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JP2011119863

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JP2011119863
An audio system according to the present invention is configured such that an audio signal
transmission destination is an existing speaker or an external speaker terminal, and the audio
signal transmission destination is an existing speaker even if the audio signal transmission
destination is an existing speaker. Provided is an audio output circuit that facilitates preventing
signals from being delivered. An amplifier, an existing speaker that generates sound based on an
audio signal sent from the amplifier, an external speaker terminal that sends an audio signal sent
from the amplifier to an external speaker connected to the amplifier, The switch for setting the
transmission destination of the audio signal from the amplifier, the determination unit for
determining which of the transmission destination of the audio signal from the amplifier is set,
and the transmission destination of the audio signal from the amplifier Audio output with upper
limit limiting means that limits the upper limit of the power of the audio signal sent from the
amplifier to a lower value when set to the existing speaker compared to when set to the external
speaker terminal Make it a circuit. [Selected figure] Figure 2
Audio output circuit and electric device
[0001]
The present invention relates to an audio output circuit that amplifies and outputs an input audio
signal, and an electrical apparatus including the same.
[0002]
Conventionally, an image display apparatus such as a television broadcast receiver or a DVD
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player is provided with an audio output circuit which amplifies an audio signal input from the
front stage side by an amplifier and sends it to the rear stage side.
Further, in recent years, with the image display apparatus becoming larger and thinner, it has
become possible for the user to view a more powerful image. In such a situation, it is desirable to
be able to adjust the volume of the sound output from the image display device to a greater
extent.
[0003]
However, as a speaker built in the image display device, generally, a small speaker is used for
space saving and the like. Such a small speaker has a relatively small rated input and can not
produce a loud sound. In addition, if it is going to incorporate a high output speaker in an image
display apparatus, it will be necessary to incorporate a comparatively large speaker, and
slimming of an image display apparatus etc. will be prevented.
[0004]
Therefore, particularly in a large-screen image display device, a relatively small existing speaker
(for example, a speaker provided in advance like a speaker incorporated in an image display
device) is a speaker which is provided in advance, and hereinafter, it is distinguished from an
external speaker For this purpose, the external speaker terminal is provided in this way, and it is
set to be switchable whether the audio signal is sent to the existing speaker or the external
speaker terminal (the audio signal transmission destination is It is conceivable to mount an audio
output circuit of a variable specification).
[0005]
According to such an image display apparatus, when space saving is important (for example, a
case used in a general home), audio is output through the existing speaker, and the space saving
property is not impaired. A viewing environment can be provided.
On the other hand, when high volume is important (for example, a large hall or a case used
outdoors), a high-output speaker (external speaker) is connected to the external speaker terminal,
and this external It is possible to output loud sound through the speaker of. This makes it
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possible to meet many needs with one image display device.
[0006]
JP, 2005-176157, A
[0007]
As described above, the image display apparatus and the like can meet more needs by providing
the audio output circuit of the specification in which the destination of the audio signal is
variable.
However, if the required power level of the audio signal differs relatively largely depending on
the destination of the audio signal, it is easy to transmit the audio signal of the appropriate power
level to any destination. Absent.
[0008]
For example, when the amplification factor of the audio signal in the audio output circuit or the
like is set based on the case where the destination of the audio signal is the existing speaker, the
appropriate power is obtained when the destination of the audio signal is the existing speaker An
audio signal of level is sent out. However, when the transmission destination of the audio signal
is an external speaker terminal, the power level of the audio signal to be transmitted is too small,
and it becomes difficult to realize high-volume audio output using an external speaker.
[0009]
On the other hand, when the amplification factor of the audio signal in the audio output circuit or
the like is set based on the case where the destination of the audio signal is the external speaker
terminal, when the destination of the audio signal is the external speaker terminal, An audio
signal of appropriate power level is delivered. However, when the destination of the audio signal
is the existing speaker, the power level of the audio signal to be transmitted is too high. In
particular, if the power level exceeds the rated input of the existing speaker, the existing speaker
may be destroyed.
