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DESCRIPTION JP2017085336

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DESCRIPTION JP2017085336
Abstract: A simple circuit configuration reduces the generation of pop noise. A phantom power
supply circuit 10 includes a phantom power supply PW for supplying power to a condenser
microphone, input-side terminals 1a, 1b and 1c to which the condenser microphone is connected,
and an output signal from the condenser microphone. Output side terminals 2a, 2b and 2c to
which an output device is connected, a signal line 3 connecting the input side terminal and the
output side terminal, and a switch SW of phantom power connected between the phantom power
and the signal line And light-emitting elements D11 and D12 which are driven when the switch is
activated, and photo-resistors PR11 and PR12 which are connected in series to the signal line
and whose resistance value changes according to the light-emitting state of the light-emitting
elements. [Selected figure] Figure 1
Phantom power circuit
[0001]
The present invention relates to a phantom power supply circuit for feeding a condenser
microphone.
[0002]
Condenser microphone (hereinafter referred to as "microphone".
) Requires the supply of power for operating the impedance converter etc. with which the
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microphone is provided. For power supply of the microphone, a phantom power supply method
defined in JEITA RC-8162A (power supply method of the microphone) is used.
[0003]
The phantom feeding method is from a direct current power supply (phantom power supply)
provided on the external device side such as a mixer or an amplifier unit, via a hot signal line and
a cold signal line which are output signal lines of an audio signal of a microphone. Supply DC
current to the microphone. The phantom power supply is connected to each of the hot signal line
and the cold signal line via the feed resistor. Therefore, the phantom power supply can supply DC
current equally distributed to the hot side signal line and the cold side signal line.
[0004]
The connection and disconnection between the microphone and the external device is usually
performed when the phantom power supply for feeding the microphone is off. However, the
connection and disconnection between the microphone and the external device are performed
when the phantom power is on due to contact with the body of the microphone and the user of
the microphone or lack of confirmation of the phantom power on / off state, etc. There is. In this
case, if the timing of connection or disconnection between the terminals connecting the
microphone and the phantom power is different between the hot side terminal and the cold side
terminal, a pulsed current with shock noise from the phantom power (hereinafter referred to as
“pulsed It is called current. Is output.
[0005]
The pulse current flows in the output signal line of the audio signal of the microphone, and is
input together with the audio signal to an output device such as a speaker via an external device.
In this case, a loud noise, so-called "pop noise" is generated from the output device. The output
device breaks down depending on the level of the popping noise.
[0006]
A phantom power supply provided with a detection circuit for detecting a pulse current and a
limiting circuit for limiting the output of the microphone as a method of reducing the generation
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of popping noise when connecting or disconnecting such a microphone and a phantom power
supply A circuit has been proposed (eg, Patent Document 1).
[0007]
The detection circuit comprises a transformer, a capacitor, a resistor, and a first transistor circuit.
The transformer is connected between the hot side signal line and the cold side signal line of the
microphone, and is pulsed when either the hot side terminal or the cold side terminal of the
microphone and the phantom power source is cut or connected first. Current flow. The detection
circuit turns on the first transistor circuit when the pulse current flows in the transformer.
[0008]
The limiting circuit comprises a second transistor circuit, a light emitting diode, a photo MOS
relay, and a resistor. When the first transistor circuit of the detection circuit is turned on, the
limiting circuit turns off the light emitting diode to release the contact of the photo MOS relay
provided on the hot signal line and the cold signal line. When the contact point of the photo MOS
relay is released, the audio signal from the microphone and the pulse current are attenuated by
the resistors respectively bypassed to the hot signal line and the cold signal line. That is, the
input to the output device side of the audio signal and the pulse current is limited. As a result, no
popping noise is generated from the output device.
[0009]
Patent No. 5545859 specification
[0010]
However, since the phantom power supply circuit disclosed in Patent Document 1 requires a
detection circuit that detects a pulse current, the circuit configuration becomes complicated.
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In addition, when the phantom power is connected to the microphone, that is, when power
supply to the microphone is started, a plurality of pop noises are generated according to stepwise
rise of FET (field effect transistor) or transistor circuit of the microphone. It may occur.
