Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-09-09
2001-11-06
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021110
Reexamination Certificate
active
06314005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC-DC converter to be provided in apparatus such as a switching power-supply switching device.
2. Description of the Related Art
FIG. 13
shows an example of a DC-DC converter. As shown in the drawing, the DC-DC converter is an isolated forward converter having a transformer
1
. The transformer
1
has a primary coil N
1
, a secondary coil N
2
, and voltage-detecting coil N
3
. A primary side circuit
3
having a switching device Q and a capacitor
2
is connected to the primary coil N
1
. An input power supply
4
is connected to the primary side circuit
3
.
Also, a secondary side circuit
5
is connected to the aforementioned secondary coil N
2
, and an output side of the secondary side circuit
5
is connected to a load
6
. In addition, a voltage-detecting circuit
8
is connected to the voltage-detecting coil N
3
. An output side of the voltage-detecting circuit
8
is connected to a control circuit
10
. An output of the control circuit
10
is connected to the switching device Q of the primary side circuit
3
.
The primary side circuit
3
has a configuration in which power is sent from the input power supply
4
to the secondary side circuit
5
via the transformer
1
. The secondary side circuit
5
rectifies and smoothes voltage from the secondary coil N
2
, and a DC voltage V
out
rectified and smoothed thereby is outputted to the load
6
.
Also, the voltage-detecting circuit
8
has a configuration that rectifies and smoothes voltage from the voltage-detecting coil N
3
. A voltage corresponding to a voltage from the aforementioned secondary coil N
2
is generated, and the voltage from the secondary coil N
2
is processed as a voltage corresponding to an output voltage V
out
of the aforementioned secondary side circuit
5
. Accordingly, the voltage-detecting circuit
8
has a configuration that outputs the aforementioned voltage rectified and smoothed into the control circuit
10
as the output voltage V
out
of the secondary side circuit
5
.
In addition, according to a detected voltage applied by the voltage-detecting circuit
8
, the control circuit
10
has a configuration that applies a pulse control signal to the switching device Q, the pulse control signal functioning to stabilize the output voltage V
out
of the secondary side circuit
5
, as shown in FIG.
12
. The pulse control signal controls on/off operations of the switching device Q, and the switching device Q performs on/off operations according to the pulse control signal.
As described above, in the DC-DC converter shown in
FIG. 13
, a voltage corresponding to the output voltage V
out
of the secondary side circuit
5
is generated in the voltage-detecting coil N
3
. This allows the voltage-detecting circuit
8
to use the voltage in the voltage-detecting coil N
3
and to indirectly detect and output the output voltage V
out
of the secondary side circuit
5
. By circuit operations of the control circuit
10
according to the detected voltage, on/off operations of the switching device Q are controlled, and the output voltage V
out
of the secondary side circuit
5
is stabilized.
In the foregoing DC-DC converter in which the output voltage V
out
of the secondary side circuit
5
is indirectly detected, problems occur because output voltage V
out
varies according to load variation and this variation is not reflected in the voltage detected by voltage detecting circuit
8
.
That is, when load variation occurs, currents I
out
to be outputted to the load
6
vary according to the load variation. This current variation causes the output voltage V
out
to also vary. On the other hand, no variation occurs in a voltage applied from the voltage-detecting circuit
8
to the control circuit
10
and the control circuit
10
does not compensate for the variations in the output voltage V
out
attributable to the variations in load
6
.
In other words, in the circuit configuration as shown in
FIG. 13
, the relationship between the current I
out
and the output voltage V
out
, as shown in
FIG. 11
, is produced, and the output voltage V
out
varies according to variation of the current I
out
caused by variations in the load
6
. This load-variation-attributed variation of the output voltage V
out
cannot be detected by the voltage-detecting coil N
3
. Therefore, in the control circuit
10
, circuit operations for compensating the variation of the output voltage V
out
do not occur. This produces problems in that the voltage V
out
varies according to the load variation, and therefore, the output voltage V
out
is not stabilized satisfactorily.
The following problems also arise in a DC-DC converter of a type in
FIG. 13
, in which the output voltage V
out
of the secondary side circuit
5
is indirectly detected. When environmental variations occur for the DC-DC converter, characteristics of components of the individual circuits vary according to variation of the temperature therein, resulting in variation of the output voltage V
out
of the secondary side circuit
5
. This causes problems in that variation of the output voltage V
out
due to temperature-variation cannot be prevented.
These problems are caused by the following reasons. As in the case where the aforementioned load variation occurs, when the output voltage V
out
varies according to environmental temperature variations, the variation of the output voltage V
out
cannot be detected using the voltage-detecting coil N
3
. In addition, the detected voltage outputted from the voltage-detecting circuit
8
to the control circuit
10
also varies according to the aforementioned environmental temperature variation without regard to the output voltage V
out
. Since on/off operations of the switching device Q are controlled by circuit operations of the control circuit
10
according to the detected voltage, problems arises in that the output voltage V
out
of the secondary side circuit
5
is very unstable because of the temperature variation.
SUMMARY OF THE INVENTION
The present invention can solve the aforementioned problems by providing a DC-DC converter that can suppress the variation of the output voltage of the secondary side circuit which is attributed to the load variation and the environmental temperature variation so as to stabilize the output voltage of the secondary side circuit.
In order to achieve the above objects, the present invention has the following configurations for solving the problems as described above. That is, a first aspect of the invention for solving the above problems provides a DC-DC converter having a primary side circuit including a switching device for performing on/off operations to output energy in a primary coil of a transformer to a secondary coil, a secondary side circuit for rectifying and smoothing a voltage outputted from the secondary coil so as to output a DC-DC voltage, a voltage-detecting circuit for rectifying and smoothing a voltage outputted from a voltage-detecting coil provided in the transformer so as to output the voltage as a detected voltage corresponding to a voltage to be outputted from the secondary side circuit, and a control circuit for applying to the switching device a pulse control signal used for controlling on/off operation of the switching device according to the voltage outputted from the voltage-detecting circuit, in which a primary side current-detecting circuit is provided for converting a working current in the primary side circuit, the working current corresponding to a current in the secondary side circuit, for performing detection thereof, for overlapping the detected voltage with the voltage outputted from the voltage-detecting circuit so as to compensate for the amount of variation of the output voltage of the secondary side circuit, the variation being attributed to a variation of the working current in the secondary side circuit, and for applying a voltage according to the overlapped voltage to the control circuit.
To solve the aforementioned problems, a second aspect of the invention p
Kitamura Koji
Matsumoto Tadahiko
Matsumoto Yoshihiro
Nishi Koji
Nishiyama Takayoshi
Laxton Gary L.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Wong Peter S.
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