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[0010]
In the audio output circuit, for example, an attenuator may be disposed in front of the amplifier,
and the attenuator may be controlled by a so-called volume control function to adjust the power
level of the audio signal. However, even with this volume adjustment function, when the power
level of the input audio signal is larger than expected, an audio signal with a power level
exceeding the rated input of the existing speaker is sent to the existing speaker There is also the
possibility of Also, when the volume control function is open to the user, it is difficult to
automatically adjust the power level of the audio signal using this volume control function.
[0011]
In view of the problems described above, the present invention is a specification in which the
destination of the audio signal is the existing speaker while the destination of the audio signal is
the specification that is variable between the existing speaker and the external speaker terminal.
An object of the present invention is to provide an audio output circuit which can easily prevent
an excessive audio signal from being transmitted to an existing speaker.
[0012]
In order to achieve the above object, an audio output circuit according to the present invention
receives an amplifier for amplifying an audio signal input from the front stage side and sends it
to the rear stage side, and an audio signal sent from the amplifier, An existing speaker that
generates voice based on a signal, an external speaker terminal that receives an audio signal sent
from the amplifier, and sends the audio signal to an external speaker connected to itself, and an
audio signal from the amplifier A switch for setting the transmission destination of either the
existing speaker or the external speaker terminal so as to be switchable, and a determination unit
for determining which one the transmission destination of the audio signal from the amplifier is
set to; When the transmission destination of the audio signal from the amplifier is set to the
existing speaker, the sound transmitted from the amplifier is compared to when it is set to the
external speaker terminal Performing a limiting action for limiting the upper limit value of the
signal power to a low value, a structure having an upper limiting means.
[0013]
According to this configuration, when the transmission destination of the audio signal from the
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amplifier is set to the existing speaker, the upper limit value of the power of the audio signal
transmitted from the amplifier is higher than when set to the external speaker terminal Is limited
to low values.
Therefore, even when the transmission destination of the audio signal is the existing speaker, it is
easy to prevent the excessive audio signal from being transmitted to the existing speaker.
[0014]
More specifically, the upper limit limiting means causes the power to be clipped to the limit value
during a period in which the power exceeds a predetermined limit value for the audio signal
transmitted from the front stage side. When the destination of the audio signal from the amplifier
is set to the external speaker terminal, the limiter circuit is invalidated, and the audio signal from
the amplifier is output. When the transmission destination of is set to the existing speaker, the
limiting operation may be performed by making the limiter circuit effective.
[0015]
More specifically, as the above configuration, the upper limit limiting means is set in advance so
that the limit value can be changed, and the power of the audio signal transmitted from the front
side exceeds the limit value. When a limit value variable limiter circuit is provided which clips the
power to the limit value and then sends it to the subsequent stage side, and the destination of the
audio signal from the amplifier is set to the external speaker terminal, When the limit value is set
to the first limit value and the destination of the audio signal from the amplifier is set to the
existing speaker, the limit value is set to the second limit value lower than the first limit value.
Thus, the restriction operation may be performed.
[0016]
Further, an electric device according to the present invention includes the audio output circuit
according to the above configuration, receives an input of an audio signal, and inputs the audio
signal to the audio output circuit to generate audio based on the audio signal. It is configured to
generate the existing speaker or an external speaker.
According to this configuration, it is possible to receive the advantage of the audio output circuit
according to the above configuration.
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[0017]
More specifically, the electric device having the above configuration may be configured as an
image display device that receives an input of an image signal and displays an image based on
the image signal.
[0018]
As described above, according to the audio output circuit according to the present invention,
when the transmission destination of the audio signal from the amplifier is set to the existing
speaker, it is transmitted from the amplifier compared to when it is set to the external speaker
terminal. The upper limit value of the power of the audio signal to be played back is limited to a
low value.
Therefore, even when the transmission destination of the audio signal is the existing speaker, it is
easy to prevent the excessive audio signal from being transmitted to the existing speaker.
[0019]
It is a block diagram of the audio | voice output circuit which concerns on Example 1 of this
invention.
It is a flowchart of the operation | movement which the audio | voice output circuit which
concerns on Example 1 of this invention performs.
It is explanatory drawing regarding the setting of amplifier limiting value. It is explanatory
drawing regarding the change of the waveform of a reference signal. It is a block diagram of the
audio | voice output circuit which concerns on Example 2 of this invention. It is a flowchart of the
operation | movement which the audio | voice output circuit which concerns on Example 2 of
this invention performs. It is a flowchart of the operation | movement which the audio | voice
output circuit which concerns on Example 3 of this invention performs.
