U.S. patent application number 09/898371 was filed with the patent office on 2002-01-10 for single phase ac-dc converter having a power factor control function.
This patent application is currently assigned to Fidelix Y.K.. Invention is credited to Nakawaga, Shin.
Application Number | 20020003713 09/898371 |
Document ID | / |
Family ID | 27344294 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003713 |
Kind Code |
A1 |
Nakawaga, Shin |
January 10, 2002 |
Single phase AC-DC converter having a power factor control
function
Abstract
The single-phase AC-DC converter includes a PFC power supply
section, where a rectified current obtained by rectifying an
electric current from an AC supply is switched; a DC-DC power
supply section, where a direct current obtained by rectifying and
smoothing an electric current from an AC supply is switched; a
first switching element for conducting a switching operation in the
PFC power supply section; a second switching element for conducting
a switching operation in the DC-DC power supply section; a drive
pulse generating circuit for generating first drive pulses for
driving said first switching element and second drive pulses for
driving said second switching element; and a servo loop for
controlling the drive pulse generating circuit. The servo loop is
constituted of only one serve loop; and the duty ratio of the drive
pulses for driving the first switching element is different from
the duty ratio of the drive pulses for driving the second switching
element from each other in a linked manner.
Inventors: |
Nakawaga, Shin; (Tokyo,
JP) |
Correspondence
Address: |
BRUCE LONDA
NORRIS, MCLAUGHLIN & MARCUS, P.A.
220 EAST 42ND STREET, 30TH FLOOR
NEW YORK
NY
10017
US
|
Assignee: |
Fidelix Y.K.
Tokyo
JP
|
Family ID: |
27344294 |
Appl. No.: |
09/898371 |
Filed: |
July 3, 2001 |
Current U.S.
Class: |
363/72 |
Current CPC
Class: |
H02M 1/4225 20130101;
Y02B 70/10 20130101; H02M 1/4208 20130101; H02M 7/05 20210501 |
Class at
Publication: |
363/72 |
International
Class: |
H02M 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2000 |
JP |
2000-240433 |
Jul 17, 2000 |
JP |
2000-250341 |
Jul 2, 2001 |
JP |
2001-200709 |
Claims
What is claimed is:
1. A single-phase AC-DC converter comprising: a PFC power supply
section, where a rectified current obtained by rectifying an
electric current from an AC supply is switched; a DC-DC power
supply section, where a direct current obtained by rectifying and
smoothing an electric current from an AC supply is switched; a
first switching means for conducting a switching operation in said
PFC power supply section; a second switching means for conducting a
switching operation in said DC-DC power supply section; a drive
pulse generating circuit for generating first drive pulses for
driving said first switching means and second drive pulses for
driving said second switching means; and a servo loop for
controlling said drive pulse generating circuit; wherein said servo
loop is constituted of only one serve loop; and wherein said
converter comprises a duty ratio controlling means for making a
duty ratio of said drive pulses for driving said first switching
means and a duty ratio of said drive pulses for driving said second
switching means different from each other in a linked manner.
2. An single phase AC-DC converter according to claim 1, wherein
said PFC power supply section comprises an input for connection to
a source of a single phase AC supply, a first rectifying circuit
for rectifying an electric current supplied from said inputs, a
first transformer where one end of the primary coil thereof is
connected to an output of said rectifying circuit and other end of
said primary coil is connected to said first switching means, and a
first secondary side rectifying circuit for rectifying an output of
the secondary side of said first transformer; wherein said DC-DC
power supply section comprises an input for connection to a source
of single phase AC supply, a second rectifying circuit for
rectifying an electric current supplied from said inputs, a
smoothing circuit for smoothing an output of said second rectifying
circuit, a second transformer where one end of the primary coil
thereof is connected to an output of said smoothing circuit and the
other end of said primary coil is connected to said second
switching means, and a second secondary side rectifying circuit for
rectifying an output of the secondary side of said second
transformer; and wherein said converter comprises an adding and
smoothing circuit for adding an output of said PFC power supply
section and an output of said DC-DC power supply section together
and smoothing the added outputs.
3. An single phase AC-DC converter according to claim 1, wherein
said PFC power supply section comprises an input for connection to
a source of single phase AC supply, a first rectifying circuit for
rectifying an electric current supplied from said inputs, a first
transformer where one end of the primary coil thereof is connected
to an output of said rectifying circuit and the other end of said
primary coil is connected to said first switching means, and a
first secondary side rectifying circuit for rectifying an output of
the secondary side of said first transformer; wherein said DC-DC
power supply section comprises an input for connection to a source
of single phase AC supply, a smoothing circuit for smoothing an
electric current supplied from said inputs, a second transformer
where one end of the primary coil thereof is connected to an output
of said smoothing circuit and the other end of said primary coil is
connected to said second switching means, and a second secondary
side rectifying circuit for rectifying an output of the secondary
side of said second transformer; wherein said converter comprises
an output adding and smoothing circuit for adding an output of said
PFC power supply section and an output of said DC-DC power supply
section together and smoothing the added outputs; and wherein an
inductor and a diode are inserted between said second switching
means and an output of said first rectifying circuit or between
said second switching means and said AC inputs.
4. A single phase AC-DC converter according to claim 1, wherein
said PFC power supply section comprises an input for connection to
a source of a single phase AC supply, a first rectifying circuit
for rectifying an electric current supplied from said inputs, a
first transformer where one end of the primary coil thereof is
connected to an output of said rectifying circuit and other end of
said primary coil is connected to said first switching means, and a
first secondary side rectifying circuit for rectifying an output of
the secondary side of said first transformer; wherein said DC-DC
power supply section comprises an input for connection to a source
of single phase AC supply, a smoothing circuit for smoothing an
electric current supplied from said inputs, a second transformer
where one end of the primary coil thereof is connected to an output
of said smoothing circuit and other end of said primary coil is
connected to said second switching means, and a second secondary
side rectifying circuit for rectifying an output of the secondary
side of said second transformer; wherein said converter comprises
an output adding and smoothing circuit for adding an output of said
PFC power supply section and an output of said DC-DC power supply
section together and smoothing the added outputs; and wherein
either one of said first transformer or said second transformer
comprises a tertiary coil, and one end of the tertiary coil is
connected to an output of said smoothing circuit and other end
thereof is connected to an output of said first rectifying circuit
via a diode or to said AC inputs via a diode.
