close

Вход

Забыли?

вход по аккаунту

?

JP2016171507

код для вставкиСкачать
Patent Translate
Powered by EPO and Google
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 JP2016171507
Abstract: To reduce back electromotive force and overcurrent generated when switching a
speaker or an amplifier. It also prevents the speaker from being destroyed when a DC voltage is
generated at the output of the amplifier. The output voltage of the amplifier is monitored and the
speaker or amplifier is switched when the output voltage of the amplifier is below a threshold.
Increase the transition time of the switch that switches the speaker or amplifier. The output
voltage of the amplifier is monitored to shut off the switch that switches the speaker or amplifier
when a DC voltage is generated at the output of the amplifier. [Selected figure] Figure 1
Sound equipment
[0001]
The present invention relates to an audio device having a speaker switching function or an
amplifier switching function.
[0002]
2. Description of the Related Art An amplifier switching device for switching a plurality of
speakers to reproduce sound, switching a speaker switching device or a plurality of amplifiers to
reproduce sound, is put to practical use.
In addition, an amplifier-speaker switching device in which a speaker switching device and an
amplifier switching device are combined is also put to practical use.
09-05-2019
1
[0003]
There are the following problems when switching a speaker or an amplifier during reproduction
of sound with an audio device incorporating a speaker switching device or an amplifier switching
device.
[0004]
Since the voice coil of the speaker has an inductance component, back electromotive force is
generated from the voice coil of the speaker when the speaker is disconnected from the amplifier
during reproduction of sound.
Let L be the inductance of the speaker, i be the current flowing to the voice coil of the speaker
just before disconnecting the speaker from the amplifier, and t be the time required to disconnect
the speaker from the amplifier. It becomes L x (di / dt). This voltage may be applied to the
components inside the speaker and to the switching device, which may cause the speaker to
break down. In an amplifier having an output transformer such as a vacuum tube amplifier, when
the amplifier and the speaker are separated, back electromotive force is generated at both ends
of the output transformer in the same principle as the speaker, and the voltage is applied to parts
of the amplifier to destroy the amplifier. It may be the cause.
[0005]
If you connect a speaker and an amplifier while playing back audio, the speaker may suddenly
make a loud volume and feel uncomfortable. If you connect the amplifier and the speaker while
playing back audio, the amplifier charges the capacitance of the speaker and the connecting
cable, and an overcurrent flows in the amplifier, speaker switching device or amplifier switching
device, and amplifier, speaker switching device or amplifier switching It may cause damage to the
device. Assuming that the maximum value of the current flowing out of the amplifier is Imax, the
output voltage of the amplifier is V, the output impedance of the amplifier, the resistance of the
changeover switch and the resistance of the connection cable is R, the current of Imax = V / R
instantaneously flows from the amplifier It decreases with the flow time.
[0006]
09-05-2019
2
If the amplifier fails and a DC voltage is generated at the output of the amplifier, the DC voltage is
applied to the speaker via the speaker switching device or the amplifier switching device, and the
speaker is broken. When an amplifier switching device or a speaker switching device is inserted
between the amplifier and the speaker, it is desirable that the switching device can be used to
protect the speaker when a DC voltage is generated at the output of the amplifier.
[0007]
In order to reduce the back EMF generated from the output transformer of the speaker or
amplifier immediately after disconnecting the speaker and the amplifier, it is necessary to reduce
the current i flowing to the speaker or output transformer just before disconnecting or to
increase the time t to disconnect Just do it. Since the current i flowing to the speaker or output
transformer is proportional to the output voltage of the amplifier, the output voltage of the
amplifier just before disconnection may be reduced.
[0008]
In order to prevent sudden loudness from the speaker when the speaker and the amplifier are
connected, the speaker and the amplifier may be connected when the output voltage of the
amplifier is low. Further, in order to reduce the current for charging the capacitance of the cable
or the like from the amplifier, connection may be performed when the output voltage of the
amplifier is low, or R may be increased at the time of connection.