[0020]
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Embodiments of the present invention will be described below by taking an audio output circuit
provided in an image display device as an example (examples 1 to 3).
[0021]
First Embodiment First, the first embodiment will be described below.
FIG. 1 is a block diagram of an audio output circuit according to the present embodiment. As
shown in the figure, the audio output circuit 1 includes an attenuator (attenuator) 11, a voltage
limiter circuit 12, an amplifier 13, a switch 14, an existing speaker 15, an external speaker
terminal 16, a control unit 17, and the like. The audio output circuit 1 is configured to receive an
analog audio signal from the front stage side (here, the main body side of the image display
device).
[0022]
The attenuator 11 attenuates the audio signal input from the front stage side of the audio output
circuit 1 according to the instruction of the control unit 17 and sends it to the rear stage side.
The degree (attenuation rate) at which the attenuator 11 attenuates the audio signal is also
determined based on the instruction of the control unit 17.
[0023]
In the voltage limiter circuit 12, the limit value (hereinafter sometimes referred to as “limiter
limit value”) of the voltage (power) to be output is set in advance, and the voltage limiter circuit
12 is set to be effective. The audio signal is sent to the subsequent stage side so that the voltage
of the audio signal sent from the attenuator 11 does not exceed the limiter limit value.
[0024]
More specifically, during a period in which the voltage of the audio signal received from the
attenuator 11 does not exceed the limiter limit value, the audio signal is allowed to pass through
to the subsequent stage side, and in a period exceeding the limiter limit value, The voltage is
clipped to the limiter limit value, and the audio signal is sent to the subsequent stage.
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Note that how the limiter limit value is set will be described again.
[0025]
However, the voltage limiter circuit 12 is configured to be switched between valid and invalid
(ON / OFF of operation) according to an instruction of the control unit 17. When the voltage
limiter circuit 12 is set to be invalid, the above-described operation is not performed, and the
audio signal sent from the attenuator 11 is passed through to the subsequent stage as it is.
[0026]
The amplifier 13 amplifies the audio signal sent from the voltage limiter circuit 12 and sends it
from the output terminal to the subsequent stage. The amplification factor of the audio signal in
the amplifier 13 is set in advance to a predetermined value, and how it is set will be described
again. Also, as is generally known, in order to distinguish from the limit value of the voltage
output by the amplifier 13 (specifically, the supplied power, etc.) from the limiter 13 (hereinafter
referred to as “amplifier limit value,” May be referred to as ").
[0027]
That is, even if the theoretical output voltage (the input voltage multiplied by the amplification
factor) exceeds the amplifier limit value, the voltage actually output from the amplifier 13 is
clipped to the amplifier limit value. Become. Note that how the amplifier limit value is set will be
described again.
[0028]
The switch 14 switchably connects the output terminal of the amplifier 13 to one of the existing
speaker 15 and the external speaker terminal 16 in accordance with an instruction from the
control unit 17. As a result, the audio output circuit 1 can set the transmission destination of the
audio signal output from the amplifier 13 to any one of the existing speaker 15 and the external
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speaker terminal 16 so as to be switchable.
[0029]
Unlike the external speaker, the existing speaker 15 is a speaker provided in advance as a
transmission destination of the audio signal from the amplifier 13 and generates sound based on
the transmitted audio signal. The existing speaker 15 is provided, for example, in the form of a
built-in speaker built in the image display device. The existing speaker 15 is smaller than an
external speaker connected to the external speaker terminal 16 and has a lower rated input.
[0030]
The external speaker terminal 16 is a terminal for connecting an external speaker, and is
provided in such a manner that the external speaker can be connected from the outside of the
image display device. If an external speaker is connected to the external speaker terminal 16, the
audio output circuit 1 can transmit an audio signal to the external speaker to generate audio.
[0031]
The control unit 17 is formed of, for example, a microcomputer, and controls various operations
of the audio output circuit 1. In addition, the control unit 17 instructs the user (for example,
changes the volume of sound to be generated) and switch switching (changes the transmission
destination of the sound signal to the existing speaker 15 or the external speaker terminal 16)
(for example, the user It is possible to receive the operation of the user interface in the image
display apparatus, and it is possible to reflect the user's intention in various operations.