[0011]
The present invention has been made to solve the problems of the prior art as described above,
and it is an object of the present invention to reduce generation of pop noise by a simple circuit
configuration.
[0012]
A phantom power supply circuit, which is a phantom power supply for supplying power to a
condenser microphone, an input side terminal to which the condenser microphone is connected,
and an output side terminal to which an output device to which an output signal from the
condenser microphone is input is connected; Connected to the signal line in series with the signal
line connecting the input and output terminals, the phantom power switch connected between
the phantom power and the signal line, and the light emitting element driven when the switch is
activated And a photo-resistor whose resistance value changes according to the light-emitting
state of the light-emitting element.
[0013]
According to the present invention, the generation of a pop noise can be reduced by a simple
circuit configuration.
[0014]
FIG. 1 is a circuit diagram showing an embodiment of a phantom power supply circuit according
to the present invention.
It is a circuit diagram showing another embodiment of the phantom power circuit concerning the
present invention.
FIG. 7 is a circuit diagram showing still another embodiment of the phantom power supply circuit
according to the present invention.
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[0015]
Hereinafter, embodiments of a phantom power supply circuit according to the present invention
will be described with reference to the drawings.
[0016]
Phantom Power Supply Circuit (1) First, an embodiment of a phantom power supply circuit
according to the present invention will be described.
[0017]
Configuration of Phantom Power Supply Circuit (1) FIG. 1 is a circuit diagram showing an
embodiment of a phantom power supply circuit according to the present invention.
The phantom power supply circuit 10 is referred to as a condenser microphone (hereinafter
referred to as "microphone") not shown.
Supply power).
The phantom power circuit 10 has an input terminal 1 to which a microphone is connected, and
an output signal from the microphone (hereinafter referred to as an "audio signal"). ), A signal
line 3 connecting between the input side terminal 1 and the output side terminal 2, a power
supply unit 4, and an attenuation circuit 5. Become.
[0018]
A microphone is connected to the input terminal 1. The input side terminal 1 includes a first
input side terminal 1a, a second input side terminal 1b, and a third input side terminal 1c. The
first input terminal 1a is connected to the ground (ground) terminal of the microphone. The
second input side terminal 1b is connected to the hot side terminal which is the output terminal
of the microphone. The third input terminal 1c is connected to a cold terminal, which is an
output terminal of the microphone.
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[0019]
An external device is connected to the output side terminal 2. The output side terminal 2 includes
a first output side terminal 2a, a second output side terminal 2b, and a third output side terminal
2c. The first output terminal 2a is connected to the first input terminal 1a and is connected to the
ground terminal of the microphone. The second output terminal 2b is connected to the second
input terminal 1b to lead an audio signal from the second input terminal 1b to an external device.
The third output terminal 2c is connected to the third input terminal 1c to lead an audio signal
from the third input terminal 1c to an external device.
[0020]
The signal line 3 connects the input side terminal 1 and the connection side terminal 3. The
signal line 3 includes a first signal line 3a, a second signal line 3b, and a third signal line 3c. The
first signal line 3a is a reference potential line connecting the first input terminal 1a and the first
output terminal 2a. The second signal line 3 b is a hot side signal line which connects the second
input side terminal 1 b and the second output side terminal 2 b. The third signal line 3c is a cold
signal line connecting the third input terminal 1c and the third output terminal 2c. The second
signal line 3b and the third signal line 3c are output signal lines through which audio signals
flow.
[0021]
The power supply unit 4 supplies power to the microphone via the second signal line 3 b and the
third signal line 3 c. The power supply unit 4 includes a phantom power supply PW and a switch
SW of the phantom power supply PW.
[0022]
The phantom power supply PW is a DC power supply that supplies power to the microphone.
The switch SW switches on and off of the phantom power supply PW. The phantom power
supply PW is connected in series between the first signal line 3a and the switch SW. The switch
SW is connected in series with each of the second signal line 3b and the third signal line 3c.
