Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-06-08
2001-09-11
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S079000
Reexamination Certificate
active
06288914
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The present invention claims priority from Japanese Patent Application No.11-161769 filed Jun. 9, 1999, the 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 source and, particularly, to a switching power source capable of reducing a standby power consumption of an electronic device as a load.
2. Description of Related Art
A conventional switching power source has been designed such that the power source efficiency becomes maximum for a load operating in a steady state. That is, the switching power source has been designed such that the power source efficiency becomes maximum for only a load of the, switching power source, which is operating normally and there has been no measure taken for power consumption when the load of the switching power source is light or the load is in a standby state. In view of this, it is usual to construct a power source with a main switching power source for a normal operation of a load and an additional switching power source such as a commercial power source transformer, the capacity of which corresponds to power required by the load in a standby state. With such power source construction, the cost of the power source for the load is increased and the size of the power source is also increased.
When the switching power source is used additionally, in order to reduce a switching loss during a standby state of a load, a switching frequency thereof during the standby state of the load is lowered. In such case, however, audible sound may be generated by the transformer.
In order to solve the problem of audible sound generation, a method for reducing power consumption when a load is light or the load is in a standby state has been proposed, in which an oscillator constituting the switching power source is controlled to oscillate intermittently while maintaining an oscillation frequency thereof, which is a switching frequency, unchanged. For example, Japanese Utility Model Application Laid-open No. H4-10588, Japanese Patent Application Laid-open No.3-243167, Japanese Patent Application Laid-open No. H4-12666 and Japanese Patent Application Laid-open No. H4-29482 disclose techniques belonging to such scheme.
However, in the techniques disclosed in Japanese Utility Model Application Laid-open No. H4-10588 and Japanese Patent Application Laid-open No.4-12666, the intermittent control of the oscillation state of oscillator is performed only when a load current is small. However, there is no description related to detail of such control. According to the technique disclosed in Japanese Patent Application Laid-open No. H3-243167, an interval of the intermittent oscillation control is determined by a CR time constant circuit. In the technique disclosed in Japanese Patent Application Laid-open No. H4-29482, the oscillation state is controlled intermittently on the basis of a voltage waveform of a commercial power source when a load is light.
In the techniques disclosed in these prior arts except that disclosed in Japanese Patent Application Laid-open No. H4-29482, the intermittent oscillation control is performed regardless of the voltage waveform of the commercial power source. Therefore, when the control is performed such that an oscillator oscillates during a time period other than a time period in which a charging capacitor constituting a primary side of a smoothing circuit for rectifying and smoothing a commercial power source voltage is charged, voltage ripple of the capacitor is increased, so that an output voltage on a secondary side of the smoothing circuit is varied.
Further, in the technique disclosed in Japanese Patent Application Laid-open No. H4-29482, the oscillation is stopped every half-wave rectified output of a commercial input power source although the intermittent oscillation control is performed correspondingly to the voltage waveform of the commercial power source. That is, the control is performed such that the oscillation is persistent for a half cycle of the commercial power source and is stopped for the other half cycle thereof. Therefore, the oscillation is persistent even for the period other than the period in which the charging of a primary side capacitor is performed and the above mentioned problem of the secondary side voltage variation is not solved.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a switching power source including a switching transformer and capable of restricting voltage variation on a secondary side of the switching transformer when an intermittent oscillation for obtaining a switching operation of the switching power source is performed under a light load condition thereof
According to the present invention, a switching power source device, which includes a rectifier, a switching transformer and a switching element and in which an input A.C. voltage is rectified by the rectifier and smoothed by a smoothing capacitor and a resultant D.C. voltage is supplied to a primary side of the switching transformer while on/off controlling the D.C. voltage by the switching element and an A.C. voltage obtained in a secondary side of the switching transformer is rectified and smoothed and a resultant D.C. voltage is supplied to a load of the switching power source device, is featured by comprising comparator means for comparing a D.C. voltage obtained by rectifying the input A.C. voltage with a reference voltage and control means for detecting a state of the load of the switching power source and intermittently controlling a switching operation of the switching element according to an output of the comparator means when the load is light.
The comparator means includes a comparator circuit for comparing the rectified D.C. voltage with the reference voltage and generating the output of the comparator means when the rectified D.C. voltage is larger than the reference voltage and the control means performs the intermittent control correspondingly to the output of the comparator means when the load is light. Further, the control means detects the state of the light load on the basis of a current supplied to the load. Alternatively, the control means detects the state of the light load by an external signal.
In intermittently controlling an oscillation for switching a power source device during a light load condition in order to reduce power consumption in a standby state thereof, the oscillation is allowed in only a peak time of an input A.C. power and a vicinity thereof and inhibited in other time period. Therefore, it becomes possible to oscillate in only a charging time of the smoothing capacitor on the primary side of the switching transformer to thereby minimize a voltage variation on the secondary side of the switching transformer.
REFERENCES:
patent: 4941078 (1990-07-01), Leonardi
patent: 6038143 (2000-03-01), Miyazaki et al.
patent: 6078508 (2000-06-01), Okamura et al.
patent: 3243167 (1991-10-01), None
patent: 412666 (1992-01-01), None
patent: 429482 (1992-01-01), None
patent: 410588 (1992-01-01), None
patent: 6-319259 (1994-11-01), None
patent: 9-308242 (1997-11-01), None
Japanese Office Action issued Jul. 4, 2000 in a related application with English translation of relevant portions.
Han Jessica
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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