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DESCRIPTION JP2013236125

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DESCRIPTION JP2013236125
Abstract: To provide a capacitor microphone provided with a switching circuit between external
power supply and built-in power supply. SOLUTION: A built-in power supply circuit from a builtin power supply to a microphone circuit, detection means for detecting presence / absence of
external power supply from the external power supply to the microphone circuit, and built-in
power supply when the detection means detects external power supply Switch means for
interrupting the power supply from the sensor, the detection means being constituted by a light
emitting diode provided in the photo-MOS relay, connected in series between the external power
supply and the microphone circuit, the switch means being the photo-MOS relay Are connected
in series between the built-in power supply and the microphone circuit, and the MOSFET is a
condenser microphone that switches the connection between the built-in power supply circuit
and the microphone circuit by blinking the light emitting diode. [Selected figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone, and more particularly to a switching
circuit between external power supply and built-in power supply.
[0002]
The condenser microphone requires an impedance converter using an FET (field effect transistor,
hereinafter the same) or the like because the impedance of the condenser microphone unit which
is an electroacoustic transducer is high.
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1
A power supply is required to operate this impedance converter. Several types of power supply
are known. For example, a built-in battery type in which a power supply is mounted on a
condenser microphone main body, and an external supply type in which power is supplied from
an external device (for example, a recording device etc.) on which the condenser microphone is
mounted. Among them, the externally supplied power supply system is called "plug-in power
system".
[0003]
There is also known a condenser microphone which uses an externally supplied type and a builtin battery type in combination. In such a condenser microphone, when the power supply from
the external power supply and the power supply from the built-in battery are simultaneously
performed, current may flow from the external power supply to the built-in battery. It is known
to cause. In order to prevent this, it is known that a circuit for supplying power from a built-in
battery to a capacitor microphone is provided with a diode switch for blocking the flow of
current from an external power supply to the built-in battery (see, for example, Patent Document
1). . )
[0004]
According to the diode switch of Patent Document 1, the diode connected in series to the built-in
battery can block the flow of current from the external power supply to the built-in battery. This
protects the internal battery from the external power supply. However, even if current flows in
the forward direction, a constant voltage (forward voltage) is applied between the terminals of
the diode. Therefore, when power is supplied from the built-in battery to the condenser
microphone, the supply voltage is lowered by the forward voltage of the diode connected in
series to the built-in battery. When this reduced voltage becomes the operating voltage of the
condenser microphone, the maximum output voltage is reduced. In order to reduce such a defect,
it is desirable that the diode is as low in forward voltage as possible, and for that purpose, a
Schottky diode may be used. However, the Schottky diode also has a forward voltage of 0.4V.
[0005]
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2
For example, assuming that the voltage of the built-in battery is 1.5V, the power supply voltage
supplied to the condenser microphone is lowered to 1.1V even if a Schottky diode is used for the
above diode switch. That is, it drops about 1.5% from 1.5V. The maximum output level
corresponds to a drop of about 2.7 db. When the maximum sound pressure level decreases, the
output signal may be distorted when a large sound pressure is input to the condenser
microphone.
[0006]
Japanese Patent Application Laid-Open No. 10-155234
[0007]
As described above, in the condenser microphone that can use both the plug-in power system
and the built-in battery type, the built-in battery is protected when using an external power
supply, and unnecessary power supply is used when using the built-in battery. It is desirable that
no voltage drop occurs.
[0008]
The present invention has been made to solve the above problems, and in a capacitor
microphone which uses an external power supply and an internal power supply in a switched
manner, the microphone circuit is supplied with power from the internal power supply. An object
of the present invention is to provide a condenser microphone which can supply a voltage close
to the voltage value of the built-in power supply to the microphone circuit with a slight drop in
the power supply voltage and can reduce the reduction in the output level of the microphone.
Another object of the present invention is to provide a condenser microphone which can
automatically shut off the power supply circuit from the built-in power supply when the external
power supply is supplied, thereby preventing the external power from flowing into the built-in
power supply. With the goal.
[0009]
The present invention relates to a condenser microphone which uses a built-in power supply and
an external power supply supplied from an external device by switching between the built-in
power supply and the microphone circuit, and an external power supply to the microphone
circuit. A light emitting diode comprising: detection means for detecting presence / absence of
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power supply; and switch means for interrupting power supply from the built-in power supply
when the detection means detects external power supply; The switch means is connected in
series between the external power supply and the microphone circuit, and the switch means is
comprised of the MOSFET provided in the photo-MOS relay, and is connected in series between
the built-in power supply and the microphone circuit. The MOSFET is connected to the built-in
power supply circuit and the microphone circuit by flashing the light emitting diode. And it
characterized mainly in that switching between.
