Switching power supply device

Details Switching power supply device Switching power supply device

2001-11-16

2003-04-01

Berhane, Adolf Deneke (Department: 2838)

Electric power conversion systems

Current conversion

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

C363S097000

Reexamination Certificate

active

06542387

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No.P2001-174291, filed on Jun. 8, 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 device capable of setting the number of ringing to a constant number generated during OFF period of switching elements in order to prevent any generation of magneto striction noise from a transformer.
2. Description of the Related Art
FIG. 4
is a diagram showing an example of a circuit configuration of a conventional switching power supply device.
In
FIG. 4
, the rectification smoothing circuit
11
inputs an alternating current (AC) supply voltage, performing a transmission-wave rectification for it through a diode bridge, for example, and smoothing it through a capacitor, and finally outputs a direct current (DC) voltage obtained to a terminal of the primary winding L
1
in the transformer
13
.
Other terminal of the primary winding L
1
of the transformer
13
is connected to the drain of the switching element Q
1
. The source of the switching element Q
1
is connected to the ground that is also connected to the ground portion of the rectification smoothing circuit
11
. A capacitor C
1
is connected in parallel between the source and the drain of the switching element Q
1
.
Magnetic energy accumulated in the primary winding L
1
of the transformer
13
is sequentially induced in a secondary winding thereof by switching operation of the switching element Q
1
controlled by ON-OFF operation of the control section
25
that will be described later. The half-wave rectification is then performed for the magnetic energy induced at the secondary winding by the diode D
1
connected to one terminal of the secondary winding L
2
, and the smoothing is performed by the capacitor C
3
, and the smoothed DC voltage is then output to the load
17
and also output to the output DC voltage detection circuit
19
.
The output DC voltage detection circuit
19
converts the output DC voltage supplied to the load
17
to a feedback signal and outputs it to the ON-period control circuit
29
mounted in the control section
25
.
The diode D
3
in the output smoothing circuit
21
performs the half-wave performs the half-wave rectification for a flyback voltage generated at an auxiliary winding L
3
in the transformer
13
and the capacitor C
5
smoothes the voltage obtained from the diode D
3
. The control section
25
inputs the smoothed voltage Vcc from the capacitor C
5
.
The control section
25
initiates oscillation when a starting voltage that is over a predetermined voltage is supplied to the starting resistance R
1
.
When the switching element Q
1
is in OFF, ringing is generated at the primary winding L
1
in the transformer
13
. The resonance frequency f is as follows:
f
=1/(2
&pgr;{square root over (L×C
1
))}.
At the same timing, the ringing is also generated at the auxiliary winding L
3
.
The ringing generation circuit
23
divides the ringing by the resistances R
3
and R
5
after the detection through the diode D
5
. The ringing signal whose high frequency components has been eliminated through the resistance R
3
and the capacitor C
7
is output to the comparator circuit
27
mounted in the control section
25
.
The comparator circuit
27
compares the ringing signal input to the comparator COMP
1
with a reference voltage Vref
1
, and outputs a High-level signal when the ringing signal is larger than the reference voltage Vref
1
.
The ON-period control circuit
29
generates an ON-period control signal to stabilize the output DC voltage to be supplied to the load
17
by adjusting the ON-period according to the feedback signal from the output DC voltage detection circuit
19
and outputs the generated one to the frequency control circuit
31
.
The frequency control circuit
31
oscillates a fixed frequency determined by a capacitor and a time constant of a resistance, for example, while controlling the time length of the ON-period according to the ON-period control signal from the ON-period: control circuit
29
and outputs the control signal to the driving circuit
33
.
The inverter INV
1
in the driving circuit
33
outputs the driving signal V
19
of High level to the switching element Q
1
when both the control signal V
3
from the comparator circuit
27
to one terminal of the OR gate OR
1
and the control signal V
18
from the frequency control circuit
31
are in Low level simultaneously.
Next, a description will be given of the explanation of the basic operation of the conventional switching power supply device with reference to the timing chart shown in FIG.
5
.
(1) When an AV voltage is supplied to the rectification smoothing circuit
11
, the control signal V
18
is output to the OR gate OR
1
at the timing to when the starting voltage which is over a predetermined voltage is supplied to the terminal Vcc through the starting resistance R
1
. At this time, because no voltage (V
2
) is generated in the auxiliary winding L
3
in the transformer
13
, the comparator circuit
27
outputs the control signal V
3
of Low level.
As a result, the switching element Q
1
enters ON state when the gate of the switching element Q
1
inputs the driving signal V
19
of High level from the inverter INV
1
, and the direct current flows from the terminal
11
c
of the rectification smoothing circuit
11
to the ground GND through the primary winding L
1
of the transformer
13
and the drain and the source of the switching element Q
1
. During this process, the magneto energy is accumulated into the transformer
13
.
(2) At timing ti, the frequency control circuit
31
outputs the control signal V
18
of High level to the OR gate OR
1
.
As a result, the driving signal V
19
of High level from the inverter INV
1
is switched to Low level, and the driving signal V
19
of Low level is transferred to the gate of the switching element Q
1
. The switching element Q
1
is thereby turned OFF and the magneto energy accumulated in the transformer
13
is induced in the secondary winding L
2
and the auxiliary winding L
3
simultaneously.
(3) At timing t
1
to timing t
2
, the electric energy discharged through the secondary winding L
2
in the transformer
13
is rectified by the diode D
1
and smoothed by the capacitor C
3
. The output voltage rectified and smoothed is then supplied to the load.
At this time, a voltage V
2
is generated at the auxiliary winding in the transformer
13
. Because the input voltage level of the comparator
27
is over the reference voltage Vref
1
, the comparator
27
outputs the output voltage V
3
of High level.
(4) Immediately before the timing t
2
, the level of the input voltage V
2
from the comparator
27
is gradually decreased.
As shown in
FIG. 5
, the voltage V
2
of the auxiliary winding L
3
is reached to a bottom level (B) at timing t
3
and then increased after the timing t
3
and reached to a high level at timing t
4
and decreased after timing t
4
again. This phenomenon is called to as “ringing”. The same ringing phenomenon is also generated in the voltage V
1
of the primary winding L
1
.
(5) At timing t
4
to timing t
5
, the ringing phenomenon that has been explained in the section (4) is occurred one time. Because the conventional switching power supply device operates by a fixed frequency, the control signal V
18
of Low level is transferred to the OR gate OR
1
at timing t
5
.
At this time, because both the input terminals of the OR gate OR
1
input the signals V
18
and V
3
of Low level when the level of the voltage V
2
is decreased by the ringing phenomenon caused in the auxiliary winding L
3
in the transformer
13
and the level of the output voltage V
3
of the comparator circuit
27
becomes Low level, the gate of the switching element Q
1
inputs the driving signal V
19
of High level from the inverter INV
1
. Thereby the switching element Q
1
is turned ON.
T

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