the auxiliary switch and the main switch are
turned off, and then the first loop and the third loop are
constituted.
[0018] When the dual-mode active clamp flyback converter of the
present disclosure is used, first determine whether the load is
light loading or heavy loading. If the load is light loading, the
clamping energy storage circuit is kept turning off, so the light
loading operates in a simple energy recovery action, that is, the
auxiliary winding releases energy to the primary-side winding of
the transformer circuit, which can reduce switching frequencies of
the main switch circuit when it operate in valley switching valley
voltage switching (VVS) (i.e., fixed frequency modulation mode, FFM
mode) to achieve the best conversion efficiency at light loading.
If the load is heavy loading, the clamping energy storage circuit
enters an active clamp forward (ACF) mode, that is, the clamping
energy storage circuit can be turned on and then be turned off, so
that the main switch circuit operates the zero-voltage switching
(ZVS) mode for the best conversion efficiency in heavy loading. For
this reason, the dual-mode active clamp flyback converter of the
present disclosure can automatically switch operating modes for
optimized efficiency in response to heavy loading or light loading
to solve the technical problem that it is difficult to improve the
conversion efficiency, and achieve the purpose of convenient
operation, improve conversion efficiency and save power consumption
costs.
[0019] In order to further understand the techniques, means, and
effects of the present disclosure for achieving the intended
purpose. Please refer to the following detailed description and
drawings of the present disclosure. The drawings are provided for
reference and description only, and are not intended to limit the
present disclosure.
BRIEF DESCRIPTION OF DRAWING
[0020] FIG. 1 is a schematic circuit diagram of a dual-mode active
clamp flyback converter of the present disclosure.
[0021] FIG. 2 is a schematic diagram of the conversion efficiency
of the dual-mode active clamp flyback converter of the present
disclosure.
[0022] FIG. 3 is a first state diagram of the dual-mode active
clamp flyback converter operating under heavy loading of the
present disclosure.
[0023] FIG. 4 is a second state diagram of the dual-mode active
clamp flyback converter operating under heavy loading of the
present disclosure.
[0024] FIG. 5 is a third state diagram of the dual-mode active
clamp flyback converter operating under heavy loading of the
present disclosure.
[0025] FIG. 6 is a fourth state diagram of the dual-mode active
clamp flyback converter operating under heavy loading of the
present disclosure.
[0026] FIG. 7 is a fifth state diagram of the dual-mode active
clamp flyback converter operating under heavy loading of the
present disclosure.
[0027] FIG. 8 is a sixth state diagram of the dual-mode active
clamp flyback converter operating under heavy loading of the
present disclosure.
[0028] FIG. 9 is a seventh state diagram of the dual-mode active
clamp flyback converter operating under heavy loading of the
present disclosure.
[0029] FIG. 10 is a first state diagram of the dual-mode active
clamp flyback converter operating under light loading of the
present disclosure.
[0030] FIG. 11 is a second state diagram of the dual-mode active
clamp flyback converter operating under light loading of the
present disclosure.
[0031] FIG. 12 is a third state diagram of the dual-mode active
clamp flyback converter operating under light loading of the
present disclosure.
[0032] FIG. 13 is a fourth state diagram of the dual-mode active
clamp flyback converter operating under light loading of the
present disclosure.
[0033] FIG. 14 is a fifth state diagram of the dual-mode active
clamp flyback converter operated under light loading of the present
disclosure.
DETAILED DESCRIPTION
[0034] The embodiments of the present disclosure are described by
way of specific examples, and those skilled in the art can readily
appreciate the other advantages and functions of the present
disclosure. The present disclosure may be embodied or applied in
various other specific embodiments, and various modifications and
changes can be made without departing from the spirit and scope of
the present disclosure.
[0035] It should be understood that the structures, the
proportions, the sizes, the number of components, and the like in
the drawings are only used to cope with the contents disclosed in
the specification for understanding and reading by those skilled in
the art, and it is not intended to limit the conditions that can be
implemented in the present disclosure, and thus is not technically
significant. Any modification of the structure, the change of the
proportional relationship, or the adjustment of the size, should be
within the scope of the technical contents disclosed by the present
disclosure without affecting the effects and the achievable effects
of the present disclosure.