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[0023]
A supply resistor is connected between the switch SW and the output signal line. The supply
resistor comprises a first resistor R1 and a second resistor R2. The first resistor R1 is connected
in series between the switch SW and the second signal line 3b. The second resistor R2 is
connected in series between the switch SW and the third signal line 3c. The first resistor R1 and
the second resistor R2 have the same resistance value. The supply current from the phantom
power supply PW is equally divided into the second signal line 3b and the third signal line 3c via
the first resistor R1 and the second resistor R2.
[0024]
The attenuation circuit 5 attenuates the audio signal flowing to the output signal line. The
attenuation circuit 5 includes a constant current diode CR10, a light emitting element D10, and a
photo resistor PR10. The attenuation circuit 5 is connected to the first signal line 3a, the second
signal line 3b, and the third signal line 3c.
[0025]
The constant current diode CR10 makes the current input from the phantom power supply PW a
constant current of a constant current value. The constant current is input to the light emitting
element D10. The constant current diode CR10 includes a first constant current diode CR11 and
a second constant current diode CR12.
[0026]
The first constant current diode CR11 is connected between the first signal line 3a and the
second signal line 3b. Specifically, the input terminal of the first constant current diode CR11 is a
connection point between the second input terminal 1b of the second signal line 3b, the first
resistor R1 and the second signal line 3b (hereinafter referred to 1 connection point. ) Connected
between P1 and
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[0027]
The second constant current diode CR12 is connected between the first signal line 3a and the
third signal line 3c. Specifically, the input terminal of the second constant current diode CR12 is
a connection point between the third input terminal 1c of the third signal line 3c, the second
resistor R2 and the third signal line 3c (hereinafter referred to 2 connection points. ) Connected
between P2 and
[0028]
The terminal on the first signal line 3a side, which is the output terminal of the first constant
current diode CR11, and the terminal on the first signal line 3a, which is the output terminal of
the second constant current diode CR12, are connected to each other It is connected to the signal
line 3a.
[0029]
The constant current diode CR10 normally has a sufficiently high AC impedance.
Therefore, even if connected to the output signal line of the microphone, the constant current
diode CR10 does not become a load of the microphone.
[0030]
The light emitting element D10 and the photo resistor PR10 are disposed opposite to each other.
The light emitting element D10 and the photo resistor PR10 constitute a photo coupler PC10.
That is, the light emitting element D10 emits light toward the photo resister PR10.
[0031]
The light emitting element D10 is driven (emits light) by the constant current from the constant
current diode CR10 when the switch SW is operated, that is, when the switch SW is in the on
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state. The light emitting element D10 is, for example, a light emitting diode. The light emitting
element D10 includes a first light emitting element D11 and a second light emitting element D12.
[0032]
The first light emitting element D11 is connected in series between the terminal on the first
signal line 3a side of the first constant current diode CR11 and the first signal line 3a. The
second light emitting element D12 is connected in series between the first signal line 3a and the
terminal on the first signal line 3a side of the second constant current diode CR12.
[0033]
The light emission state of the light emitting element D10 is a state in which light is not emitted
(hereinafter referred to as "first light emission state"). And the light emitting state (hereinafter
referred to as "second light emitting state"). And. The brightness of the second light emission
state is constant according to the constant current from the constant current diode CR10.
[0034]
Photoresistor PR10 changes its resistance value according to the light emitting state of light
emitting element D10. The photo resister PR10 is, for example, a light receiving element of CdS
(cadmium sulfide). The photo resistor PR10 includes a first photo resistor PR11 and a second
photo resistor PR12.
[0035]
The resistance value of the photo resistor PR10 is referred to as the resistance value when the
light emitting element D10 is in the first light emitting state (hereinafter referred to as "first
resistance value"). And the resistance value when the light emitting element D10 is in the second
light emitting state (hereinafter referred to as "second resistance value"). It changes continuously
between) and. The first resistance value is higher than the second resistance value. Further, the
resistance value of the photo resistor PR10 changes to the second resistance value after the light
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emission state of the light emitting element D10 is switched from the first light emission state to
the second light emission state. That is, there is a predetermined time lag until the resistance
value of the photo resistor PR10 changes from the first resistance value to the second resistance
value.
