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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Braun tube discharge apparatus, and
relates especially to a Braun tube discharge apparatus that includes a
so-called spot killer function.
2. Description of the Related Art
A conventional Braun tube discharge apparatus that includes a spot killer
function, such as is shown in FIG. 5, is disclosed in Japanese Patent
Unexamined Publication No. Hei. 10-248019.
In FIG. 5, a vertical pulse signal, obtained by the performance of a
synchronous separation operation at a one-chip IC 1, is output via a
vertical drive signal output terminal 1a, and is input to a vertical
deflection IC 2 via a vertical trigger input terminal 2a. Upon receiving
the vertical pulse signal, the vertical deflection IC 2 generates a
saw-toothed voltage signal that it outputs via a vertical amplitude
control terminal 2b. The saw-toothed signal is employed to drive an
electron beam vertically. As for the saw-toothed signal, the side above a
predetermined center potential corresponds to the scan location in the
upper portion of the screen, and the side below the predetermined center
potential corresponds to the scan location in the lower portion of the
screen.
Upon receiving a power-OFF instruction, the one-chip IC 1 outputs a spot
killer command signal via a spot killer command terminal 1b, and upon
receiving this command signal, a spot killer circuit discharges, within a
short period of time, a residual electrical charge that is held by the
anode of a Braun tube. When the electrical charge that is discharged
strikes the screen, the screen glows momentarily. At that time, when an
impact point is fixed, an electrical charge will concentrate on that point
every time the power is turned off, and a burn in the Braun tube will
occur. Therefore, even when the power-OFF instruction is issued, the
vertical deflection IC 2 is activated to validate the vertical drive, so
that the electrical charge can be dispersed vertically when it is
discharged.
However, if only the vertical drive is validated, a lightning-shaped flash
of light will be displayed vertically on the screen. This may frighten a
user, or the user may assume that a specific failure has occurred.
Therefore, in the discharge apparatus shown in FIG. 5, the path between
the collector and the emitter of a transistor Q1 is rendered conductive in
accordance with the output of the spot-killer command signal, and a
vertical pulse signal transmission path is grounded. Then, the voltage
input at the vertical trigger input terminal 2a goes to a low level and
the scan location is moved to the lower portion of the screen. On the
other hand, when the vertical pulse signal transmission path is grounded,
the base voltage of a transistor Q2 is changed, so that the path between
the collector and the emitter of the transistor Q2 is rendered conductive,
and the emitter potential is drastically reduced. Accordingly, there is a
drastic increase in the amplitude of a saw-toothed signal, and the length
of the vertical axis of the screen is increased. That is, when the
residual electrical charge is discharged from the anode of the Braun tube,
the scan location is moved to the lower portion of the screen, so that it
is difficult for a user to recognize it. Further, since the length of the
vertical axis of the screen is increased, even when a point on the screen
glows, the light-emitting point is moved outside the screen frame, and the
lightning-shaped flash of light is not displayed.
According to a Braun tube discharge apparatus disclosed in Japanese Patent
Unexamined Publication No. Hei. 5-191753, when the power is switched off,
the screen is turned off at a constant timing in synchronism with a
vertical sync signal. In this publication, it is taught that in this
manner the quality for the turning off of the screen can be improved.
The following problem is encountered in the above conventional apparatuses.
Since it is presumed that the first conventional apparatus is employed for
the vertical deflection IC of a vertical pulse drive type or the like,
this apparatus can not be employed for a vertical deflection IC of a
so-called vertical ramp drive type or the like. This is because when a
vertical deflection IC of the vertical ramp drive type receives a vertical
ramp drive signal, it returns part of the output as negative feedback
input, performs differential amplification of the negative feedback input,
and outputs the result. Even when grounding of the path for the input of
the vertical ramp drive signal is synchronized with the spot killer
circuit, the same effects can not be obtained.
For the second conventional apparatus, although the screen is turned off in
accordance with a constant timing, the above-described arrangement can not
prevent the display of a flash of light.
SUMMARY OF THE INVENTION
To resolve the above shortcomings, it is an object of the present invention
to provide a Braun tube discharge apparatus that can be employed for a
vertical deflection IC of the vertical ramp drive type, and that can
protect a Braun tube and prevent the display of a flash of light.
To achieve the above object, according to a first aspect of the invention,
there is provided a Braun tube discharge apparatus comprising: vertical
ramp signal differential amplification means for receiving a vertical ramp
signal to control a vertical amplitude and for returning a part of an
output thereof as a negative feedback input, and for performing
differential amplification of the vertical ramp signal and supplying the
result to a vertical deflection coil; spot killer means for discharging a
remaining electrical charge in a Braun tube when a power is turned off;
and negative feedback input path voltage control means for, in
synchronization with the spot killer means, dropping, to a low level, a
voltage along a negative feedback input path in the vertical ramp signal
differential amplification means.