5. A single phase AC-DC converter according to claim 5, wherein the
PFC power supply section comprises an input for connection to a
source of a single phase AC supply, a first rectifying circuit for
rectifying an electric current supplied from said inputs, a choke
coil where one end of the coil thereof is connected to an output of
said rectifying circuit and other end of the coil is connected to
said first switching means; wherein said DC-DC power supply
comprises a second rectifying circuit for rectifying an output of
said choke coil, a first smoothing circuit for smoothing an output
of said second rectifying circuit, a transformer where one end of
the primary coil thereof is connected to an output of said
smoothing circuit and the other end of the primary coil is
connected to said second switching means, a secondary side
rectifying circuit for rectifying an output at the secondary side
of said transformer, and a second smoothing circuit for smoothing
an output of said secondary side rectifying circuit.
6. A single phase AC-DC converter according to claim 1, wherein the
PFC power supply section comprises an input for connection to a
source of a single phase AC supply, a first rectifying circuit for
rectifying an electric current supplied from said inputs, a first
transformer where one end of the primary coil thereof is connected
to an output of said rectifying circuit and other end of the
primary coil is connected to said first switching means, and a
first secondary side rectifying circuit for rectifying an output at
the secondary side of said first transformer; wherein said DC-DC
power supply comprises a second rectifying circuit for rectifying
an output at the primary side of said first transformer, a first
smoothing circuit for smoothing an output of said second rectifying
circuit, a second transformer where one end of the primary coil
thereof is connected to an output of said first smoothing circuit
and other end of the primary coil is connected to said second
switching means, a second secondary side rectifying circuit for
rectifying an output at the secondary side of said second
transformer, a second smoothing circuit for smoothing an output of
said second secondary side rectifying circuit; and wherein said
converter comprises an adding and smoothing means for adding an
output of said PFC power supply section and an output of said DC-DC
power supply section together and smoothing the added output.
7. A single phase AC-DC converter according to claim 1, wherein the
drive pulses for driving the first switching means and the drive
pulses for driving the second switching means turn on at a
different timing from each other but turn off at the same
timing.
8. A single phase AC-DC converter according to claim 1, wherein the
ON time of the drive pulses for driving the first switching means
and the ON time of the drive pulses for driving the second
switching means are different from each other keeping a given
relation therebetween, whereby the ratio between the duty ratio of
the first switching means and the duty ratio of the second
switching means becomes constant.
9. A single phase AC-DC converter according to claim 1 further
comprising a drive pulses intermittent oscillation control means by
which the drive pulse generating means generate the drive pulses
intermittently.
10. A single phase AC-DC converter according to claim 9, wherein
said drive pulses intermittent oscillation control means comprises
a comparator having a hysteresis characteristic and/or a time
constant so that the drive pulse output of the drive pulse
generating means is controlled in accordance with the output of
said comparator.
11. A single phase AC-DC converter according to claim 1 further
comprising a starting-up circuit for starting the drive pulse
generating circuit up; wherein said starting-up circuit comprises
an input for connection to a source of single phase AC supply, a
rectifying circuit for rectifying an electric current supplied from
said inputs, a smoothing circuit for smoothing an output of said
rectifying circuit, and starting-up capacitors being provided
between said AC inputs and said rectifying circuits.
12. A single phase AC-DC converter according to claim 11, wherein
said rectifying circuit is constituted of a bridge rectifying
circuit; and wherein said starting-up circuit further comprises a
voltage detecting circuit after said rectifying circuit, and a
switch element, which is driven by the output of the voltage
detecting circuit, being provided at an output side either one of
the starting-up capacitors.
Description
BACKGROUND OF THE INVENTION
[0001] 1) Field of the Invention
[0002] The present invention relates to a single phase AC-DC
converter, and particularly, relates to a single phase AC-DC
converter having a construction that a PFC (Power Factor Control)
power supply section, where a rectified current obtained by
rectifying an electric current from an AC supply is switched, and a
DC-DC power supply section, where a direct current obtained by
rectifying and smoothing an electric current from an AC supply is
switched, are combined together; the switching elements for
switching both the sections are driven and controlled with only one
servo loop.
[0003] 2) Related Art
[0004] The present inventor discloses a single phase AC-DC
converter where a PFC power supply section and a DC-DC power supply
section are combined together in Japanese Patent Preliminarily
Publication No. 11-356046. In the power supply apparatus, a PFC
switching power supply section (rectified current side) having a
smaller current smoothing function and a DC-DC switching power
supply section (direct current side) having a greater current
smoothing function are combined in a parallel manner; the rectified
outputs of these sections are added together; thereby a harmonics
current can be restricted ,the size of the converter becomes
compact, and a high efficiency can be obtained. In this apparatus,
the rectified current side contributes to restrict a harmonics
current, while the direct current side keeps a holding time
sufficiently and reduces a ripple voltage. By making a balance of
power between the rectified current side section and the direct
current side section, a switching power supply apparatus is
realized, which is small in size and has a high efficiency while
satisfying the Class A standard for harmonics by the IEC
(International Electrotechnical Commission).
[0005] In addition, so-called two-stage type AC-DC converters are
also developed, which also have a PFC power supply section and a
DC-DC power supply section being connected together in a cascade
manner in order to restrict a harmonics current.
[0006] However, according to the AC-DC converter mentioned in
Japanese Preliminarily Patent Publication 11-356046, in order to
set the electric current ratio between the rectified current side
section and the direct current side section so as to satisfy said
standard for harmonics by IEC, it is necessary to keep the
inductance at the rectified current side section considerably low.