[0036] The technical content and detailed description of the
present disclosure will be described below in conjunction with the
drawings.
[0037] Please refer to FIG. 1, the FIG. 1 is a schematic circuit
diagram of a dual-mode active clamp flyback converter of the
present disclosure. A dual-mode active clamp flyback converter of
the present disclosure includes a transformer circuit 10, a
clamping energy storage circuit 20 and a main switch circuit 30.
The transformer circuit 10 is coupled to a load 40, and the
transformer circuit 10 includes an auxiliary winding N.sub.1 and a
secondary-side winding N.sub.s coupled to the load 40. A
primary-side winding N.sub.p is coupled in parallel to a
magnetizing inductance L.sub.m of the transformer circuit 10, and
is coupled to the magnetizing inductance L.sub.m of the transformer
circuit 10, and is coupled to an input voltage V.sub.in through a
leakage inductance L.sub.k of the transformer circuit 10. In the
present disclosure, the load 40 is coupled to an output diode
D.sub.o and an output capacitor C.sub.o.
[0038] The clamping energy storage circuit 20 is coupled to the
transformer circuit 10. If the load 40 as a heavy loading, the
clamping energy storage circuit 20 turns on then turn off, and if
the load 40 as a light loading, the clamping energy storage circuit
20 is kept turning off. Further, the clamping energy storage
circuit 20 includes an auxiliary switch S.sub.aux, a clamping
capacitor C.sub.clamp, and a diode D.sub.reg that are coupled to
each other. The auxiliary switch S.sub.aux is coupled to the input
voltage V.sub.in and the leakage inductance L.sub.k, the clamping
capacitor C.sub.clamp is coupled to the magnetizing inductance
L.sub.m, the primary-side winding N.sub.p, and the main switch
circuit 30, and the diode D.sub.reg is coupled to the auxiliary
winding N.sub.1.
[0039] The main switch circuit 30 is coupled to the transformer
circuit 10, when the main switch circuit 30 is turned on, the
auxiliary winding N.sub.1 releases energy to the primary-side
winding N.sub.p of the transformer circuit 10. After the clamping
energy storage circuit 20 turns on and then turns off, the main
switch circuit 30 enters a zero-voltage switching (ZVS) mode. The
main switch circuit 30 includes a main switch S.sub.main, one end
of the main switch S.sub.main is coupled to the primary-side
winding N.sub.p, the magnetizing inductance L.sub.m, and the
clamping capacitor C.sub.clamp, the other end of the main switch
S.sub.main is coupled to the auxiliary winding N.sub.1 and the
input voltage V.sub.in.
[0040] Please refer to FIG. 1 and FIG. 2, the FIG. 2 is a schematic
diagram of the conversion efficiency of the dual-mode active clamp
flyback converter of the present disclosure. Under a condition that
inputting a fixed voltage (i.e., V.sub.in) to the transformer
circuit 10, a turning point P of a conversion efficiency can be
obtained according to a conversion efficiency ratio of the load 40
coupled to the transformer circuit 10. That is, a relationship
curve E1 between conversion efficiency and output power (unit:
watt) obtained when the load 40 is operated in a light loading
mode, and a relationship curve E2 between conversion efficiency and
output power obtained when the load 40 is operated in a heavy
loading mode. The crossing point where E1 and E2 overlap with each
other is the turning point P of conversion efficiency. When a value
of an actual output power is less than a value of an output power
corresponding to the turning point P of the conversion efficiency,
the load 40 as the light loading, that is, the dual-mode active
clamp flyback converter of the present disclosure operates in the
light loading mode. When the value of the actual output power is
greater than the value of the output power corresponding to the
turning point P of the conversion efficiency, the load 40 as the
heavy loading, that is, the dual-mode active clamp flyback
converter of the present disclosure operates in the heavy loading
mode. The dual-mode active clamp flyback converter of the present
disclosure only operates on the real line portions of E1 and E2 as
shown in FIG. 2 during the load 40 switching between the heavy
loading mode or the light loading mode.