[0036]
The resistance value of the first photo resistor PR11 changes in accordance with the light
emitting state of the first light emitting element D11. The first photo register PR11 is a
connection point between the second input terminal 1b and the first constant current diode
CR11 and the second signal line 3b in the second signal line 3b (hereinafter referred to as "third
connection point"). It is connected in series between) and P3. That is, the second input terminal
1b is connected to the switch SW via the first photo resistor PR11.
[0037]
The resistance value of the second photo resister PR12 changes in accordance with the light
emitting state of the second light emitting element D12. The second photo resister PR12 is a
connection point between the third input terminal 1c of the third signal line 3c, the second
constant current diode CR12 and the third signal line 3c (hereinafter referred to as "fourth
connection point"). It is arrange | positioned in series between) and P4. That is, the third input
terminal 1c is connected to the switch SW via the second photo resistor PR12.
[0038]
As described above, by connecting the photo resister PR10 in series to the signal line 3, the audio
signal flowing through the output signal line passes through the photo resister PR10. Here, when
the resistance value of the photo resistor PR10 is the first resistance value, the audio signal
flowing through the output signal line is blocked by the photo resistor PR10. Further, when the
resistance value of the photo resistor PR10 is a resistance value between the first resistance
value and the second resistance value, the audio signal flowing through the output signal line is
attenuated by the photo resistor PR10 according to the resistance value. Furthermore, when the
resistance value of the photo resistor PR10 is the second resistance value, the audio signal
flowing through the output signal line passes through the photo resistor PR10 without being
attenuated.
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[0039]
The first photo resistor PR11 and the first light emitting element D11 constitute a first photo
coupler CP11. The second photoresistor PR12 and the second light emitting element D12
constitute a second photocoupler CP12.
[0040]
A first capacitor C1 is connected between the first connection point P1 and the second output
terminal 2b of the second signal line 3b. A second capacitor C2 is connected between the second
connection point P2 and the third output terminal 2c in the third signal line 3c. The first
capacitor C1 and the second capacitor C2 are blocking capacitors that block the direct current of
the phantom power supply PW from being input to the output device side. The terminal on the
second output terminal 2b side of the first capacitor C1 is connected to the first signal line 3a via
a third resistor R3 that determines the potential at both ends of the first capacitor C1. The
terminal on the third output terminal 2c side of the second capacitor C2 is connected to the first
signal line 3a via a fourth resistor R4 that determines the potential at both ends of the second
capacitor C2.
[0041]
Operation of Phantom Power Supply Circuit (1) Next, the operation of the phantom power supply
circuit 10 will be described.
[0042]
First, the operation of the phantom power supply circuit 10 when the switch SW is off will be
described.
When the switch SW is in the off state, the current from the phantom power supply PW is not
input to the constant current diode CR10. Therefore, the light emitting element D10 is in the first
light emitting state. That is, the light emitting element D10 is not in a light emitting state. In this
case, the resistance value of the photo resistor PR10 is the first resistance value.
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[0043]
Next, the operation of the phantom power supply circuit 10 when the switch SW is switched
from the off state to the on state will be described.
[0044]
When the switch SW is switched from the off state to the on state, the current from the phantom
power supply PW flows to the output signal line through the supply resistor.
At this time, the switch SW causes so-called chattering for a very short time. During this time, a
pulsed current is generated in the phantom power supply PW. The pulsed current flows to the
output signal line through the supply resistor.
[0045]
The current from the phantom power supply PW flowing through the output signal line is input
to the constant current diode CR10. The current input to the constant current diode CR10
becomes a constant current by the constant current diode CR10. The constant current is input to
the light emitting element D10 from the terminal (output terminal) on the first signal line 3a side
of the constant current diode CR10. The light emitting element D10 emits light by the input of a
constant current, and switches from the first light emitting state to the second light emitting
state. The light of the light emitting element D10 is emitted to the photo resister PR10.
