Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-12-04
2001-08-28
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S047000
Reexamination Certificate
active
06282103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an improved switching power supply wherein an inductor device is provided to suppress a harmonic current therein, and wherein she power factor thereof is improved.
2. Description of the Prior Art
A conventional switching power supply is shown, for example, in
FIG. 1
, and comprises an AC power source AC connected to a diode bridge
11
, consisting of diodes D
1
-D
4
, and a smoothing capacitor C
1
connected in parallel to diode bridge
11
. Diode bridge
11
is a rectifying circuit used to rectify the output of power source AC. The positive terminal of smoothing capacitor C
1
is connected to terminal
21
of primary winding N
1
of a transformer TR. The primary winding terminal
22
of winding N
1
is connected to the negative terminal of smoothing capacitor C
1
through switch Q. The terminals
23
and
24
of secondary winding N
2
of transformer Tr are connected to rectifying circuit
25
consisting of diode
27
and smoothing capacitor C
2
. The output of rectifying circuit
25
is connected to a load circuit
31
.
A control circuit
26
controls the output voltage of the rectifying circuit
25
and provides control signal GSW to switch Q so that the output voltage of rectifying circuit
25
is kept constant. Transformer TR, rectifying circuit
25
, switch Q and control circuit
26
comprise a DC/DC converter
20
that performs an electrically isolated transfer of DC power, applied to the primary side of transformer TR to the secondary side thereof.
In switching power supply
10
, a DC voltage VC
1
, obtained by AC/DC converting the output of AC power supply AC, by means of diode bridge
11
and smoothing capacitor C
1
, is applied to the terminal
21
of transformer TR of DC/DC converter
20
, and is turned ON or OFF by switch Q, made for example, of a field effect transistor (FET). Hence, a switching current IN
2
is induced in secondary winding N
2
because current IN
1
flows, as a train of pulses, through primary winding N
1
. Switching current IN
2
is then converted to a DC current by rectifying circuit
25
which consists of diode D
7
and smoothing capacitor C
2
, and is supplied to load circuit
31
.
The switching power supply
10
AC/DC converts the output of AC power supply source AC, applied to rectifying circuit
11
, using rectifying circuit
11
and smoothing capacitor C
1
. The DC power signal thus obtained is isolated by means of DC/DC converter
20
, and then is supplied to load circuit
31
. Accordingly, switching power supply
10
supplies a DC power signal which is isolated from the AC power source AC.
However, the input current ICI of smoothing capacitor C
1
is not turned ON when the rectified voltage Vrec of AC power source AC is lower than voltage VC
1
, provided across smoothing capacitor C
1
. Hence, input current Iin (i.e. output current of AC power source AC) of switching power supply
10
takes the waveform of a pulse train, causing the conduction angle of input current Iin to become smaller. This results in decrease of the power factor and increase in harmonic current.
FIG. 2
shows waveforms of input voltage Vin and input current Iin of switching power supply
10
, rectified voltage Vrect, and voltage VC
1
provided across smoothing capacitor C
1
. As is evident from
FIG. 2
, input current Iin is not turned ON during interval T
2
, in which rectified voltage Vrec is lower than voltage VC
1
provided across smoothing capacitor C
1
. In contrast, input current Iin is caused to flow as a series of pulses during interval T
1
, in which rectified voltage Vrec is higher than voltage VC
1
provided across smoothing capacitor C
1
.
Accordingly, input current Iin flows as a series of pulses and causes the conduction angle of the input current Iin to become smaller. Thus, disadvantageously, in the conventional switching power supply, the power factor thereof is caused to decrease and the harmonic current is caused to increase.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to overcome the aforementioned and other deficiencies, disadvantages and problems of the prior art.
Another object is to provide a switching power supply comprising an inductor device having a center tap, wherein harmonic current is prevented from being generated, and wherein power factor thereof is increased.
REFERENCES:
patent: 5673184 (1997-09-01), Rilly et al.
patent: 5751561 (1998-05-01), Ho et al.
patent: 5790389 (1998-08-01), Hua
Hashimoto Masaki
Naito Yoshinao
Ota Maki
Takada Koji
Yasuda Kazunori
Kojima Moonray
Riley Shawn
Yokogawa Electric Corporation
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