[0032]
Next, the flow of the operation in the audio output circuit 1 will be described with reference to
the flowchart of FIG.
[0033]
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The control unit 17 continuously monitors whether the user has issued a volume adjustment
instruction (step S11) and whether a switch switching instruction has been issued (step S12).
When the volume adjustment instruction is issued (Y in step S11), the control unit 17 adjusts the
attenuation factor of the audio signal in the attenuator 11 based on the user's instruction (step
S13). Thus, the user can set the volume of the sound emitted from the existing speaker 15 or an
external speaker to a desired state.
[0034]
When a switch switching instruction is issued (Y in step S12), the control unit 17 switches the
switch 14 (step S14). As a result, the user can listen to the voice through a desired voice
generation device (the existing speaker 15 or an external speaker connected to the external
speaker terminal 16).
[0035]
When the switch 14 is switched to the existing speaker 15 side by the operation of step S14
("existing speaker side" of step S15), the control unit 17 sets the voltage limiter circuit 12 to be
effective (step S16). . On the other hand, when the switch 14 is switched to the external speaker
terminal 16 side ("external speaker terminal side" in step S15), the control unit 17 sets the
voltage limiter circuit 12 to be invalid (step S17). After the operation of step S16 or step S17 is
performed, the control unit 17 repeats the operation of step S11.
[0036]
By the operation described above, when the transmission destination of the audio signal from the
amplification circuit 13 is the existing speaker 15, the voltage limiter circuit 12 is validated, and
when the transmission destination is the external speaker terminal 16, the voltage limiter circuit
12 Will be invalidated. Next, how the limiter limit value and the amplifier limit value described
above are set will be described.
[0037]
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First, with regard to the limiter limit value (the set value related to the voltage limiter circuit 12),
the state in which the voltage limiter circuit 12 is made effective (and an audio signal of any size
input from the front stage side of the audio output circuit 1) The attenuation factor of the
attenuator 11 is set to a value such that the output from the amplifier 13 does not exceed the
rated input of the existing speaker 15).
[0038]
For example, when 5 W is permitted as the input of the existing speaker 15, the limiter limit
value is set so that the audio signal transmitted from the amplifier 13 always falls within 5 W or
less.
It is possible to set the limiter limit value in this way after the amplification factor of the amplifier
13 has been set.
[0039]
As for the amplifier limit value (the set value for the amplifier 13), what is from the front stage
side of the audio output circuit 1 in the state where the voltage limiter circuit 12 is disabled (and
the attenuation factor of the attenuator 11 is zero). Even if an audio signal of a magnitude is
input, the output from the amplifier 13 is set to a value that does not exceed the rated input of
the external speaker.
[0040]
For example, when the rated input of an external speaker is 10 W / 8 ohms, with a load of 8
ohms connected to the external speaker terminal 16, the audio signal sent from the amplifier 13
must be 10 W or less. A limit value has been set.
Such setting of the amplifier limit value is possible after the amplification factor of the amplifier
13 has been set.
[0041]
Since the limiter limit value and the amplifier limit value are set as described above, according to
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the audio output circuit 1 performing the above-described series of operations (steps S11 to
S17), the destination of the audio signal is the existing speaker 15 and In any of the external
speaker terminals 16, an audio signal exceeding the rated input is not input to the existing
speaker 15 or an external speaker.
[0042]
That is, when the transmission destination of the audio signal after amplification is the external
speaker terminal 16, the power of the signal is limited according to the amplifier limit value, and
falls within the range below the rated input of the external speaker.
Also, when the transmission destination of the audio signal after amplification is the existing
speaker 15, the power of the signal is limited according to the limiter limit value, so that the
rated input of the existing speaker 15 (compared to the rated input of the external speaker Low
value) or less. Therefore, it is possible to prevent the situation in which these speakers are
destroyed.
[0043]
From the above description, in the audio output circuit 1, when the transmission destination of
the audio signal from the amplifier 13 is set to the existing speaker 15, compared with the case
where it is set to the external speaker terminal 16, It can be said that an operation (restriction
operation) is performed to limit the upper limit value of the power of the transmitted audio signal
to a low value.
