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JP2012023560

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DESCRIPTION JP2012023560
An object of the present invention is to prevent an electric shock even when a human body
touches an electrode of an electrostatic speaker. SOLUTION: An addition signal of sine waves
outputted from an oscillator 140 is added to an acoustic signal by an adder 150. The acoustic
signal is amplified by the amplifier unit 130, boosted by the transformer 110, and output to the
electrodes 20U and 20L of the electrostatic speaker. When the human body of the electrodes
20U and 20L touches, the current flowing to the resistor R4 increases. The detection circuit 210
outputs a signal according to the current value of the current flowing through the resistor R4.
The filter 220 passes the component of the frequency of the addition signal among the signals
output from the detection circuit 210. When the voltage value of the signal that has passed
through filter 220 exceeds a predetermined threshold, control unit 230 controls switches SW1 to
SW3 to maintain the open state. As a result, the output of the acoustic signal to the electrostatic
speaker 1 is stopped. [Selected figure] Figure 3
Drive circuit
[0001]
The present invention relates to a drive circuit for driving an electrostatic speaker.
[0002]
In the condenser type headphone disclosed in Patent Document 1, a polarized voltage output unit
for applying a voltage to a fixed pole is housed inside a housing of the headphone.
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If there is a polarization voltage output unit outside the headphones, a cable for connecting the
headphones and the polarization voltage output unit is required. In this case, if a human body
touches the terminal to which the cable is connected, there is a risk of an electric shock. On the
other hand, in the headphone disclosed in Patent Document 1, the polarization voltage output
unit is inside the housing of the headphone. For this reason, there is no need for the user to
connect the headphone and the polarization voltage output unit with a cable, and the risk of
electric shock is reduced.
[0003]
Unexamined-Japanese-Patent No. 2006-41569
[0004]
By the way, in the headphone disclosed in Patent Document 1, since a high voltage is applied to
the fixed electrode, there is a possibility that an electric shock may occur if a human body
touches the fixed electrode.
In the invention of Patent Document 1, although there is a low possibility that the human body
will touch between the fixed pole and the polarized voltage output unit to cause electric shock,
no measures have been taken against the electric shock by touching the fixed pole. .
[0005]
The present invention has been made under the above-mentioned background, and its object is to
prevent an electric shock even when the human body touches the electrode of the electrostatic
speaker.
[0006]
In order to solve the problems described above, the present invention comprises addition signal
generation means for generating an addition signal of a determined frequency, and addition
means for adding the addition signal generated by the addition signal generation means to an
input acoustic signal. An amplification means for amplifying an acoustic signal to which the
addition signal has been added by the addition means; a boosting means for boosting the
acoustic signal amplified by the amplification means; and an acoustic signal boosted by the
boosting means. An output means for outputting to an electrode of the electro-speaker, a second
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2
signal generation means for generating a signal representing a current value of the acoustic
signal amplified by the amplification means or the acoustic signal boosted by the boosting
means; A filter through which the component of the frequency of the signal generated by the
second signal generation means passes, and the acoustic signal to the electrode when the voltage
of the signal passed through the filter exceeds a predetermined threshold value To provide a
driving circuit having a control means, a to stop the output of.
[0007]
In the present invention, the control means may be configured to stop the output of the acoustic
signal to the electrode by blocking the supply of the acoustic signal from the amplification means
to the boosting means.
Further, in the present invention, the control means is configured to stop the output of the
acoustic signal to the electrodes by interrupting the supply of power from the power source for
driving the amplification means to the amplification means. It is also good.
Further, in the present invention, the frequency is a current exceeding the predetermined
threshold from the electrode to the human body, the impedance of the electrostatic speaker
according to the signal of the frequency when no current flows from the electrode to the human
body. The frequency may be higher than the impedance of the electrostatic speaker when the
current flows.
[0008]
According to the present invention, it is possible to prevent an electric shock even when the
human body touches the electrode of the electrostatic speaker.