Therefore, the current waveform at the primary side of the
rectified current side section becomes a narrow triangle and thus
the route-mean-square current increases there. As a result, the
efficiency cannot be improved as expected.
[0007] The current International Standard for harmonics current is
IEC61000-3-2. According to the AC-DC converter mentioned in
Japanese Preliminarily Patent Publication 11-356046, in the case
that the converter is designed for accepting an input voltage in a
range of 100V to 240V, the current waveform belongs to the Class A
of the IEC62000-3-2, so that the converter satisfies the harmonics
spectrum standard defined by the Class A without problem.
[0008] However, it is planned to change the International Standard
of the IEC in future, and a provisional standard has been defined
at the end of 2000. According to the provisional standard, it is
required for certain appliances, i.e. personal computers,
televisions, or monitors, to meet the Class D, which is stricter
than the Class A. The converter according to the Japanese
Preliminarily Patent Publication 11-356046 satisfies the harmonics
standard in Class D if the converter is so designed as to accept an
input voltage of 100.about.120V or an input voltage of
200.about.240V. However, if the converter is designed to accept an
input voltage in a wider range, i.e. 100.about.240V, it is
difficult to satisfy the harmonics standard in Class D.
[0009] On the other hand, according to the conventional two-stage
type AC-DC converter, where the rectified-line side section and the
direct current side section are combined together in a cascade
manner, satisfies the harmonics current standard in Class D by the
IEC, the efficiency, however, is poor and it is difficult to make
the size of the converter compact. Further, power consumption
during standby time cannot be reduced in a sufficient manner and
the cost for manufacturing the converter is still high.
SUMMARY OF THE INVENTION
[0010] In order to solve the above-mentioned problems, an AC-DC
converter according to the present invention comprises a PFC power
supply section where a rectified current obtained by rectifying an
electric current from an AC supply is switched, a DC-DC power
supply section where a direct current obtained by rectifying and
smoothing an electric current from an AC supply is switched, a
first switching means for conducting a switching operation in said
PFC power supply section, a second switching means for conducting a
switching operation in said DC-DC power supply section, a drive
pulse generating circuit for generating first drive pulses for
driving said first switching means and second drive pulses for
driving said second switching means, and a servo loop for
controlling said drive pulse generating circuit; wherein said servo
loop is constituted of only one serve loop; and wherein said
converter comprises a duty ratio controlling means for making a
duty ratio (ON time) of said drive pulses for driving said first
switching means and a duty ratio (ON time) of said drive pulses for
driving said second switching means different from each other in a
linked manner.
[0011] In this manner, according to the AC-DC converter of the
present invention, a duty ratio controlling means is provided, by
which the duty ratio (ON time) of the drive pulses for driving the
first switching means and the duty ratio (ON time) of the drive
pulses for driving the second switching means become different from
each other in a linked manner, so that efficiency is improved and
the size of the converter can be made compact.
[0012] Further, the AC-DC converter according to the present
invention has a characteristic in that said PFC power supply
section comprises an input for connection to a source of a single
phase AC supply, a first rectifying circuit for rectifying an
electric current supplied from said inputs, a first transformer
where one end of the primary coil thereof is connected to an output
of said rectifying circuit and the other end of said primary coil
is connected to said first switching means, and a first secondary
side rectifying circuit for rectifying an output of the secondary
side of said first transformer; said DC-DC power supply section
comprises an input for connection to a source of a single phase AC
supply, a second rectifying circuit for rectifying an electric
current supplied from said inputs, a smoothing circuit for
smoothing an output of said second rectifying circuit, a second
transformer where one end of the primary coil thereof is connected
to an output of said smoothing circuit and other end of said
primary coil is connected to said second switching means, and a
second secondary side rectifying circuit for rectifying an output
of the secondary side of said second transformer; and said
converter comprises an adding and smoothing circuit for adding an
output of said PFC power supply section and an output of said DC-DC
power supply section together and smoothing the added outputs.
[0013] According to the construction in that the PFC power supply
section and the DCDC power supply section are operated with
different duty ratios and that the PFC power supply section and the
DC-DC power supply section are combined in a parallel manner and
the outputs of both power supply sections are added together and
smoothed, the efficiency of the converter can be more improved.
[0014] Further, the AC-DC converter according to the present
invention has a characteristic in that said PFC power supply
section comprises an input for connection to a source of a single
phase AC supply, a first rectifying circuit for rectifying an
electric current supplied from said inputs, a first transformer
where one end of the primary coil thereof is connected to an output
of said rectifying circuit and other end of said primary coil is
connected to said first switching means, and a first secondary side
rectifying circuit for rectifying an output of the secondary side
of said first transformer; said DC-DC power supply section
comprises an input for connection to a source of a single phase AC
supply, a smoothing circuit for smoothing an electric current
supplied from said inputs, a second transformer where one end of
the primary coil thereof is connected to an output of said
smoothing circuit and other end of said primary coil is connected
to said second switching means, and a second secondary side
rectifying circuit for rectifying an output of the secondary side
of said second transformer; and said converter comprises an output
adding and smoothing circuit for adding an output of said PFC power
supply section and an output of said DC-DC power supply section
together and smoothing the added outputs; and wherein an inductor
and a diode are inserted between said second switching means and an
output of said first rectifying circuit or between said second
switching means and said AC inputs.
