Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-09-19
2002-12-17
Toatley, Jr., Gregory J. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021020, C363S097000
Reexamination Certificate
active
06496389
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power circuit equipped with a power factor improving circuit.
Previously to date the present applicant proposed a variety of power circuits each having a resonance type converter on its primary side, and also other various power circuits each having a power factor improving circuit to achieve improvement of the power factor for a resonance type converter.
FIG. 6
is a circuit diagram showing an exemplary switching power circuit of a configuration based on the invention filed previously by the present applicant. This power circuit is equipped with a power factor improving circuit to attain improvement of the power factor for a self-excited voltage resonance type switching converter.
In the switching power circuit shown in this diagram, there are provided a common mode choke coil CMC and an across capacitor CL which constitute a noise filter to remove the common mode noise with regard to an alternating current power AC.
The alternating current power AC is full-wave rectified by a bridge rectifier circuit Di consisting of four diodes, and the rectified output is supplied to charge a smoothing capacitor Ci via a power factor improving circuit
20
. The circuit configuration of the power factor improving circuit
20
and the operation thereof will be described later.
In this diagram, the voltage resonance type switching converter has a switching element Q
1
consisting, for example, of a high-voltage withstanding bipolar transistor. That is, this switching converter is in a single end form.
The base of the switching element Q
1
is connected to the positive side of the smoothing capacitor Ci via a starting resistor RS, so that a base current at the start is obtained from a rectifier smoothing line. The base of the switching element Q
1
is connected also to a switching drive circuit
2
.
The switching drive circuit
2
consists of a self-excited oscillation driver for driving the switching element Q
1
by self-excitation, and a switching frequency controller for stabilizing the voltage by varying the oscillation frequency (i.e., switching frequency) in the self-excited oscillation driver.
In a specific configuration of such switching drive circuit
2
, as seen in the various power circuits proposed previously by the present applicant, the self-excited oscillation driver consists, for example, of a resonance circuit composed of a driving coil and a resonance capacitor, and a detection coil for transferring the alternating voltage to the driving coil. Although not shown here, the detection coil is connected practically in series to a primary winding N
1
for example. That is, the switching element Q
1
is driven through switching by the resonance output of the resonance circuit in the self-excited oscillation driver, and the resonance frequency thereof is used as a switching frequency.
The switching frequency controller has a structure adapted to vary the resonance frequency. For this purpose, a control transformer PRT is provided to vary the inductance of the driving coil for example. In this control transformer PRT, the driving coil and the detection coil for example are transformer-coupled to each other, and a control coil is wound in such a manner that the winding direction thereof is not coincident with that of the driving coil and the detection coil. A DC control current outputted from the control circuit
1
is supplied to the control coil.
In the control circuit
1
, a control current of a level corresponding to a secondary side DC output voltage Eo is supplied to the control coil. In the control transformer PRT, the inductance of the driving coil is varied in accordance with the level of the control current flowing in the control coil. As the inductance of the driving coil is thus varied, the resonance frequency of the self-excited oscillation driver, i.e., the switching frequency, is also varied under control.
A detailed description will be given later on a constant voltage regulating action executed with such switching frequency control.
The collector of the switching element Q
1
is connected to the positive terminal of the smoothing capacitor Ci via the primary winding N
1
of the insulating converter transformer PIT, and the emitter thereof is grounded.
In this case, a clamp diode DD is connected between the collector and emitter of the switching element Q
1
, thereby forming a path where a damper current flows at the off-time of the switching element Q
1
.
A first resonance capacitor Cr constitutes a parallel resonance circuit in combination with a second resonance capacitor Cr
1
in an undermentioned power factor improving circuit
2
and principally with the leakage inductance of the primary winding N
1
of the insulating converter transformer PIT. Due to the action of this parallel resonance circuit, the switching operation of the switching element Q
1
is performed in a voltage resonance mode. And the end voltage VCP between the collector and emitter of the switching element Q
1
is obtained in a waveform of sinusoidal pulses during the off-period of the switching element.
The insulating converter transformer PIT transfers the switching output of the switching element Q
1
to the secondary side.
As shown in
FIG. 12
, the insulating converter transformer PIT has an EE-shaped core where E-shaped cores CR
1
and CR
2
composed of ferrite for example are combined with each other in such a manner that magnetic legs thereof are opposed mutually, and the primary windings N
1
and the secondary windings N
2
thereof are coiled in a split state respectively by the use of a split bobbin B with regard to the center magnetic leg of the EE-shaped core. And a gap G is formed to the center magnetic leg as shown in the diagram, whereby loose coupling is attained with a required coupling coefficient.
The gap G can be formed by shaping the center magnetic leg of each of the E-shaped cores CR
1
and CR
2
to be shorter than the two outer magnetic legs thereof. The coupling coefficient k is set as, e.g., k≈0.85 suited to attain loose coupling, hence avoiding a saturated state correspondingly thereto.
One end of the primary winding N
1
of the insulating converter transformer PIT is connected to the collector of the switching element Q
1
, while the other end thereof is connected to the positive side (rectified smoothed voltage Ei) of the smoothing capacitor Ci.
On the secondary side of the insulating converter transformer PIT, an alternating voltage induced by the primary winding N
1
is generated in the secondary winding N
2
. In this case, since a secondary side parallel resonance capacitor C
2
is connected to the secondary winding N
2
, a parallel resonance circuit is formed by the leakage inductance L
2
of the secondary winding N
2
and the capacitance of the secondary side parallel resonance capacitor C
2
. The alternating voltage thus produced in the secondary winding N
2
is turned into a resonance voltage in the parallel resonance circuit. That is, a voltage resonance operation is performed on the secondary side.
More specifically, this power circuit has, on its primary side, a parallel resonance circuit to execute the switching operation in a voltage resonance mode, and also has, on its secondary side, another parallel resonance circuit to perform a voltage resonance operation in the rectifier circuit. In this specification, the switching converter of a configuration equipped with resonance circuits on its primary and secondary sides as mentioned above will be referred to as “composite resonance type switching converter”.
In the secondary side parallel resonance circuit formed as described, a center tap is provided for the secondary winding N
2
, and there is also provided a half-wave rectifier circuit consisting of a rectifier diode D
0
and a smoothing capacitor Co. This half-wave rectifier circuit receives an input resonance voltage supplied from the secondary side parallel resonance circuit and delivers a DC output voltage Eo therefrom.
In the insulating converter transformer PIT, the mutual i
Frommer William S.
Frommer & Lawrence & Haug LLP
Laxton Gary L.
Simon Darren M.
Sony Corporation
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