[0009]
In Non-Patent Document 1 and Non-Patent Document 3, the above problem is solved by setting
the output voltage of the amplifier to zero and switching the speaker, and returning the output
level of the amplifier after switching is completed. Although this method can reduce back
electromotive force and overcurrent, it has a problem of increased cost because it requires a
dedicated controller or amplifier operating in conjunction with the speaker switching device.
[0010]
09-05-2019
3
Further, in the speaker switching device and the amplifier switching device using the mechanical
switch shown in Non-Patent Document 2, it is difficult to suppress the back electromotive force
and the excessive current generated when switching the switch during the reproduction of
sound.
[0011]
In the speaker switching device and the amplifier switching device shown in Non-Patent
Document 1, Non-Patent Document 2 and Non-Patent Document 3, the speaker can not be
protected when a DC voltage is generated at the output of the amplifier.
[0012]
In a speaker switching device or an amplifier switching device using a mechanical switch, it is
difficult for the user of the device to operate the mechanical switch, and disconnecting and
connecting the speaker and the amplifier at the moment when the output voltage of the amplifier
is low.
In addition, since the transition time of the opening and closing of the mechanical switch is
almost zero, a large back electromotive force may be generated in the output transformer of the
speaker or the amplifier.
In addition, since the resistance value of the switch immediately after the mechanical switch is
closed is low, an excessive current may flow from the amplifier. It was also difficult to disconnect
the speaker and the amplifier immediately when direct current was generated at the output of
the amplifier.
[0013]
In a speaker switching device using a relay or a semiconductor switch, the output voltage of the
amplifier is monitored, and when the output voltage is less than a threshold value, generation of
a back electromotive force can be suppressed if the switch is disconnected. Also, by monitoring
the output voltage of the amplifier and closing the switch below the threshold value, it is possible
to prevent the speaker from suddenly generating a loud volume and prevent an overcurrent from
flowing from the amplifier. Also, when a direct current voltage is generated at the output of the
09-05-2019
4
amplifier, the speaker can be protected from destruction if all relays or semiconductor switches
are shut off.
[0014]
However, in the speaker switching device and the amplifier switching device, it has been difficult
to monitor the output voltage of the amplifier without deteriorating the quality of the reproduced
sound. FIG. 10 is a block diagram of an audio device including a speaker switching device, an
amplifier and a speaker. For simplicity, only one speaker switching switch is described. In order
to monitor the voltage between the output 52 and the output 53 of the amplifier circuit 13 by
the switch control means 251 of the speaker switching device 22, it is necessary to connect the
reference potentials of the amplifying device 13 and the speaker switching device 22. In FIG. 10,
the output 53 is connected to the ground which is the reference potential of the amplifier 13 and
the speaker switching device 22. The output of the amplifier 13 is supplied to the speaker 16a
via the output 52 and is returned to the amplifier via the output 53. The amplifier 13 and the
speaker switching device 22 are operated by the commercial power supply 51. The power supply
circuit 132 and the power supply circuit 252 generate a power supply for operating the
amplifier 13 and the speaker switching device 22 from the commercial power supply 51. The
power supply circuit 132 and the power supply circuit 252 have a capacitance between the
ground and the commercial power supply 51. Therefore, part of the current for driving the
speaker 16a passes through the path 62. A current flows in the path 62 for operating the
amplifier 13 and the speaker switching device 22. Therefore, a voltage is generated in the path
62 by the impedance of the path 62 and the current. This voltage is superimposed on the voltage
for driving the speaker 16a as noise to degrade the quality of sound reproduced from the
speaker 16a. In order not to cause such voice quality deterioration, the grounds of the amplifier
13 and the speaker switching device 22 must be separated. However, when the grounds of the
amplifier 13 and the speaker switching device 22 are separated, the output voltage of the
amplifier can not be monitored by the switch control means 251.