[0015] Furthermore, the AC-DC converter according to the present
invention has a characteristic in that said PFC power supply
section comprises an input for connection to a source of a single
phase AC supply, a first rectifying circuit for rectifying an
electric current supplied from said inputs, a first transformer
where one end of the primary coil thereof is connected to an output
of said rectifying circuit and other end of said primary coil is
connected to said first switching means, and a first secondary side
rectifying circuit for rectifying an output of the secondary side
of said first transformer; said DC-DC power supply section
comprises an input for connection to a source of single phase AC
supply, a smoothing circuit for smoothing an electric current
supplied from said inputs, a second transformer where one end of
the primary coil thereof is connected to an output of said
smoothing circuit and the other end of said primary coil is
connected to said second switching means, and a second secondary
side rectifying circuit for rectifying an output of the secondary
side of said second transformer; and said converter comprises an
output adding and smoothing circuit for adding an output of said
PFC power supply section and an output of said DC-DC power supply
section together and smoothing the added outputs; wherein either
said first transformer or said second transformer comprises a
tertiary coil, and one end of the tertiary coil is connected to an
output of said smoothing circuit and the other end thereof is
connected to an output of said first rectifying circuit via a diode
or to said AC inputs via a diode.
[0016] According to the construction above, harmonics which are
generated in the DCDC power supply section can be reduced, so that
an AC-DC converter satisfying the strict standard in Class D by the
IEC can be realized.
[0017] Moreover, the AC-DC converter according to the present
invention has a characteristic in that the PFC power supply section
comprises an input for connection to a source of single phase AC
supply, a first rectifying circuit for rectifying an electric
current supplied from said inputs, a choke coil where one end of
the coil thereof is connected to an output of said rectifying
circuit and the other end of the coil is connected to said first
switching means; said DC-DC power supply comprises a second
rectifying circuit for rectifying an output of said choke coil, a
first smoothing circuit for smoothing an output of said second
rectifying circuit, a transformer where one end of the primary coil
thereof is connected to an output of said smoothing circuit and the
other end of the primary coil is connected to said second switching
means, a secondary side rectifying circuit for rectifying an output
at the secondary side of said transformer, and a second smoothing
circuit for smoothing an output of said secondary side rectifying
circuit.
[0018] Moreover, the AC-DC converter according to the present
invention has a characteristic in that the PFC power supply section
comprises an input for connection to a source of a single phase AC
supply, a first rectifying circuit for rectifying an electric
current supplied from said inputs, a first transformer where one
end of the primary coil thereof is connected to an output of said
rectifying circuit and other end of the primary coil is connected
to said first switching means, and a first secondary side
rectifying circuit for rectifying an output at the secondary side
of said first transformer; said DC-DC power supply comprises a
second rectifying circuit for rectifying an output at the primary
side of said first transformer, a first smoothing circuit for
smoothing an output of said second rectifying circuit, a second
transformer where one end of the primary coil thereof is connected
to an output of said first smoothing circuit and other end of the
primary coil is connected to said second switching means, a second
secondary side rectifying circuit for rectifying an output at the
secondary side of said second transformer, a second smoothing
circuit for smoothing an output of said second secondary side
rectifying circuit, and an adding and smoothing means for adding an
output of said PFC power supply section and an output of said DC-DC
power supply section together and smoothing the added output.
[0019] In this manner, the PFC power supply section and the DC-DC
power supply section may be connected together in a cascade manner.
According to the construction, a two-stage type AC-DC converter can
be realized where the size is small and power consumption during
standby time can be made sufficiently low.
[0020] In the AC-DC converter according to the present invention it
is preferred that the drive pulses for driving the first switching
means and the drive pulses for driving the second switching means
turn ON at a different timing from each other but turn off at the
same timing.
[0021] It is further preferred that the ON time of the drive pulses
for driving the first switching means and the ON time of the drive
pulses for driving the second switching means are different from
each other keeping a given relation, whereby the ratio between the
duty ratio of the first switching means and the duty ratio of the
second switching means becomes constant.
[0022] By keeping the ratio between the duty ratio of the first
switching means and the duty ratio of the second switching means
constant, the AC-DC converter operates in a suitable manner without
regarding the input voltage condition or the load current
condition.
[0023] Furthermore, the AC-DC converter according to the present
invention has a characteristic in that said drive pulse generating
means comprises a drive pulse intermittently oscillation control
means by which the drive pulse generating means generates the drive
pulses intermittently.
[0024] By providing the drive pulses intermittently oscillation
control means, the power consumption during standby time can be
more reduced.
[0025] It is preferred that the drive pulses intermittently
oscillation control means comprises a comparator having a
hysteresis characteristic and/or a time constant so that the drive
pulse output of the drive pulse generating means is controlled in
accordance with the output of said comparator.
[0026] Furthermore, the AC-DC converter according to the present
invention comprises a starting-up circuit for starting the drive
pulse generating means up; said starting-up circuit comprises an
input for connection to a source of single phase AC supply, a
rectifying circuit for rectifying an electric current supplied from
said inputs, a smoothing circuit for smoothing an output of said
rectifying circuit, and starting-up capacitors being provided
between said AC inputs and said rectifying circuits. According to
the construction, an reactive current can be used to start up the
drive pulse generating means and thus no starting-up resistor is
required. Therefore, the power consumption there can be reduced
more.
[0027] Moreover, it is preferred that the rectifying circuit is
constituted of a bridge rectifying circuit, and the starting-up
circuit has a voltage detecting circuit after said rectifying
circuit, and a switch element, which is driven by the output of the
voltage detecting circuit, being provided at an output side of
either one of the starting-up capacitors.
[0028] According to the construction, when the input voltage is
low, the rectifying circuit operates as a full-wave rectifying
circuit, while when the input voltage is high it works as a
half-wave rectifying circuit. Therefore, even if the converter is
operated with a high input voltage, no current is wasted in the
starting-up circuit, so that power consumption can be more
reduced.
[0029] By the way, it should be noted that in this specification
the DC-DC power supply section includes the rectifying circuit and
the smoothing circuit at the primary side.
