AC-to-DC converter

Details AC-to-DC converter AC-to-DC converter

2002-02-25

2003-12-09

Berhane, Adolf D. (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C323S222000, C323S288000, C363S090000

Reexamination Certificate

active

06661684

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power-factor control circuit in an AC-to-DC converter, and, more particularly, to a small-sized AC-to-DC converter which can be manufactured at low cost and maintains an output voltage thereof with high efficiency.
2. Description of the Related Art
AC-to-DC converters are used generally as switching regulators for audio system.
FIG. 1
shows an example of the structure of a conventional AC-to-DC converter. A full-wave rectifier, comprising four diodes
72
to
75
in a power-factor control circuit
71
shown in
FIG. 1
, rectifies a voltage applied by an AC power source
70
. A switching controller
80
applies a driving signal to a switching device
79
, in order to control the “open” and “closed” conditions of the switching device
79
. In the case where the switching device
79
is closed, the electromagnetic energy is accumulated in an inductor
76
. In this case, the current flowing to and through the inductor
76
increases in proportion to time. In the case where the switching device
79
is open, the electromagnetic energy is transmitted from the inductor
76
to a capacitor
81
through a diode
77
. As a result, the capacitor
81
is charged. To prevent the switching device
79
from being destructed due to heat and prevent an increase in the loss of power consumption, an output current of the power-factor control circuit
71
is limited by a non-illustrative protecting circuit. Without the protecting circuit, the copper loss or iron loss in the inductor
76
increases. Otherwise, the core saturation may occur in the inductor
76
.
In accordance with a switching operation of such a switching device
79
, an output voltage (i.e. a voltage of the capacitor
81
) of the power-factor control circuit
71
is retained at a constant voltage greater than the amplitude of the voltage supplied from the AC power source
70
, regardless of the size of a voltage input from the AC power source
70
to the power-factor control circuit
71
. For example, in the case where the AC power source
70
is 100 volt AC, the output voltage of the power-factor control circuit
71
is retained at 160V or 190V. In the case where the AC power source
70
is 240 volt AC, the output voltage of the power-factor control circuit
71
is retained at 400V.
Two switching devices
83
and
84
included in a DC-to-DC converter
82
connected to the capacitor
81
are complementary switching devices. In other words, when the switching device
83
is open, the switching device
84
is closed, and when the switching device
83
is closed, the switching device
84
is open. As a result of this switching operation of the switching devices
83
and
84
, currents flow to the primary winding of the transformer
85
alternatively, and an AC voltage is generated by the secondary winding of the transformer
85
. A rectification circuit comprising diodes
88
to
91
rectifies a voltage received from the transformer
85
, to generate a DC voltage. The DC voltage output from the rectification circuit is applied to capacitors
92
and
93
. The voltage at the capacitors
92
and
93
are retained at a constant level by a non-illustrative voltage controller. The voltage at the capacitors
92
and
93
are applied to loads
94
and
95
, and resulting in that DC power is transmitted to the loads
94
and
95
.
In the normal use of the audio system, when an audio system generates a big sound, the average power consumed by the loads
94
and
95
is in a range between {fraction (1/50)} and ⅛ of the maximum power consumption. Even in the case where the audio system generates a rare extremely big noise, the average power consumed by the loads
94
and
95
is in a range between one sixteenth and half of the maximum power consumption. Though the average consumed power is very little, it is necessary to design the switching regulator not to be destructed even in the state where the maximum power is consumed. As a result, the power can not effectively be consumed in the normal use of the AC-to-DC converter, and the improvement of the power factor can not result in a desirable effect. In addition, the cost of each component included in the AC-to-DC converter increases.
In contrast to the above, a large amount of power is consumed in a moment, when sounds of musical instrument (e.g. sounds of piano, drum, etc.) which have low frequency components and have an attack sound segment having the large amplitude, or when a mixed sound of a high tone sound and a low tone sound is output. By the effect of the restriction in an output current of the power-factor control circuit
71
, currents flowing to and through the loads
94
and
95
are restricted as well. Hence, in the case where the power consumed by the loads
94
and
95
exceeds its restriction, the voltage applied to the loads
94
and
95
suddenly drops.
FIG. 2
shows the relationship between output power of a DC-to-DC converter
82
and an output voltage of a power-factor control circuit
71
, in the AC-to-DC converter shown in FIG.
1
. As shown in
FIG. 2
, when the output power of the DC-to-DC converter
82
is the maximum power consumption Pmax [W], the output voltage of the power-factor control circuit
71
suddenly drops. In such circumstances, the linearity of the audio output from the audio system will remarkably be deteriorated. In the power-factor control circuit
71
wherein the output current is restricted in association with the power consumed by the loads
94
and
95
, the inductor
76
, the switching device
79
and the diode
77
are large in size, and hence the volume of the power-factor control circuit
71
will be increased. For example, the volume of the power-factor control circuit
71
, whose output current is limited in association with the maximum consumption power of the loads
94
and
95
, increases two or sixteen times more than that in the general case where the output current is controlled by the protecting circuit. Additionally, there will be an increase in the component cost and the cost of manufacturing the AC-to-DC converter.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above. It is accordingly an object of the present invention to provide an AC-to-DC converter which is small in size, can be manufactured at low cost, and operates with high efficiency.
Another object thereof is to provide an AC-to-DC converter, whose output-voltage variation can be restricted, in the case where the AC-to-DC converter outputs a large amount of power.
In order to attain the above objects, according to one aspect of the present invention, there is provided an AC-to-DC converter comprising:
a power-factor control circuit which is coupled to an AC power source;
a capacitor which has a first electrode and a second electrode, and whose charge/discharge operation is controlled by the power-factor control circuit; and
a converter which is coupled to the capacitor, and
wherein the power-factor control circuit includes
a rectifier which is coupled to the AC power source,
a detector which detects a peak output voltage of the rectifier,
a switching device which executes a switching operation for charging the capacitor, and
a switching controller which controls the switching operation of the switching device, based on a detected result of the detector.
In this structure, the power-factor control circuit may charge the capacitor in accordance with the switching operation of the switching device, such that a voltage in the capacitor will be equal to the peak output voltage detected by the detector or greater than a peak output voltage of the detector by a predetermined amount of voltage.
The power-factor control circuit may include:
an inductor which has a first terminal, coupled to a positive output terminal of the rectifier, and a second terminal; and
a first device which is conducted to the capacitor in order to supply the capacitor with a current, and which is coupled between the second terminal of the inductor and the fir

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