[0044]
Although various values can be set for the amplification factor of the amplifier 13, a setting
method based on the EIAJ [Electronic Industries Association of Japan] standard will be described
as an example.
[0045]
Hereinafter, a case will be described where transmission of an audio signal based on the EIAJ
standard is performed when an external speaker is used.
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According to the EIAJ standard, it is defined that the distortion factor of the audio signal
(indicating how much the signal at the time of output is distorted from the signal at the time of
input) falls within 10%.
Therefore, when an audio signal of a standard power level (hereinafter referred to as "reference
signal") is input to the audio output circuit 1, the distortion factor of the amplified reference
signal is about 10% at maximum. The amplification factor of the amplifier 13 is set.
[0046]
More specifically, the attenuation factor in the attenuator 11 is made zero, the voltage limiter
circuit 12 is made invalid, the switch 14 is connected to the external speaker terminal 16 side,
and an external speaker (or equivalent to the external speaker terminal 16). When the reference
signal is input to the audio output circuit 1 with the load connected, the distortion factor of the
amplified reference signal (that is, the reference signal sent to the external speaker) is
approximately 10%. , Adjust the amplification factor of the amplifier 13.
[0047]
In the process of adjusting the amplification factor of the amplifier 13, the audio signal sent to
the external speaker terminal 16 is as shown in FIG. 3, for example.
In FIG. 3, (a) shows the case where the amplification factor is α1, (b) the case where the
amplification factor is α2 (> α1), and (c) the case where the amplification factor is α3 (> α2). .
In any case, the voltage of the reference signal after amplification is clipped (fixed) to the
amplifier limit value in a period in which the voltage of the reference signal multiplied by the
amplification factor exceeds the amplifier limit value. Then, as the degree of clipping (which can
be regarded as the degree of correction) is larger, the waveform of the reference signal after
amplification is greatly distorted from the waveform before amplification, and the distortion
factor becomes larger.
[0048]
When the amplification factor is α1, the distortion factor of the reference signal after
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amplification is approximately zero (sufficiently smaller than 10%). Therefore, it can be said that
the amplification factor α1 in this case is too small in consideration of the EIAJ standard (there
is no problem in suppression of distortion, but the signal is not amplified so much).
[0049]
When the amplification factor is α3, as a result of amplification of the reference signal, the
degree of clipping to the amplifier limit value is relatively large, and the distortion factor of the
reference signal after amplification is about 20% (compared to 10%). The Therefore, it can be
said that the amplification factor α3 in this case is too large in consideration of the EIAJ
standard (even if the reference signal is inputted to the audio output circuit 1, there is a
possibility that the EIAJ standard may be deviated).
[0050]
When the amplification factor is α2, the amplified reference signal is clipped to the amplifier
limit value to some extent, but the distortion factor of the amplified reference signal is about
10%. Therefore, the amplification factor α2 is adopted (set) as the amplification factor of the
amplifier 13. In this manner, when the amplification factor of the amplifier 13 is set, the volume
adjustment is maximized when an audio signal having a power level equal to or lower than that
of the reference signal is input to the audio output circuit 1 (attenuator 11 The distortion factor
of the audio signal sent to the external speaker does not deviate from the EIAJ standard, even
when the attenuation factor of
[0051]
Here, the situation in which the existing speaker 15 is used is considered. If the reference signal
input to the voice output circuit 1 enters the voltage limiter circuit 12 while maintaining its
power level, the reference signal is largely corrected by the action of the voltage limiter circuit
12, and the corrected reference signal There is a possibility that the signal (which is transmitted
to the existing speaker 15 after amplification) may not conform to the EIAJ standard (the
distortion factor is within 10%).
[0052]
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14
In this respect, if the user gives an instruction to reduce the sound volume sufficiently, the
attenuation factor at the attenuator 11 increases accordingly (see the operation of steps S11 and
S13), and distortion of the corrected reference signal is caused. The rate will be in accordance
with the EIAJ standard. However, in the voice output circuit 1, the attenuation rate in the
attenuator 11 may be automatically adjusted even if the user does not make such an instruction.
