Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2003-01-30
2004-06-08
Sherry, Michael (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S017000, C363S132000
Reexamination Certificate
active
06747883
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply circuit provided as a power supply in various electronic apparatus.
Switching power supply circuits employing switching converters such for example as flyback converters and forward converters are widely known. These switching converters form a rectangular waveform in switching operation, and therefore there is a limit to suppression of switching noise. It is also known that because of their operating characteristics, there is a limit to improvement of power conversion efficiency.
Accordingly, various switching power supply circuits using various resonance type converters have been previously proposed by the present applicant. A resonance type converter can readily obtain high power conversion efficiency, and achieve low noise because the resonance type converter forms a sinusoidal waveform in switching operation. The resonance type converter has another advantage of being able to be formed by a relatively small number of parts.
FIG. 18
is a circuit diagram showing an example of configuration of a switching power supply circuit that can be formed on the basis of an invention of Japanese Patent Publication No. 2955582 previously proposed by the present applicant. This power supply circuit employs a self-excited current resonance type converter.
The switching power supply circuit shown in the figure is provided with a voltage doubler rectifier circuit formed by rectifier diodes Di
1
and Di
2
and smoothing capacitors Ci
1
and Ci
2
as a rectifying and smoothing circuit for receiving an alternating input voltage VAC. The voltage doubler rectifier circuit generates a rectified and smoothed voltage Ei equal to twice the alternating input voltage VAC across the serially connected smoothing capacitors Ci
1
and Ci
2
.
The switching converter of the power supply circuit is connected such that two switching devices Q
1
and Q
2
are coupled by half-bridge coupling, and inserted between a node on the positive electrode side of the smoothing capacitor Ci
1
and a ground, as shown in FIG.
18
. In this case, a bipolar transistor (BJT; junction transistor) is employed as the switching devices Q
1
and Q
2
.
An orthogonal type control transformer PRT (Power Regulating Transformer) is provided to drive the switching devices Q
1
and Q
2
and effect constant-voltage control as later described.
The orthogonal type control transformer PRT is formed as an orthogonal type saturable reactor in which driving windings NB
1
and NB
2
and a resonance current detecting winding ND for detecting resonance current are wound as shown in
FIG. 22
, and a control winding NC is wound in a direction orthogonal to these windings.
An isolation converter transformer PIT
1
(Power Isolation Transformer) transmits a switching output of the switching devices Q
1
and Q
2
to a secondary side.
As shown in
FIG. 20
, the isolation converter transformer PIT
1
has an E-E-shaped core formed by combining E-shaped cores CR
1
and CR
2
of for example a ferrite material in such a manner that magnetic legs of the core CR
1
are opposed to magnetic legs of the core CR
2
, and has a primary winding N
1
and a secondary winding N
2
(N
3
) wound around a central magnetic leg of the E-E-shaped core in a state of being divided from each other by a dividing bobbin B. In this case, the primary winding N
1
and the secondary windings N
2
and N
3
are each formed by winding a litz wire of about 60 mm&phgr; around the dividing bobbin B.
In this case, a gap G of 0.5 mm to 1.0 mm is formed in the central magnetic leg of the E-E-shaped core, whereby a state of loose coupling at a coupling coefficient k≠0.85, for example, is obtained between the primary winding N
1
and the secondary windings N
2
and N
3
.
One end of the primary winding N
1
of the isolation converter transformer PIT
1
is connected to a node (switching output point) of an emitter of the switching device Q
1
and a collector of the switching device Q
2
via the resonance current detecting winding ND, and thereby obtains the switching output. Another end of the primary winding N
1
is connected to the primary-side ground via a primary-side series resonant capacitor Cr
1
formed by a film capacitor, for example.
A primary-side parallel resonant capacitor Cr
2
for primary-side partial voltage resonance is connected in parallel with the collector and emitter of the switching device Q
2
. The primary-side parallel resonant capacitor Cr
2
is provided for ZVS (Zero Voltage Switching) operation and ZCS (Zero Current Switching) operation of the switching devices Q
1
and Q
2
.
The secondary windings N
2
and N
3
are wound independently of each other on the secondary side of the isolation converter transformer PIT
1
in FIG.
18
. The secondary winding N
2
is connected with a bridge rectifier diode DBR and a smoothing capacitor C
01
, whereby a direct-current output voltage E
01
is generated. The secondary winding N
3
is provided with a center tap. The secondary winding N
3
is connected with rectifier diodes D
01
and D
02
and a smoothing capacitor C
02
as shown in the figure, whereby a full-wave rectifier circuit formed by the rectifier diodes D
01
and D
02
and smoothing capacitor C
02
generates a direct-current output voltage E
02
.
In this case, the direct-current output voltage E
01
is also inputted from a branch point to a control circuit
1
.
The control circuit
1
for example supplies, as a control current, a direct current whose level is changed according to level of the secondary-side direct-current output voltage E
01
to the control winding NC of the orthogonal type control transformer PRT, and thereby effects constant-voltage control.
FIG. 19
is a circuit diagram showing an example of configuration of another power supply circuit that can be formed on the basis of an invention previously proposed by the present applicant. The same parts as in the power supply circuit shown in
FIG. 18
are identified by the same reference numerals, and their description will be omitted.
The power supply circuit shown in
FIG. 19
is also provided with a current resonance type converter in which two switching devices Q
11
and Q
12
are coupled by half-bridge coupling. However, a driving system for the current resonance type converter is an external excitation system. In this case, a MOS-FET or an IGBT (Insulated Gate Bipolar Transistor) is used as the switching devices Q
11
and Q
12
.
In this case, a rectifying and smoothing circuit formed by a bridge rectifier circuit Di and a smoothing capacitor Ci rectifies and smoothes an alternating input voltage VAC of a commercial alternating-current power supply AC, and thereby generates a direct-current input voltage equal to a peak value of the alternating input voltage VAC multiplied by unity, for example.
Gates of the switching devices Q
11
and Q
12
are connected to an oscillating and driving circuit
11
. The switching device Q
11
has a drain connected to a positive electrode of the smoothing capacitor Ci, and a source connected to a primary-side ground via a primary winding N
1
and a primary-side series resonant capacitor Cr
1
. The switching device Q
12
has a drain connected to the source of the switching device Q
11
, and a source connected to the primary-side ground.
Also in this case, a primary-side parallel resonant capacitor Cr
2
for primary-side partial voltage resonance is connected in parallel with the drain and the source of the switching device Q
12
.
Further, a clamp diode DD
1
is connected in parallel with the drain and the source of the switching device Q
11
, and a clamp diode DD
2
is connected in parallel with the drain and the source of the switching device Q
12
.
The switching devices Q
11
and Q
12
are driven by the oscillating and driving circuit
11
for switching operation described earlier with reference to FIG.
18
.
Specifically, a control circuit
2
in this case supplies a current or a voltage varied in level according to variation in a direct-current output voltage E
01
to the oscillating an
Laxton Gary L.
Maioli Jay H.
Sherry Michael
Sony Corporation
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