Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-09-26
2004-03-02
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S047000, C363S056100, C323S284000
Reexamination Certificate
active
06700801
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to electric power supplies, and particularly to a switching power supply capable of a.c.-to-d.c. voltage conversion, featuring provisions for attainment of closer approximation of the input current waveform to a sinusoidal wave, and for that of a higher power factor, than by the comparable prior art.
The switching power supply or voltage regulator has long been familiar which comprises a rectifying and smoothing circuit to be coupled to a source of a.c. power, and a d.c.-to-d.c. converter circuit connected to the rectifying and smoothing circuit. The rectifying and smoothing circuit comprises a rectifier circuit and a smoothing capacitor. Although so simple in configuration, this known rectifying and smoothing circuit possesses the disadvantage of a somewhat poor power factor as a result of the fact that the smoothing capacitor is charged only at or adjacent the peaks of the a.c. voltage of sinusoidal waveform. Another drawback is that the input current is not favorable in waveform.
Designed to defeat these shortcomings, a more advanced switching power supply has also been suggested which comprises an inductor connected between the rectifier circuit and the smoothing capacitor, and a switch which is connected between the pair of outputs of the rectifier circuit and which is controllable via the inductor. The smoothing capacitor is connected in parallel with the switch via the rectifying diode. This known circuit comprising the inductor and the switch is sometimes referred to as the step-up power-factor improvement circuit. As the switch is turned on and off at a repetition frequency higher than the frequency of the input a.c. voltage, the current flowing through the inductor has a peak value in proportion with the instantaneous value of the input a.c. voltage. The results are a close approximation of the input current waveform to a sinusoidal waveform, and an improvement in power factor. It is also possible to make the voltage across the smoothing capacitor higher than the maximum value of the a.c. voltage.
It has also been known and practiced to connect a capacitor in parallel with the switch for on-off control of the rectifier output voltage, in order to protect this switch from overcurrent and to lessen its noise production. The capacitor will be charged when the switch is off, thereby preventing a rapid voltage buildup across the switch. However, when the switch is turned on, the energy that has been stored on the capacitor will be released through the switch, with consequent power loss.
An additional problem arises when a d.c.-to-d.c. converter circuit is coupled to the aforesaid step-up power-factor improvement circuit, the latter being then used as d.c. power supply. Including a switch for on-off control of the d.c. voltage, the d.c.-to-d.c. converter circuit provides another source of switching loss. A provision of separate circuits for on-off control of the switch in the power-factor improvement circuit and that in the d.c.-to-d.c. converter circuit, and for zero-voltage turning-on of both switches, would make the complete power supply system too complex in construction and expensive of manufacture.
It must also be taken into consideration that the on-off control of the power-factor improvement circuit switch and d.c.-to-d.c. converter circuit switch at the same repetition frequency is undesirable. Noise might then be produced, or the switches might become unstable in operation, as a result of the frequency interference of both switches.
Japanese Unexamined Patent Publication No. 8-154379 suggests a different type of switching power supply. The switch in the d.c.-to-d.c. converter circuit is utilized for switching both the d.c. voltage across the smoothing capacitor and the current through the inductor for power factor improvement. One switch performs the dual purpose of power factor improvement and d.c.-to-d.c. conversion, but to lesser extents than by two switches.
SUMMARY OF THE INVENTION
The present invention has it among its objects, in a step-up power supply of the type defined, to reduce power loss and noise production due to switching by simpler means than heretofore and without the difficulties so far experienced.
Another object of the invention is to further improve the power factor of the power supply and, at the same time, to most effectively and inexpensively lessen power losses due to the switch included in the power-factor improvement circuit and that in the d.c.-to-d.c. converter.
Briefly, the present invention may be summarized as a switching power supply capable of translating a.c. voltage of sinusoidal waveform into d.c. voltage. Included is a rectifier circuit connected to a pair of input terminals for rectifying the input a.c. voltage, the rectifier circuit having a first and a second output for providing a rectifier output voltage. A main switch is connected to the first output of the rectifier circuit via a main inductor on one hand and, on the other hand, to the second output of the rectifier circuit. The main switch has capacitance means for its soft switching, the capacitance means being in the form of either a discrete capacitor connected in parallel therewith or its parasitic capacitance. A rectifying diode is connected to the rectifier circuit via the main inductor. A smoothing capacitor is connected in parallel with the main switch via the rectifying diode. An ancillary inductor is connected to an input terminal or an output terminal of the main inductor and electromagnetically coupled thereto. An ancillary switch is connected to the input terminal or the output terminal of the main inductor via the ancillary inductor on one hand and, on the other hand, to the second output of the rectifier circuit. A first reverse-blocking diode is connected in series with the ancillary inductor. Also included is a switch control circuit which is connected to the primary switch for on-off control thereof at a repetition frequency higher than the frequency of the input a.c. voltage, and to the ancillary switch for on-off control thereof at such a repetition frequency, and with such conducting periods, as to assure soft turn-on of the main switch.
The invention as summarized above features the ancillary inductor electromagnetically coupled to the main inductor, and the ancillary switch connected in series with the ancillary inductor. Voltage will be impressed to the ancillary inductor when the ancillary switch is turned on earlier than the main switch. This ancillary inductor voltage will act to cause a rapid decrease in the magnitude of the current charging the smoothing capacitor due to the energy stored on the main inductor. When the rectifying diode, connected to the smoothing capacitor for charging the same, becomes nonconductive, the soft-switching capacitor connected in parallel with the main switch will release the energy that has been stored thereon. The main switch may be turned on after the current charging the smoothing capacitor has dropped to zero and the soft-switching capacitor has completed its energy release. The main switch will then be turned on at zero or very low voltage, and at zero or very low current. Thus is accomplished the so-called soft switching of the main switch.
The soft-switching capacitor and the ancillary inductor constitute in combination a resonant circuit conducive to the soft switching of the main switch. As a result, less power loss and less noise occur at the main switch, and the power factor is improved with the power loss kept at a minimum.
Preferably, the switching power supply according to the invention additionally comprises a transformer, a rectifying and smoothing circuit connected to the transformer for providing output d.c. voltage, a second main switch connected to the smoothing capacitor via the transformer, second soft-switching capacitance means such as a capacitor connected in parallel with the second main switch, a second ancillary inductor electromagnetically coupled to a primary winding of the transformer and having one extremity connected to a ju
Morita Koichi
Yamagishi Toshiyuki
Han Jessica
Sanken Electric Co. Ltd.
Woodcock & Washburn LLP
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