[0015]
In the speaker switching device and the amplifier switching device using the relay, the back EMF
generated in the output transformer of the speaker and the amplifier can not be sufficiently
lowered because the transition time of the switch opening and closing is short. In addition, it is
difficult to sufficiently reduce the current flowing to the amplifier, the speaker switching device,
or the amplifier switching device at the moment of connecting the speaker and the amplifier.
09-05-2019
5
[0016]
JAI Corporation, "Multi Changer MC-333 Product Information", [online], [March 4, 2015 search,
Internet (URL: http://www.orb.co.jp/audio/mc333.html ) Audio Design Co., Ltd. “Selector HAS
Series Product Information”, [online], [Search on March 4, 2015], Internet (URL:
http://www.audiodesign.co.jp/HAS.htm)
[0017]
Sophisonant Audio "Speaker changer product information", [online], [search on February 26,
2015], Internet (URL: http://sophisonant.com/products/category1/)
[0018]
There is a problem that when the speaker and the amplifier are disconnected during
reproduction of sound by an audio device incorporating the speaker switching device or the
amplifier switching device, back electromotive force is generated in the output transformer of the
speaker or the amplifier.
[0019]
There has been a problem that when a speaker switching device or an amplifier switching device
is incorporated into an audio device and audio is being played back, connecting the speaker and
the amplifier causes the speaker to suddenly emit a loud volume, which causes discomfort.
In addition, there is a problem that when the speaker and the amplifier are connected while
reproducing the sound by the audio device incorporating the speaker switching device or the
amplifier switching device, an excessive current flows from the amplifier.
[0020]
When a DC voltage is generated at the output of the amplifier due to a failure of the amplifier,
the DC voltage is applied to the speaker via the speaker switching device or the amplifier
switching device, and the speaker is broken.
[0021]
The present invention seeks to solve the problems that such conventional speaker switching
09-05-2019
6
devices and amplifier switching devices have, so that switching of the speaker or amplifier during
sound reproduction does not generate back electromotive force. The purpose is to prevent
excessive current flow and sudden loudness from the speaker.
[0022]
Another object of the present invention is to prevent the speaker switching device or the
amplifier switching device from being broken when the DC voltage is generated at the output of
the amplifier.
[0023]
The audio apparatus according to the present invention includes a changeover switch, switch
control means for opening and closing the changeover switch, and voltage monitoring means for
monitoring the voltage of the input of the changeover switch.
[0024]
The changeover switch of the acoustic device according to the present invention may be a relay
or a semiconductor switch.
[0025]
The changeover switch of the acoustic device according to the present invention is a
semiconductor switch, and a transition time of opening and closing of the semiconductor switch
is a predetermined time.
[0026]
An output signal of the voltage monitoring means of the acoustic device according to the present
invention is connected to the switch control means.
[0027]
The switch control means opens and closes the changeover switch when the voltage monitoring
means of the acoustic device according to the present invention indicates that the voltage of the
input of the changeover switch is smaller than a threshold.
[0028]
When the state in which the voltage monitoring means of the acoustic device according to the
09-05-2019
7
present invention indicates that the input voltage of the changeover switch is larger than a
threshold continues for a predetermined time or more, the switch control means opens the
changeover switch.
[0029]
The changeover switch of the audio device according to the present invention may be a switch
for switching a speaker or an amplifier.
[0030]
According to the speaker switching device and the amplifier switching device of the present
invention, even if the speaker or amplifier is switched during sound reproduction, no back
electromotive force is generated from the output transformer of the speaker or amplifier, no
overcurrent flows from the amplifier, and the speaker is suddenly There is an advantage that no
loud sound is emitted.
The speaker switching device and the amplifier switching device of the present invention have an
advantage that the speaker can be prevented from being destroyed when a DC voltage is
generated at the output of the amplifier.