[0041] Please refer to FIG. 3 to FIG. 9, there are first state to
seven state diagrams of the dual-mode active clamp flyback
converter operating under heavy loading of the present
disclosure.
[0042] As shown in FIG. 3, when dual-mode active clamp flyback
converter in first state under heavy loading, the auxiliary switch
S.sub.aux is turned off and the main switch S.sub.main is turned
on. The input voltage V.sub.in, the leakage inductance L.sub.k, the
primary-side winding N.sub.p, and the main switch S.sub.main
constitute a first loop L.sub.n1. In the first loop L.sub.n1, as
the current flowing through the primary-side winding N.sub.p
increases, the leakage inductance L.sub.k performs energy storage,
and the magnetizing inductance L.sub.m performs magnetization.
[0043] As shown in FIG. 4, when dual-mode active clamp flyback
converter in second state under heavy loading, the auxiliary switch
S.sub.aux and the main switch S.sub.main are turned off. The
leakage inductance L.sub.k, the primary-side winding N.sub.p, the
clamping capacitor C.sub.clamp, and a body diode D.sub.aux
parasitic to the auxiliary switch S.sub.aux constitute a fourth
loop L.sub.n4. In the fourth loop L.sub.n4, the leakage inductance
L.sub.k performs energy release, and the magnetizing inductance
L.sub.m performs demagnetization. Since the body diode D.sub.aux
parasitic to the auxiliary switch S.sub.aux is turned on, a
parasitic capacitance C.sub.aux parasitic to the auxiliary switch
S.sub.aux is discharged. At this time, if the auxiliary switch
S.sub.aux is turned on, zero-voltage switching (ZVS) of the
auxiliary switch S.sub.aux can be realized.
[0044] As shown in FIG. 5, when dual-mode active clamp flyback
converter in third state under heavy loading, it is substantially
the same as the second state of heavy loading. The auxiliary switch
S.sub.aux and the main switch S.sub.main are turned off. The
leakage inductance L.sub.k, the primary-side winding N.sub.p, the
clamping capacitor C.sub.clamp, and a body diode D.sub.aux
parasitic to the auxiliary switch S.sub.aux constitute a fourth
loop L.sub.n4. However, the magnetizing inductance L.sub.m starts
to release energy to the secondary-side winding N.sub.s. At this
time, because the energy has been transferred to the secondary-side
winding N.sub.s, the output diode D.sub.o is turned on, and the
output capacitor C.sub.o stores energy.
[0045] As shown in FIG. 6, when dual-mode active clamp flyback
converter in fourth state under heavy loading, it is substantially
the same as the third state of heavy loading. The auxiliary switch
S.sub.aux and the main switch S.sub.main are turned off. However,
all energy of the leakage inductance L.sub.k is released, and the
energy of the magnetizing inductance L.sub.m continues to release
to the secondary-side winding N.sub.s.
[0046] As shown in FIG. 7, when dual-mode active clamp flyback
converter in fifth state under heavy loading, after the fourth loop
L.sub.n4 is constituted, the auxiliary switch S.sub.aux is turned
on and the main switch S.sub.main is turned off. The leakage
inductance L.sub.k, the primary-side winding N.sub.p, the clamping
capacitor C.sub.clamp, and the auxiliary switch S.sub.aux
constitute a fifth loop L.sub.n5. In the fifth loop L.sub.n5, the
leakage inductance L.sub.k performs energy storage, and the
magnetizing inductance L.sub.m performs demagnetization. At this
time, the clamping capacitor C.sub.clamp returns energy to the
leakage inductance L.sub.k, and the current flowing through the
leakage inductance L.sub.k is negative.
