Switching power-supply circuit

Details Switching power-supply circuit Switching power-supply circuit

2000-09-22

2001-10-30

Riley, Shawn (Department: 2838)

Electric power conversion systems

Current conversion

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

C363S021070

Reexamination Certificate

active

06310786

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a switching power-supply circuit having a power-factor improvement circuit.
The applicant for a patent of the present invention earlier proposed a variety of switching power-supply circuits each having a resonance-type converter on the primary side. In addition, there have been proposed a variety of switching power-supply circuits each having a power-factor improvement circuit for improving a power factor for the resonance-type converter.
FIG. 9
is a circuit diagram showing a typical switching power-supply circuit with a configuration based on an invention proposed earlier by the applicant for a patent of the present invention. To put it in detail, the configuration of this switching power-supply circuit includes a power-factor improvement circuit for improving the power factor of a switching converter of a current-resonance type based on a self-excitation technique.
The switching power-supply circuit shown in the figure includes a bridge rectifier circuit Di for full-wave rectification of the commercial AC power supply AC. A rectified output obtained as a result of the full-wave rectification by the bridge rectifier circuit Di is electrically charged into a smoothing capacitor Ci by way of a power-factor improvement circuit
20
. As a result, a rectified and smoothed voltage Ei corresponding to a 1-time level of the AC input voltage VAC appears between the terminals of the smoothing capacitor Ci.
In addition, a rush-current limitation resistor Ri is inserted into a circuit comprising the bridge rectifier circuit Di and the smoothing capacitor Ci on a rectified-current path thereof. To put it in detail, the rush-current limitation resistor Ri limits a rush current flowing to the smoothing capacitor Ci when the power supply is turned on.
The power-factor improvement circuit
20
shown in the figure includes a filter choke coil LN and a high-speed recovery diode D
1
, which are connected to each other in series between a positive-electrode output terminal of the bridge rectifier circuit Di and the positive-electrode terminal of the smoothing capacitor Ci. One end of a choke coil LS is connected to the cathode of the high-speed recovery diode D
1
.
One terminal of a filter capacitor CN is connected to a connection between the anode of the high-speed recovery diode D
1
and the positive-electrode terminal of the smoothing capacitor Ci. The other terminal of the filter capacitor CN is connected to the other end of the choke coil LS. The filter capacitor CN functions as a normal-mode low-pass filter in conjunction with the filter choke coil LN.
The connection point between the high-speed recovery diode D
1
and the choke coil LS in the power-factor improvement circuit
20
is connected to a terminal of the primary side of a transformer PIT (Power Isolation Transformer) to be described later by a capacitor C
1
, which forms a series-resonance circuit in conjunction with an inductor L
1
of a winding N
1
on the primary side. With such a connection, a switching output generated by switching devices to be described later is fed back to the series-resonance circuit.
A power-factor improvement operation of the power-factor improvement circuit
20
will be described later.
The switching power-supply circuit also includes a converter of a current-resonance type adopting a self-excitation technique. This self-excitation current-resonance converter uses a rectified and smoothed voltage Ei appearing between the terminals of the smoothing capacitor Ci as an operation power supply.
As shown in the figure, the converter employs 2 switching devices Q
1
and Q
2
wired to each other in half-bridge connection between the positive-electrode terminal of the smoothing capacitor Ci and the ground to which the negative-electrode terminal of the smoothing capacitor Ci is connected. The switching devices Q
1
and Q
2
are each a bipolar transistor.
A start resistor RS
1
is connected between the collector and the base of the switching device Q
1
. By the same token, a start resistor RS
2
is connected between the collector and the base of the switching device Q
2
. A resistor RB
1
connected to the base of the switching device Q
1
through a resonance capacitor CB
1
sets a base current (also referred to as a drive current) of the switching device Q
1
. Similarly, a resistor RB
2
connected to the base of the switching device Q
2
through a resonance capacitor CB
2
sets a base current (also referred to as a drive current) of the switching device Q
2
. A clamp diode DD
1
is connected between the emitter and the base of the switching device Q
1
. Likewise, a clamp diode DD
2
is connected between the emitter and the base of the switching device Q
2
. The clamp diode DD
1
forms a current path of a clamp current flowing through the base and the emitter of the switching device Q
1
when the switching device Q
1
is put in an off state. By the same token, the clamp diode DD
2
forms a current path of a clamp current flowing through the base and the emitter of the switching device Q
2
when the switching device Q
2
is put in an off state.
The resonance capacitor CB
1
forms a seriesresonance circuit for self-excitation oscillation in conjunction with a driving winding NB
1
employed in a drive transformer PRT (power regulating transformer) to be described next, and sets the switching frequency of the switching device Q
1
. Likewise, the resonance capacitor CB
2
forms a series-resonance circuit for self-excitation oscillation in conjunction with a driving winding NB
2
employed in the drive transformer PRT, and sets the switching frequency of the switching device Q
2
. It should be noted that the series-resonance circuit is also referred to as a self-excitation oscillation driving circuit.
The drive transformer PRT drives the switching devices Q
1
and Q
2
as well as executes constant-voltage control by controlling variations in switching frequency. In the switching power-supply circuit shown in the figure, the driving windings NB
1
and NB
2
, a resonance-current detection winding ND and a control winding NC oriented in a direction perpendicular to the driving windings NB
1
and NB
2
and the resonance-current detection winding ND form an orthogonal saturatable reactor.
One end of the driving winding NB
1
employed in the drive transformer PRT is connected to the base of the switching device Q
1
by a series connection of the resistor RB
1
and the resonance capacitor CB
1
whereas the other end of the driving winding NB
1
is connected to the emitter of the switching device Q
1
. By the same token, one end of the driving winding NB
2
employed in the drive transformer PRT is connected to the base of the switching device Q
2
by a series connection of the resistor RB
2
and the resonance capacitor CB
2
whereas the other end of the driving winding NB
2
is connected to the emitter of the switching device Q
2
. The driving windings NB
1
and NB
2
are wound in such directions that a voltage generated by the former has a polarity opposite to a voltage generated by the latter.
An insulating converter transformer PIT (Power Isolation Transformer) delivers outputs of the switching devices Q
1
and Q
2
on the secondary side. By connecting one end of the primary winding N
1
of the insulating converter transformer PIT to a connection point (or a switching-output point) between the emitter of the switching device Q
1
and the collector of the switching device Q
2
through the resonance-current detection winding ND, a switching output is obtained.
As described above, the other end of the primary winding N
1
is connected by the series-resonance capacitor C
1
to a connection point between the cathode of the high-speed recovery diode D
1
and the choke coil LS in the power-factor improvement circuit
20
.
That is to say, the series-resonance capacitor C
1
is connected in series to the primary winding N
1
. The capacitance of the series-resonance capacitor C
1
and the leakage inductance of the insulating converter transformer PIT including the inductan

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