BRIEF EXPLANATION OF THE DRAWINGS
[0030] FIG. 1 is a circuit diagram showing a construction of the
first embodiment according to the present invention;
[0031] FIG. 2 is a circuit diagram depicting a construction of the
second embodiment according to the present invention;
[0032] FIG. 3 is a circuit diagram representing a construction of a
modification for the second embodiment depicted in FIG. 2;
[0033] FIG. 4 is a circuit diagram illustrating a construction of
the third embodiment according to the present invention;
[0034] FIG. 5 is a circuit diagram showing a construction of the
fourth embodiment according to the present invention;
[0035] FIG. 6 is a circuit diagram depicting another example of the
turn-on timing delaying circuit provided in the converter shown in
FIG. 1;
[0036] FIG. 7 is a timing chart representing an operation of the
turn-on timing delaying circuit depicted in FIG. 6; and
[0037] FIG. 8 is a circuit diagram illustrating a construction of
the fifth embodiment according to the present invention.
DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS
[0038] FIG. 1 is a circuit diagram showing a construction of the
first embodiment of the AC-DC converter according to the present
invention. In the AC-DC converter of the first embodiment, the PFC
power supply section and the DC-DC power supply section are
connected in a parallel manner and the outputs of both the sections
are added together and smoothed to be outputted.
[0039] The AC-DC converter of the first embodiment has an AC power
supply 100, an LC noise filter 101, a PFC power supply section 102,
a DC-DC power supply section 103, an output adding and smoothing
section 104 for adding outputs of the PFC power supply section and
the DC-DC power supply section, a PWM control circuit 105, an ON
time delay circuit 106, a first switching element 301 for switching
the PFC power supply section and a second switching element 302 for
switching the DC-DC power supply section.
[0040] The PFC power supply section 102 comprises a bridge diode
102a, a .pi. shaped noise filter 102b, a first transformer 102c, a
rectifying diode 102d for rectifying the secondary output of the
first transformer 102c. One end of the primary coil of the first
transformer 102c is connected to the bridge diode 102a via the .pi.
shaped filter 102b and the other end of the primary coil is
connected to the first switching element 301.
[0041] While, the DC-DC power supply section 103 has a rectifying
diodes 103a, a smoothing capacitor 103b, a second transformer 103c
and a secondary rectifying diode 103d for rectifying the secondary
output of the transformer 103c. One end of the primary coil of the
second transformer 103c is connected to the smoothing capacitor
103b and the other end thereof is connected to the second switching
element 302.
[0042] The output of the PFC power supply section 102 and the
output of the DC-DC power supply section 103 are added together and
smoothed in the adding and smoothing section 104, then outputted to
a load.
[0043] In the converter, the output of the adding and smoothing
section 104 is taken out and inputted to the PWM control circuit
105 in order to conduct a servo control for operating the switching
elements 301 and 302. It should be noted that only one servo
control loop is provided for both the switching elements 301 and
302.
[0044] The operation of the switching elements 301 and 302 is
controlled by drive pulses PW1 and PW2 generated in the PWM control
circuit 105. In the first embodiment, turn-on timing delaying
circuit 106 is provided between the PWM control circuit 105 and the
second switching element 302, so that the turn-on timing of the
drive pulse PW2, which is for the second switching element, is
delayed from the turn-on timing of the drive pulse PW1 for the
first switching element with a given ratio. That is to say, the
delay of PW2 from PW1 varies being linked with the ON time of the
drive pulse Pw1.
[0045] More concretely, the output PW1 from the PWM control circuit
105 is supplied to the first switching element 301, while to the
second switching element it is supplied via the turn on timing
delaying circuit 106. The turn-on timing delaying circuit 106 has a
comparing circuit constituted of a comparator 106a; a triangular
wave generating circuit, which is provided on the plus side of the
comparator 106a, being constituted of a resistor 106b, a capacitor
106c, and a diode 106d; and a averaging circuit, which is provided
on the minus input side of the comparator 106a, constituted of
resistors 106e and 106f, and a capacitor 106g. The time constant of
the averaging circuit is set at a value which does not respond to
the switching frequency of the second switching element 302 but
responds to the commercial frequency. Therefore, the pulse width of
the output PW2 of the turnon timing delaying circuit 106 becomes
smaller than that of the output PW1 of the PWM control circuit 105
with a given ratio (the duty ratio of PW2/the duty ratio of
PW1).
[0046] In this manner, the first switching element 301 is driven by
the output PW1 of the PWM control circuit 105 and the second
switching element 302 is driven by the output PW2 of the turn-on
timing delaying circuit 106, by which the turn-on timing of the PW1
is delayed from that of the PW1 with a given ratio (the duty ratio
of PW2/the duty ratio of PW1); therefore, the duty ratio of the
first switching element 301 becomes greater than that of the second
switching element 302. As a result, the difference between the
inductance of the first transformer 102c and the inductance of the
second transformer 103c becomes shorter, compared to the case that
both the transformers are switched by the switching signals driven
by the signals having the same pulse width, so that the efficiency
can be more improved and the size of the converter becomes more
compact.
[0047] The minus terminal of the comparator 106a may be connected
to a fixed voltage. In this case, the pulse width of the output PW2
of the turn-on timing delaying circuit 106 becomes different from
that of the output PW1 of the PWM control circuit 105 with a fixed
difference.
[0048] FIG. 2 is a circuit diagram showing a construction of the
second embodiment of the AC-DC converter according to the present
invention. It should be noted that in the embodiments explained
below the same numerical references are used for the same elements
as those in the first embodiment, and the explanation for the
elements is omitted here.
[0049] In the second embodiment, a diode 201 and an inductor 202
are inserted between the bridge diode 102a and the second switching
means 302 in a series manner; the other construction maintains the
same condition as that of the first embodiment. According to the
construction, whenever the second switching element 302 becomes ON,
the inductor 202 is excited, and then, when the second switching
element 302 is OFF, the excited current generated in the inductor
202 is supplied to the smoothing capacitor 103b through the primary
coil of the second transformer 103c, so that the capacitor 103b is
charged. Therefore, the electric current coming from the rectifying
circuit 103a to the smoothing capacitor 103b is reduced in the
DC-DC power supply section 103, so that the generation of harmonics
in the rectifying circuit 103a can be reduced.