[0031]
The figure which showed an example of the implementation method of the speaker switching
apparatus.
The example of a switch of a speaker switching device.
MOS-FET characteristics.
FIG. 2 is a block diagram of an audio device that includes a speaker switching device.
09-05-2019
8
FIG. 2 is a block diagram of an acoustic device that includes an amplifier switching device.
FIG. 2 is a block diagram of an acoustic device including an amplifier-speaker switching device.
The block diagram of a speaker switching apparatus.
The block diagram of an amplifier switching device.
The block diagram of an amplifier speaker switching apparatus.
Problems with the speaker switching device.
Speaker switching flowchart.
DC protection flow chart.
[0032]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings. The embodiments described below do not limit the contents of the present
invention described in the claims. In addition, not all of the configurations and the like described
below are necessarily essential configuration requirements of the present invention.
[0033]
Prior to the description of the embodiment of the present invention, the configurations of the
conventional speaker switching device, the amplifier switching device, and the amplifier-speaker
switching device will be described, and only the embodiment of the speaker switching device will
be described. And indicates that the operation of the amplifier-speaker switching device can be
easily inferred.
09-05-2019
9
[0034]
FIG. 4 is a block diagram showing an example of an audio device including a speaker switching
device.
The source device 11 is a device such as a CD player or a tuner that outputs sound. The
preamplifier 12 is an amplifier for amplifying the audio signal supplied from the source device
11 and adjusting the signal level. The power amplifier 13 is an amplifier for amplifying an audio
signal supplied from the preamplifier 12 to a power capable of driving a speaker. The speaker
switching device 22 is a device for selecting a single speaker from the speaker 16a, the speaker
16b, and the speaker 16c and connecting it to the output of the power amplifier 13. The speaker
16a, the speaker 16b, and the speaker 16c are devices for converting the electric signal supplied
from the power amplifier into a compression wave of air. Although the preamplifier 12 and the
power amplifier 13 are independent in FIG. 4, they may be integrated.
[0035]
FIG. 5 is a block diagram showing an example of an acoustic device including an amplifier
switching device. The source device 11 is a device such as a CD player or a tuner that outputs
sound. The preamplifier 12 is an amplifier for amplifying the audio signal supplied from the
source device 11 and adjusting the signal level. The power amplifier 13a, the power amplifier
13b, and the power amplifier 13c are amplifiers for amplifying an audio signal supplied from the
preamplifier 12 to a power capable of driving a speaker. The amplifier switching device 31 is a
device for selecting a single power amplifier from the power amplifier 13a, the power amplifier
13b, and the power amplifier 13c and connecting it to the speaker 16. The speaker 16 is a device
for converting an electrical signal supplied from the power amplifier into a compressional wave
of air. Although the preamplifier 12, the power amplifier 13a, the power amplifier 13b, and the
power amplifier 13c are independent in FIG. 5, any one of the preamplifier 12 and the power
amplifier may be integrated.
[0036]
FIG. 6 is a block diagram showing an example of an acoustic device including an amplifierspeaker switching device. The source device 11 is a device such as a CD player or a tuner that
outputs sound. The preamplifier 12 is an amplifier for amplifying the audio signal supplied from
09-05-2019
10
the source device 11 and adjusting the signal level. The power amplifier 13a, the power amplifier
13b, and the power amplifier 13c are amplifiers for amplifying an audio signal supplied from the
preamplifier 12 to a power capable of driving a speaker. The amplifier / speaker switching device
41 selects a single power amplifier from among the power amplifier 13a, the power amplifier
13b, and the power amplifier 13c, and selects a single speaker from the speaker 16a, the speaker
16b, and the speaker 16c, It is a switch for connecting the output of the selected power amplifier
and the selected speaker. The speaker 16a, the speaker 16b, and the speaker 16c are devices for
converting the electric signal supplied from the power amplifier into a compression wave of air.
