Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-01-19
2001-03-27
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S131000
Reexamination Certificate
active
06208533
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching power supply to stabilize the voltage of a DC output by controlling the switching of a switching transistor according to a voltage error of the DC output, and in more detail, to a switching power supply, in which, when the switching transistor conducts the intermittent switching, the maximum value of a current of the switching transistor is limited to a current value smaller than the current value determined by the output of an error detection circuit.
2. Description of the Related Art
There is an RCC type switching power supply as one of switching power supplies for use in a power supply section of a television receiver. However, in the RCC type switching power supply, when the electric power consumed on the secondary side is smaller than the electric power supplied by the primary side because the load is greatly lightened, the intermittent switching in which switching is stopped at a period of several mS to several 100 &mgr;S, occurs. Accordingly, a disadvantage that unpleasant oscillation noise in the audio band is generated from the transformer, occurs.
A conventional technique to solve such a disadvantage is proposed in Japanese Patent Unexamined Publication No. Hei. 7-163143. That is, in this technique, a second oscillation stop command section to intermittently drive the switching circuit at a set period out of the audio range when a standby signal showing the stoppage of the supply of the electric power to the load is sent out, is provided. Accordingly, the switching circuit conducts an intermittent switching operation whose period is forced, according to the output of the second oscillation stop command section. Accordingly, because the period of the intermittence is the period out of the audio band, the oscillation noise generated from the transformer becomes also the frequency out of the audio band, thereby, the unpleasant oscillation noise is prevented from generating.
However, when the above structure is used, the following problems occur. That is, the period when the second oscillation stop command section intermittently drives the switching circuit, is set by a time constant circuit composed of a smoothing capacitor and a resistor for a time constant.
Accordingly, in order to put the period of the intermittent drive out of the audio band, it is necessary to reduce the time constant. On one hand, in order to reduce the time constant, there are two methods; one in which the capacity of the smoothing capacitor is reduced, and the other in which the resistance value is reduced. However, in the case where the capacity of the smoothing capacitor is reduced, when a predetermined current is supplied to the load, the capacity of the capacitor is insufficient, and a DC output having a lot of ripples is supplied to the load. On the other hand, in the case where the resistance value is reduced, because the current value flowing to the resistor is increased, a problem occurs that a loss is increased.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and an object of the invention is to provide a switching power supply by which, in the case where the switching transistor conducts the intermittent switching, even when the oscillation noise of the transformer is in the audio band, the oscillation noise of the transformer can be made so as to be inaudible.
In order to achieve the above object, according to the invention, there is provided a switching power supply comprising: a switching transistor for switching a current flowing through a primary coil wound around a transformer; a rectifying and smoothing circuit for rectifying and smoothing an output of a secondary coil wound around the transformer; and an error detection circuit for detecting a voltage error of a DC output sent from the rectifying and smoothing circuit, wherein a voltage of the DC output is stabilized by controlling the switching of the switching transistor according to an output of the error detection circuit, and wherein when the switching transistor conducts an intermittent switching, a maximum value of the current flowing through the primary coil is limited to a current value smaller than a maximum value of a current determined corresponding to the output of the error detection circuit.
That is, when the maximum value of the current flowing through the primary coil is reduced, the force to oscillate the transformer is reduced. Therefore, the sound volume of the oscillation noise generated from the transformer is reduced.
REFERENCES:
patent: 4327404 (1982-04-01), Horiguchi
patent: 5063491 (1991-11-01), Shigeo
patent: 5909363 (1999-06-01), Yoon
patent: 5917714 (1999-06-01), Ogawa
patent: 5917716 (1999-06-01), Cho
patent: 5952795 (1999-09-01), Kofune et al.
patent: 7-163143 (1995-06-01), None
Berhane Adolf Deneke
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Funai Electric Co. Ltd.
LandOfFree
Switching power supply for stabilizing a DC output voltage does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switching power supply for stabilizing a DC output voltage, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switching power supply for stabilizing a DC output voltage will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2539524