Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-10-20
2001-11-27
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000, C363S131000
Reexamination Certificate
active
06324081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching power source apparatus that is suitably used in a computer display monitor or a large-sized television image receiver in which a high resolution video signal is displayed using, for example, a cathode ray tube. More particularly, the invention is intended, in a display monitor or television image receiver, which uses, for example, a cathode ray tube, to enable the generation of a plurality of voltages including the generation of a high voltage efficiently.
2. Description of the Related Art
As a power source apparatus used in a computer display monitor, etc. for making display of a video signal having a high resolution, there has hitherto been used an apparatus such as that illustrated in FIG.
9
. This apparatus uses an insulated type switching power source circuit, a horizontal deflection circuit, and a high-voltage generation circuit.
Namely, in
FIG. 9
, a commercially available alternating power source (AC)
100
is connected to a smoothing capacitor
102
through a diode bridge rectification circuit
101
. A negative-polarity end of the capacitor
102
is grounded and a positive-polarity end thereof is connected to an oscillation drive circuit
104
through a resistor
103
. This positive-polarity end of the capacitor
102
is grounded through a switching circuit part
105
comprised of a serial circuit of switching elements Qa
1
and Qa
2
. And, these switching elements Qa
1
and Qa
2
are driven so that these elements may be alternately made conductive by a prescribed frequency by the oscillation drive circuit
104
.
Further, the switching circuit part
105
constitutes a half-bridge circuit; the positive-polarity end of the capacitor
102
is connected to the drain of the switching element Qa
1
; and the source of the switching element Qa
2
is grounded. Also, to the switching elements Qa
1
and Qa
2
there are respectively connected in parallel damper diodes Da
1
and Da
2
. And, a point of connection between the source of the switching element Qa
1
and the drain of the switching element Qa
2
is grounded through a resonance capacitor
106
, a choke coil
107
, and a primary winding La
1
of an insulated type converter transformer
108
.
As a result of this, into the primary winding La
1
of the converter transformer
108
there is made to flow a resonance current that is inverted according to the oscillating frequency of the oscillation drive circuit
104
. Thereby, a so-called “separately-excited type” of current-resonance type of converter power source circuit is constructed. Namely, in this circuit, the fundamental operation on a primary side of the converter transformer
108
, when typically illustrated, is as illustrated in
FIGS. 10A
to
10
C. In these
FIGS. 10A
to
10
C, an equivalent circuit that is prepared when the switching element Qa
1
has been made “on” by a drive pulse output from the oscillation drive circuit
104
illustrated in
FIG. 10A
is illustrated in FIG.
10
B. And, an equivalent circuit that is prepared when the switching element Qa
2
has been made “on” by that drive pulse is illustrated in FIG.
10
C.
On this account, when the switching element Qa
1
has been made “on”, a switch
201
corresponding to the switching element Qa
1
in the equivalent circuit in
FIG. 10B
is closed. Therefore, there is constructed a serial resonance circuit that is comprised of a direct current voltage source
203
corresponding to the positive-polarity end of the capacitor
102
, the resonance capacitor
106
, an inductor
204
including the choke coil
107
and primary winding La
1
, and a resistor
205
. And, using the direct current voltage source
203
as a power source, a positive-polarity resonance current is made to flow through that circuit by way of the switch
201
.
Next, when the switching element Qa
2
has been made “on”, a switch
202
corresponding to the switching element Qa
2
in the equivalent circuit in
FIG. 10C
is closed. Therefore, by way of this switch
202
, a negative-polarity resonance current is made to flow through the serial resonance circuit that is comprised of the resonance capacitor
107
, the inductor
204
, and the resistor
205
. And, in this way, the positive-polarity and negative-polarity resonance currents are alternately generated according to the drive pulses output from the oscillation drive circuit
104
, whereby a desired frequency of alternating current is made to flow through the serial resonance circuit.
Further, the waveforms of the currents flowing through respective portions of each of the equivalent circuits illustrated in
FIGS. 10A
to
10
C are illustrated in
FIGS. 11A
to
11
C. Here, FIG.
11
A and
FIG. 11B
illustrate the waveforms of the current IQ
1
and current IQ
2
flowing, respectively, through the switching elements Qa
1
and Qa
2
while
FIG. 11C
illustrates the waveform of a resonance current I
1
flowing through the serial resonance circuit. Also, in
FIG. 12
, illustration is made of the relationship between the resonance current I
1
flowing through the serial resonance circuit and the frequency f. In
FIG. 12
, f
0
represents the resonance frequency of the serial resonance circuit of
FIGS. 10A
to
10
C and fsw represents the repetitive operating frequency of the switching circuit part
105
that is driven by the oscillation drive circuit
104
.
In this case, assume that C, L, and R represent the values of the resonance capacitor
106
, inductor
204
, and resistor
205
, respectively, and that Z represents the impedance of the serial resonance circuit with respect to each frequency &ohgr;. Determining the admittance under this assumption, the admittance Y is expressed in the form of the following [equation no. 1].
Y
=
1
/
Z
=
R
-
j
(
ω
L
-
1
/
ω
C
)
R
2
+
(
ω
L
-
1
/
ω
C
)
2
[
Equation
No
.
1
]
On the other hand, the resonance frequency f
0
of the serial resonance circuit is expressed in the form of the following [equation no. 2].
f0
=
1
2
π
(
LC
)
[
Equation
No
.
2
]
Here, because the current I is in proportion to the Y of the [equation no. 1], when showing the magnitude of the current I
1
as measured with respect to the frequency by the use of that Y, the variation thereof is as indicated by a curve of FIG.
12
. The resonance current has a maximum value at the resonance frequency f
0
. Also, the repetitive operating frequency fsw of the switching circuit part
105
comprised of the switching elements Qa
1
and Qa
2
is so set as to move along the right side of this resonance current curve, i.e., so that, in these frequencies, the relationship of fsw>f
0
may be satisfied.
On this account, standing on the above-described fundamental operation, the entire circuit operation of
FIG. 9
will now be explained in detail. The switching operation of the power source circuit in the circuit construction of this
FIG. 9
is performed as follows. First, using as the charging current the rectification current that is obtained by rectifying the commercially available alternating power source
100
, which is closed, with the diode bridge rectification circuit
101
, a rectified and smoothed voltage is generated across the both ends of the smoothing capacitor
102
. Further, using this rectified and smoothed voltage as the operating power source, a power source is supplied to the oscillation drive circuit
104
through the resistor
103
. And the drive pulses that are alternately generated in the oscillation drive circuit
104
are supplied to the switching elements Qa
1
and Qa
2
, respectively.
And, with certain timing, from the oscillation drive circuit
104
, for example, a positive drive pulse is supplied to the switching element Qa
1
and, conversely, a negative drive pulse is supplied to the other switching element Qa
2
constituting the switching circuit part
105
. As a res
Iwai Kenji
Sakamoto Hiroshi
Laxton Gary L.
Maioli Jay H.
Sony Corporation
Wong Peter S.
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