[0046]
Here, as described above, when the switch SW is in the OFF state, the resistance value of the
photo resistor PR10 is a first resistance value that cuts off the audio signal flowing through the
output signal line. In addition, when the switch SW is switched to the on state, the resistance
value of the photo resistor PR10 is the first resistance value until the light emitting element D10
is in the second light emitting state. When the light emitting element D10 switches from the first
light emitting state to the second light emitting state, the resistance value of the photo resistor
PR10 changes to the second resistance value through the time lag described above.
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[0047]
While the resistance value of the photo resistor PR10 changes from the first resistance value to
the second resistance value, the audio signal flowing through the output signal line is blocked or
attenuated by the photo resistor PR10. That is, the audio signal flowing through the second
signal line 3b is blocked or attenuated by the first photo resister PR11. The audio signal flowing
through the third signal line 3c is blocked or attenuated by the second photo resistor PR12.
Therefore, even if the pulsating current is input to the output device together with the audio
signal, the generation of the popping noise is reduced.
[0048]
The pulsed current flowing through the output signal line flows into the photo resistor PR10.
Here, the pulsed current flowing through the output signal line is blocked or attenuated by the
photo resistor PR10 until the resistance value of the photo resistor PR10 changes from the first
resistance value to the second resistance value. That is, the pulsed current flowing in the second
signal line 3b toward the second input terminal 1b is blocked or attenuated by the first photo
resistor PR11. In addition, the pulsed current flowing in the third signal line 3c toward the third
input terminal 1c is blocked or attenuated by the second photo resistor PR12.
[0049]
In the normal state where the switch SW is on and no pulse current is generated, the audio signal
passes through the photo resistor PR10 without being attenuated or blocked, and is input to the
external device.
[0050]
According to the embodiment described above, when the switch SW is turned on, the audio signal
flowing through the output signal line is blocked by the photo resistor PR10 until the resistance
value of the photo resistor PR10 is sufficiently reduced. Or is attenuated.
The blocking and attenuation of the audio signal is realized by the attenuation circuit 5 having a
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simple configuration of the constant current diode CR10, the light emitting element D10, and the
photo resistor PR10. That is, the phantom power supply circuit 10 can reduce generation of a
popping noise when power supply to the microphone is started by a simple circuit configuration.
[0051]
In addition, the pulse current flowing in the second signal line 3b toward the second input
terminal 1b is blocked or attenuated by the first photo resistor PR11. The pulsed current flowing
toward the third input terminal 1c is blocked or attenuated by the second photo resistor PR12.
That is, the phantom power supply circuit 10 can reduce the influence of the pulse current on
the microphone.
[0052]
Furthermore, there is a time lag in the time until the resistance value of the photoresistor PR10
changes from the first resistance value to the second resistance value. Therefore, when the
switch SW is switched from the off state to the on state and power supply to the microphone is
started, the audio signal flowing through the output signal line is blocked or attenuated by the
photo resistor PR10 during the time lag. That is, the phantom power supply circuit 10 can
reduce generation of a popping noise when power supply to the microphone is started by a
simple circuit configuration.
[0053]
Phantom Power Supply Circuit (2) Next, another embodiment of the phantom power supply
circuit according to the present invention will be referred to as the above-described embodiment
(hereinafter referred to as “first embodiment”). It explains focusing on the part which differs
from). The phantom power supply circuit according to the present embodiment differs from the
first embodiment in the connection position of the attenuation circuit.
[0054]
Configuration of Phantom Power Supply Circuit (2) FIG. 2 is a circuit diagram of another
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embodiment of the phantom power supply circuit according to the present invention. The
phantom power supply circuit 20 includes an attenuation circuit 5A.
[0055]
The attenuation circuit 5A attenuates the audio signal flowing to the output signal line. The
attenuation circuit 5A includes a constant current diode CR20, a light emitting element D20, and
a photo resistor PR20. The attenuation circuit 5A is connected to the first signal line 3a, the
second signal line 3b, and the third signal line 3c.
[0056]
The constant current diode CR20 makes the current input from the phantom power supply PW a
constant current. The constant current diode CR20 includes a first constant current diode CR21
and a second constant current diode CR22.
