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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
coil counter electromotive voltage detection device that can be used to simulate the movement of
a speaker or the like. A technology for electrically detecting the movement of cone paper of the
prior art speaker and returning the detection signal to the front stage of the power amplifier to
control the vibration of the cone paper is generally called M F B (MOtinna I Feedback). , Is
known. (For example, "Speaker and Speaker System" published by 1st Daily Kogyo Shimbun,
published by Sakamoto, 87th to 100th negative). It is also known to provide a detection coil
separately from the voice coil as a conventional photographing movement detection method in
this type of eyebrow system. However, in this method, the structure is complicated, and the mass
of the imaging part is increased and the cost is high. In addition, a detection coil is provided, and
a method of detecting the movement of the voice coil by a bridge circuit with one side of the
speaker is also mentioned. Problems to be solved by the invention However, the method vc which
uses a bridge circuit detects that it is difficult to balance the bridge correctly-· when the
resistance value changes due to a defect and @ summer change. If the accuracy decreases-there
are 5 drawbacks. Now, as for the speaker (· described above, there is a similar problem even with
similar devices. Therefore, an object of the present invention is to provide a device capable of
detecting the back electromotive voltage of the coil relatively accurately and easily regardless of
the change of the degree. Means for Solving the Problems The device according to the present
invention is to detect a back electromotive voltage Vac of a coil to which an alternating voltage
Eac is applied, a detection resistor connected in series to the coil, and A weak DC voltage
connected in series with the coil and the detection resistor. A DC power supply for supplying the
current value, a resistance value of the detection resistor, a current value flowing through the coil
and the detection resistor based on the AC voltage EacK, and a coil value based on the weak DC
voltage V0. And the value of the current flowing through the detection resistor. , 5 + U gain,
based on the detection of the voltage across the detection resistor-A (I. +1a。 A variable gain
amplifier for outputting a voltage of r, a filter for extracting a direct current component Arl6
from the output of the variable gain amplifier, a voltage V0 of the direct current power supply
and an output voltage ArI of the filter. Generates an output voltage corresponding to the
difference between the voltage V0 and the output voltage V0 = ArI. Differential amplifier for
controlling the gain gain A of the variable gain amplifier so as to hold the difference between the
AC voltage Eac and the output voltage A (I6 + IH) r of the variable gain amplifier A Ea, -I ,.
a circuit for obtaining a voltage corresponding to rA) as a back electromotive voltage detection
voltage of the coil. Operation According to the above invention, the gain A of the variable gain
amplifier is V0 = I. Since rA is established, it is possible to accurately detect the back
electromotive force despite the temperature change of the coil. A speaker circuit according to an
embodiment of the present invention will be described with reference to the drawings. In the
drawings, (1) is an audio signal input terminal, (2+ is an addition circuit of a feedback circuit, (3)
is a power amplifier, (4j is a voice coil of a speaker, + 5J is a detection resistor, 16) is It is a weak
DC voltage valve. The voice coil (4), the detection resistor t5J, and the DC voltage source +67 are
connected in series to the power amplifier (the output stage of 31 in order). The power amplifier
(31 supplies the AC voltage Eac to the voice coil (4), the voice coil (4) generates the back
electromotive voltage Vac, has a DC resistance R, and the detection resistance (5) is a resistance.
It has a value r and the DC voltage source (6) supplies a weak DC voltage V0. Thereby, based on
the alternating voltage Eac---- Flow, DC voltage ■. Electrician based on. Flows. (7) is a variable
gain amplifier, and the voltage r (I2 ° + IO) across the resistor f5J is increased by A times A (I).
+1a。 ) And sends out the output voltage. By the way, since the current flowing through the
voice coil + 4) K is not always constant but changes, this temperature also changes. Accordingly,
the direct current resistance R also changes with temperature, and the direct current To also
changes. Therefore, in the present embodiment, ■. To gain as you nullify the change of? I l l l J
仇. In order to perform this gain control, a DC voltage source (6) is connected to one input
terminal of the first differential amplifier (8), and a DC voltage Vo is input here. Also, the output
voltage A (I) of the TfJ variable gain amplifier 7 is applied to the other input terminal of the first
differential amplifier 8. 10 ac) From r, a DC molecule I obtained by extracting with a resistor (9
(and a low pass filter consisting of a capacitor αQ). A inputs. As a result, Vo and r engineering
from differential amplifier (8). Output of difference with A occurs, Vo = r ■. The gain A of the
variable gain amplifier (7) is controlled such that A always holds. (I21 is a second M working
amplifier of gain B, the variable gain amplifier of the previous stage is connected to this one input
terminal (the power output terminal is connected, the power amplifier (the output terminal of 31
is connected to the other input terminal ing.
Therefore, this differential amplifier power is AC voltage Eac and A (I. + IaC) Corresponding to
the difference between r and (Ea (-r AIB -AI). r) The output of B is obtained. Since the output
stage of the second differential amplifier bet is provided with a DC component cut-off circuit αJ,
(Ea (−− AI aor) B = V, 1 (B is obtained at this output, It is supplied to the feedback circuit +
circuit +21. Arrows indicate that a voltage corresponding to the back electromotive voltage Vac
of the voice coil (4) is obtained at the output terminal of the differential amplifier (121. The
following equation is established for the AC voltage Eacvc. EB (-= 'YB + l R + r) 1 B (= mountain
voice coil (counter electromotive force V at arrow 弐 f21, to detect duty of 44). If you ask for Vac
"Esc (R + r) IB------. + 21 One, DC voltage V. The following equation holds for K: Vo = (R + r) Io. ""
I31 The following +41 equation is obtained from the equation (3j). By substituting the equation
(4) into the equation (2+), the following equation is obtained. = Eao-IaCr (A) Therefore, the
differential amplifier (V0 by the output of 8J = AI). If a variable gain amplifier is controlled to
obtain a gain A satisfying r (the control of 77 is not affected by the temperature change, (Eao-a).
rA) B: The back electromotive voltage of vac B can be detected. The present invention is not
limited to the embodiments described above. It is further deformable. For example, the back emf
of a device having a coil similar to the voice coil (4) K of a speaker can be simulated as well. また
。 It is apparent from the above that even if direct current cutting is performed on the input side
of the 82 working amplifiers U, the effect of the invention is clear from the above (according to
the present invention, the coil reverse is correctly An electromotive voltage can be detected.
Brief description of the drawings
The drawing is a block diagram showing a speaker circuit according to an embodiment of the
present invention.
131 · · · power increase 11 @, (4) · · · voice coil, + 51 · · · · resistance for detection, (6) · · · weak DC
voltage, (power · · · variable gain amplifier, (8) ... Differential amplifier, (Ill ... low pass filter, (1 ...
differential amplifier,