[0010]
According to the present invention, since the supply path of the built-in power is shut off when
the external power is supplied, the built-in power can be protected by preventing the flow of
current from the external power to the built-in power.
Make sure that the power supply voltage supplied from the built-in power supply to the
microphone circuit is close to the built-in power supply voltage, because the switch that shuts off
the built-in power supply does not have a voltage drop or has a small voltage drop even if there
is a voltage drop. The maximum allowable input sound pressure level can be increased even
when using the built-in battery.
[0011]
It is a circuit diagram showing an embodiment in a state where an external power supply is
attached to a condenser microphone according to the present invention.
It is a circuit diagram showing an embodiment in the state where an external power supply is
removed from the above-mentioned condenser microphone.
[0012]
Hereinafter, an embodiment of a condenser microphone according to the present invention will
be described with reference to the drawings. FIG. 1 is a circuit diagram showing an example of a
state in which the condenser microphone 1 is attached to the external device 2. FIG. 2 is a circuit
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diagram showing an example of a state in which the condenser microphone 1 is removed from
the external device 2. In FIG. 1 and FIG. 2, the condenser microphone unit indicated by reference
numeral 10 is composed of an electroacoustic converter and an impedance converter, the source
terminal of the FET constituting the impedance converter is grounded, and the drain terminal is
an operating power supply. It is configured to be supplied.
[0013]
The operation power is supplied from either the built-in battery 11 or the external power supply
21 provided in the external device 2. When the condenser microphone 1 is attached to the
external device 2, operating power is supplied from the external power supply 21 through the
load resistor 22. At this time, power supply to the condenser microphone unit 10 is performed
via a light emitting diode (LED) 131 provided in the photo-MOS relay 13.
[0014]
The power supply from the external power supply 21 to the condenser microphone 1 is supplied
via the signal line of the condenser microphone unit 10. That is, in the condenser microphone 1,
the signal line and the power supply line are formed by a common line.
[0015]
The photo-MOS relay 13 includes an LED 131 and a switch 132 that opens and closes in
accordance with the light emission state of the LED 131. When the LED 131 is on, the switch
132 opens the contacts, and when the LED 131 is off, the contacts are closed.
[0016]
As shown in FIG. 1, when the condenser microphone 1 is attached to the external device 2, a
current supplied from the external power supply 21 flows to the LED 131 of the photo-MOS
relay 13 via the load resistor 22. As a result, the LED 131 is turned on, and the condenser
microphone unit 10 is supplied with operating power. When the LED 131 lights up, the contact
of the switch 132 is opened. Then, the internal battery 11 is disconnected from the power supply
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circuit to the condenser microphone unit 10. That is, when the power is supplied from the
external power supply 21, the switch 132 is opened and the current from the external power
supply 22 does not flow into the internal battery 11. As described above, it is possible to prevent
heat generation and liquid leakage of the built-in battery 11 due to the current from the external
power supply 21 flowing into the built-in battery 11.
[0017]
Also, by opening the switch 132, the load resistor 12 does not become a load of the condenser
microphone unit 10. When the load resistor 12 and the load resistor 22 are simultaneously
connected to the capacitor microphone 10, distortion occurs in the output signal, but in the
present embodiment, such a problem does not occur.
[0018]
When the condenser microphone 1 is attached to the external device 2 and the operation power
is supplied from the external power supply 21, the output signal from the condenser microphone
unit 10 is output through the bypass capacitor 14 that cuts the DC component.
[0019]
On the other hand, as shown in FIG. 2, when there is no plug-in power supply from the external
device which is the signal output destination of the condenser microphone 1, no current flows in
the LED 131 of the photo-MOS relay 13 and the light goes off. .
Then, the switch 132 is in the state of closing the contact. When the contact of the switch 132 is
closed, operating power is supplied from the built-in battery 11 to the condenser microphone
unit 10 through the load resistor 12. At this time, since the load resistor 22 used for power
supply from the external power supply 21 is not connected to the signal line of the microphone
unit 10, the load of the capacitor microphone unit 10 is too large, which causes distortion of the
output signal. There is no.
[0020]
Further, since the power supplied from the internal battery 11 does not cause an unnecessary
voltage drop until it is supplied to the condenser microphone unit 10, even if the microphone
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unit 10 is operated by the internal battery 11, The maximum allowable input sound pressure
level of the condenser microphone 1 can be increased.
[0021]
Even when the external device 2 is removed and the plug-in power operation power is not
supplied from the external power supply 21, the output signal from the condenser microphone
unit 10 is through the bypass condenser 14 that cuts the DC component. It is output.
[0022]
DESCRIPTION OF SYMBOLS 1 capacitor microphone 10 capacitor microphone unit 11 built-in
battery 12 load resistance 13 photo-MOS relay 14 bypass capacitor 21 external power supply 22
load resistance
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