[0057]
The first constant current diode CR21 is connected between the first signal line 3a and the
second signal line 3b. Specifically, the input terminal of the first constant current diode CR21 is
connected between the first connection point P1 and the second output side terminal 2b of the
second signal line 3b. The second constant current diode CR22 is connected between the first
signal line 3a and the third signal line 3c. Specifically, the input terminal of the second constant
current diode CR22 is connected between the third output terminal 2c and the connection point
between the second resistor R2 and the third signal line 3c in the third signal line 3c. Connected
to The output terminal of the first constant current diode CR21 and the output terminal of the
second constant current diode CR22 are connected to each other and connected to the first
signal line 3a.
[0058]
The light emitting element D20 is driven (emits light) by a constant current flowing when the
switch SW is operated. The light emitting element D20 includes a first light emitting element D21
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and a second light emitting element D22. The first light emitting element D21 and the second
light emitting element D22 are connected in series between the terminal on the first signal line
3a side of the constant current diode CR20 and the first signal line 3a.
[0059]
The light emitting state of the light emitting element D20 is the same as the light emitting state
of the light emitting element 10 of the first embodiment.
[0060]
Photoresistor PR20 changes its resistance value according to the light emitting state of light
emitting element D20.
The photo resistor PR20 includes a first photo resistor PR21 and a second photo resistor PR22.
The resistance value of the photo resistor PR20 changes in the same manner as the resistance
value of the photo resistor PR10 of the first embodiment. That is, there is a predetermined time
lag until the resistance value of the photo resistor PR20 changes from the first resistance value
to the second resistance value.
[0061]
The first photo resistor PR21 is connected in series between the third connection point P3 and
the second output terminal 2b of the second signal line 3b. That is, the second output terminal
2b is connected to the switch SW via the first photo resistor PR21.
[0062]
The second photo register PR22 is connected in series between the fourth connection point P4
and the third output terminal 2c of the third signal line 3c. That is, the third output side terminal
2c is connected to the switch SW via the second photo resistor PR22.
[0063]
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The first photo resister PR21 and the first light emitting element D21 constitute a first photo
coupler CP21. The second photoresistor PR22 and the second light emitting element D22
constitute a second photocoupler CP22.
[0064]
Operation of Phantom Power Supply Circuit (2) Next, the operation of the phantom power supply
circuit 20 will be described.
[0065]
First, the operation of the phantom power circuit 20 when the switch SW is in the off state is the
same as the operation of the phantom power circuit 10 of the first embodiment.
[0066]
Next, the operation of the phantom power circuit 20 when the switch SW is switched from the off
state to the on state will be described focusing on differences from the operation of the phantom
power circuit 10 of the first embodiment.
[0067]
The audio signal flowing to the output signal line is blocked or attenuated by the photo resistor
PR20 until the resistance value of the photo resistor PR20 changes from the first resistance value
to the second resistance value.
That is, the audio signal flowing through the second signal line 3b is blocked or attenuated by the
first photo resister PR21.
Further, the audio signal flowing to the third signal line 3c is blocked or attenuated by the second
photo resister PR22.
Therefore, even if the pulsating current is input to the output device together with the audio
signal, the generation of the popping noise is reduced.
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[0068]
The pulsed current flowing through the output signal line is blocked or attenuated by the photo
resistor PR20 until the resistance value of the photo resistor PR20 changes from the first
resistance value to the second resistance value. That is, the pulsed current flowing through the
second signal line 3b toward the second output terminal 2b is blocked or attenuated by the first
photo resistor PR21. Further, the pulsed current flowing in the third signal line 3c toward the
third output terminal 2c is blocked or attenuated by the second photo resistor PR22.
[0069]
According to the embodiment described above, the audio signal flowing through the output
signal line is blocked or attenuated by the photo resistor PR20 until the resistance value of the
photo resistor PR20 is sufficiently reduced. That is, the phantom power supply circuit 20 can
reduce generation of a popping noise when power supply to the microphone is started with a
simple circuit configuration.
[0070]
Further, the pulsed current flowing toward the second output terminal 2b of the second signal
line 3b is blocked or attenuated by the first photo resistor PR21. Further, the pulsed current
flowing in the third signal line 3c toward the third output terminal 2c is blocked or attenuated by
the second photo resistor PR22. That is, the phantom power supply circuit 20 can reduce the
influence of the pulsed current on the output device.
