Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-05-11
2001-11-06
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021090, C363S097000, C363S019000
Reexamination Certificate
active
06314004
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a switching power source in which the voltage error of a secondary side DC output is fed back to a switching circuit through an insulating element, thereby to stabilize the output voltage, and more particularly to a switching power source in which a switching circuit is caused to perform an intermittent switching operation with pulses applied to an error detecting circuit.
2. Description of the Related Art
The efficiency of a switching power source is lowered when its load is extremely low. Therefore, a variety of techniques have been proposed in the art to prevent the lowering of the efficiency when the load is low. An example of the techniques has been disclosed in Japanese Patent Unexamined Publication No. Hei. 4-29482. In the technique, a standby control section is provided which connects the base of a switching transistor to the ground (level) and disconnects it from the ground (level). Further, the standby control section is so designed that the connection is made for a half of one cycle of the commercial power source, or for a predetermined period of the same. Hence, every one cycle of the commercial power source, the switching stop occurs for a half cycle, or for a predetermined period. Therefore, the average value of the switching loss is decreased, so that the conversion efficiency is improved.
However, the above-described conventional technique suffers from the following problems: That is, only in the case where the load becomes low, it is necessary to perform the switching operation intermittently. In the case where the load is ordinary, it is necessary to perform the switching operation continuously. Hence, in the case of the ordinary load, it is necessary to generate a stop signal to stop the operation of the standby control section, and to apply the stop signal thus generated to the standby control section. On the other hand, the standby control section is the primary side block, and the stop signal is generated by the secondary side block. Therefore, it is necessary to provide a photocoupler in the path of transmission of the stop signal. However, the photocoupler is expensive, which means that the resultant switching power source is high in manufacturing cost.
SUMMARY OF THE INVENTION
The invention was made to solve the above-described problems, and it is an object of the invention to provide a switching power source in which without addition of an insulating element for switching control, two kinds of operations, that is, a continuous switching operation and an intermittent switching operation, are switched from the secondary side.
In order to achieve the above object, according to the invention, there is provided a switching power source comprising: an error detecting circuit for detecting a voltage error of a secondary side DC output; a switching circuit for switching a current flowing in a primary coil, to which the voltage error detected by the error detecting circuit is fed back through an insulating element, thereby to stabilize the voltage of the secondary side DC output; and a pulse generating section for applying, irrespective of the voltage of the secondary side DC output, a pulse to the error detecting circuit with the level of which the error detecting circuit determines that the voltage of the secondary side DC output has been increased, whereby a switching operation of the switching circuit is changed into an intermittent operation corresponding to the pulse.
That is, when the pulse generating section provides a predetermined level (for instance “H” level) indicating a pulse, the error detecting circuit determines that the voltage of the DC output has been increased, and the drive current of the insulating element is increased. As a result, the output current of the insulating element is greatly increased, and therefore the switching operation of the switching circuit is stopped. On the other hand, when the pulse generating section provides a level (for instance “L” level) which does not correspond to a pulse, the error detecting circuit drives the insulating element with a current corresponding to the voltage error of the DC output. Hence, the switching circuit performs the switching operation with a cycle corresponding to the output of the insulating element. That is, in the case where the pulses are provided, the level corresponding to the pulses and the level which does not correspond to the pulses are alternately applied to the error detecting circuit, so that the switching circuit performs an intermittent switching operation. On the other hand, in the case where the level which does not correspond to the pulses is continuously applied to the error detecting circuit, the switching circuit performs a continuous switching operation.
REFERENCES:
patent: 4330816 (1982-05-01), Imazeki et al.
patent: 4862339 (1989-08-01), Inou et al.
patent: 5034871 (1991-07-01), Okamoto et al.
patent: 5297014 (1994-03-01), Saito et al.
patent: 5774347 (1998-06-01), Nakanishi
patent: 5903452 (1999-05-01), Yang
patent: Publ. 3323371 A1 (1985-01-01), None
patent: Publ. 4244530 A1 (1994-07-01), None
patent: Publ. 0386 989 A2 (1990-09-01), None
patent: 4-29482 (1992-01-01), None
patent: Appln. 06002417 (1994-01-01), None
patent: 7-213054 (1995-08-01), None
patent: 30-40910 (1997-06-01), None
Funai Electric Co. Ltd.
Patel Rajnikant B.
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