[0050] FIG. 3 is a circuit diagram showing a modification of the
AC-DC converter mentioned in the second embodiment. In this
modification, diodes 203 and 204 and an inductor 202 are inserted
between the AC inputs and the second switching element 302 in a
series manner. According to the construction, when a high input
voltage of 200V or more, for instance, is applied, harmonics can be
reduced more effectively. It should be noted that both in the
converters shown in FIGS. 2 and 3, if a necessary amount of
electric current is supplied from the inductor 202 to the smoothing
capacitor 103b, the rectifying circuit 103a of the DC-DC power
supply section may be omitted.
[0051] FIG. 4 is a circuit diagram showing a construction of the
AC-DC converter according to the third embodiment of the present
invention. In the third embodiment, a tertiary coil 401 is provided
in the first transformer 102c (or the second transformer 103c) in
addition to the basic construction mentioned in FIG. 1; one of the
ends of the tertiary coil 401 is connected to the smoothing circuit
103b of the DC-DC power supply section 103 and the other end
thereof is connected to the noise filter 102b of the PFC power
supply via a diode 402. According to the construction, the high
frequency voltage generated in the switching element provided on
the section where the tertiary coil 401 is provided is added to the
rectified voltage so that a continuity angle of the diode402 can be
made widened. In FIG. 4, the tertiary coil 401 is provided in the
first transformer 102c of the PFC power supply section 102,
however, it may be possible to provide a tertiary coil 401 in the
second transformer 103c of the DC-DC power supply section 103.
Further, the tertiary coil 401 is connected in a forward mode here,
however it may be connected in a flyback mode.
[0052] Furthermore, the other end of the tertiary coil 401 may be
connected to the AC inputs. In this case, diodes should be inserted
into both lines, respectively.
[0053] In the third embodiment shown in FIG. 4, an inductor 403 is
inserted between the tertiary coil 401 and the smoothing capacitor
103b of the DC-DC power supply section 103. However, an external
inductor can be also used, a leakage inductor from the tertiary
coil 401 can also be used therefor.
[0054] In the third embodiment, if a necessary current is supplied
to the smoothing capacitor 103b of the DC-DC power supply section
103 from the tertiary coil 401 and/or the inductor 403, the
rectifying diodes 103a of the DC-DC power supply section 103 can be
omitted.
[0055] Furthermore, the diode 201 and the inductor 202 shown in
FIG. 2 and/or the diodes 203, 204 and the inductor 202 shown in
FIG. 3 may be added to the third embodiment. In this case, the
diode 201 and the diode 403 can be used commonly. In addition, the
inductor 202 can be omitted so that only the diode is connected
there.
[0056] It should be noted that in the AC-DC converters according to
the second and third embodiments, even if the pulse widths of the
drive pulses PW1, PW2 for driving the first and second switching
elements 301 and 302 are the same, it is possible to restrict the
harmonics by the circuit constructions mentioned above. However, if
the turn-on timing delaying circuit 106 such as that shown in FIG.
1 is provided between the PWM control circuit 105 and the second
switching element 302, efficiency can be more improved.
[0057] FIG. 5 is a circuit diagram illustrated the construction of
the fourth embodiment according to the invention. In the fourth
embodiment, a two-stage type AC-DC converter is shown, where the
PFC power supply section 102 and the DC-DC power supply section 103
are connected together in a cascade manner.
[0058] According to the fourth embodiment, the PFC power supply
section has a rectifying diode 102a, a .pi. shaped filter 102b, and
a choke coil 102c; to an output of the choke coil 102c, is
connected the DC-DC power supply section 103 in a cascade manner,
which includes a rectifying diode 103a, a smoothing capacitor 103b,
a second transformer 103c, and a secondary rectifying circuit 103d.
The output of the chock coil 102c is connected to the first
switching element 301; during when the first switching element 301
is made ON, the choke coil 102c is excited; then the excited
current in the choke coil 102c is stored in the smoothing capacitor
103b via the diode 103a while the first switching element 301 is
OFF; then the voltage at the capacitor 103b is switched by the
second switching element 302 through the primary coil of the second
transformer 103c.
[0059] In the fourth embodiment, a first turn-on timing delaying
circuit 106-1 and a second turn-on timing delaying circuit 106-2,
which operate in a linked manner, are provided between the PWM
control circuit 105 and the switching elements 301 and 302,
respectively.
[0060] The first turn-on timing delaying circuit 106-1, which
supplies drive pulses to the first switching element 301, has a
comparing circuit constituted of a comparator 106-1a, a triangular
wave generating circuit, which is provided at the plus input side
of the comparator 106-1a, constituted of a resistor 106-1b, a
capacitor 106-1c and a diode 106-1d, and an averaging circuit,
which is provided at the minus input side of the comparator 106-1a,
constituted of resistors 106-1h, 106-1i and a capacitor 106-1g.
[0061] The second turn-on timing delaying circuit 106-2, which
supplies drive pulses to the second switching element 302, has a
comparing circuit constituted of a comparator 106-2a, and a
triangular wave generating circuit, which is provided at the plus
input side of the comparator 106-2a, constituted of a resistor
106-2b, a capacitor 106-2c and a diode 106-2d; the minus input side
of the comparator 106-2a is connected to a fixed voltage
106-2j.
[0062] It should be noted that to the minus input side of the
comparator 106-1a of the first turn-on timing delaying circuit
106-1, a voltage at smoothing capacitor 103b of the DC-DC power
supply section 103 is supplied, being divided by the resistors
106-1h and 106-1i.
[0063] According to the construction, when the input voltage is low
(100V, for instance), the ON time of the first switching element
301 becomes wider than that of the second switching element 302;
while, when the input voltage is high (240V, for instance), the ON
time of the second switching element 302 becomes wider than that of
the first switching element 301. Therefore, by selecting a suitable
circuit constant, the voltage at the smoothing capacitor 103b can
be set at a voltage at which the best efficiency can be obtained.