[0053]
For example, at the design stage of the audio output circuit 1, when the attenuation factor of the
attenuator 11 is any value, the distortion factor of the reference signal output from the voltage
limiter circuit 12 (limiter limit value is already set) is about 10%. (If this value is "specific value").
Then, when the transmission destination of the audio signal from the amplifier 13 is switched to
the existing speaker 15, the attenuation factor in the attenuator 11 is automatically adjusted so
as not to fall below this specific value. good. In this way, the distortion factor of the reference
signal after correction becomes a grade that conforms to the EIAJ standard.
[0054]
At this time, while the minimum value of the attenuation factor in the attenuator 11 is fixed to
the specific value, the attenuation factor may be changeable according to a user's instruction
within a range not falling below the minimum value. In this way, it is possible to reflect the
volume adjustment intention of the user on the volume of the existing speaker 15 as much as
possible while avoiding the situation where an audio signal having a large distortion factor is sent
to the existing speaker 15.
[0055]
When the attenuation factor of the attenuator is set to the specific value, the waveform of the
reference signal changes as shown in FIG. When a reference signal having a waveform as shown
in FIG. 4 (a) is inputted to the audio output circuit 1, this reference signal is first attenuated by
the attenuator 11 and becomes a waveform as shown in FIG. 4 (b). The reference signal having
such a waveform is further input to the voltage limiter circuit 12, and a period exceeding the
limiter limit value is corrected to the limiter limit value. As a result, the reference signal has a
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waveform as shown in FIG. 4C, and the distortion rate of the reference signal at this time is about
10%.
[0056]
The reference signal is further input to the amplifier 13 and amplified. The reference signal after
amplification does not reach the amplifier limit value. Therefore, as shown in FIG. 4D, the
waveform of the reference signal is expanded without changing the distortion factor (about 10%).
The reference signal is sent to the existing speaker 15 after being changed to such a waveform.
[0057]
Second Embodiment Although the switch 14 according to the first embodiment is switched
according to an instruction from the control unit 17, the switch may be directly executed by the
user. The audio output circuit 1 in this case will be described below as a second embodiment.
[0058]
FIG. 5 is a block diagram of the audio output circuit 1. As shown in FIG. 5, in the present
embodiment, a slide switch (a kind of mechanical switch) 14a is provided instead of the switch
14. The slide switch 14 a connects the output terminal of the amplifier 13 switchably to one of
the speaker 15 and the external speaker terminal 16 in the same manner as the switch 14.
However, this switching is realized not by the instruction of the control unit 17 but by the user
directly operating the slide switch 14a.
[0059]
When the slide switch 14a is switched to the existing speaker 15 side, an H level (Vcc) signal is
sent to the control unit 17 in conjunction with this, and when the slide switch 14a is switched to
the external speaker terminal 16 side, In conjunction with this, an L level (GND) signal is sent to
the control unit 17. The control unit 17 can determine how the slide switch 14a is switched
based on the signal output from the slide switch 14a. Then, when the slide switch 14a is
switched to the existing speaker 15 side, the control unit 17 sets the voltage limiter circuit 12
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16
effective, and when the slide switch 14a is switched to the external speaker terminal 16 side, the
control circuit 17 invalidates the voltage limiter circuit 12. Set
[0060]
The flow of the operation in this embodiment is shown in the flow chart of FIG. Basically, it is the
same as the flow of the operation according to the first embodiment, but in the present
embodiment, the control unit 17 does not monitor whether the user instructs switching of the
switch 14 (step S12). It is monitored whether the switch 14a has been switched (step S21).
Further, since the slide switch 14a is switched by the user, the control unit 17 does not perform
the operation of switching the switch (step S14).
[0061]
The signal output from the slide switch 14a described above may be sent directly to the voltage
limiter circuit 12. In this case, the voltage limiter circuit 12 may be set to be valid or invalid
according to the signal sent from the slide switch 14a. In this way, switching between valid and
invalid in the voltage limiter circuit 12 is realized without increasing the processing load of the
control unit 17.
[0062]
Third Embodiment In the first embodiment, the valid / invalid state of the voltage limiter circuit
12 is switched according to which of the transmission destinations of the audio signal after
amplification is set, but instead thereof The limiter limit value may be switched. In the present
embodiment, the voltage limiter circuit 12 is always valid and not invalid. The audio output
circuit 1 in this case will be described below as a third embodiment.