[0009]
FIG. 1 is an external view of an electrostatic speaker according to an embodiment of the present
invention.
1. AA sectional view taken on the line of FIG. The exploded view of electrostatic type speaker 1.
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FIG. 2 is a diagram showing an electrical configuration according to the electrostatic speaker 1.
[0010]
Embodiment FIG. 1 is an external view of an electrostatic speaker 1 according to an embodiment
of the present invention, and FIG. 2 is a cross-sectional view of the electrostatic speaker 1 taken
along line AA. 3 is an exploded view of the electrostatic speaker 1, and FIG. 4 is a diagram
showing the electrical configuration of the electrostatic speaker 1. As shown in FIG. In the figure,
the directions are indicated by the orthogonal X-axis, Y-axis, and Z-axis, and the horizontal
direction when the electrostatic speaker 1 is viewed from the front is the X-axis direction, and the
depth direction is the Y-axis direction. The height direction is the direction of the Z axis. Further,
in the drawings, those in which “•” is described in “o” means an arrow directed from the
back to the front of the drawing. Further, in the drawings, those in which “x” is described in
“o” means an arrow directed from the front to the back of the drawing.
[0011]
As shown in the figure, the electrostatic loudspeaker 1 includes a vibrator 10, electrodes 20U
and 20L, elastic members 30U and 30L, spacers 40U and 40L, and protection members 60U and
60L. In the present embodiment, the configurations of the electrode 20U and the electrode 20L
are the same, and the configurations of the elastic member 30U and the elastic member 30L are
the same. Therefore, when there is no particular need to distinguish between the two in these
members, the descriptions such as "L" and "U" are omitted. Further, the configurations of the
spacer 40U and the spacer 40L are the same, and the configurations of the protective member
60U and the protective member 60L are the same. For this reason, also in these members, when
it is not necessary to distinguish between the two, the description of "L", "U", etc. is omitted. Also,
the dimensions of the respective components such as the vibrator and electrodes in the drawing
are different from the actual dimensions so that the shapes of the components can be easily
understood.
[0012]
(Configuration of Each Part of Electrostatic Speaker 1) First, each part of the electrostatic speaker
1 will be described. The rectangular vibrating body 10 viewed from the point on the Z axis is
made of a film (insulating layer) of an insulating and flexible synthetic resin such as PET
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(polyethylene terephthalate) or PP (polypropylene). A conductive metal is deposited on one
surface of the film to form a conductive film (conductive layer). In the present embodiment, the
conductive film is formed on one side of the film, but may be formed on both sides of the film.
[0013]
The elastic member 30 is a non-woven fabric in this embodiment and can pass air and sound
without passing electricity, and its shape is rectangular when viewed from a point on the Z axis.
Also, the elastic member 30 has elasticity, and deforms when an external force is applied, and
returns to its original shape when an external force is removed. The elastic member 30 may be a
member having insulation, sound transmission, and elasticity, and it may be formed by applying
heat to the batt and compressing it, woven cloth, and synthetic resin having insulation. Or the
like. In the present embodiment, the length of the elastic member 30 in the X-axis direction is
longer than the length of the vibrating body 10 in the X-axis direction, and the length of the
elastic member 30 in the Y-axis direction is the vibrating body 10 in the Y-axis direction. It is
longer than the length.
[0014]
The spacer 40 is a non-woven fabric in this embodiment and can pass air and sound without
passing electricity, and its shape is rectangular as viewed from the point on the Z axis. Also, the
elastic member 30 has elasticity. In the present embodiment, the spacer 40 is made of the same
material as the elastic member 30. However, the spacer 40 may not be electrically conductive
and may not have elasticity as long as air and sound can pass therethrough. Further, in the
present embodiment, the spacer 40 has the same length in the X-axis direction and the length in
the Y-axis direction as the elastic member 30.