Although the preamplifier 12, the power amplifier 13a, the power amplifier 13b, and the power
amplifier 13c are independent in FIG. 6, any of the preamplifier 12 and the power amplifier may
be integrated.
[0037]
FIG. 7 shows an internal configuration of the speaker switching device 22 shown in FIG. The
audio signal input to the input terminal 221 is selected by the switch 222, the switch 223, and
the switch 224, and is output to any one of the output terminal 225, the output terminal 226,
and the output terminal 227. The switch 222, the switch 223, and the switch 224 are configured
by mechanical switches or relays or semiconductor switches.
[0038]
FIG. 8 shows an internal configuration of the amplifier switching device 31 shown in FIG. The
audio signal input to the input terminal 311, the input terminal 312, and the input terminal 313
is selected by the switch 314, the switch 315, and the switch 316, and is output to the output
terminal 317. The switch 314, the switch 315, and the switch 316 are configured by mechanical
switches or relays or semiconductor switches.
[0039]
FIG. 9 shows an internal configuration of the amplifier / speaker switching device 41 shown in
FIG. The audio signal input to the input terminal 411, the input terminal 412, and the input
terminal 413 is selected by the switch 414, the switch 415, and the switch 416, and is further
selected by the switch 417, the switch 418, and the switch 419 to the output terminal 41a, the
output It is outputted to the terminal 41 b and the output terminal 41 c. The switch 414, the
09-05-2019
11
switch 415, the switch 416, the switch 417, the switch 418, and the switch 419 are configured
by mechanical switches or relays or semiconductor switches.
[0040]
As shown in FIGS. 7 and 8, the speaker switching device and the amplifier switching device have
the same configuration except that the input terminal and the output terminal are horizontally
reversed. Further, as shown in FIG. 9, the amplifier-speaker switching device is configured such
that the amplifier switching device and the speaker switching device are connected in series. As
described above, the amplifier switching device and the amplifier-speaker switching device have
the same configuration as the speaker switching device, and the embodiment of the speaker
switching device will be described. Only the included acoustic devices are described below.
[0041]
An embodiment of the speaker switching device will be described with reference to FIG. The
audio signal input to the input terminal 221 is selected by the switch 222, the switch 223, and
the switch 224, and is output to any one of the output terminal 225, the output terminal 226,
and the output terminal 227. The switch 222, the switch 223, and the switch 224 are formed of
semiconductor switches. The MCU 228 is a controller that controls the speaker switching device.
The input device 229 is a means for operating the speaker switching device, and receives the
user's operation and transmits it to the MCU 228. Examples of the input device 229 include a
switch, a keyboard, a variable resistor, and a receiver of a remote control. The MCU 228 controls
the switch 222, the switch 223, and the switch 224 through the output port 230. The
photocoupler 231 detects whether the voltage of the audio signal at the input terminal 221 is
above or below the threshold value and transmits it to the MCU 228. Since the forward voltage
VF of the LED of the photocoupler 231 is about 1.2 V, when the voltage of the input terminal
221 is ± 1.2 V or less, the photocoupler output 232 becomes H level and the voltage of the
input terminal 221 is ± 1. When the voltage is 2 V or more, the photocoupler output 232
becomes L level. The resistor 233 supplies a sufficient current to the photocoupler LED, and does
not exceed the maximum rating of the LED and is set to a resistance value sufficiently larger than
the impedance of the speaker. The display device 234 is used to indicate the operation state of
the speaker switching switch, and an LED, an LCD, an EL display, or the like is used. In this
embodiment, by using a photocoupler to monitor the output voltage of the amplifier, the output
voltage of the amplifier can be monitored without connecting the ground of the amplifier and the
ground of the speaker switching device. Although the voltage of the input terminal 221 is
monitored in the present embodiment, the current flowing through the speaker switching device
09-05-2019
12
may be monitored using a transformer, a Hall element or the like.