According to the Braun tube discharge apparatus thus arranged, the vertical
ramp signal differential amplification means receives a vertical ramp
signal to control vertical amplitude, returns a part of the output as a
negative feedback input, performs differential amplification of the
vertical ramp signal, and outputs the resultant signal to the vertical
deflection coil. When the spot killer means discharges the residual
electrical charge from the Braun tube when the power is turned off, the
negative feedback input path voltage control means reduces, to a low
level, the voltage along the negative feedback input path of the vertical
ramp signal differential amplification means. Then, the DC voltage along
the negative feedback input path is drastically reduced, and the center DC
value of a signal output by the vertical ramp signal differential
amplification means is increased. At the same time the AC element of the
negative feedback input path is lost, and the amplitude of a signal to be
output is increased.
Specifically, relative to the signal output by the vertical ramp signal
differential amplification means, a predetermined center DC value
corresponds to the middle scan location along the vertical axis of the
screen, and as the DC value is changed above or below the center DC value,
the DC value corresponds to the scan location at the ends of the vertical
axis. Therefore, as the center DC value is increased, the scan location is
moved along the vertical axis to the bottom edge of the screen, and as the
amplitude is increased, the length of the vertical axis of the screen is
also increased. Therefore, it is highly probable that the position whereat
the residual charge is discharged by the spot killer means will lie
outside the screen frame, and even if the point whereat the residual
charge is discharged should lie within the screen frame, any
light-emitting point will momentarily be pushed outside the screen frame,
so that a flash of light will not be displayed on the screen.
According to a second aspect of the invention, there is provided a Braun
tube discharge apparatus comprising: vertical ramp signal differential
amplification means for receiving a vertical ramp signal to control a
vertical amplitude and returning a part of an output thereof as a negative
feedback input, and for performing differential amplification of the
vertical ramp signal and supplying the resultant signal to a vertical
deflection coil; spot killer means for discharging a residual electrical
charge held in a Braun tube when a power is turned off; and vertical
output operation means for, in synchronization with the spot killer means,
changing a center potential of a signal output by the vertical ramp signal
differential amplification means, and increasing the amplitude of the
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram showing the arrangement of a television
set that employs a Braun tube discharge apparatus according to an
embodiment of the present invention.
FIGS. 2(a) and 2(b) are waveform diagrams respectively showing a vertical
ramp signal and a vertical output signal.
FIG. 3 is a circuit diagram showing the essential portion of the Braun tube
discharge apparatus.
FIGS. 4(a) to 4(d) are timing charts showing various signal waveforms.
FIG. 5 is a circuit diagram showing the essential portion of a conventional
Braun tube discharge apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will now be described.
FIG. 1 is a schematic block diagram showing the arrangement of a television
set that employs a Braun tube discharge apparatus according to the
embodiment of the present invention.
In FIG. 1, a tuner 10 selects only a necessary signal from a television
broadcast signal, performs high-frequency amplification to convert the
selected signal into an intermediate-frequency signal, and outputs the
intermediate-frequency signal to a VIF circuit 20. The VIF circuit 20
performs video intermediate-frequency amplification for the received
signal, and outputs the resultant signal to a one-chip IC 30. The one-chip
IC 30 performs video detection for the signal received from the VIF
circuit 20, performs a predetermined signal process for the detected
output, and generates a video signal and supplies it to a Braun tube 40.
Also, the one-chip IC 30 separates the detected output into a horizontal
sync signal and a vertical sync signal, and outputs a horizontal drive
signal and a vertical drive signal that are synchronized respectively with
the horizontal and vertical sync signals.
The horizontal drive signal output by the one-chip IC 30 is supplied to a
horizontal IC 51, and the horizontal IC 51 generates a predetermined
horizontal output signal and transmits it to a horizontal deflection coil
(not shown) in the Braun tube 40. As a result, an electron beam is driven
horizontally. A high-frequency pulse generated by the horizontal IC 51 is
supplied to a high voltage circuit 52 that is constituted by a flyback
transformer and the like. The high voltage circuit 52 generates a high
voltage to be applied to the anode of the Braun tube 40, or a high voltage
that may be requested for another circuit or the like.