[0015]
The electrode 20 uses a film (insulating layer) of insulating synthetic resin such as PET or PP as a
substrate, and a conductive metal is deposited on one surface of the film to form a conductive
film (conductive layer). It is a structure. The electrode 20 is rectangular when viewed from the
point on the Z-axis, and has a plurality of holes penetrating from the front surface to the back
surface, which allows air and sound to pass therethrough. In the drawings, the illustration of the
holes is omitted. In the present embodiment, the length in the X-axis direction of the electrode 20
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and the length in the Y-axis direction are the same as those of the elastic member 30.
[0016]
The protective member 60 is a cloth having an insulating property. The protective member 60 is
rectangular when viewed from a point on the Z-axis, and allows passage of air and sound. In the
present embodiment, the length in the X axis direction of the protective member 60 and the
length in the Y axis direction are the same as those of the elastic member 30.
[0017]
(Structure of Electrostatic Speaker 1) Next, the structure of the electrostatic speaker 1 will be
described. In the electrostatic loudspeaker 1, the vibrating body 10 is disposed between the
lower surface of the elastic member 30U and the upper surface of the elastic member 30L. The
adhesive is applied to the elastic member 30U and the elastic member 30L with a width of
several mm from the edge in the left-right direction and the edge in the depth direction, and the
portion to which the adhesive is applied The inner side is not fixed to the elastic member 30U
and the elastic member 30L. In addition, the adhesive is applied to the elastic member 30U and
the elastic member 30L with a width of several mm from the edge to the inside, and they are
fixed to each other.
[0018]
The electrode 20U is bonded to the upper surface of the elastic member 30U. The electrode 20L
is bonded to the lower surface of the elastic member 30L. The electrode 20U is coated with an
adhesive with a width of several mm from the edge in the left-right direction and the edge in the
depth direction and is adhered to the elastic member 30U, and the electrode 20L has the edge in
the left-right direction and the depth direction An adhesive is applied with a width of several mm
from the edge to the inside and adhered to the elastic member 30L. The electrode 20 is not fixed
to the elastic member 30 on the inner side of the portion to which the adhesive is applied. The
electrode 20U is in contact with the elastic member 30U at the side with the conductive film, and
the electrode 20L is in contact with the elastic member 30L at the side with the conductive film.
[0019]
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The spacer 40U is bonded to the top surface of the electrode 20U. The spacer 40L is bonded to
the lower surface of the electrode 20L. The spacer 40U is coated with an adhesive with a width
of several mm from the edge in the lateral direction and the edge in the depth direction and is
adhered to the electrode 20U, and the spacer 40L has the edge in the lateral direction and the
edge in the depth direction An adhesive is applied in a width of several mm from the inside to
adhere to the electrode 20L. The spacer 40 is in a state where it is not fixed to the electrode 20
inside the portion to which the adhesive is applied.
[0020]
The protective member 60U is bonded to the top surface of the spacer 40U. The protective
member 60L is bonded to the lower surface of the spacer 40L. Incidentally, the protective
member 60U is coated with an adhesive with a width of several mm from the lateral edge and the
edge in the depth direction and is adhered to the spacer 40U, and the protective member 60L
has the lateral edge and the depth direction An adhesive is applied in a width of several mm from
the edge of and is adhered to the spacer 40L. The protective member 60 is not fixed to the
spacer 40 on the inner side of the portion to which the adhesive is applied.
[0021]
(Electrical Configuration of Electrostatic Loudspeaker 1) Next, the electrical configuration of the
electrostatic loudspeaker 1 will be described. As shown in FIG. 4, the electrostatic speaker 1
receives an amplifier unit 130, a transformer 110, a bias power supply 120 for applying a DC
bias to the vibrating body 10, an oscillator 140, and an acoustic signal representing a sound. The
drive circuit 100 provided with the adder 150 is connected.