[0047] As shown in FIG. 8, when dual-mode active clamp flyback
converter in sixth state under heavy loading, after the fifth loop
L.sub.n5 is constituted, the auxiliary switch S.sub.aux and the
main switch Smain are turned off. The input voltage V.sub.in, the
leakage inductance L.sub.k, the primary-side winding N.sub.p, and a
body diode D.sub.main parasitic to the main switch S.sub.main
constitute a sixth loop L.sub.n6. In the sixth loop L.sub.n6, the
leakage inductance L.sub.k performs energy release. At this time,
the current of the leakage inductance L.sub.k is negative, and the
leakage inductance L.sub.k releases energy in series resonance to
the parasitic capacitance C.sub.main parasitic to the main switch
S.sub.main. The voltage of the parasitic capacitance C.sub.main
starts to decrease until the current of the leakage inductance
L.sub.k is cut off. The parasitic capacitance C.sub.main releases
energy in an LC series resonance to the leakage inductance L.sub.k
and the magnetizing inductance L.sub.m, and then the voltage of the
parasitic capacitance C.sub.main drops to zero. So, zero-voltage
switching (ZVS) of the main switch S.sub.main can be realized.
[0048] As shown in FIG. 9, when dual-mode active clamp flyback
converter in seventh state under heavy loading, after the sixth
loop L.sub.n6 is constituted, the auxiliary switch S.sub.aux is
turned off and the main switch S.sub.main is turned on. The input
voltage V.sub.in, the leakage inductance L.sub.k, the primary-side
winding N.sub.p, the clamping capacitor C.sub.clamp, the diode
D.sub.reg and the auxiliary winding N.sub.1 constitute a second
loop L.sub.n. If the clamping capacitor C.sub.clamp has temporarily
stored energy from the leakage inductance L.sub.k, the clamping
capacitor C.sub.clamp, the main switch S.sub.main, the auxiliary
winding N.sub.1, and the diode D.sub.reg constitute a third loop
L.sub.n3. In the second loop L.sub.n2, the magnetizing inductance
L.sub.m performs magnetization. In the third loop L.sub.n3, the
clamping capacitor C.sub.clamp releases energy to the primary-side
winding N.sub.p through the auxiliary winding N.sub.1. That is, the
energy of the leakage inductance L.sub.k temporarily stored in the
clamping capacitor C.sub.clamp is transmitted to an input end of
the transformer circuit 10.
[0049] Please refer to FIG. 10 to FIG. 14, there are first state to
fifth state diagrams of the dual-mode active clamp flyback
converter operating under light loading of the present
disclosure.
[0050] As shown in FIG. 10, when dual-mode active clamp flyback
converter in first state under light loading, the auxiliary switch
S.sub.aux is turned off and the main switch S.sub.main is turned
on. The input voltage V.sub.in, the leakage inductance L.sub.k, the
primary-side winding N.sub.p, and the main switch S.sub.main
constitute the first loop L.sub.n1. In the first loop L.sub.n1, as
the current flowing through the primary-side winding N.sub.p
increases, the leakage inductance L.sub.k performs energy storage,
and the magnetizing inductance L.sub.m performs magnetization.
[0051] As shown in FIG. 11, when dual-mode active clamp flyback
converter in second state under light loading, the auxiliary switch
S.sub.aux and the main switch S.sub.main are turned off. The
leakage inductance L.sub.k, the primary-side winding N.sub.p, the
clamping capacitor C.sub.clamp, and a body diode D.sub.aux
parasitic to the auxiliary switch S.sub.aux constitute a fourth
loop L.sub.n4. In the fourth loop L.sub.n4, as the current of the
leakage inductance L.sub.k flows through the clamping capacitor
C.sub.clamp and the body diode D.sub.aux parasitic to the auxiliary
switch S.sub.aux, the leakage inductance L.sub.k releases energy
and the magnetizing inductance L.sub.m performs demagnetization.
Since the body diode D.sub.aux parasitic to the auxiliary switch
S.sub.aux is turned on, the parasitic capacitance C.sub.aux
parasitic to the auxiliary switch S.sub.aux is discharged. At this
time, if the auxiliary switch S.sub.aux is turned on, zero-voltage
switching (ZVS) of the auxiliary switch S.sub.aux can be
realized.