[0063]
The overall configuration of the audio output circuit 1 according to this embodiment is basically
the same as that of the first embodiment (see FIG. 1). However, the voltage limiter circuit 12
according to the present embodiment can switch the limiter limit value to either the first limiter
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17
limit value or the second limiter limit value according to an instruction from the control unit 17.
It has become.
[0064]
Here, the first limit value is set in advance to a value obtained by dividing the amplifier limit
value set in the amplifier 13 of the first embodiment by the amplification factor of the amplifier
13. That is, the first limit value is set in the same manner as the amplifier limit value in the first
embodiment. The second limit value is preset to a value equal to the limiter limit value set in the
voltage limiter circuit 12 of the first embodiment. As a result, the second limit value is set to a
value lower than the first limit value.
[0065]
Then, the control unit 17 sets the limiter limit value to the second limiter limit value when the
switch 14 is switched to the existing speaker 15 side, and when the switch 14 is switched to the
external speaker terminal 16 side, the limiter limit value 1 Set the limiter limit value.
[0066]
The flow of the operation in this embodiment is shown in the flow chart of FIG.
Basically, it is the same as the flow of the operation according to the first embodiment, but in this
embodiment, the limiter limit value is set to the second limiter limit value instead of setting the
voltage limiter circuit to be effective (step S16). (Step S31) Further, instead of setting the voltage
limiter circuit to be invalid (step S17), the limiter limit value is set to the first limiter limit value
(step S32).
[0067]
According to this embodiment, the action of the voltage limiter circuit 12 not only prevents the
audio signal of the rated input or more from being transmitted to the existing speaker 15, but
also transmits the audio signal of the rated input or more to the external speaker It is also
possible to prevent that.
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[0068]
As described above, the audio output circuit 1 according to each of the embodiments receives the
amplifier 13 for amplifying the audio signal input from the front stage side and sending it to the
rear stage side, and the audio signal sent from the amplifier 13; An existing speaker 15 for
generating voice based on the voice signal, an external speaker terminal 16 for receiving the
voice signal sent from the amplifier 13 and sending the voice signal to an external speaker
connected to the amplifier, the amplifier 13 And a switch 14 for setting the transmission
destination of the audio signal from any one of the existing speaker 15 and the external speaker
terminal 16 so as to be switchable.
[0069]
Further, the audio output circuit 1 has a function (determining function) of determining to which
destination the transmission destination of the audio signal from the amplifier 13 is set, and the
transmission destination of the audio signal from the amplifier 13 is set to the existing speaker
15 Function unit having a function (limit function) for limiting the upper limit value of the power
of the audio signal sent from the amplifier 13 to a lower value than when it is set to the external
speaker terminal 16 (mainly , The voltage limiter 12 and the control unit 17).
Therefore, even when the transmission destination of the audio signal is the existing speaker 15,
it is possible to prevent an excessive audio signal from being transmitted to the existing speaker
15.
[0070]
As described above, the audio output circuit 1 is provided in an image display device (for
example, a device such as a television broadcast receiver that receives an input of an image
signal and displays an image based on the image signal).
In particular, by being provided in a thin image display device for which space saving is desired,
the audio output circuit 1 can amplify and output sound without inhibiting this thinning as much
as possible.
[0071]
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However, the audio output circuit 1 is not limited to the image display device, and can be
provided in various electric devices that handle audio signals. The electric device provided with
the audio output circuit 1 receives an input of an audio signal, and inputs this audio signal to the
audio output circuit 1 to make an audio based on the audio signal into the existing speaker 15 or
an external speaker. Can be generated.
[0072]
As mentioned above, although embodiment of this invention was described, this invention is not
limited to this content. Furthermore, various modifications can be made to the embodiment of the
present invention without departing from the spirit of the present invention.
[0073]
The present invention can be used for various electrical devices that output sound.
[0074]
1 voice output circuit 11 attenuator 12 voltage limiter circuit (limiter circuit) 13 amplifier 14
switch 14 a slide switch 15 existing speaker 16 external speaker terminal 17 control unit
09-05-2019
20
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