[0022]
The electrode 20U is connected to the terminal T1 on the secondary side of the transformer 110,
and the electrode 20L is connected to the other terminal T2 on the secondary side of the
transformer 110. The terminals T1 and T2 function as output means for outputting an acoustic
signal to the electrostatic speaker 1. The vibrating body 10 is also connected to the switch SW3
via the resistor R1. The switch SW3 is connected to the bias power supply 120. The terminal T3
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at the midpoint of the transformer 110 is connected to the ground GND, which is the reference
potential of the drive circuit 100, through the resistor R2.
[0023]
An acoustic signal is input to the amplifier unit 130. The amplifier unit 130 amplifies the input
acoustic signal and outputs the amplified acoustic signal. The amplifier unit 130 has terminals
TA1 and TA2 for outputting an acoustic signal, the terminal TA1 is connected to the switch SW1,
and the terminal TA2 is connected to the switch SW2. The switch SW1 is connected to the
terminal T4 on the primary side of the transformer 110 via the resistor R3, and the switch SW2
is connected to the other terminal T5 on the primary side of the transformer 110 via the resistor
R4 .
[0024]
The adder 150 is addition means for adding the signal supplied from the oscillator 140 to the
input acoustic signal. The acoustic signal to which the signal output from the oscillator 140 is
added is input to the amplifier unit 130. The oscillator 140 outputs a sine wave signal of a
predetermined frequency, and is connected to the adder 150. The oscillator 140 is a signal
generation unit that generates a signal of a predetermined constant frequency, and generates and
outputs a sine wave signal having a frequency of 60 Hz, for example. Since the signal output
from the oscillator 140 is added to the acoustic signal in the adder 150, the signal output from
the oscillator 140 is hereinafter referred to as an addition signal.
[0025]
The detection circuit 210 is a circuit that generates and outputs a signal of a voltage
corresponding to the current value of the current flowing through the resistor R4. The detection
circuit 210 is connected to both ends of the resistor R4. Specifically, the detection circuit 210
includes resistors R5 to R8 and an operational amplifier 2101. One terminal of the resistor R5 is
connected to the line between the resistor R4 and the switch SW2, and the other terminal of the
resistor R5 is connected to the resistor R6 and the non-inverting input terminal of the
operational amplifier 2101. The terminal of the resistor R6 opposite to the terminal connected to
the resistor R5 is connected to the ground GND. One terminal of the resistor R7 is connected to
the line between the resistor R4 and the terminal T5, and the other terminal of the resistor R7 is
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connected to the resistor R8 and the inverting input terminal of the operational amplifier 2101.
The terminal of the resistor R8 opposite to the terminal connected to the resistor R7 is connected
to the output terminal of the operational amplifier 2101.
[0026]
The output terminal of the operational amplifier 2101 is connected to the filter 220. When the
current flowing to the resistor R4 changes and the voltage applied to the resistor R4 changes, the
voltage of the signal output from the output terminal of the detection circuit 210 changes
according to the change of the current flowing to the resistor R4. Specifically, when the current
flowing to the resistor R4 increases and the voltage applied to the resistor R4 increases, the
voltage of the signal output from the output terminal of the operational amplifier 2101 increases
and the current flowing to the resistor R4 decreases. When the voltage applied to the resistor R4
decreases, the voltage of the signal output from the output terminal of the operational amplifier
2101 decreases.
[0027]
The filter 220 is connected to the control unit 230. The filter 220 is a low pass filter that blocks
signals of a frequency higher than a predetermined frequency and passes signals of a frequency
lower than the predetermined frequency. In the present embodiment, the filter 220 passes a
signal having the same frequency as the frequency of the addition signal output from the
oscillator 140. The control unit 230 is connected to the switches SW1 to SW3. The controller
230 detects the voltage value of the signal output from the filter 220. The control unit 230
controls the switches SW1 to SW3 such that the switches SW1 to SW3 are closed when the
detected voltage is equal to or less than a predetermined threshold. Further, the control unit 230
controls the switches SW1 to SW3 so that the switches SW1 to SW3 are opened when the
detected voltage exceeds a predetermined threshold, and the switches SW1 to SW3 are
maintained in the open state. Do.