The vertical drive signal output by the one-chip IC 30 is transmitted to a
vertical IC-61. The vertical drive signal is a vertical ramp signal having
the saw-toothed shape shown in FIG. 2(a). The vertical IC 61 receives the
vertical ramp signal, feeds back a part of the output via a control
circuit 62, performs differential amplification for this output, and
generates a vertical output signal shown in FIG. 2(b). The vertical output
signal is then transmitted to a vertical deflection coil of the Braun tube
40 to drive an electron beam vertically. As is shown in FIG. 2(b), toward
the top, the portion of the signal corresponds to the scan location in the
upper portion of the screen, and toward the bottom, the portion
corresponds to the scan location in the lower portion of the screen.
Predetermined areas in the top and bottom of the signal are vertical
blanking periods, and the middle area is a vertical deflection period that
affects the scan location on the actual screen.
In this embodiment, an instruction for selecting a channel for the tuner
10, or for powering on or off, can be issued by operating a remote
controller 70. Specifically, when a user depresses an operation button on
the remote controller 70, an infrared remote control signal associated
with the depressed button is transmitted. A microcomputer 80 in the main
body receives the infrared remote control signal via a remote control
signal light-receiving unit (not shown), detects the contents of the
signal, and selects a channel at the tuner 10 or turns the power on or
off.
Further, in this embodiment, a spot killer circuit 63 is provided for
discharging a remaining electrical charge held by the anode of the Braun
tube 40 when the power is turned off. When a power-OFF instruction is
issued by the remote controller 70, the microcomputer 80 cuts off the
supply of power to the internal circuits in accordance with a
predetermined sequence. When the microcomputer 80 cuts off the supply of
power to the high voltage circuit 52, the microcomputer 80 also outputs a
spot killer pulse signal and activates the spot killer circuit 63. In this
embodiment, the spot killer circuit 63 and the microcomputer 80 for
instructing the activation of the spot killer circuit 63 constitute the
spot killer means.
When the spot killer circuit 63 is activated and electron beams discharged
by the anode of the Braun tube 40 strike the screen, light is emitted at
the points that are struck. If the driving of the electron beam is halted,
the light-emitting points will be concentrated at one location and burn in
the Braun tube 40 will occur. Therefore, even after the supply of power to
the high voltage circuit 52 is halted, operation of the one-chip IC 30 and
the vertical IC 61 is continued for a short period of time, so that the
vertical drive is validated and disperses the light-emitting points.
However, since a flash of light will be vertically displayed on the screen
if merely the vertical drive is validated, a user may be frightened by
that light or may fear that it is a symptom of the occurrence of a unit
failure. Therefore, the apparatus in this embodiment is so designed that
burn in the Braun tube 40 is prevented, and a flash of light is not
displayed on the screen. This arrangement will now be described.
FIG. 3 is a circuit diagram showing the essential portion of the Braun tube
discharge apparatus according to this embodiment.
In FIG. 3, an operational amplifier 61a is included in the vertical IC 61,
and a vertical ramp signal from the one-chip IC 30 is supplied to the
non-inversion input terminal of the operational amplifier 61a, while a
vertical deflection coil DY is connected to the output terminal. In
addition, resistors R1 to R6, capacitors C1 and C2 and the like, which
constitute the control circuit 62 shown in FIG. 1, are provided
appropriately, so that a part of the output of the operational amplifier
61a is returned as a negative feedback to the inversion input terminal.
That is, the operational amplifier 61a receives a part of the output as a
negative feedback and performs the differential amplification of it. As a
result, the operational amplifier 61a removes a noise element that is
common to the two inputs, and renders the vertical deflection coil DY
active for the performance of the vertical drive. In this embodiment, the
above circuit structure constitutes the vertical ramp signal differential
amplification means.
The collector of an NPN switching transistor T1, the emitter of which is
grounded, is connected to the junction of the resistors R5 and R6, and the
base of the NPN switching transistor T1 is connected via a resistor R7 to
the signal output path for a spot killer pulse signal. As is described
above, when a spot killer pulse signal is output by the microcomputer 80,
the base voltage of the switching transistor T1 is changed and the path
between the collector and the emitter is rendered conductive. However,
since the emitter of the switching transistor T1 is grounded, the negative
feedback input path of the operational amplifier 61a is grounded.
Therefore, in this embodiment, the thus arranged switching transistor T1,
the resistor R7 and the microcomputer 80 constitute the negative feedback
input path voltage control means.
It can be easily understood that the grounding of the negative feedback
input path of the operational amplifier 61a means that a DC voltage
carried on the negative feedback input path will be reduced, and
accordingly, the center DC value of the vertical output signal shown in
FIG. 2(b) will be increased. Further, the grounding of the negative
feedback input path also means that the AC element carried on the negative
feedback input path will be lost, and accordingly, the amplitude of the
vertical output signal will be increased. In other words, as the center DC
value is increased, the scan location is moved upward on the screen, and
as the amplitude of the vertical output signal is increased, the length of
the vertical axis of the screen is increased.