[0071]
Phantom Power Supply Circuit (3) Next, with regard to still another embodiment of the phantom
power supply circuit according to the present invention, the first embodiment and another
embodiment described above (hereinafter, “second embodiment”) It is said. And different parts
will be mainly described. The phantom power supply circuit according to the present
embodiment differs from the first and second embodiments in the attenuation circuit.
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[0072]
Configuration of Phantom Power Supply Circuit (3) FIG. 3 is a circuit diagram of still another
embodiment of the phantom power supply circuit according to the present invention. The
phantom power supply circuit comprises an attenuation circuit 5B.
[0073]
The attenuation circuit 5B attenuates the audio signal flowing to the output signal line. The
attenuation circuit 5B includes a constant current diode CR30, a light emitting element D30, and
a photo resistor PR30. The attenuation circuit 5B is connected to the first signal line 3a, the
second signal line 3b, and the third signal line 3c.
[0074]
The constant current diode CR30 makes the current input from the phantom power supply PW a
constant current. The constant current diode CR30 includes a first constant current diode CR31
and a second constant current diode CR32.
[0075]
The first constant current diode CR31 is connected between the first signal line 3a and the
second signal line 3b, as in the second embodiment. The second constant current diode CR32 is
connected between the first signal line 3a and the third signal line 3c, as in the second
embodiment.
[0076]
The light emitting element D30 is driven (emits light) by a constant current flowing when the
switch SW is operated. The light emitting element D30 includes a first light emitting element
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D31, a second light emitting element D32, a third light emitting element D33, and a fourth light
emitting element D34. The first light emitting element D31, the second light emitting element
D32, the third light emitting element D33, and the fourth light emitting element D34 are
disposed between the first signal line 3a of the constant current diode CR30 and the first signal
line 3a. Connected in series.
[0077]
The light emitting state of the light emitting element D30 is the same as the light emitting state
of the light emitting element D10 of the first embodiment.
[0078]
Photoresistor PR30 changes its resistance value in accordance with the light emitting state of
light emitting element D30.
The photo register PR30 includes a first photo register PR31, a second photo register PR32, a
third photo register PR33, and a fourth photo register PR34. The resistance value of the photo
resistor PR30 changes in the same manner as the resistance value of the photo resistor PR10 of
the first embodiment. That is, there is a predetermined time lag until the resistance value of the
photo resistor PR30 changes from the first resistance value to the second resistance value.
[0079]
The first photo resistor PR31 is connected in series between the third connection point P3 and
the second output terminal 2b of the second signal line 3b. That is, the second output terminal
2b is connected to the switch SW via the first photo resistor PR31.
[0080]
The second photo register PR32 is connected in series between the fourth connection point P4
and the third output terminal 2c of the third signal line 3c. That is, the third output terminal 2c is
connected to the switch SW via the second photo resistor PR32.
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[0081]
The third photoresistor PR33 is connected in series between the first connection point P1 and
the second input terminal 1b of the second signal line 3b. That is, the second input terminal 1b is
connected to the switch SW via the third photo resistor PR33.
[0082]
The fourth photo resister PR34 is connected in series between the second connection point P2
and the third input side terminal 1 c of the third signal line 3 c. That is, the third input terminal
1c is connected to the switch SW via the fourth photo resister PR34.
[0083]
The first photo resistor PR31 and the first light emitting element D31 form a first photo coupler
CP31. The second photoresistor PR32 and the second light emitting element D32 constitute a
second photocoupler CP32. The third photoresistor PR33 and the third light emitting element
D33 constitute a third photocoupler CP33. The fourth photo resistor PR34 and the fourth light
emitting element D34 constitute a fourth photo coupler CP34.
[0084]
As described above, the first photo resister PR31 and the third photo resister PR33 are
connected in series to the second signal line 3b. Therefore, the series resistance of the second
signal line 3b has a resistance value approximately twice that of the second signal line 3b of the
embodiment described above. In addition, the second photo resister PR32 and the fourth photo
resister PR34 are connected in series to the third signal line 3c. Therefore, the series resistance
of the third signal line 3c has a resistance value about twice that of the series resistance of the
third signal line 3c of the embodiment described above.