[0028]
(Operation of Electrostatic Speaker 1) Next, the operation of the electrostatic speaker 1 will be
described. When an AC acoustic signal is input to the amplifier unit 130, the input acoustic signal
is amplified and supplied to the primary side of the transformer 110. Then, when a potential
04-05-2019
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difference is generated between the electrode 20U and the electrode 20L by the supplied voltage,
the vibrator 10 between the electrode 20U and the electrode 20L is drawn to either side of the
electrode 20U or the electrode 20L. Such electrostatic force works.
[0029]
Specifically, the polarity of the second acoustic signal output from the terminal T2 is opposite to
that of the first acoustic signal output from the terminal T1. When a positive acoustic signal is
output from the terminal T1 and a negative acoustic signal is output from the terminal T2, a
positive voltage is applied to the electrode 20U, and a negative voltage is applied to the electrode
20L. Since a positive voltage is applied to the vibrating body 10 by the bias power supply 120,
the electrostatic attractive force between the vibrating body 10 and the electrode 20U to which a
positive voltage is applied is weakened while a negative voltage is applied. Since the electrostatic
attractive force between the electrode 20L and the electrode 20L becomes strong, a suction force
works on the electrode 20L side according to the difference of the electrostatic attractive force
applied to the vibrator 10, and the electrode 20L side (opposite to the Z direction) Displace.
[0030]
In addition, when the first negative acoustic signal is output from the terminal T1 and the second
negative acoustic signal is output from the terminal T2, a negative voltage is applied to the
electrode 20U, and a positive voltage is applied to the electrode 20L. Be done. Since a positive
voltage is applied to the vibrating body 10 by the bias power supply 120, the electrostatic
attractive force between the vibrating body 10 and the electrode 20L to which the positive
voltage is applied is weakened, and a negative voltage is applied. The electrostatic attraction
between the electrode 20U and the electrode 20U is intensified. In accordance with the
difference in electrostatic attractive force applied to the vibrator 10, a suction force is exerted on
the electrode 20U side, and the electrode 20U is displaced to the electrode 20U side (Z-axis
direction).
[0031]
Thus, the vibrating body 10 is displaced (deflection) in the positive direction of the Z-axis and the
negative direction of the Z-axis in accordance with the acoustic signal (deflection), and the
displacement direction changes sequentially to become vibration, and the vibration state ( A
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sound wave corresponding to the frequency, amplitude, phase) is generated from the vibrator 10.
The generated sound waves pass through the elastic member 30 having sound permeability, the
electrode 20, the spacer 40, and the protective member 60, and are emitted as sound to the
outside of the electrostatic speaker 1.
[0032]
The electrostatic speaker 1 is electrically equivalent to a capacitor, and the impedance is high for
low frequency components of the acoustic signal and low for high frequency components of the
acoustic signal. Since the addition signal output from the oscillator 140 and added to the acoustic
signal has a low frequency of 60 Hz in this embodiment, when the human body is not in contact
with the electrode 20, an electrostatic type is used for the addition signal. The impedance of the
speaker 1 is high and the amount of voltage drop in the resistor R4 is small. When an acoustic
signal flows through the resistor R4, the voltage of the signal output from the detection circuit
210 changes in accordance with the current flowing through the resistor R4. Among the signals
output from the detection circuit 210, the component corresponding to the addition signal
passes through the filter 220, but the addition signal passes through the filter 220 because the
voltage drop amount is small in the resistor R4 and the flowing current is small. The voltage
value of the signal does not exceed a predetermined threshold. When the amplitude of the signal
input from the filter 220 does not exceed the threshold, the control unit 230 controls each
switch so that the switches SW1 to SW3 are closed. In addition, since the sound pressure of the
low-frequency sound output from the electrostatic speaker 1 is lower than that of the highfrequency sound, even if the low-frequency addition signal is added to the acoustic signal, The
sound of the frequency of the addition signal is hard to hear in the sense of hearing.
