Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-03-29
2002-05-14
Toatley, Gregory (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S049000
Reexamination Certificate
active
06388902
ABSTRACT:
TECHNICAL FIELD
This invention relates to a switching power supply circuit which can be incorporated as a power supply in various electronic apparatus.
BACKGROUND ART
A switching power supply circuit which adopts a switching converter in the form of, for example, a flyback converter or a forward converter is widely known. Because switching converters of these types employ a rectangular waveform signal to control a switching operation, these switching converters are limited in the amount of switching noise they can suppress. It is also known that these switching converters also are limited in power conversion efficiency because of their operation characteristics.
Thus, various switching power supply circuits that employ resonance type converters have been proposed by the assignee of the present application. A resonance type converter is advantageous in that a high power conversion efficiency can be readily obtained while maintaining low noise characteristics because the waveform controlling the switching operation is a sine waveform. This resonance type converter is also advantageous in that it can be simply formed from a comparatively small number of parts.
FIG. 7
shows an example of a switching power supply circuit which has been previously proposed by the assignee of the present application. Referring to
FIG. 7
, a power supply circuit
700
includes a voltage resonance type converter including a single switching element Q
1
that performs a switching operation in a self-excited manner in accordance with a single end system.
Switching power supply circuit
700
includes a rectifier smoothing circuit for receiving a commercial ac power supply (ac input voltage VAC) and producing a DC input voltage. The rectifier smoothing circuit is formed as a full-wave rectifier circuit, comprising a bridge rectifier circuit Di and a smoothing capacitor Ci. The rectifier smoothing circuit produces a rectified smoothed voltage Ei of a level equal to the ac input voltage VAC. Further, an inrush current limitation resistor Ri is interposed in a rectifier current path of the rectifier smoothing circuit in order to suppress any initial inrush current spike from flowing into a smoothing capacitor Ci, for example, when an initial power supply is provided to the circuit. Further, in power supply circuit
700
an AC switch SW is interposed in the commercial ac power supply line. AC switch SW is switched on/off to start/stop flow of power to power supply circuit
700
.
A voltage resonance type switching converter is provided in power supply circuit
700
. This switching converter, as described above, has a self-exciting construction including switching element Q
1
. In this instance, switching element Q
1
may be formed of a bipolar transistor (BJT: junction transistor) having a high voltage withstanding property. As is shown in
FIG. 7
, the base of switching element Q
1
is connected to the positive electrode side of smoothing capacitor Ci (rectified smoothed voltage Ei) through a starting resistor RS so that the base current upon start-up of the circuit may be obtained from the rectifier smoothing circuit. Further, a resonance circuit adapted to be driven in a self-excited oscillation state is connected between the base of switching element Q
1
and a primary side ground
710
. The resonance circuit is formed from the series circuit connection of an induction characteristic LB of a detection driving winding NB, a resonance capacitor CB, and a base current limiting resistor RB.
A damper diode DD is interposed between the base of the switching element Q
1
and the negative electrode (set at a primary side ground) of smoothing capacitor Ci and forms a path for damper current which flows when the switching element Q
1
is switched off. The collector of switching element Q
1
is connected to an end of a primary winding N
1
of an insulating converter transformer PIT. The emitter of switching element Q
1
is grounded.
A parallel resonance capacitor Cr is connected in parallel between the collector and the emitter of switching element Q
1
. Parallel resonance capacitor Cr forms, based on a capacitance thereof and a leakage inductance L
1
of primary winding N
1
of insulating converter transformer PIT, a primary side parallel resonance voltage resonance type converter circuit. Although detailed description is omitted here, when the switching element Q
1
is off, a voltage resonance type operation is obtained by an action of the parallel resonance circuit which causes the voltage Vcp across resonance capacitor Cr to actually exhibit a pulse wave of a sine waveform.
An orthogonal control transformer PRT shown in
FIG. 7
is a saturatable reactor on which a detection winding ND, a drive winding NB and a control winding NC are wound. Orthogonal control transformer PRT is provided for driving switching element Q
1
and controlling an output voltage to be constant. Though not shown, orthogonal control transformer PRT is formed with a structure wherein a three dimensional core is formed such that two double channel-shaped cores each having four magnetic legs are joined to each other at the ends of the magnetic legs thereof. Detection winding ND and Drive winding NB are wound in the same winding direction around two predetermined ones of the magnetic legs of the three dimensional core, and the control winding NC is wound around two predetermined ones of the magnetic legs of the three dimensional core such that the winding direction thereof is orthogonal to detection winding ND and the drive winding NB.
Detection winding ND of orthogonal control transformer PRT (frequency variation means) is interposed in series between the positive electrode of smoothing capacitor Ci and primary winding N
1
of insulating converter transformer PIT so that a switching output of the switching element Q
1
is transmitted to detection winding ND through primary winding N
1
. In orthogonal control transformer PRT, the switching output obtained in detection winding ND is excited in driving winding NB via transformer coupling, and consequently, an alternating drive voltage is generated in driving winding NB. The drive voltage is output as drive current from the series resonance circuit (NB and CB), which forms the self-excited oscillation drive circuit, to the base of switching element Q
1
through base current limiting resistor RB. Consequently, switching element Q
1
performs a switching operation at a switching frequency determined by the resonance frequency of the series resonance circuit (NB and CB). Insulating converter transformer PIT transmits a switching output of the switching element Q
1
to the secondary side thereof, including secondary winding N
2
.
Referring next to
FIG. 8
, the structure of insulating converter transformer PIT will be described. Insulating converter transformer PIT includes an EE-shaped core which includes a pair of E-shaped cores CR
1
and CR
2
made of, for example, a ferrite material and coupled with each other such that magnetic legs thereof are opposed to each other. A primary winding N
1
and a secondary winding N
2
are wound separately from each other on the central magnetic legs of the EE-shaped core using a split bobbin B. As seen from
FIG. 8
, a gap G is formed between the central magnetic legs of the EE-shaped core. Consequently, a loose coupling having a required coupling coefficient can be obtained. The gap G can be formed by providing the central magnetic legs of the E-shaped cores CR
1
and CP
2
shorter than the other two outer magnetic legs. The coupling coefficient k in this instance is, for example, k
0
0.85 which is a coupling coefficient of a loose coupling. Consequently, a saturation condition is less likely to be obtained as much.
Referring back to
FIG. 7
, one end of primary winding N
1
of insulating converter transformer PIT is connected to the collector of the switching element Q
1
. The other end of primary winding N
1
is connected to the positive electrode of smoothing capacitor Ci (rectified smoothed voltage Ei) through a series connection of detection winding ND.
Frommer William S.
Frommer & Lawrence & Haug LLP
Laxton Gary L.
Sony Corporation
Toatley Gregory
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