As is described above, since the top side of the vertical output signal is
a vertical blanking period, and since the center DC value is increased,
the possibility becomes greater that a remaining electrical charge held by
the anode of the Braun tube 40 will be discharged in a time period
corresponding to the vertical blanking period. In this case, no light
emission occurs on the screen. If a remaining charge held by the anode of
the Braun tube 40 is discharged in a time period corresponding to the
vertical deflection period, light-emitting points will appear on the
screen. However, since vertically the size of the screen has been
increased, the light-emitting points are pushed momentarily outside the
screen frame, and a flash of light will not be displayed.
The operation of the embodiment constructed as described above will now be
described while referring to timing charts for various signal waveforms
shown in FIGS. 4(a) to 4(d).
Assume that the powering off of the television set is instructed by
operating the remote controller 70, and a predetermined infrared remote
control signal is transmitted by the remote controller 70 and is received
by the microcomputer 80 of the television set. At this time, as is shown
in FIG. 4(a), the supply of power to the one-chip IC 30 and the vertical
IC 61 is not halted, while as is shown in FIG. 4(b), a spot killer pulse
signal is transmitted at the time at which the power-OFF instruction is
issued. As a result, the vertical output signal of the vertical IC 61 has
the waveform shown in FIG. 4(c), and, as is shown in FIG. 4(d), following
a slight delay after the power-OFF instruction is issued, the supply of
power to the high voltage circuit 52 is halted.
When the spot killer pulse signal is output, the base voltage of the
switching transistor T1, the emitter of which is grounded, is changed, the
path between the collector and the emitter is rendered conductive, and the
inversion input terminal of the operational amplifier 61a of the vertical
IC 61 falls to the ground level. A vertical ramp signal from the one-chip
IC 30 is received at the non-inversion input terminal of the operational
amplifier 61a, and the vertical deflection coil DY is connected to the
output terminal. Further, a part of the output is input as a negative
feedback to the inversion input terminal to perform differential
amplification. When the path between the collector and the emitter of the
switching transistor T1 is rendered conductive, the DC voltage of the
negative feedback input path is reduced, and the center DC value of the
vertical output signal is increased, as is shown in FIG. 4(c). In
addition, when the negative feedback input path falls to the ground level,
it means that the AC element has been lost, and accordingly, the amplitude
of the vertical output signal is increased.
In accordance with the output of the spot killer pulse signal, the spot
killer circuit 63 discharges a remaining electrical charge held by the
anode of the Braun tube 40. At this time, as well as at the time a normal
television image is received, an electron beam is driven vertically by the
vertical output signal. Incidentally, as is shown in FIG. 2(b), the
portion toward the top of the vertical output signal corresponds to the
scan location in the upper portion of the screen, and the portion toward
the bottom corresponds to the scan location in the lower portion of the
screen. The predetermined areas in the top and bottom portions are
vertical blanking periods, and the middle area is a vertical deflection
period that affects the scan location on the actual screen. Then, as the
center DC value is increased, the possibility becomes greater that a
remaining electrical charge held by the anode of the Braun tube 40 will be
discharged in a time period corresponding to the vertical blanking period,
and in this case, areas of the screen will not glow. If the remaining
electrical charge held by the anode of the Braun tube 40 is discharged in
a time period corresponding to the vertical deflection period, a
light-emitting point will appear on the screen. However, since the
vertical size of the screen has been extended, the light-emitting point
will be pushed momentarily outside the screen frame, and a flash of light
will not appear.
As is described above, the operational amplifier 61a included in the
vertical IC 61 receives the vertical ramp signal from the one-chip IC 30
at the non-inversion input terminal. The operational amplifier 61a also
receives a part of the output as a negative feedback to the inversion
input terminal, and performs differential amplification of it and
transmits the results to the vertical deflection coil DY. At the time the
spot killer circuit 63 discharges a remaining electrical charge held by
the Braun tube 40 when the power is turned off, the switching transistor
T1 is rendered conductive by using the spot killer pulse signal that
instructs the activation of the spot killer circuit 63. When the negative
feedback input side of the operational amplifier 61a drops to the ground
level, the center DC value of the vertical output signal is increased, and
the amplitude is increased. Therefore, a Braun tube discharge apparatus
can be provided whereby when the power is turned off the electrical
discharge range can be increased so that it extends outside the screen
frame, and whereby the appearance of a flash of light can be prevented.
As is described above, according to the present invention, a Braun tube
discharge apparatus can be provided that can be applied for a vertical IC
of the vertical ramp drive type or the like, and that can protect a Braun
tube and prevent the display of a flash of light when the power is turned
off.
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