Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2001-03-14
2003-06-17
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S040000
Reexamination Certificate
active
06580624
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching power circuit and a control method for the switching power circuit and more particularly relates to the switching power circuit for controlling a harmonic current of an AC (Alternating Current) power such as a commercial power and an external form of the switching power circuit is made small.
The present application claims priority of Japanese Patent Application No. 2000-073177 filed on Mar. 15, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
A condenser-input switching power circuit rectifies an AC (Alternating Current) power such as a commercial power and smoothes the AC power with a condenser, and then converts the AC power into a predetermined DC voltage level with a DC—DC converter so as to keep an output voltage constant by a negative feedback control regardless of changes of an input voltage, a load and a like.
A conventional switching power circuit, as shown in
FIG. 4
, is provided with a rectification circuit
1
, a smoothing condenser
2
, a switching circuit
3
, a transformer
4
, a rectification circuit
5
, a smoothing condenser
6
, a voltage change detecting circuit
7
and a control circuit
8
.
The rectification circuit
1
executes a full-wave (or half-wave) rectification to an AC power “in” such as a commercial power and outputs a first pulsating voltage.
The smoothing condenser
2
is an aluminum electrolytic condenser, and smoothes the first pulsating voltage so as to output a DC voltage V
2
.
The switching circuit
3
controls ON/OFF of the DC voltage V
2
based on a given control signal CTA and outputs an AC voltage V
3
having a pulse width corresponding to the control signal CTA at a predetermined frequency f (such as 20 kHz to 500 kHz).
The transformer
4
transforms the AC voltage V
3
to a predetermined voltage, namely, an AC voltage V
4
.
The rectification circuit
5
rectifies the AC voltage V
4
to a pulsating voltage V
5
.
The smoothing condenser
6
is an aluminum electrolytic condenser, and smoothes the pulsating voltage V
5
so as to output a DC voltage V
6
to a load not shown.
The voltage change detecting circuit
7
detects a change of the DC voltage V
6
and outputs a detection signal V
7
.
The control circuit
8
gives the control signal CTA having a pulse width corresponding to the detection signal V
7
to the switching circuit
3
at a predetermined frequency f.
In the switching power circuit, the AC voltage “in” is full-wave rectified in the rectification circuit
1
, the first pulsating voltage is output and smoothed in the smoothing condenser
2
, and then the DC voltage V
2
is output. The DC voltage V
2
is ON/OFF controlled in the switching circuit
3
based on the control signal CTA, and the AC voltage V
3
of the pulse width corresponding to the control signal CTA at the predetermined frequency f is output.
The AC voltage V
3
is transformed to the AC voltage V
4
in the transformer
4
, the AC voltage V
4
is rectified in the rectification circuit
5
and the pulsating voltage V
5
is output. The pulsating voltage V
5
is smoothed in the smoothing condenser
6
and the DC voltage V
6
is supplied to the load. Also, the change of the DC voltage V
6
is detected in the voltage change detecting circuit
7
and the detection signal V
7
is output. The detection signal V
7
is input to the control circuit
8
. When the level of the detection signal V
7
is lower than a reference value, the pulse width of the control signal CTA is controlled so that a time of an ON state in the switching circuit
3
becomes long, and thereby the negative feedback control is executed so that the DC voltage V
6
becomes constant. Also, when the level of the detection signal V
7
is higher than the reference value, the pulse width of the control signal CTA is controlled so that the time of the ON state in the switching circuit
3
becomes short, and thereby the negative feedback control is executed so that the DC voltage V
6
becomes constant.
However, there are following problems in the conventional switching power circuit.
FIG. 5A
is a graph showing a voltage waveform Va of the AC power “in” and
FIG. 5B
is a graph showing a current waveform Ia of the AC power “in”. In
FIG. 5A
, an axis of ordinates indicates a voltage value V and an axis of abscissas indicates a time t. In
FIG. 5B
, an axis of ordinates indicates a current value I and an axis of abscissas indicates a time t.
In the conventional switching power circuit, as shown in FIG.
5
A and
FIG. 5B
, a large pulse current flows instantaneously near a peak of the voltage waveform (sine wave) Va caused by a peak of the current waveform Ia and an harmonic current flows at a side of the AC power “in”. The harmonic current produces a harmful influence on the AC power “in”, and therefore, there are problems in that a fault occurs in another electronic apparatus connected to the AC power “in” and a transmission loss becomes large. For example, when a video apparatus and an audio apparatus are commonly connected to the AC power “in” to which the switching power circuit is connected, there are harmful influences in that an image quality of the video apparatus and a tone quality of the audio apparatus deteriorate caused by the harmonic current. Therefore, a restriction is determined against the harmonic voltage at present.
Also, the switching power circuit is provided with the smoothing condenser
2
and the smoothing condenser
6
which are aluminum electrolytic condensers of comparatively large sizes, and therefore it is difficult to make an outside form of the switching power circuit small. Therefore, there is a problem in that the switching power circuit can not be installed in a small-size apparatus.
To solve these problems, a switching power circuit is proposed in which measures are taken against the harmonic voltage with an unique circuit configuration. The switching power circuit is discussed in “power harmonic measure technique and design example”, written by Morio Sato, on page 321 of Transistor Technique (CQ Publisher), April 1998.
FIG. 6
is a circuit diagram showing an example of the switching power circuit discussed in this paper (Transistor Technique).
The switching power circuit, as shown in
FIG. 6
, is provided with a rectification circuit
11
, a coil
12
, a diode
13
, a condenser
14
, a condenser
15
, an N-channel MOSFET (hereafter, called an NMOS)
16
, a transformer
17
, a diode
18
, a coil
19
, a diode
20
and a condenser
21
. The condenser
15
and the condenser
20
are aluminum electrolytic condensers.
In the switching power circuit, when the NMOS
16
becomes OFF, a current indicated by a current rout L flows by a fly-back voltage which generates in a first coil
17
a
of the transformer
17
, and the condenser
14
is charged. Then, when the NMOS
16
is turned ON, the condenser
14
is discharged. Since a discharge current rout M always passes through the AC power, the AC current is forcibly taken. As a result, a current flows also in a section in which a voltage between output ends of the rectification circuit
11
is lower than a voltage of the condenser
15
. Therefore, a current flows also in a section though no current flows in the condenser-input switching power circuit, an conducting angle (namely, a period in which an AC current flows) enlarges and no harmonic current flows to the AC power “in”. Further, since the coil
12
is excited by a current indicated by the discharge current rout M of the condenser
14
, excited energy is discharged as a current indicated by a current rout N and the AC current is forcibly taken. Then, the excited energy moves from the condenser
14
to the coil
12
and the condenser
15
. Then, the voltage of the condenser
15
is ON/OFF controlled by the NMOS
16
, and an operation approximately similar to that of the switching power circuit shown in
FIG. 4
is executed.
In the switching power circuit, the problem of the harmonic current at the side of the AC power “in” is solved. However, ther
Berhane Adolf Deneke
NEC Tokin Corporation
LandOfFree
Switching power circuit with a filter for controlling noise... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switching power circuit with a filter for controlling noise..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switching power circuit with a filter for controlling noise... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3127689