The best efficiency can be obtained, for example, at DC 260V at the
smoothing capacitor 103b when the input voltage is low (100V, for
instance), and at DC370V at the smoothing capacitor 103b when the
input voltage is high (240V).
[0064] In the AC-DC converter shown in FIG. 5, the first switching
element 301 is connected to the output of the choke coil 102c.
However, it may be arranged such that the switching element 301 is
connected to a tap provided in the choke coil 102c. Further, it is
also possible to arrange such that a tertiary coil is added to the
choke coil 102c and an output of the tertiary coil is rectified by
the diode 103a. In case that the tertiary coil is added, the other
end of the tertiary coil may be connected either to the plus side
or the minus side of the noise filter 102b.
[0065] It should be noted that the choke coil 102c of the PFC power
supply section 102 may be substituted by a first transformer as
shown by a broken line in FIG. 5. By adding a diode 102d to the
first transformer, a bypass route of electric power is made there,
so that efficiency can be improved.
[0066] According to the construction of the fourth embodiment, the
manufacturing cost for the converter can be reduced because an IC
for conducting a power factor correction, or a multiplier, which
are required in normal two-stage type converters, are not
necessary. In addition, another advantage can be expected that the
switching noise becomes low because the switching frequency at the
PFC power supply section and that at the DC-DC power supply section
are the same. Furthermore, according to the invention, only one
servo circuit is required for operating the switching elements 301
and 302; therefore, the loss can be reduced and the power
consumption during standby time can be reduced.
[0067] FIG. 6 shows a modification of the pulse width control
circuit (turn-on timing delaying circuit) for the AC-DC converter
according to the invention. In the modification, the operation of
the turn on timing delaying circuit 106 mentioned in the first
embodiment, namely, the operation for making the ON time of the
second switching element 302 narrower than that of the first
switching element 301 with a given ratio, is realized in another
way.
[0068] The ON time control circuit 500 comprises a current control
circuit 501, a first comparator 502, a second comparator 503, an OR
gate 504, a resistor 505, and a diode 506. The output PW1 of the
PWM control circuit 105 is supplied to an input CLK of the current
control circuit 501. The relation among terminals, ia, ib, 4ia and
4ib, of the current control circuit 501 is:
4.times.ia=4.times.ib=4ia=4ib. The terminals ia and 4ia are
connected to the minus side of the first comparator 502 and the
terminals ib and 4ib are to the minus side of the second comparator
503, respectively. The output of the comparators 502, 503 are
supplied to the OR circuit 504 and the STP terminals STTPa and STPb
of the current control circuit 501, respectively.
[0069] FIG. 7 is a timing chart of the operation in the ON time
control circuit 500. During the term 0, no electric current flows
at any of the terminals of the current control circuit 501. During
the term 1, a current flows to an output terminal ia and the
voltage Vca gradually increases; during the term 2, the current at
the output terminal ia stops to flow, and the voltage Vca is held.
Then, during the term 3, four times current of the current at the
terminal ia flows to the terminal 4ia, so that the voltage at Vca
goes down to 0V with a four times speed of that when the voltage
Vca goes up during the term 1. When the voltage at Vca becomes 0V,
the output of the first comparator 502 becomes high, so that a
current stop signal is supplied to the current stop signal input
terminal STPa to stop the current flow to the terminal 4ia. The
high condition of the first comparator 502 is kept until the end of
the term 4.
[0070] On the other hand, during the term 3, a current starts up to
flow to an output terminal ib and the same operation mentioned
above is carried out at the output terminal ib, the second
comparator 503, the input terminal 4ib and the current stop signal
input terminal STPb, but with a delay from the output signal PW1 of
the PWM control circuit 105 by one cycle thereof. The voltage at
Vcb varies in the same manner as the voltage at Vca.
[0071] As a result, the outputs OUTa and OUT b of the first and
second comparators 502 and 502 are outputted alternatively as pulse
signals having a delay with the rising time from that of PW1 by a
given amount. These pulse signals are added at the OR circuit 504
to generate an output WS, which is supplied to the second switching
element 302 via the resistor 505 and the diode 506. The output WS
has the same frequency as that of the PW1 of the PWM control
circuit 105, and a given LOW time corresponding to the LOW term of
the output PW1 by the resistor 505 and the diode 506. The objected
output PW2, where the ON time is narrower than that of the PW1 with
a given ratio, is obtained in this manner.
[0072] It should be noted that according to the construction shown
in FIG. 6, the objected pulse PW2 is generated being delayed by 1
or 2 pulses just after the control has been started up. However,
the converter would have no problem by this delay at the
beginning.
[0073] The same operation in the ON time control circuit 500 can
also be obtained by providing counters instead of the comparators
502 and 503. That is to say, the current control circuit 501 is
arranged such that clocks having a frequency sufficiently higher
than that of the PW1 are generated; the output current at the
terminal ia is replaced to count-up pulses by the counter, and the
current at the terminal 4ia is replaced to countdown pulses having
a four times counting speed. The MSB outputs of the counters
correspond to the outputs of the comparators 502, 503. In a case
that binary counters are used, the counted-up pulse signals should
be shifted by two bits and rounded off, and the count-down
operation should be conducted with the same speed of the count up
operation.
[0074] By repeating the above-mentioned operation, the ON time of
the first switching element 301 becomes 1.33 times of that of the
second switching element 302.
[0075] It is preferred to make difference in the turn-on timing and
turn it OFF at the same timing, because an electric current can be
detected easily , it is convenient for conducting a PWM control in
an electric current mode or for conducting an over current
protection pulse by pulse.
[0076] Furthermore, the pulse width changing circuit (ON time
control circuit) mentioned in all of the above explained
embodiments can also be realized by using a DSP (Digital Signal
Processor) where the pulse widths of the two switching elements are
preliminarily programmed.