[0033]
On the other hand, when a human body with a low resistance value touches the electrode 20 and
current flows from the electrode 20 to the ground via the human body, the current flow
increases compared to the case where the human body does not touch the electrode 20 and The
amount of voltage drop increases. Among the signals output from the detection circuit 210, the
component corresponding to the addition signal passes through the filter 220, but when the
human body touches the electrode 20, the current flowing to the resistor R4 increases. The
voltage value will exceed a predetermined threshold. When the voltage of the signal input from
the filter 220 exceeds a threshold, the control unit 230 controls the switches SW1 to SW3 to
maintain the open state. Then, the acoustic signal is not supplied from the transformer 110 to
the electrostatic speaker 1, and the bias voltage is not applied from the bias power supply 120 to
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the vibrating body 10. That is, since the current does not flow to the electrostatic speaker 1, it is
possible to prevent an electric shock of the human body.
[0034]
[Modifications] Although the embodiment of the present invention has been described above, the
present invention is not limited to the above-described embodiment, and can be practiced in
various other forms. For example, the above-described embodiment may be modified as follows
to implement the present invention. The above-described embodiment and the following
modifications may be combined with each other.
[0035]
In the embodiment described above, the detection circuit 210 is connected to both ends of the
resistor R4, but the detection circuit 210 may be connected to both ends of the resistor R3
instead of the both ends of the resistor R4. In the embodiment described above, the current
flowing to the primary side of the transformer 110 is detected by the detection circuit 210, but
the current flowing to the secondary side is detected by the detection circuit 210 to control the
switches SW1 to SW3. It is also good. In the embodiment described above, the control unit 230
controls the switch SW3. However, the switch SW3 may not be provided, and only the switch
SW1 and the switch SW2 may be controlled. In the embodiment described above, the switch SW1
may be connected to the terminal T1, and the switch SW2 may be connected to the terminal T2.
In this case, the terminal of the switch SW1 opposite to the terminal T1 is connected to the
electrode 20U, and the terminal of the switch SW2 opposite to the terminal T2 is connected to
the electrode 20L.
[0036]
In the above-described embodiment, the detection circuit 210 may detect the current flowing
from the power supply (not shown) for driving the amplifier unit 130 to the amplifier unit 130
and control the switches SW1 to SW3. In the embodiment described above, a switch is provided
between the power supply (not shown) for driving the amplifier unit 130 and the amplifier unit
130, and the control unit 230 detects the voltage of the input signal when it exceeds the
threshold. The switch may be opened to interrupt the power supply from the power supply to the
amplifier unit 130. Also in this configuration, since the driving of the amplifier unit 130 is
04-05-2019
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stopped and the acoustic signal is not supplied to the electrostatic speaker 1, it is possible to
prevent an electric shock of the human body.
[0037]
In the embodiment described above, the frequency of the addition signal output from the
oscillator is 60 Hz, but the frequency of the addition signal is not limited to 60 Hz, and may be
another frequency. The electrostatic loudspeaker 1 has a high impedance for high frequency
signals, and there is little difference in the amount of voltage drop in the resistor R4 between
when the human body does not touch the electrode 20 and when the human body touches it. For
this reason, the frequency of the addition signal is a frequency at which a difference appears
between the voltage drop amount at the resistor R4 when the human body does not touch the
electrode 20 and the voltage drop amount at the resistor R4 when the human body touches the
electrode 20 Is preferred.
