Switching power supply

Details Switching power supply Switching power supply

2001-11-01

2002-11-19

Berhane, Adolf Deneke (Department: 2838)

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

C363S098000, C363S132000

Reexamination Certificate

active

06483723

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply for supplying a stabilized DC voltage to industrial or consumer electronics equipments.
A power supply for a television set, a VTR, a personal computer, and so on, is required to stably supply a steady DC voltage. A switching power supply is preferable as such a power supply. The switching power supply uses semiconductor devices, e.g. MOSFETs, IGBTs, and thyristors, as switches to once convert an input DC voltage into an AC voltage by repeated cycles of ON/OFF states of the switches. The converted AC voltage is further converted into a steady DC voltage through the sequence of a transformer, a rectifying circuit, and a smoothing circuit, and the steady DC voltage is then output. In the switching power supply, a transfer factor, i.e. the ratio of the output voltage to the input voltage, is substantially determined by the duty factor of the switches. Accordingly, the switching power supply controls the duty factor of the switches by the control over the switches, and thereby stabilizes the output DC voltage.
Since a switching loss, i.e. the power loss caused by switching, is generally small, the switching power supply can supply power at high efficiency. Hence, the switching power supply is excellent for energy saving.
The transfer factor of the switching power supply substantially depends on only the duty factor of the switches, but does not substantially depend on the switching frequency, i.e. the frequency of the turning ON/OFF of the switches. Furthermore, in the switching power supply, when the switching frequency is raised higher, reactive elements, such as transformers, inductors, and capacitors, is miniaturized with the respective performances of the elements preserved. Therefore, the switching power supply is miniaturized with relative ease, maintaining a steady output voltage.
The following is the description of a switching power supply performing hard switching that is an example of a conventional switching power supply.
FIG. 6
is the circuit diagram of the conventional switching power supply
100
.
In the switching power supply
100
, four switching sections
101
H,
101
L,
102
H, and
102
L, form a full-bridge on the primary side of a transformer
3
. The switching sections
101
H and
102
H connected to a high-potential input terminal
1
a
of the full-bridge are referred to as high-side switching sections. The switching sections
101
L and
102
L connected to a low-potential input terminal
1
b
of the full-bridge are referred to as low-side switching sections. The four switching sections include respective switching devices
1
HS,
1
LS,
2
HS and
2
LS. These switching devices are semiconductor devices, for example, IGBTs. The four switching sections include respective parasitic capacitors
1
HC,
1
LC,
2
HC and
2
LC, in parallel with the switching devices. A switching control circuit
70
controls the turning-ON/OFF of the four switching sections.
FIG. 7
is a diagram showing the waveforms of the currents and voltages occurring at various sections of the circuit shown in
FIG. 6
, according to the hard switching by the switching control circuit
70
. In this diagram, positive directions of the currents and voltages at the various sections of the circuit are defined as.
The switching control circuit
70
outputs switching signals G
1
, G
2
, G
3
, and G
4
to the switching devices
1
HS,
1
LS,
2
HS, and
2
LS, respectively. The switching signals G
1
, G
2
, G
3
, and G
4
are rectangular waves. Each switching device is ON during the interval that the switching signal corresponding thereto stays high (H), and OFF during the interval that the switching signal stays low (L).
The switching control circuit
70
performs hard switching for the turning ON/OFF of the four switching sections. Here, hard switching refers to the switching for the simultaneous turning-ON/OFF between one of the high-side switching sections and one of the low-side switching sections. In the hard switching of the switching control circuit
70
, the following three periods are sequentially achieved with predetermined time lengths and predetermined cycle periods: (1) A first period corresponds to the period T
0
-T
1
in FIG.
7
. During the first period, the first high-side switching section
101
H and the second low-side switching section
102
L are ON, and the second high-side switching section
102
H and the first low-side switching section
101
L are OFF. (2) A second period corresponds to the period T
2
-T
3
in FIG.
7
. During the second period, the first high-side switching section
101
H and the second low-side switching section
102
L are OFF, and the second high-side switching section
102
H and the first low-side switching section
101
L are ON. (3) A third period corresponds to each of the period T
1
-T
2
and the period T
3
-T
4
, and is achieved during intervals between the first period and the second period. During the third period, all the four switching sections are OFF.
The following is the description of the hard switching of the switching control circuit
70
in the time sequence from the time T
0
to the time T
4
shown in FIG.
7
.
<Period T
0
-T
1
>
At the time T
0
, the switching control circuit
70
simultaneously changes the first switching signal G
1
and the fourth switching signal G
4
from L to H, thereby turning ON the first high-side switching section
101
H and the second low-side switching section
102
L. On the other hand, the first low-side switching section
101
L and the second high-side switching section
102
H are both OFF.
During the period T
0
-T
1
, a substantially steady and positive input voltage Vin is applied across the primary winding
3
a
of the transformer
3
via the first high-side switching section
101
H and the second low-side switching section
102
L. Thus, a primary voltage Vt, i.e. the voltage across the primary winding
3
a
, is substantially equal to the input voltage Vin. Furthermore, the primary current It of the transformer
3
flows from the first junction point P to the second junction point Q of the primary winding
3
a
. In other words, the primary current It flows in the direction of the arrow shown in FIG.
6
. Then, a positive voltage Vin
is induced across each of the first secondary winding
3
b
and the second secondary winding
3
c
of the transformer
3
.
Here, the turn ratio of the primary winding
3
a
, the first secondary winding
3
b
, and the second secondary winding
3
c
of the transformer
3
is n:1:1, where n is a positive real number. Since a first rectifying diode
4
b
is ON, the voltage V
5
across a smoothing inductor
5
is substantially equal to Vin
−Vout. Here, an output voltage Vout, i.e. the voltage across a smoothing capacitor
6
, is positive. The output voltage Vout may be assumed to be substantially steady, since the smoothing capacitor
6
has a sufficiently large capacitance. Accordingly, the current I
5
flowing through the smoothing inductor
5
increases linearly in the direction of the arrow indicated in
FIG. 6
during the period T
0
-T
1
. Note that the current
15
increases slowly, since the inductance of the smoothing inductor
5
is sufficiently large. The voltage Vc across a second rectifying diode
4
c
is substantially equal to +2Vin
, where the positive direction of the voltage is defined as the direction of the arrow shown in
FIG. 6
, i.e. the direction of the reverse bias applied to the diode. Accordingly, the second rectifying diode
4
c
is OFF. Therefore, the current
15
of the smoothing inductor
5
is substantially equal to the current Ib flowing through the first rectifying diode
4
b
. As a result, during the period T
0
-T
1
, the secondary current of the transformer
3
flows only through the first secondary winding
3
b
, and increases linearly.
The primary current It of the transformer
3
is equal to the sum of the exciting current for the transformer
3
and the equivalent primary current depending on the secondary current of the transformer
3
. As shown

Affiliated with

Also associated with

Rating

Switching power supply 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 supply, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switching power supply will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2945649