Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-07-03
2001-05-22
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S134000
Reexamination Certificate
active
06236579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply apparatus which outputs a high-tension alternating voltage used in a copying machine, a printer or the like to perform image formation in an electrophotographic method, a control method for the power supply apparatus, and an image formation apparatus which contains the power supply apparatus.
2. Related Background Art
In general, a high-tension alternating voltage might be used in an image formation apparatus such as a copying machine or the like which performs image formation in an electrophotographic method.
FIG. 5
is a circuit diagram showing a structure of a power supply device (a high-tension output device) used in a conventional image formation apparatus. In order to generate the above high-tension alternating voltage, as shown in
FIG. 5
, a center-tap converter transformer in which a primary winding
302
a
has a center tap is sometimes used.
In
FIG. 5
, numeral
301
denotes a converter transformer driving circuit, and numeral
302
denotes a center-tap converter transformer (simply referred as a transformer hereinafter). Numeral
303
denotes an output terminal which is connected to a not-shown load used for the image formation. Each of symbols Tr
1
and Tr
2
denotes an N-channel MOSFET (metal oxide semiconductor field-effect transistor: simply referred as a transistor hereinafter).
The transistors Tr
1
and Tr
2
are connected to the transformer
302
. When the transistors Tr
1
and Tr
2
are on-off controlled, power is generated at a secondary side of the transformer
302
and then supplied to each load through the output terminal
303
.
When control signals (oscillation signals) IN
1
and IN
2
shown in
FIG. 6
are input respectively to gates of the transistors Tr
1
and Tr
2
, these transistors Tr
1
and Tr
2
perform switching at on/off timing as shown as waveforms of the control signals IN
1
and IN
2
. Thus, when the transistors Tr
1
and Tr
2
alternately perform the switching, the transformer
302
is excited, and a high-tension alternating voltage according to a turns ratio is generated on the side of a secondary winding
302
b
. The generated voltage is output from the output terminal
303
(a waveform OUT in
FIG. 6
) to the load.
However, in the above conventional power supply device (the high-tension output device) which uses the center-tap converter transformer, when both the control signals IN
1
and IN
2
are off, the output oscillation is stopped. Thus, as shown at a part “C” of
FIG. 6
, at the instant that an operation state changes from a driving state to a stop state, an overshoot or a resonant voltage may occur in an output voltage. This output voltage changes due to the load or floating capacity, thereby generating unstable output voltage.
Thus, there is some fear that this output voltage influences the image formation and thus invites image quality deterioration, whereby there is a problem that a stability of the image quality decreases.
SUMMARY OF THE INVENTION
The present invention was made in consideration of the above-described conventional problem.
An object of the present invention is to provide a power supply apparatus which can prevent an unstable output voltage when output oscillation is stopped, a control method for this power supply apparatus, and an image formation apparatus which contains this power supply apparatus.
A power supply apparatus according to the present invention is the power supply apparatus which supplies a high-tension alternating voltage to a load, comprising:
a converter transformer containing a primary winding and a secondary winding, wherein the primary winding has a center tap to which power is supplied from a power supply;
first and second switching elements disposed between both ends of the converter transformer and the ground respectively;
a third switching element disposed between the center tap and the power supply; and
a driving circuit for generating driving signals to cause the first to third switching elements to be on or off respectively,
wherein the driving circuit causes the third switching element to be on and causes the first and second switching elements to alternately perform switching at the same frequency, thereby generating the high-tension alternating voltage on the side of the secondary winding of the converter transformer, and
when the generation of the high-tension alternating voltage is stopped, the driving circuit is controlled to cause the third switching element to be off and cause the first and second switching elements to be on.
Another power supply apparatus according to the present invention is the power supply apparatus which supplies a high-tension alternating voltage to a load, comprising:
a converter transformer containing a primary winding and a secondary winding, wherein the primary winding has a center tap to which power is supplied from a power supply;
first and second switching elements disposed between both ends of the converter transformer and the ground respectively;
a voltage control element disposed between the center tap and the power supply; and
a driving circuit for generating driving signals of the first and second switching elements and the voltage control element,
wherein the driving circuit causes the voltage control element to supply a predetermined voltage to the center tap and causes the first and second switching elements to alternately perform switching at the same frequency, thereby generating the high-tension alternating voltage on the side of the secondary winding of the converter transformer, and
when the generation of the high-tension alternating voltage is stopped, the driving circuit is controlled to drive the voltage control element to stop supplying the voltage to the center tap and cause the first and second switching elements to be on.
A power supply apparatus control method according to the present invention is the control method for a power supply apparatus which has a converter transformer and supplies a high-tension alternating voltage to a load, in the converter transformer first and second switching elements are disposed between both ends of a primary winding and the ground respectively and a third switching element is disposed between a center tap of the primary winding and a power supply, the method comprising the steps of:
causing the third switching element to be on and causing the first and second switching elements to alternately perform switching at the same frequency, thereby generating the high-tension alternating voltage on the side of a secondary winding of the converter transformer; and
causing the third switching element to be off and causing the first and second switching elements to be on, when the generation of the high-tension alternating voltage is stopped.
Another power supply apparatus control method according to the present invention is the control method for a power supply apparatus which has a converter transformer and supplies a high-tension alternating voltage to a load, in the converter transformer first and second switching elements are disposed between both ends of a primary winding and the ground respectively and a voltage control element is disposed between a center tap of the primary winding and a power supply, the method comprising the steps of:
driving the voltage control element to supply a predetermined voltage to the center tap and causing the first and second switching elements to alternately perform switching at the same frequency, thereby generating the high-tension alternating voltage on the side of a secondary winding of the converter transformer; and
driving the voltage control element to stop supplying the voltage to the center tap and causing the first and second switching elements to be on, when the generation of the high-tension alternating voltage is stopped.
An image formation apparatus according to the present invention is the image formation apparatus which contains a power supply device having a converter transformer and supplying a high-tension alternating voltage to a load, the c
Motoyama Hajime
Watanabe Michiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Matthew
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