[0038]
Specifically, the impedance Z2 on the secondary side of the transformer 110 is expressed by the
following equation. (F: Frequency, C: Capacitance of Electrostatic Loudspeaker) Assuming that the
winding ratio of the transformer is n and this is viewed from the primary side, the impedance is
as follows. If the winding ratio n is, for example, a value of 30 to 50, and if the frequency of the
addition signal is f = 20 kHz, then n <2> in the equation 2 is 900 to 2,500, so Z1 is 4Ω to 8Ω
The electrostatic speaker 1 is designed to be Assuming that the resistance value of the human
body at the time of electric shock is assumed to be 500 Ω, it will be 0.56 Ω to 0.2 Ω in terms of
primary side, and even if the impedance is 4 Ω to 8 Ω, the voltage drop of resistor R4 at the
time of electric shock Detection is possible. However, assuming that the resistance of the human
body is 500 Ω, an electric shock can not be detected on the primary side of the transformer 110
unless a very large current such as 4400 mA flows in the human body, so even if a current lower
than this flows in the human body Need to be able to detect For example, if the voltage applied to
the electrode 20 from the secondary side of the transformer 110 is 200 V, and it is determined
that an electric shock occurs when a current of about 1 mA flows to the human body due to an
electric shock, the frequency of the addition signal is set lower than f = 20 kHz Assuming that the
impedance on the secondary side of transformer 110 is about 200 kΩ, the difference between
the voltage drop of resistor R4 at the time of an electric shock and the voltage drop of resistor R4
at the time of an electric shock is larger than when f = 20 kHz. Can detect that a current of 1 mA
flows to the human body. When the impedance on the secondary side is about 200 kΩ, n <2> in
the equation (2) is 900 to 2500, and if 200 kΩ is divided by 900 to 2500, Z1 is 80 Ω to 222 Ω.
04-05-2019
13
If the frequency of the addition signal is set such that Z1 has a value larger than 80Ω to 222Ω,
it is possible to detect an electric shock by detecting that a current exceeding 1 mA flows in the
human body. As described above, Z1 is 4Ω to 8Ω at 20 kHz, so if the frequency of the addition
signal is 1/50 of 20 kHz and 400 Hz or less, Z1 becomes 200Ω to 400Ω, which is larger than
80Ω to 222Ω. Therefore, if the frequency of the addition signal is 400 Hz or less, the difference
between the voltage drop amount of the resistor R4 at the time of electric shock and the voltage
drop amount of the resistor R4 at the time of non-electric shock becomes larger than at f = 20
kHz, It can be detected that a current exceeding 1 mA has flowed.
[0039]
In the present invention, the detection circuit 210 is not limited to the circuit using the abovedescribed operational amplifier 2101 as long as the detection circuit 210 is a circuit that outputs
a signal according to the current flowing through the resistor R4. Circuit). Further, although the
filter 220 is a low pass filter in the above-described embodiment, it may be a band pass filter that
passes the component of the frequency of the addition signal.
[0040]
In the present invention, the level of the acoustic signal before being input to the adder 150 may
be detected by a circuit that detects the level of the signal, and the level of the addition signal
may be changed according to the detected level. Specifically, the level of the addition signal is
reduced as the level of the detected acoustic signal decreases, and the level of the addition signal
is increased as the detected level increases. According to this configuration, when the level of the
acoustic signal is small, the level of the addition signal also decreases, so the level of the sound of
the frequency of the addition signal output from the electrostatic speaker 1 decreases.
[0041]
DESCRIPTION OF SYMBOLS 1 ... Electrostatic type speaker, 10 ... Vibrator, 20, 20 U, 20 L ...
Electrode, 30, 30 U, 30 L ... Elastic member, 40, 40 U, 40 L ... Spacer, 60, 60 U, 60 L ... Protective
member, 100 ... Drive circuit , 110: transformer, 120: bias power source, 130: amplifier unit,
140: oscillator, 150: adder, 210: detection circuit, 220: filter, 230: control unit, SW1 to SW3:
switch, R1 to 4: resistance vessel
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