[0052] As shown in FIG. 12, when dual-mode active clamp flyback
converter in third state under light loading, it is substantially
the same as the second state of light loading. The auxiliary switch
S.sub.aux and the main switch S.sub.main are turned off. The
leakage inductance L.sub.k, the primary-side winding N.sub.p, the
clamping capacitor C.sub.clamp, and a body diode D.sub.aux
parasitic to the auxiliary switch S.sub.aux constitute a fourth
loop L.sub.n4. However, the magnetizing inductance L.sub.m starts
to release energy to the secondary-side winding N.sub.s. At this
time, because the energy has been transferred to the secondary-side
winding N.sub.s, the output diode D.sub.o is turned on, and the
output capacitor C.sub.o stores energy.
[0053] As shown in FIG. 13, when dual-mode active clamp flyback
converter in fourth state under light loading, it is substantially
the same as the third state of light loading. The auxiliary switch
S.sub.aux and the main switch S.sub.main are turned off. However,
all energy of the leakage inductance L.sub.k is released, and the
energy of the magnetizing inductance L.sub.m continues to release
to the secondary-side winding N.sub.s.
[0054] As shown in FIG. 14, when dual-mode active clamp flyback
converter in fifth state under heavy loading, after the fourth loop
L.sub.n4 is constituted, the auxiliary switch S.sub.aux and the
main switch S.sub.main are turned off, and then the first loop
L.sub.n1 and the third loop L.sub.n3 are constituted. The input
voltage V.sub.in, the leakage inductance L.sub.k, the primary-side
winding N.sub.p, and the main switch S.sub.main constitute the
first loop L.sub.n1. If the clamping capacitor C.sub.clamp has
temporarily stored energy from the leakage inductance L.sub.k, the
clamping capacitor C.sub.clamp, the main switch S.sub.main, the
auxiliary winding N.sub.1, and the diode D.sub.reg constitute the
third loop L.sub.n3. In the first loop L.sub.n1, the magnetizing
inductance L.sub.m performs magnetization. In the third loop
L.sub.n3, the clamping capacitor C.sub.clamp releases energy to the
primary-side winding N.sub.p through the auxiliary winding N.sub.1.
That is, the energy of the leakage inductance L.sub.k temporarily
stored in the clamping capacitor C.sub.clamp is transmitted to the
input end of the transformer circuit 10.
[0055] When the dual-mode active clamp flyback converter of the
present disclosure is used, first determine whether the load 40 is
light loading or heavy loading. If the load 40 is light loading,
the clamping energy storage circuit 20 is kept turning off, so the
light loading operates in a simple energy recovery action, that is,
the energy of the leakage inductance L.sub.k temporarily stored in
the clamping capacitor C.sub.clamp releases to the primary-side
winding N.sub.p of the transformer circuit 10 thought the auxiliary
winding N.sub.1, which can reduce switching frequencies of the main
switch circuit 30 when it operates in valley switching valley
voltage switching (VVS) (i.e., fixed frequency modulation mode, FFM
mode) to achieve the best conversion efficiency at light loading.
If the load 40 is heavy loading, the clamping energy storage
circuit 20 enters an active clamp forward (ACF) mode, that is, the
auxiliary switch S.sub.aux of the clamping energy storage circuit
20 can be turned on and then be turned off, so that the main switch
S.sub.main of the main switch circuit 30 operates the zero-voltage
switching (ZVS) mode for the best conversion efficiency in heavy
loading. For this reason, the dual-mode active clamp flyback
converter of the present disclosure can automatically switch
operating modes for optimized efficiency in response to heavy
loading or light loading to solve the technical problem that it is
difficult to improve the conversion efficiency, and achieve the
purpose of convenient operation, improve conversion efficiency and
save power consumption costs.
[0056] The above is only a detailed description and drawings of the
preferred embodiments of the present disclosure, but the features
of the present disclosure are not limited thereto, and are not
intended to limit the present disclosure. All the scope of the
present disclosure shall be subject to the scope of the following
claims. The embodiments of the spirit of the present disclosure and
its similar variations are intended to be included in the scope of
the present disclosure. Any variation or modification that can be
easily conceived by those skilled in the art in the field of the
present disclosure can be covered by the following claims.
* * * * *