Electric power conversion systems – Current conversion – With starting arrangement
Reexamination Certificate
2000-05-16
2001-06-12
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
With starting arrangement
C363S056070, C323S901000, C323S908000
Reexamination Certificate
active
06246596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a so-called dual-converter switching power supply having e.g. a power factor improvement circuit and a main switching circuit therein, and more particularly to a switching power supply including a start-up circuit for controlling start-up of two control circuits that control switching operation of the dual converter circuits, respectively.
2. Description of the Related Art
As a dual-converter switching power supply of this kind, there has been conventionally used a power supply
60
shown in
FIG. 3
which is a schematic block diagram providing a conceptual representation of the power supply
60
. The power supply
60
is comprised of a diode stack
61
for full-wave rectification of an AC current output from an AC power source
2
, a power factor improvement converter circuit
62
for boosting a pulsating voltage (voltage of a pulsating current) VD generated by the diode stack
61
and thereby generating a DC voltage V
DC
, and a main switching circuit
64
for switching the DC voltage V
DC
via a primary winding
63
a of a transformer
63
. Further, the power supply
60
includes a control IC
65
for controlling switching operation of the power factor improvement converter circuit
62
, a capacitor circuit
66
formed e.g. by a capacitor, for supplying an operating current to the control IC
65
, a start-up circuit
67
for controlling start-up of the control IC
65
, a control IC
68
for controlling switching operation of the main switching circuit
64
, a capacitor circuit
69
formed e.g. by a capacitor, for supplying operating current to the control IC
68
, and a start-up circuit
70
for controlling start-up of the control IC
68
. Moreover, the power supply
60
has a diode
81
arranged on the side of a secondary winding
63
b
of the transformer
63
, for rectifying a voltage induced in the secondary winding
63
b
and a capacitor
82
also arranged on the secondary winding side, for smoothing the rectified pulsating current.
In the power supply
60
, when the power is turned on, the capacitor circuit
66
is charged by a current caused to flow therein via a current path, not shown, by the pulsating voltage V
D
. Subsequently, when a charging voltage of the capacitor circuit
66
has reached a predetermined voltage, the start-up circuit
67
starts up the control IC
65
. This causes the control IC
65
to start controlling the switching operation of the power factor improvement converter circuit
62
, whereby the converter circuit
62
boosts the pulsating voltage V
D
to thereby generate the DC voltage V
DC
. On the other hand, the capacitor circuit
69
is also charged with a current caused to flow therein via a current path, not shown, by the DC voltage V
DC
and when the charging voltage of the capacitor circuit
69
has reached a predetermined voltage, the start-up circuit
70
starts up the control IC
68
. This causes the control IC
68
to start controlling the switching operation of the main switching circuit
64
, whereby the main switching circuit
64
switches the DC voltage V
DC
via a primary winding
63
a
of the transformer
63
. As a result, a voltage is induced in the secondary winding
63
b of the transformer
63
. The induced voltage is rectified by the diode
81
, and the rectified DC voltage is smoothed by the capacitor
82
, whereby an output voltage V
O
is generated.
As described above, according to this power supply
60
, first at the initial stage of power-on, the start-up circuit
67
starts up the control IC
65
, and then the start-up circuit
70
starts up the main switching circuit
64
, whereby the power factor improvement converter circuit
62
and the main switching circuit
64
are continuously operated for continuous generation of the output voltage V
O
.
However, the power supply
60
suffers from the following problems: Firstly, in the power supply
60
, the start-up circuit
67
for controlling start-up of the control IC
65
and the start-up circuit
70
for controlling start-up of the control IC
68
are arranged separately and independently of each other, which results in increased manufacturing costs and an increased size of the power supply
60
due to an increase in the number of component parts thereof. Secondly, since the start-up circuits
67
and
70
control the respective control ICs
65
and
68
separately and independently of each other, it is difficult to ensure a reliable start-up sequence of the two control ICs
65
and
68
. As a result, the DC voltage V
DC
generated by the power factor improvement converter circuit
62
can be switched by the main switching circuit
64
before its voltage value is stable, which can cause a failure in start-up of the main switching circuit
64
.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an inexpensive and small-sized switching power supply which is capable of reliably and stably starting up dual converters thereof.
To attain the above object, the present invention provides a switching power supply including a first converter circuit for switching an input voltage for voltage conversion, a second converter circuit for switching a DC voltage generated by the first converter circuit, to thereby generate an output voltage, a first control circuit for controlling switching operation of the first converter circuit, a second control circuit for controlling switching operation of the second converter circuit, first energy-storing capacitor means for supplying an operating current to the first control circuit, second energy-storing capacitor means for supplying an operating current to the second control circuit, and at least one start-up circuit for controlling start-up of the two control circuits.
The switching power supply according to the invention is characterized by comprising an auxiliary power supply circuit for charging the first energy-storing capacitor means with a DC voltage generated by the second converter circuit, and in that the at least one start-up circuit is a single start-up circuit which comprises first charging means for charging the first energy-storing capacitor means with the input voltage, a unidirectional element via which energy stored in the first energy-storing capacitor means is supplied to the second energy-storing capacitor means when a charging voltage of the first energy-storing capacitor means is higher than a charging voltage of the second energy-storing capacitor means by a voltage equal to or higher than a predetermined voltage, and second charging means for charging the second energy-storing capacitor means with the DC voltage generated by the first converter circuit.
According to this power supply, when the power is turned on, the first charging means of the single start-up circuit charges the first energy-storing capacitor means with the input voltage. Then, when the charging voltage of the first energy-storing capacitor means is increased to a voltage which is higher than a charging voltage of the second energy-storing capacitor means by a predetermined voltage, the unidirectional element operates to allow the second energy-storing capacitor means to be charged by a current dependent on energy stored in the first energy-storing capacitor means. Thereafter, when the charging voltage of the first energy-storing capacitor means exceeds an operation-enabling voltage level of the first control circuit, the first control circuit is started by being supplied with an operating current from the first energy-storing capacitor means. As a result, the first control circuit controls the switching operation of the first converter circuit, whereby the voltage conversion by the first converter circuit is started to generate a DC voltage. Thereafter, the second charging means charges the second energy-storing capacitor means with the DC voltage generated by the first converter circuit. At this time, start-up of the first converter circuit can cause a decrease in the charging voltage of the first energy-storing capacitor means. In such a case, howeve
Greenblum & Bernstein P.L.C.
Han Jessica
Nagano Japan Radio Co. Ltd.
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