Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-08-09
2002-09-24
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S044000
Reexamination Certificate
active
06456509
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply circuit suitable for use in various video apparatus such as a color television receiver and a projector apparatus.
Some video apparatus such as a television receiver and a projector apparatus have an analog circuit and a digital circuit, for example, as circuit blocks for carrying out various signal processing.
Such video apparatus having the analog and digital circuit blocks are provided with a constant-voltage power supply for supplying constant operating voltage to the circuit blocks.
As an example of a conventional power supply circuit provided in such a video apparatus,
FIG. 8
shows configuration of a switching power supply circuit provided in a large-sized color television receiver, for example.
A bridge rectifier circuit Di and a smoothing capacitor Ci in the power supply circuit generate a rectified and smoothed voltage Ei corresponding to an alternating input voltage VAC from a commercial alternating-current power.
A self-excited voltage resonance type converter that includes a switching device Q
1
and performs switching operation by a so-called single-ended system is provided as a switching converter for interrupting the rectified and smoothed voltage Ei inputted thereto.
The switching device Q
1
is driven by a selfoscillation driving circuit formed by a series connection circuit of a driving winding NB, a resonant capacitor CB, and a base current limiting resistance RB. Switching frequency of the switching device Q
1
is determined by resonance frequency of a resonant circuit formed by the driving winding NB and the resonant capacitor CB.
A starting resistance RS is provided to supply the switching device Q
1
with a starting current obtained in a rectifying and smoothing line at the turn-on of the commercial alternating-current power.
The switching device Q
1
is connected with a clamp diode DD
1
and a primary-side parallel resonant capacitor Cr shown in FIG.
8
. Capacitance of the primary-side parallel resonant capacitor Cr and leakage inductance L
1
of the primary winding N
1
side of an isolating converter transformer PIT form a primary-side parallel resonant circuit of the voltage resonance type converter.
An orthogonal type control transformer PRT-
1
is a saturable reactor provided with a resonance current detecting winding ND, the driving winding NB, and a control winding NC
1
. The orthogonal type control transformer PRT-
1
is provided to drive the switching device Q
1
and effect control for constant voltage.
The isolating converter transformer PIT (Power Isolation Transformer) transmits switching output of the switching device Q
1
to the secondary side of the switching power supply circuit.
As shown in
FIG. 8
, a secondary-side winding is formed on the secondary side of the isolating converter transformer PIT by winding secondary windings N
2
, N
3
, N
4
, and N
5
.
In this case, as shown in
FIG. 8
, a point of connection between the secondary winding N
4
and the secondary winding N
5
is connected to a secondary-side ground. A secondary-side parallel resonant capacitor C
2
is connected between the secondary-side ground and an ending point of the secondary winding N
2
in parallel with the secondary-side winding.
The parallel resonant circuit to convert switching operation into voltage resonance type operation is provided on the primary side of the isolating converter transformer PIT, and the voltage resonant circuit to provide voltage resonance operation is provided on the secondary side of the isolating converter transformer PIT. In the present specification, the switching converter provided with such resonant circuits on the primary side and the secondary side is referred to as a “complex resonance type switching converter.”
The secondary winding connected in parallel with the secondary-side parallel resonant capacitor C
2
is provided with a half-wave rectifying and smoothing circuit formed by a rectifier diode D
01
and a smoothing capacitor C
01
, so that a direct-current output voltage E
01
of 135 V for horizontal deflection is obtained from the half-wave rectifying and smoothing circuit.
Also, the secondary winding formed by the secondary windings N
3
and N
4
is provided with a half-wave rectifying and smoothing circuit formed by a rectifier diode D
02
and a smoothing capacitor C
02
, so that a direct-current output voltage E
02
of 15 V for vertical deflection is obtained from the half-wave rectifying and smoothing circuit. The secondary winding N
5
is connected with a rectifier diode D
03
and a smoothing capacitor C
03
shown in
FIG. 8
, so that a direct-current output voltage E
03
of −15 V for the same vertical deflection is obtained from a half-wave rectifying and smoothing circuit formed by the rectifier diode D
03
and the smoothing capacitor C
03
.
Thus, the direct-current output voltages E
02
and E
03
(±15 V) for vertical deflection are obtained from voltages induced in the secondary winding (N
3
+N
4
) and the secondary winding N
5
on the secondary side of the isolating converter transformer PIT. Hence, the secondary winding (N
3
+N
4
) and the secondary winding N
5
have the same number of turns.
In this case, the secondary-side direct-current output voltage E
01
is also inputted from a branch point to a control circuit
1
.
The control circuit
1
uses the direct-current output voltage E
02
as its operating voltage. The control circuit
1
variably controls the inductance LB of the driving winding NB wound in the orthogonal type control transformer PRT-
1
by changing the level of a control current flowing through the control winding NC
1
according to change in the level of the direct-current output voltage E
01
. This results in a change in resonance conditions of the resonant circuit including the inductance LB of the driving winding NB in the self-oscillation driving circuit. This represents an operation of changing the switching frequency of the switching device Q
1
. This operation makes constant the direct-current output voltages outputted from the secondary side of the isolating converter transformer PIT.
Even with such a configuration for constant-voltage control including the orthogonal type control transformer PRT-
1
, since the primary-side switching converter is of the voltage resonance type, it may be considered that the power supply circuit variably controls the switching frequency of the switching device Q
1
and at the same time, effects PWM control of the switching device Q
1
within a switching cycle. This complex control operation is realized by a single control circuit system.
In addition, a direct-current output voltage E
04
of 9 V to be supplied to the analog circuit block is obtained from output of the secondary winding (N
3
+N
4
) in the power supply circuit, and also a direct-current output voltage E
05
of 5 V to be supplied to the digital circuit block is obtained from output of the secondary winding N
4
.
In this case, the output of the secondary winding (N
3
+N
4
) is inputted to a half-wave rectifying and smoothing circuit formed by a rectifier diode D
04
and a smoothing capacitor C
04
via an inductor L
21
(4.7 &mgr;H) to reduce power loss. The half-wave rectifying and smoothing circuit first converts the output of the secondary winding (N
3
+N
4
) into a direct-current output voltage E
07
of 11 V. Then, the direct-current output voltage E
04
of 9 V to be outputted to the analog circuit block is obtained from the direct-current output voltage E
07
.
The output of the secondary winding N
4
is inputted to a half-wave rectifying and smoothing circuit formed by a rectifier diode D
05
and a smoothing capacitor C
05
. The half-wave rectifying and smoothing circuit converts the output of the secondary winding N
4
into a direct-current output voltage E
08
of 6.5 V. Then, the direct-current output voltages E
05
(5 V) and E
06
(3.3 V) to be outputted to the digital circuit block are obtained from the direct-current output voltage E
08
.
The direct-current
Berhane Adolf Deneke
Maioli Jay H.
Sony Corporation
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