Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-09-16
2004-03-30
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S037000, C363S089000, C363S097000
Reexamination Certificate
active
06714425
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No.P2001-364379, filed on Nov. 29, 2001; the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching power supply having a configuration in which a DC—DC converter is connected to an output side of a power factor improving converter, in particular, to a switching power supply capable of reducing its power consumption.
2. Description of the Related Art
Conventionally, switching power supplies are known, in which an alternating current power (AC) is converted to a direct current power (DC) by switching the operation and the obtained DC power is output to a load.
FIG. 1
is a circuit diagram showing a configuration of such a switching power supply according to a related art.
The switching power supply comprises a rectifier
2
, a power factor improving converter
26
connected to the output side of the rectifier
2
, a DC—DC converter
27
connected to the output side of the converter
26
, and a controller
15
. This controller
15
, forming a part of both the converters
26
and
27
, controls the operation of the power factor improving converter
26
and the DC—DC converter
27
.
The rectifier
2
rectifies an AC voltage from an AC power source
1
and outputs the rectified voltage is supplied to the power factor improving converter
26
. The converter
26
improves the power factor of the AC voltage including a ripple current and converts the rectified voltage to a DC voltage which is higher than the rectified AC voltage. The DC—DC converter
27
converts the DC voltage from the converter
26
to the converted DC voltage as the DC power for the load.
The controller
15
comprises a DC/DC controller
12
and a power factor controller (PFC)
13
. The DC/DC controller
12
controls the operation of the DC—DC converter
27
and the PFC controller
13
controls the operation of the power factor improving converter
26
.
Next, a description will be given of the operation of the switching power supply having the configuration described above.
The voltage rectified by the rectifier
2
is supplied to the DC—DC converter
27
through the power factor improving converter
26
. When the voltage is supplied to the DC—DC converter
27
, the voltage also supplied to both the DC/DC controller
12
and the PFC controller
13
. This supply of the voltage starts up both the DC/DC controller
12
and the PFC controller
13
.
The PFC controller
13
performs switching (ON/OFF) control for a first switching element
4
made up of a metal oxide semiconductor (MOS) transistor with a predetermined frequency in order to convert the voltage from the rectifier
2
to a DC voltage by increasing its voltage level.
That is, during ON period of the first switching element
4
, a current flows through a reactor
3
a
, the energy stored in the reactor
3
a
during the OFF period of the first switching element
4
is supplied to and then charged in a smoothing capacitor
6
through a diode
5
.
At this time, the PFC controller
13
performs the ON/OFF switching the operation of the first switching element
4
so that the current flowing through the first switching element
4
becomes the same phase of a sine wave of the AC voltage and the voltages between both terminals of the smoothing capacitor
6
becomes a constant value.
On the other hand, the DC/DC controller
12
performs the switching of a second switching element
8
made up of a MOS transistor in the DC—DC converter
27
, for example, with a predetermined frequency, and supplies the power from a secondary winding
9
b
in a transformer
9
to a load
20
. At this time, a voltage is induced in a thirdly winding
9
c
and the induced voltage is then smoothed by a diode
10
and a capacitor
11
.
The smoothed voltage is supplied to both the DC/DC controller
12
and the PFC controller
13
as the power for the controller
15
.
However, the power factor improving converter
26
connected to the DC—DC converter
27
in the switching power supply of a related art operates at light load for which no operation of the power factor improving converter is necessary. Accordingly, the power consumption of the switching power supply becomes increased in the light load state. Thus, the switching power supply of the related art involves a drawback that it is difficult to increase its power efficiency.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is, with due consideration to the drawbacks of the technique of a related art, to provide a switching power supply capable of improving its power efficiency.
According to an embodiment, a switching power supply has a power factor improving converter, a DC—DC converter, and a control section. The power factor improving converter has a first switching element converting an alternating current (AC) voltage to a direct current (DC) voltage which is greater in voltage level than that of the AC voltage by performing a ON/OFF control for the first switching element. The DC—DC converter has a second switching element converting the DC voltage from the power factor improving converter to a DC voltage by performing a ON/OFF control for the second switching element. The control section judges a load state according to a pulse signal to be used for performing the ON/OFF control for the second switching element, and stops the operation of the power factor improving converter when the judgment result indicates a light load state, and starting the operation of the power factor improving converter when the judgment result indicates a heavy load state which is rather in load than the light load state.
According to another embodiment, the control section in the switching power supply has a load state judgment circuit and a power factor improving converter (PFC) ON/OFF switching circuit. The load state judgment circuit judges a load state according to the pulse signal to be used for performing the ON/OFF control for the second switching element. The power factor improving converter (PFC) ON/OFF switching circuit stops the operation of the power factor improving converter when the judgment result indicates a light load state, and starts the operation of the power factor improving converter when the judgment result indicates a heavy load state rather than the light load state.
In addition, according to another embodiment, the load state judgment circuit in the switching power supply has a reference period generation circuit and an ON period comparison circuit. The reference period generation circuit generates a first pulse signal of a first reference ON period according to the light load state and a second pulse signal of a second reference ON period, that is shorter in time than the first reference ON period of the first pulse signal, according to the heavy load state. The ON period comparison circuit compares one of the first reference ON period and the second reference ON period with an ON period of the pulse signal to be used for performing the ON/OFF operation of the second switching element, and switches the output of the reference period generation circuit from the second pulse signal of the second reference ON period to the first pulse signal of the first reference ON period when the judgment result indicates the current state of the load is the light load state.
Further, according to another embodiment, in the switching power supply, the ON period comparison circuit switches the output of the reference period generation circuit from the first pulse signal of the first reference ON period to the second pulse signal of the second reference ON period when the judgment result indicates the current state of the load is the heavy load state.
Moreover, according to another embodiment, the reference period generation circuit in the switching power supply has a hysteresis characteristic in which the reference period generation circuit outputs the first pulse signal o
Shimada Masaaki
Yamada Tomoyasu
Kilpatrick & Stockton LLP
Sanken Electric Co. Ltd.
Sterrett Jeffrey
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