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JP2003179992

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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 JP2003179992
[0001]
The present invention relates to an apparatus having an external audio output terminal that also
uses a horn jack such as an earphone jack different from a speaker terminal used for audio
equipment as a speaker output terminal, and an internal speaker. The present invention relates to
an audio output circuit.
[0002]
2. Description of the Related Art Since a speaker terminal used for audio equipment is large, in
order to miniaturize the equipment, a horn jack such as an earphone jack having a small
component area may be used as an external sound output terminal.
[0003]
FIG. 2 shows the configuration of a conventional audio output circuit in which a horn jack is used
as an external audio output terminal.
[0004]
In FIG. 2, 1 and 2 are ICs whose output gain can be changed from mute (output stop) to about 12 db to +6 db by a DC voltage called VCA (Voltage Control Amplifier), which corresponds to a
pre-amplifier.
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The ICs 1 and 2 change the amplitudes of the input signals L and R according to the volume
control voltage Vol applied thereto.
When the volume control voltage Vol is GND, the ICs 1 and 2 are muted, and the output voltages
of the ICs 1 and 2 increase as the volume control voltage Vol rises.
[0005]
The output signals of the ICs 1 and 2 are sent to an audio output IC 3 (main amplifier) and
amplified at a constant amplification factor. The audio signals of the left and right channels
output from the IC 3 are sent to the horn jack 6, which is an external audio output terminal, via
the capacitors 4 and 5 which cut off the direct current component for external output.
[0006]
When the external terminal is not inserted into the horn jack 6, the output sound signals of the
left and right channels are respectively sent to and outputted from the left and right speakers 7,
8 inside.
[0007]
When an external terminal is inserted in the horn jack 6, the contact in the horn jack 6 is
disconnected, and the output sound signals of the left and right channels are sent only to the
inserted external terminal.
Accordingly, since no current flows in the internal speakers 7 and 8, the internal speakers 7 and
8 are not driven. Instead, current flows to the external terminal side to drive the external speaker.
[0008]
In the conventional audio output circuit, both the internal speaker and the audio output terminal
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(horn / jack) for stereo output are used. However, even in an audio output circuit for outputting a
stereo signal, in order to miniaturize a device on which the audio output circuit is mounted, it is
conceivable to use one internal speaker.
[0009]
The present invention is an audio output circuit for outputting a stereo signal, wherein an audio
output circuit capable of automatically switching the signal and achieving power saving in a
single monaural internal speaker. Intended to provide.
[0010]
The invention according to claim 1 comprises an external audio output terminal, and a monaural
internal speaker connected to the external audio output terminal when the external terminal is
not connected to the external audio output terminal. A mixing circuit for mixing the input sound
signal of the left channel and the input sound signal of the right channel, and one of the left
channel and the right channel as a first channel and the other as a second channel. Output signal
of the first channel and the input audio signal of the first channel, the switching circuit for
switching and outputting those signals, the output audio signal of the switching circuit and the
output audio signal of the first channel or monaural audio A first audio signal generation circuit
for generating a signal, an input audio signal of a second channel is input and an output sound of
a second channel Second audio signal generation circuit for generating a signal, detection circuit
for detecting whether an external terminal is connected to the external audio output terminal,
switching circuit when the external terminal is not connected to the external audio output
terminal Controls the switching circuit so that the output signal of the mixing circuit is output
from the switching circuit, and switches so that the input audio signal of the first channel is
output from the switching circuit when the external terminal is connected to the external audio
output terminal A control circuit for controlling the circuit, and a power consumption reducing
means for reducing power consumption of the second audio signal generation circuit when an
external terminal is not connected to the external audio output terminal. .
[0011]
According to the invention of claim 2, in the invention of claim 1, the power consumption
reducing means mutes the output audio signal of the second channel when the external terminal
is not connected to the external audio output terminal. It is characterized in that it controls an
audio signal generation circuit.
[0012]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, an
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embodiment in which the present invention is applied to an audio output circuit used in a liquid
crystal projector will be described.
[0013]
FIG. 1 shows the configuration of the audio output circuit of the present invention used in a
liquid crystal projector.
In FIG. 1, the same components as those in FIG.
[0014]
The difference between the audio output circuit of the present invention of FIG. 1 and the
conventional example of FIG. 2 is that the internal speaker is monaural in the audio output circuit
of the present invention.
That is, the internal speaker 8 of the right channel in FIG. 2 is not provided, and only the internal
speaker 7 of the left channel is provided.
[0015]
Since the internal speakers are monaural, in this embodiment, the mixing circuit 11 for mixing
the input audio signals L and R of the left and right channels, the one mixing the input audio
signals L and R, and the original A switch IC 12 for switching between the left channel audio
input signal L and the left channel audio input signal L is added.
[0016]
In addition, a control circuit for controlling the switch IC 12 is added.
In addition, a circuit for bringing the preamplifier (IC2) for the audio input signal R of the right
channel into a non-operation state (mute state) is added based on the output of the control
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circuit.
