Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2004-05-14
2004-12-14
Berhane, Adolf (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06831846
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a switching power supply circuit provided as a power supply for various electronic apparatus.
BACKGROUND ART
Various switching power supply circuits formed with various resonance type converters, for example, have been proposed. Resonance type converters readily obtain high power conversion efficiency and achieve low noise by forming a sinusoidal waveform in switching operation. The resonance type converters have another advantage of being able to be formed by a relatively small number of parts.
FIG. 14
is a circuit diagram showing an example of a prior art switching power supply circuit. As a fundamental configuration of the power supply circuit shown in
FIG. 14
, a voltage resonance type converter is provided as a switching converter on the primary side.
In the power supply circuit shown in
FIG. 14
, a bridge rectifier circuit Di and a smoothing capacitor Ci generate a rectified and smoothed voltage Ei from a commercial alternating-current power.
The voltage resonance type converter for receiving and interrupting the rectified and smoothed voltage Ei employs a single-ended system using one transistor. A self-excited configuration is employed as a driving system. In this case, a bipolar transistor such as a high withstand voltage BJT (Bipolar Junction Transistor) is selected as a switching device Q
1
for forming the voltage resonance type converter. A primary-side parallel resonant capacitor Cr is connected in parallel with a collector and an emitter of the switching device Q
1
. A clamp diode DD is connected between a base and the emitter of the switching device Q
1
. The parallel resonant capacitor Cr forms a primary-side parallel resonant circuit in conjunction with leakage inductance L
1
obtained at a primary winding N
1
of an isolation converter transformer PIT, whereby operation of the voltage resonance type converter is obtained.
The base of the switching device Q
1
is connected with a self-oscillation driving circuit comprising a driving winding NB, a resonant capacitor CB, and a base current limiting resistance RB. The switching device Q
1
is supplied with a base current based on an oscillating signal generated in the self-oscillation driving circuit, and is thereby driven for switching operation. Incidentally, at the time of a start, the switching device Q
1
is started by a starting current flowing from a line of the rectified and smoothed voltage Ei to the base of the switching device Q
1
via a starting resistance Rs.
FIG.
15
A and
FIG. 15B
show a structure of an orthogonal type control transformer PRT.
FIG. 15A
is an external perspective view of assistance in explaining a general structure of the orthogonal type control transformer PRT.
FIG. 15B
is a sectional perspective view of assistance in explaining winding directions of windings wound in the orthogonal type control transformer PRT.
The orthogonal type control transformer PRT is formed by winding a control winding Nc in a winding direction orthogonal to a winding direction of the driving winding NB and a resonance current detecting winding ND.
The orthogonal type control transformer PRT has a gap length G of 10 &mgr;m at junctions of magnetic legs
21
a
to
21
d
and magnetic legs
22
a
to
22
d
, respectively.
The control winding Nc of the orthogonal type control transformer PRT is formed by a 60 &mgr;m &phgr; polyurethane-covered copper wire wound by 1000 T (turns), for example; the detecting winding ND is formed by a 0.3 mm &phgr; polyurethane-covered copper wire wound by 1 T; and the driving winding NB is formed by a 0.3 mm &phgr; polyurethane-covered copper wire wound by 3 T.
The isolation converter transformer PIT transmits a switching output of the switching converter obtained on the primary side to the secondary side.
As shown in
FIG. 16
, for example, the isolation converter transformer PIT has an E—E-shaped core formed of E-shaped ferrite cores CR
1
and CR
2
. As shown in
FIG. 16
, the primary winding N
1
and a secondary winding N
2
each formed by a litz wire are wound in respective divided regions using a dividing bobbin B.
A gap G is formed in a central magnetic leg of the E—E-shaped core, as shown in FIG.
16
. Gap length of the gap G determines leakage inductance in the isolation converter transformer PIT. Also, loose coupling at a required coupling coefficient is obtained by the gap length of the gap G. The coupling coefficient in this case is 0.85, for example, to obtain a state of loose coupling, and accordingly saturation is not readily reached. The gap G can be formed by making the central magnetic leg of the E-shaped cores CR
1
and CR
2
shorter than two outer magnetic legs of the E-shaped cores CR
1
and CR
2
. The gap length in this case is about 1 mm.
As shown in
FIG. 14
, the primary winding N
1
of the isolation converter transformer PIT has one end connected to the line of the direct-current input voltage (rectified and smoothed voltage Ei) via the current detecting winding ND, and another end connected to the collector of the switching device Q
1
. The switching device Q
1
performs switching operation on the direct-current input voltage. With the above-described form of connection, the switching output of the switching device Q
1
is supplied to the primary winding N
1
and the current detecting winding ND, and thus an alternating voltage having a cycle corresponding to switching frequency occurs.
An alternating voltage induced by the primary winding N
1
of the isolation converter transformer PIT occurs in the secondary winding N
2
. In this case, a secondary-side parallel resonant capacitor C
2
is connected in parallel with the secondary winding N
2
. Thereby, leakage inductance L
2
of the secondary winding N
2
and capacitance of the secondary-side parallel resonant capacitor C
2
form a parallel resonant circuit. The parallel resonant circuit converts the alternating voltage induced in the secondary winding N
2
to a resonance waveform. That is, a voltage resonance operation is obtained on the secondary side.
On the secondary side of the isolation converter transformer PIT in this case, an anode of a rectifier diode D
01
is connected to the secondary winding N
2
and a cathode of the rectifier diode D
01
is connected to a smoothing capacitor C
01
, whereby a half-wave rectifier circuit is formed. The half-wave rectifier circuit provides a secondary-side direct-current output voltage E
01
across the smoothing capacitor C
01
.
Further, in this case, the secondary winding N
2
is provided with a tap. As shown in
FIG. 14
, a half-wave rectifier circuit comprising a rectifier diode D
02
and a smoothing capacitor C
02
is formed for the tap output. The half-wave rectifier circuit provides a secondary-side direct-current output voltage E
02
lower than the secondary-side direct-current output voltage E
01
.
The secondary-side direct-current output voltages E
01
and E
02
are each supplied to a required load circuit. The secondary-side direct-current output voltage E
01
is also outputted from a branch point as a detection voltage for a control circuit
1
.
The control circuit
1
functions as an error amplifier receiving the direct-current output voltage E
01
as a detection input. Specifically, a voltage obtained by dividing the direct-current output voltage E
01
by resistances R
3
and R
4
is inputted as a control voltage to a control terminal of a shunt regulator Q
3
. Hence the shunt regulator Q
3
allows a current having a level corresponding to the direct-current output voltage E
01
to flow as a control current Ic to the control winding Nc. That is, the level of the control current flowing through the control winding Nc is variably controlled.
Since the level of the control current flowing through the control winding Nc is changed, the orthogonal type control transformer PRT effects control so as to change inductance LB of the driving winding NB. Thereby resonance frequency of a resonant circuit comprising the driving winding NB and the resonant capacitor CB in the self-oscillation driving cir
Berhane Adolf
Maioli Jay H.
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