[0042]
FIG. 2 shows the configuration of the switch 222 of FIG. The switch 223 and the switch 224 in
FIG. 2 have the same configuration as the switch 222. As a changeover switch, a MOS-FET 2221,
a MOS-FET 2222, a MOS-FET 2223, and a MOS-FET 2224 are used. Since a MOS-FET has a
parasitic diode between the drain and the source, the MOS-FETs are connected in series as shown
in FIG. 2 for use as a switch. The control means 2225 is a voltage source for supplying a voltage
required to turn on the MOS-FET between the gate and the source of the MOS-FET 2221 and the
MOS-FET 2222. Control means 2226 is a voltage source for supplying a voltage necessary for
turning on the MOS-FET between the gate and the source of the MOS-FET 2223 and the MOSFET 2224. The control means 2225 and the control means 2226 always supply a constant
voltage between the gate and the source of the MOS-FET even if the source voltage of the MOSFET changes. As an example, a floating power supply or a photo coupler can be used as a control
means. When the MCU 228 sends a signal for turning on the MOS-FET to the control means
2225 and the control means 2226 through the output port 230, the control means 2225 and the
control means 2226 include the MOS-FET 2221, the MOS-FET 2222, the MOS-FET 2223, and the
MOS-FET 2224. A voltage is supplied between the gate and the source to turn on these MOSFETs. When the MCU 228 sends a signal for turning off the MOS-FET to the control means 2225
and the control means 2226 through the output port 230, the control means 2225 controls the
MOS-FET 2221, the MOS-FET 2222, the MOS-FET 2223, and the MOS-FET 2224. The voltage
between the gate and the source of the MOSFET is made zero to turn off these MOS-FETs. Thus,
the switch 222 is opened and closed under the control of the MCU 228.
[0043]
Assuming that the output impedance of the control means 2225 and the control means 2226 is
R and the input capacitance of the MOS-FET is Ci, the voltage between the gate and source of the
MOS-FET rises and falls with a time constant determined by R and Ci. That is, if the output
impedances of the control means 2225 and the control means 2226 are set to appropriate
values, the rise and fall times of the voltage between the gate and the source of the MOS-FET can
be set to predetermined values. According to the relationship between the gate-source voltage
and the on-resistance of the MOS-FET shown in FIG. 3, it can be seen that the on-resistance also
changes over time if the voltage between the gate and the source rises or falls over time. When
the output impedances of the control means 2225 and the control means 2226 are set to
appropriate values in accordance with the input capacitance of the MOS-FET, the switch 222 is
09-05-2019
13
opened after the resistance increases for a fixed time from the closed state. Also, the switch 222
is closed after a certain time from the open state after the resistance decreases. In this way, since
the switch 222 can arbitrarily set the switching transition time, the back electromotive force V =
L x (di / dt) generated in the output transformer of the speaker or amplifier when the switch is
opened increases the back electromotive force V can be reduced. Further, since the on-resistance
of the MOS-FET immediately after closing the switch is large, it is possible to increase R of the
maximum current Imax = V / R flowing from the amplifier to the capacitance of the speaker and
connecting cable via the switch when closing the switch. Therefore, Imax decreases. As described
above, by appropriately setting the transition time of the opening and closing of the switch, it is
possible to reduce the back electromotive force generated when the switch is opened. It also
reduces the value of the current drawn from the amplifier when the switch is closed.
[0044]
The speaker selection operation will be described with reference to FIG.
[0045]
The user operates the input device 229 in FIG. 1 to select the speaker number N.