[0017]
A control circuit for controlling the switch IC 12 comprises a switching transistor 26, resistors
21, 22, 23, 24 and a capacitor 25.
[0018]
The base of the switching transistor 26 is connected to a DC power supply B via a resistor 22, an
internal speaker connection terminal of the right channel of the horn jack 6 and a resistor 21.
The connection point between the base of the switching transistor 26 and the resistor 22 is
grounded via the resistor 23 and also grounded via the capacitor 25.
[0019]
The emitter of the switching transistor 26 is grounded.
The collector of the switching transistor 26 is connected to the DC power supply B via a resistor
24.
The collector voltage of the switching transistor 26 is used as a switching control signal of the
switch IC 12.
[0020]
The circuit for bringing the preamplifier (IC 2) into the inoperative state comprises a first
switching transistor 31 controlled on and off by the switching transistor 26 and a second
switching circuit controlled on and off by the first switching transistor 31. A transistor 32 is
provided.
[0021]
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The base of the first switching transistor 31 is connected to the collector of the switching
transistor 26 via a resistor 33.
The emitter of the first switching transistor 31 is grounded. The collector of the first switching
transistor 31 is connected to the DC power supply B via a resistor 34.
[0022]
The base of the second switching transistor 32 is connected to the collector of the first switching
transistor 31. The emitter of the second switching transistor 32 is grounded. The collector of the
second switching transistor 32 is connected to the control voltage supply terminal of the
preamplifier (IC2).
[0023]
The operation will be described separately in the case where an external terminal is not
connected to the horn jack 6 and when the external terminal is connected to the horn jack 6.
[0024]
(1) Operation when external terminal is not connected to horn jack 6
[0025]
The resistance 21 is set to several tens of kΩ or more, for example, 40 kΩ so that the influence
on the speaker connected to the horn jack 6 is 1/1000 or less.
When an external terminal is not connected to horn jack 6, the potential applied via resistor 21 is
the terminal for the internal speaker connection of the right channel of horn jack 6 and the base
of switching transistor 26 via resistor 22. Switching transistor 26 is turned on.
[0026]
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The resistors 22 and 23 are set to, for example, about 20 KΩ.
Therefore, the potential applied to the base of the switching transistor 26 is about (1/4) × B. The
capacitor 25 is provided to prevent the operation of the switching transistor 26 from being
disturbed by the audio signal.
[0027]
When the switching transistor 26 is turned on, the collector voltage of the switching transistor
26 (the switching control signal of the switch IC 12) becomes Lo. When the switching control
signal of the switch IC 12 is Lo, the switch IC 12 selects and outputs the output of the mixing
circuit 11.
[0028]
Therefore, the mixed signal output from the mixing circuit 11 is sent to the internal speaker 7
through the switches IC 12, IC 1, IC 3, the capacitor 4 and the horn jack 6.
[0029]
On the other hand, when the collector voltage of the switching transistor 26 becomes Lo, the first
switching transistor 31 is turned off and the second switching transistor 32 is turned on.
As a result, the control voltage of the right channel side preamplifier (IC2) becomes GND.
Therefore, the preamplifier on the right channel side (IC2) is in the audio mute state, and the
output of IC2 becomes a DC component. By eliminating the DC signal in the circuit on the right
channel side, that is, the audio signal of the right channel, the power consumption of the audio
output circuit can achieve power saving of about 40%.
[0030]
(2) Operation when external terminal is connected to horn jack 6
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[0031]
When an external terminal is connected to the horn jack 6, the contact in the horn jack 6 is
released, so that one end of the resistor 22 is disconnected from the horn jack 6 and becomes
open.
Therefore, no voltage is applied to the resistor 22 and the charge stored in the capacitor 25 is
discharged through the resistor 23, so the switching transistor 26 is immediately turned off.
[0032]
When the switching transistor 26 is turned off, the collector voltage of the switching transistor
26 (the switching control signal of the switch IC 12) becomes Hi. When the switching control
signal of the switch IC 12 becomes Hi, the switch IC 12 selects and outputs the input audio signal
L of the left channel.
[0033]
On the other hand, when the collector voltage of the switching transistor 26 becomes Hi, the first
switching transistor 31 is turned on and the second switching transistor 32 is turned off. As a
result, the control voltage on the right channel side is supplied to the preamplifier (IC2) on the
right channel side. That is, the preamplifier on the right channel side (IC2) is released from the
audio mute state, and an audio signal is output from the preamplifier on the right channel side
(IC2).
[0034]
Therefore, the input audio signals L and R of the left and right channels are sent to the external
terminals through the preamplifiers (IC1 and IC2), the IC 3 for audio output, the capacitors 4 and
5, and the horn jack 6.
[0035]
When the IC 3 for audio output has a function of enabling the right channel and the left channel
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to be separate and enable, the IC 3 for audio output also has a circuit for the right channel.
Similar control may be performed.
[0036]
According to the present invention, an audio output circuit for outputting a stereo signal, which
has a single monaural internal speaker, can automatically switch the signal and save Power can
be realized.
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