Electrical transmission or interconnection systems – Plural load circuit systems – Selectively connected or controlled load circuits
Reexamination Certificate
2000-03-17
2002-01-15
Riley, Shawn (Department: 2838)
Electrical transmission or interconnection systems
Plural load circuit systems
Selectively connected or controlled load circuits
C307S031000
Reexamination Certificate
active
06339262
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply that delivers electric power from a DC power supply to a DC load via a transformer.
Referring to
FIG. 19
, a conventional fly-back-type switching power supply includes a bridge rectifier Rec that rectifies an AC input and produces pulsating DC power. The pulsating DC power passes through an input reactor L
1
and a series diode D
4
to a primary winding N
1
of a transformer Tr. A switch Q
1
is connected in series with primary winding N
1
. The series combination including input reactor L
1
, switch Q
1
and primary winding N
1
is connected in parallel with bridge rectifier Rec. A capacitor C
1
, preferably an electrolytic capacitor, is connected in parallel with the series combination of primary winding N
1
and switch Q
1
. A snubber capacitor Cs is connected in parallel with switch Q
1
. A switch Q
3
is connected between the output of input reactor L
1
and a common connection of bridge rectifier Rec.
When switch Q
1
is ON, energy is stored in primary winding N
1
. When switch Q
1
is OFF, stored energy is released through a secondary winding N
2
. The output voltage is regulated by controlling the ON and OFF times of switch Q
1
.
In the circuit of
FIG. 19
, so-called soft switching (zero voltage switching), causes switch Q
1
to switch ON when the voltage across snubber capacitor Cs is at its lowest value. This is accomplished by selecting values of the leakage inductance of primary winding N
1
and the capacitance of snubber capacitor Cs so that these elements resonate at the switching speed. Soft switching reduces power loss and improves noise suppression.
Switch Q
3
is switched ON to produce input current flow through input reactor L
1
. The input current flow improves the power-factor of the circuit. When switch Q
3
is switched ON, energy stored in the input reactor L
1
is fed to electrolytic-type capacitor C
1
. Switching switch Q
3
ON and OFF improves the power-factor even when the input voltage is low, since input current flows whenever the switching power supply is operating.
The OFF-period of switch Q
1
is set to a length of time determined by the resonant frequency of the series combination of the leakage inductance of primary winding N
1
and snubber capacitor Cs. The OFF-period of switch Q
1
must be related to the resonant frequency to produce soft switching in the switching power supply of FIG.
19
. In contrast, the output voltage is regulated only by the ON-period of switch Q
1
. Since the ON-period and the OFF-period of switch Q
1
are governed by different criteria, the switching frequency of switch Q
1
must therefore vary to regulate the output voltage while maintaining soft switching.
Switching power supplies used in television sets and display devices have switching frequencies that are generally synchronized with the deflection frequency. Therefore, a conventional switching power supply that depends on its switching frequency to regulate output voltage is not useful in such variable frequency applications.
The use of two separate switches Q
1
, Q
3
for voltage regulation and power-factor improvement respectively, increases the noise level of the resulting output of the switching power supply. In addition, diode D
4
in series with switch Q
1
causes a voltage drop when current flows and decreases the switching power supply efficiency.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a switching power supply which overcomes the above-described drawbacks ofthe prior art.
It is a further object of the present invention to provide a switching power supply that facilitates soft switching at arbitrary frequencies.
It is another object of the present invention to provide a switching power supply with an improved power factor using a simplified scheme.
It is still another object of the present invention to provide a switching power supply that takes advantage of soft switching.
It is yet another object of the present invention to provide a switching power supply that facilitates switching at arbitrary frequencies, takes advantage of soft switching and obtains an improved power factor using a simplified scheme.
It is a still further object of the present invention to provide a switching power supply that has an improved efficiency when driving loads substantially lighter than a rated load.
It is a yet further object of the present invention to provide a switching power supply with switches and control circuits that are integrated into a single integrated circuit.
Briefly stated, the present invention provides a switching power supply that uses zero-current and zero-voltage switching to reduce switching noise. A main switch and an auxiliary switch channel current and voltage between various component paths to maintain a DC output voltage while switching in zero-current or zero-voltage states. Switch ON-OFF time ratios are controlled with a simple scheme to improve the circuit power factor. The switching rate is set to arbitrary frequencies, with switch ON time and OFF time being controlled independently. Conventional losses in efficiency when driving a load substantially less than the rated load are avoided. The switches and control functions can be implemented on an integrated circuit, reducing size and improving efficiency. Thus a flexible, simple design improves efficiency while reducing noise and manufacturing costs.
According to a first aspect of the invention, there is provided a switching power supply that includes a DC power supply; a transformer connected to the DC power supply, the transformer including a primary winding and a secondary winding; a rectifying and smoothing circuit connected to the secondary winding of the transformer; an input reactor; a main semiconductor switch connected in series to the primary winding; a first diode connected in opposite parallel to the main semiconductor switch; a snubber capacitor connected in parallel with the main semiconductor switch; a series circuit for discharging the electric charge of the snubber capacitor, the series circuit including a resonance reactor and an auxiliary semiconductor switch; a second diode connected in opposite parallel to the auxiliary semiconductor switch; and a capacitor connected in parallel to the primary winding.
Advantageously, the series circuit further includes a resonance capacitor. Advantageously, the switching power supply further including a tertiary winding interposed between the primary winding of the transformer and the main semiconductor switch; and a third diode connected between the auxiliary semiconductor switch and the connection point of the primary winding and the tertiary winding, the third diode connecting the capacitor in parallel to the primary winding.
Advantageously, the switching power supply including a reactor interposed between the primary winding of the transformer and the main semiconductor switch; and a third diode connected between the auxiliary semiconductor switch and the connection point of the primary winding and the reactor, the third diode connecting the capacitor in parallel to the primary winding.
According to a second aspect of the invention, there is provided a switching power supply that includes a DC power supply; a transformer connected to the DC power supply, the transformer including a primary winding and a secondary winding; a rectifying and smoothing circuit connected to the secondary winding of the transformer; an input reactor; a main semiconductor switch connected in series to the primary winding; a first diode connected in opposite parallel to the main semiconductor switch; a snubber capacitor connected in parallel to the main semiconductor switch; a series circuit for discharging the electric charges of the snubber capacitor, the series circuit including a resonance capacitor, a resonance reactor and an auxiliary semiconductor switch; and a second diode connected in opposite parallel to the auxiliary semiconductor switch.
Advantageously, the transformer further incl
Igarashi Seiki
Suzuki Akio
Fuji Electric & Co., Ltd.
Morrison Law Firm
Riley Shawn
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