Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-09-03
2003-10-28
Berhane, Adolf D. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S056030
Reexamination Certificate
active
06639811
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to switching power supply units for supplying DC stabilized voltages. More specifically, the present invention relates to a switching power supply unit which operates in a current-continuation mode by allowing two switching elements to alternately turn on/off so as to perform self-excited oscillation.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 11-187664 discloses a switching power supply unit, in which first and second switching elements Q
1
and Q
2
are connected on the primary side of a transformer T, switching control circuits for alternately turning on/off the first and second switching elements, with a period when both the first and second switching elements are turned off therebetween, are provided, energy is stored in a primary winding and an inductor L during an ON-period of the first switching element Q
1
, the energy is emitted from a secondary winding during an OFF-period of the first switching element Q
1
, and the first and second switching elements Q
1
and Q
2
perform self-excited oscillation. The switching power supply unit having this configuration is called a flyback self-excited oscillation switching power supply unit including two switching elements.
Other examples of flyback switching power supply units including two switching elements are disclosed, for example, in Japanese Unexamined Patent Application Publication No. 4-87560, Japanese Unexamined Utility Model Registration Application Publication No. 6-36392, and PCT Japanese Translation Patent Publication No. 10-500834. The flyback switching power supply units disclosed in these publications have the same configuration as that of the switching power supply unit disclosed in Japanese Unexamined Patent Application Publication No. 11-187664 such that two switching elements are provided on the primary side of the transformer T. However, the two switching elements of these switching power supply units do not perform self-excited oscillation. In addition, these switching power supply units operate in a current-continuation mode. In the current-continuation mode, a current is applied to the secondary side of a transformer T and is then applied continuously to the primary side without a pause such that the waveform of the current applied to the primary switching element is trapezoidal. On the other hand, a current-discontinuation mode includes a pause such that a current is applied to neither the primary side nor the secondary side, and the waveform of the current applied to the primary switching element is triangular.
However, the above-described known switching power supply units have the following defects.
Next, the defects of the flyback self-excited oscillation switching power supply unit disclosed in Japanese Unexamined Patent Application Publication No. 11-187664 will be described.
In this switching power supply unit, the waveform of the current applied to the primary winding is always triangular, such as in ringing choke converters. Accordingly, a peak current on the primary side increases under heavy load and the effective current increases. When an effective current increases, copper loss of the transformer and conduction loss of the switching elements increase, and thus, efficiency decreases. This prevents miniaturization of a switching power supply unit.
Furthermore, since the waveform of the current applied to the primary winding is triangular, an ON-time of the switching element increases under heavy load. In addition, an OFF-time also increases in accordance with the extension of the ON-time. Accordingly, the switching period increases and the switching frequency decreases. As a result, a large transformer, a smoothing capacitor on the secondary side, and other components are required, which prevents miniaturization of a switching power supply unit.
Next, defects of the flyback two-element switching power supply unit which operates in a current-continuation mode disclosed in Japanese Unexamined Patent Application Publication No. 4-87560 will be described.
The waveform of the current applied to the primary winding is trapezoidal, and thus, copper loss of the transformer and conduction loss of the switching elements is reduced. However, since this type of switching power supply unit does not perform self-excited oscillation, a high-pressure-resistance drive IC or a pulse transformer is required for driving an oscillation circuit, a totem-pole circuit for driving, and an upper switching element at a different ground level, as a drive control circuit for alternately turning on/off the two switching elements. As a result, miniaturization and cost reduction for a switching power supply unit cannot be sufficiently achieved.
SUMMARY OF THE INVENTION
In order to overcome the above-described problems, preferred embodiments of the present invention provide a highly efficient switching power supply unit having greatly reduced size and weight and which is produced at a greatly reduced cost.
Preferred embodiments of the present invention provide a new technique for combining the operation characteristic of the known flyback two-element switching power supply unit operating in a current-continuation mode with a self-excited oscillation method. The switching power supply unit of various preferred embodiments of the present invention includes the following combination and arrangement of elements.
According to a first preferred embodiment of the present invention, a switching power supply unit operating in a current-continuation mode includes a transformer including a primary winding, a secondary winding, a first drive winding, and a second drive winding, an inductor, a first switching circuit connected in series to a series circuit including the primary winding and the inductor, the first switching circuit including a parallel circuit having a first switching element, a first diode, and a first capacitor, an input power supply connected in series to the series circuit, a second switching circuit connected in parallel to the series circuit, the second switching circuit including a parallel circuit having a second switching element, a second diode, and a second capacitor, a capacitor connected in parallel to the series circuit, a rectifying and smoothing circuit which includes a rectifying element and which is connected to the secondary winding, and first and second switching control circuits for alternately turning on/off the first and second switching elements, with a period when both the first and second switching elements are turned off therebetween, the first switching control circuit being connected between the first drive winding and a control terminal of the first switching element and the second switching control circuit being connected between the second drive winding and a control terminal of the second switching element.
Energy is stored in the primary winding and the inductor during an ON-period of the first switching element and the energy is emitted from the secondary winding during an OFF-period of the first switching element such that the first and second switching elements perform self-excited oscillation. The inductor and the capacitor define a resonance circuit which resonates during the OFF-period of the first switching element. The first switching control circuit includes a first ON-time control circuit in which a time constant is set such that the first switching element is turned off at a desired time after the first switching element is turned on. The second switching control circuit includes a second ON-time control circuit in which a time constant is set such that the second switching element is turned off in order to interrupt a resonance current applied to a series circuit including the second switching element and the inductor after the second switching element is turned on and before the energy is completely emitted from the secondary winding.
With this configuration, the first ON-time control circuit and the second ON-time control circuit defining the f
Hosotani Tatsuya
Takemura Hiroshi
Berhane Adolf D.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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