[0077] Moreover, in the above-explained embodiments, a flyback
converter is explained; however, the present invention can also be
applied to forward type converters, half bridge type converters,
and full bridge type converters, etc. Furthermore, there is no
limitation in the switching element control system to be used in
the converter according to the invention; that is to say,
controlling systems other than a PWM system, i.e. PFM controlling
system, a self-oscillating controlling system or a frequency
controlling system, can be applied to the present invention.
[0078] FIG. 8 is a block diagram showing a construction of the
fifth embodiment of the AC-DC converter according to the present
invention. In FIG. 8, the numerical reference 601 refers a power
supply section including the PFC power supply section 102 and the
DC-DC power supply section 103, and the first and second switching
elements 301 and 302, etc.; the numerical reference 602 represents
a driving control section of the switching elements, and 603
represents a starting-up circuit for the driving control section
602.
[0079] The switching element driving control section 602 comprises
a pulse width control circuit 611, a gate circuit 612, an
oscillating circuit 613, and an intermittent oscillation control
circuit 614 for controlling the operation of the pulse width
control circuit 611.
[0080] Under the condition that a rated load is applied, the
driving control section 602 operates as follows; an output of the
oscillator 613 is supplied to the pulse width control circuit 611
via the gate circuit 612 to generate the pulse outputs PW1 and PW2,
then the pulse outputs PW1 and PW2 are supplied to the switching
elements 301 and 302 in the power supply section 601 to obtain a DC
output. The DC output of the power supply section 601 is taken out
and returned to the control circuit 611 side via a reference
voltage 614a and a photo coupler 614b; then supplied to the FB
input terminal of the control circuit 611.
[0081] When the load of the DC output of the power supply section
601 is light, the voltage at the FB terminal comes down, then when
the voltage becomes lower than the voltage supply 614d, the output
of the comparator 614e increases to stop the output of the gate
circuit 612. Thereby, the output of the pulse width control circuit
611 stops to output, so that the pulse outputs PW1 and PW2 stops to
be supplied. A positive feed back is applied to the comparator 614e
by the resistors 614f and 614g, so that the comparator 614e has a
hysteresis characteristic. Therefore, when the DC output of the
power supply section 601 becomes lower than a predetermined
voltage, the voltage at the FB terminal increases, and the gate
circuit 612 opens again to re-start the switching operation. As a
result, when the load of the power supply 601 is light, the
switching elements 301 and 302 oscillate intermittently. The
intermittent frequency becomes low by the hysteresis effect of the
comparator 614e, so that the strange sounds is reduced to be
generated. At the minus terminal of the comparator 614e, a time
constant circuit constituted of a capacitor 614h and a resistor
614i is provided; thereby the intermittent frequency of the
switching operation can be made lower.
[0082] In the embodiment shown in FIG. 8, the hysteresis effect is
obtained by the positive feedback applied on the comparator 614e,
however, it may be also obtained by a combination of two
comparators and a latch circuit.
[0083] The starting-up circuit 603 comprises a bridge diode 621,
starting-up capacitors 622 and 623, which work as a reactance
dropper, being provided between the bridge diode 621 and AC inputs,
a voltage detecting circuit 624 provided after the bridge diode
601, a switch element 625 provided between the voltage detecting
circuit 624 and one of the starting-up capacitors 623, a diode 626
connected to a VCC terminal from a VCC coil (not shown) of the
power supply section 601, and a smoothing capacitor 627. The
electric current flowing through the starting-up capacitors 621 and
622 is rectified by the bridge diode 603, then smoothed by the
smoothing capacitor 627 to start up the switching element driving
section 602. A power consumption can be reduced by using the
capacitors 621 and 622 in the starting-up circuit 603 instead of a
starting-up resistor.
[0084] Under the condition that the smoothing capacitor 627 is so
designed to suitably operate for accepting an input voltage 100V,
when an input voltage 240V is applied, the voltage at the capacitor
627 becomes too high. In the present invention, the voltage
detecting circuit 624 is provided in the present invention, so that
when the input voltage becomes higher than a predetermined value,
the switch element 625 is shortened. Thereby, when a high input
voltage, for instance, 240V is applied, the current flowing the
starting-up capacitor 623 becomes invalid so that the current is
not stored at the smoothing capacitor 627. In this manner, the
power loss, which is caused when the input voltage is high (240V)
can be prevented by adding the voltage detecting circuit 624 and
the switch 625. It may be possible to give a hysteresis
characteristic to the voltage detecting circuit 625. Further, it
may also be arranged such that the power necessary to drive the
control circuit 611 is obtained from the VCC terminal of the power
supply section 601 via the diode 627.
[0085] The scope of the present invention is not limited to the
above explained embodiments and modifications, so that other
modifications or variations can be applied. For instance, the .pi.
shaped filter 102b is provided after the bridge diode 102a,
however, the capacitor constituted of the filter has a very small
capacitor only in comparison to that of the smoothing capacitor
103b and has almost no smoothing function. Therefore, only one
capacitor may be altered therefor or both the capacitors may be
omitted.
[0086] Further, the starting-up circuit 603 and/or the switching
element driving control circuit 602 can be applied to any
embodiments shown in FIGS. 1 to 5.
[0087] As explained above, according to the present invention, it
is arranged such that the duty ratio of the switching element of
the PFC power supply section is higher than that of the switching
element of the DC-DC power supply to make the inductance at the
rectified current side power supply section high, so that the
current waveform becomes a wide triangle shape or a trapesoidal
shape. Therefore, the route-mean-square current is decreased and
thus a high efficiency can be realized. Further, an AC-DC converter
which satisfies the IEC standard 61000-3-2 Class D without
respective to the height of the input voltage, can be provided.
Furthermore, a two-stage type AC-DC converter, where power
consumption during standby time can be reduced and the
manufacturing cost thereof can also be reduced.
* * * * *