[0085]
Operation of Phantom Power Supply Circuit (3) Next, the operation of the phantom power supply
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circuit 30 will be described.
[0086]
First, the operation of the phantom power circuit 30 when the switch SW is in the off state is the
same as the operation of the phantom power circuit 10 of the first embodiment.
[0087]
Next, with regard to the operation of the phantom power circuit 30 when the switch SW is
switched from the off state to the on state, the operation of the phantom power circuit 10 of the
first embodiment and the operation of the phantom power circuit 20 of the second embodiment ,
I will focus on different points.
[0088]
The audio signal flowing to the output signal line is blocked or attenuated by the photo resistor
PR30 until the resistance value of the photo resistor PR30 changes to the second resistance
value.
That is, the audio signal flowing through the second signal line 3b is blocked or attenuated by the
first photo resister PR31 and the third photo resister PR33.
Further, the audio signal flowing through the third signal line 3c is blocked or attenuated by the
second photo resister PR32 and the fourth photo resister PR34.
Therefore, even if the pulsating current is input to the output device together with the audio
signal, the generation of the popping noise is reduced.
[0089]
The pulsed current flowing through the output signal line is blocked or attenuated by the photo
resistor PR30 until the resistance value of the photo resistor PR30 changes from the first
resistance value to the second resistance value. That is, the pulsed current flowing toward the
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second output terminal 2b of the second signal line 3b is blocked or attenuated by the first photo
resistor PR31. In addition, the pulsed current flowing in the third signal line 3c toward the third
output terminal 2c is blocked or attenuated by the second photo resistor PR32. Further, the
pulsed current flowing in the second signal line 3b toward the second input terminal 1b is
blocked or attenuated by the third photo resistor PR33. In addition, the pulse current flowing in
the third signal line 3c toward the third input terminal 1c is blocked or attenuated by the fourth
photo resistor PR34.
[0090]
According to the embodiment described above, the audio signal flowing through the output
signal line is blocked or attenuated by the photo resistor PR30 until the resistance value of the
photo resistor PR30 is sufficiently reduced. Here, in the present embodiment, two photo resisters
are connected in series to the second signal line 3 b and the third signal line 3 c, respectively.
Therefore, the degree of attenuation of the audio signal in the present embodiment is larger than
the degree of attenuation in the first embodiment or the second embodiment. That is, the
phantom power circuit 30 can reduce the generation of the pop noise more than the phantom
power circuit 10 or the phantom power circuit 20.
[0091]
In addition, the pulsed current flowing in the second signal line 3b toward the second output
terminal 2b is blocked or attenuated by the first photo resistor PR31. In addition, the pulsed
current flowing in the third signal line 3c toward the third output terminal 2c is blocked or
attenuated by the second photo resistor PR32. Furthermore, the pulsed current flowing toward
the second input terminal 1b on the second signal line 3b is blocked or attenuated by the third
photo resistor PR33. Furthermore, the pulsed current flowing through the third signal line 3c
toward the third input terminal 1c is blocked or attenuated by the fourth photo resistor PR34.
That is, the phantom power source 30 blocks or attenuates both the pulse current flowing the
output signal line toward the input side terminal 1 and the pulse current flowing the output
signal line toward the output side terminal 2 Can. That is, the phantom power supply circuit 30
can reduce the influence of the pulse current on the microphone and the output device.
[0092]
1 input side terminal 1a first input side terminal 1b second input side terminal 1c third input
side terminal 2 output side terminal 2a first output side terminal 2b second output side terminal
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2c third output side terminal 3 signal line 3a first Signal line 3b Second signal line 3c Third
signal line 4 Power supply unit 5 Attenuation circuit 5A Attenuation circuit 5B Attenuation
circuit 10 Phantom power circuit 20 Phantom power circuit 30 Phantom power circuit PW
Phantom power circuit SW Switch CR Constant current diode PC Photo coupler D Light emission
Element PR Photoresistor
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