(ステップS10)
[0046]
The MCU 228 of FIG. 1 waits until the level of the photocoupler output 232 of FIG. 1 becomes H
level, that is, the voltage of the power terminal 221 of FIG. 1 becomes less than ± 1.2V. (ステッ
プS20)
[0047]
If the level of the photocoupler output 232 of FIG. 1 is H, the MCU 228 of FIG. 1 opens all
switches through the output port 230 of FIG. (ステップS30)
09-05-2019
14
[0048]
The MCU 228 of FIG. 1 waits until the level of the photocoupler output 232 of FIG. 1 becomes H
level. (ステップS40)
[0049]
If the level of the photocoupler output 232 of FIG. 1 is H, the MCU 228 of FIG. 1 closes the
switch corresponding to the speaker number N selected through the output port 230. (Step S50)
For example, when the speaker 1 is selected, the switch 222 of FIG. 1 is closed.
[0050]
Since the switch can be opened and closed when the voltage of the input terminal 221 is ± 1.2 V
or less by the above operation, the back electromotive force V = L generated in the output
transformer of the speaker and the amplifier immediately after the speaker and the amplifier are
separated. The back electromotive force V can be reduced by decreasing i of x (di / dt). Further,
since V of current Imax = V / R flowing from the amplifier can be reduced when closing the
changeover switch, Imax can be reduced. In addition, the speaker can be prevented from
suddenly emitting a loud volume.
[0051]
As described above, when separating the speaker and the amplifier, it is possible to reduce i of
the back electromotive force V = L x (di / dt) and to increase t to reduce the back electromotive
force V. Further, when connecting the speaker and the amplifier, V of Imax = V / R can be
reduced and R can be increased to reduce Imax flowing out of the amplifier. An example of
theoretical values of the back electromotive force V generated from the speaker and the current
Imax flowing from the amplifier will be shown below. Amplifier output resistance = 16mΩ,
Speaker switching device ON resistance = 10mΩ, Speaker cable resistance = 100mΩ, Speaker
cable and speaker capacitance = 3000pF, Speaker impedance = 8Ω, Speaker inductance =
0.5mH, mechanical switch The transition time of the semiconductor switch is 100 nanoseconds,
and the transition time of the semiconductor switch is 1 millisecond. When the output of the
amplifier is a sine wave of 100 W, the maximum value of the back electromotive force generated
09-05-2019
15
from the speaker is calculated when switching the switch of the speaker switching device. The
effective value of the voltage at the terminal 221 = (100 × 8) <1/2> = about 28 Vrms. This peak
value is about 80 Vp-p. Therefore, the maximum value of the current flowing to the speaker is 80
÷ 8 = 10A. A back electromotive force V = L x (di / dt) = 0.5 x 10 <-3> x (10/100 x 10 <-9>) =
50, 000 V immediately after opening the mechanical switch is generated. In practice, the back
emf will be less than 50,000 V due to the resistances and capacitances of parts and wires but still
generate a large voltage. Next, according to this embodiment, the back electromotive force when
the voltage of the input terminal 221 is 1.2 V or less when the switch is opened is calculated. The
current flowing to the speaker just before opening the switch is 1.2 ÷ 8 = 0.15A. Therefore, the
back electromotive force V = L x (di / dt) = 0.5 x 10 <-3> x (0.15 / 100 x 10 <-9>) = 750 V is
reduced. When a semiconductor switch is used, the back electromotive force V = L x (di / dt) =
0.5 x 10 <-3> x (0.15 / 1 x 10 <-3>) = 75 mV can be reduced. The calculation of the back EMF
generated from the output transformer can reduce the back EMF according to the same principle
but not shown here.
[0052]
At the moment of closing the switch, the maximum current Imax flowing from the amplifier is
determined. Since R = 16 mΩ + 10 mΩ + 100 mΩ = 126 mΩ, a current of Imax = V / R =
80/126 x 10 <-3> = 634 A flows. Thereafter, due to the inductance of the voice coil of the
speaker, the current of the speaker increases with time, and finally a current flows according to
the output voltage of the amplifier. In the above example, a current I = 80/8 = 10 A, which is
determined by the output voltage of the amplifier and the impedance 8 Ω of the speaker, flows,
and then the current I changes in accordance with the change of the audio signal. According to
this embodiment, when the voltage at the moment of closing the switch is set to 1.2 V or less,
Imax = 1.2 / 126 × 10 <−3> = 9.5 A immediately after closing the switch can be reduced. If the
amplifier charges the speaker cable and the capacitance of the speaker, its time constant is 126
mΩ × 3000 pF = 0.378 ns. The semiconductor switch closes for 1 millisecond, which is
sufficiently longer than the time constant, so that at the moment the switch is closed, no current
flows to charge the speaker cable and the capacitance of the speaker. Immediately after closing
the switch, the speaker's voice coil inductance increases with time due to the inductance of the
speaker's voice coil, and finally a current of 1.2 V and the speaker impedance of 8 Ω I = 1.2 / 8 =
0.15 A flows. The current I changes according to the change of the audio signal.
[0053]
In this embodiment, a photocoupler is used as the voltage monitoring means, and a
09-05-2019
16
semiconductor switch is used as the changeover switch. As a result, suppression of back
electromotive force, suppression of overcurrent, prevention of sudden generation of a large
volume, and high sound quality are simultaneously realized. It is also possible to use a
comparator or an A / D converter as a voltage monitoring means if the deterioration of the sound
quality is allowed. It is also possible to use a relay as a changeover switch if it is possible to
suppress the back electromotive force and the overcurrent sufficiently.
[0054]
The operation when a DC voltage is generated at the output of the amplifier will be described
with reference to FIG. The MCU 228 generates an interrupt at regular intervals by an internally
mounted timer. The case where a timer interrupt occurs every 5 milliseconds will be described as
an example. When a timer interrupt occurs, the process of FIG. 12 is performed. Set the counter
value to 0 before enabling the timer interrupt. (ステップS100)
[0055]
Timer interrupt occurs every 5 milliseconds
[0056]
Check the value of the photocoupler output 232 in FIG.
If the value is L level, that is, the voltage between the terminals of the input terminal 221 of FIG.
1 is ± 1.2 V or more, the process proceeds to step S120. Otherwise, the process proceeds to step
S150. (ステップS110)
[0057]
カウンタをインクリメントする。 (ステップS120)
[0058]
09-05-2019
17
Check if the counter value is 100 or more. If the value of the counter is less than 100, the
interrupt processing is ended. If the value of the counter is 100 or more, the process proceeds to
step S140. (ステップS130)
[0059]
If the value of the counter is 100 or more, it is determined that a DC voltage is generated, and the
switch 222, the switch 223, and the switch 224 of FIG. 1 are opened. Thereafter, the interrupt
processing is ended. (ステップS140)
[0060]
The value of the counter is set to 0 and the interrupt processing is ended. (ステップS150)
[0061]
As described above, the output voltage of the amplifier is sampled every 5 milliseconds, and if it
is ± 1.2 V continuously for 100 times, ie, 0.5 seconds continuously, it is determined that a DC
voltage is generated at the output of the amplifier. Open the switch to protect the speakers. The
sampling interval of the photocoupler output and the condition for judging that the DC voltage is
generated are one example, and other methods may be used. Further, although the detection of
the DC voltage is performed using integration by software in this embodiment, integration may
be performed by hardware.
[0062]
REFERENCE SIGNS LIST 11 source device 12 preamplifier 13 power amplifier 22 speaker
switching device 16 a speaker 16 b speaker 16 c speaker 221 input terminal 222 switch 223
switch 224 switch 225 output terminal 226 output terminal 228 MCU 229 input device 230
output port 231 photocoupler 232 photo Coupler output 233 resistance 234 display device
2221 MOS-FET 2222 MOS-FET 2223 MOS-FET 2224 MOS-FET 2225 control means 2226
control means
09-05-2019
18
Документ
Категория
Без категории
Просмотров
0
Размер файла
29 Кб
Теги
jp2016171507
1/--страниц
Пожаловаться на содержимое документа