JPH01108804A - Drive circuit for speaker - Google Patents

Abstract

PURPOSE:To attain reproduction with high fidelity by making a current flowing through a drive coil of a speaker correspondent to an input electric signal so as to obtain an accurate output sound pressure level in response to the input electric signal. CONSTITUTION:A current flowing to drive coils 11, 12 of a speaker 1 is detected by 1st and 2nd current detection means, outputs are added and given to integration circuits 31, 31a and subtracted from an input electric signal. Thus, a duty signal from comparator circuits 32, 32a varied in response to the output from the integration circuits 31, 31a makes the current flowing to the drive coils 11,12 of the speaker 1 correspondent to the input electric signal. Thus, even with the dispersion in the drive coils 11,12, or heating or fluctuation of the voltage of a power supply 27 occurred therein, an accurate output sound pressure level corresponding to the input electric signal is obtained from the speaker 1 and reproduction with high fidelity is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a speaker drive circuit that is suitably implemented, for example, when duty-controlling a current flowing through a drive coil of a speaker in response to an acoustic signal level.

Background Art FIG. 5 is a block diagram showing the configuration of a typical prior art. The acoustic signal from the acoustic signal source 51 is applied to the switching element 53 via the duty conversion circuit 52 on the positive side. The acoustic signal from the acoustic signal source 51 is also provided to the switching element 56 from the phase inversion circuit 54 via the duty conversion circuit 55 on the negative side. The switching element 53, the voice coil 62 of the speaker 57, and the direct current source 58 are connected in series to form a closed circuit.
Current flows in the direction. Similarly, the switching element 56, the voice coil 62, and the DC power supply 60 are connected in series to form a closed circuit, and when the switching element 56 is conductive, a current flows in the direction of the arrow 61.

The duty exchange circuits 52 and 55 derive a duty signal having a pulse frequency of, for example, about 20 kHz in accordance with the input acoustic signal level. According to this duty signal, the switching elements 53 and 56 conduct conduction/cutoff operations, and the speaker 57 is driven. The switching elements 53 and 56 are realized by output transistors, field effect transistors, etc., for example.

By controlling the duty of the switching elements 53, 56 as described above, the switching elements 53, 56 can operate in either conduction or interruption, and therefore can operate with high efficiency of nearly 100%. Therefore, it has the characteristics that heat generation can be suppressed and large output can be controlled with small switching elements 53 and 56.

Problems to be Solved by the Invention In the prior art as described above, the switching element 53.5
6 is accurately duty-controlled in accordance with the input audio signal level. However, in the voice coil 62 of the speaker 57, the load current is not constant even at the same duty due to manufacturing variations, variations in load resistance due to heat generation, fluctuations in power supply voltage, manufacturing variations in inductance, etc. , hence the load current,
That is, the output sound pressure level cannot be stabilized at a value proportional to the input sound signal level, and faithful sound reproduction cannot be performed.

An object of the present invention is to provide a speaker drive circuit with improved fidelity that can obtain an accurate output sound pressure level corresponding to an input signal level.

Means for Solving the Problems The present invention provides an integration circuit which receives an input electrical signal at one input and subtracts and outputs an integral value of the electrical signal given at the other input; an oscillation circuit that derives a periodic voltage waveform in which the voltage changes; the output of the integration circuit is given to one input; the output of the oscillation circuit is given to the other input; A comparator circuit that derives a high level output when one voltage is higher than the other voltage and a low level output when one voltage is lower than the other voltage, and a coil that drives the vibrating member of the speaker. a switching element that is connected to conduction/cutoff in response to the output of the comparison circuit; a first current detection means that detects a current flowing through the drive coil when the switching element is turned on; The second one detects the current flowing through the
A speaker drive circuit comprising: current detection means; and means that responds to the outputs of the first and second current detection means, adds the outputs, and applies the sum to the other input of the integrating circuit. be.

Operation According to the invention, an input electrical signal, such as an acoustic signal, is applied to one input of the integrating circuit.

This integrating circuit subtracts the integral value of the electrical signal given to the other input from the input electrical signal and supplies the result to one input of the comparator circuit. The other input of the comparator circuit is given a periodic voltage waveform from the oscillation circuit in which the output voltage changes over time. When the output voltage from the integrating circuit is greater than or equal to the output voltage from the oscillating circuit, the comparator circuit
A high level output is derived to the switching element, and a low level output is derived when the output voltage of the integrating circuit is less than the output voltage of the oscillation circuit. The switching element is
performs a conduction/cutoff operation in response to the output of the comparison circuit;
A drive current is applied to a coil that drives the vibrating member of the speaker, and the speaker is thus duty-controlled.

The current flowing through the drive coil of the speaker is detected by the first current detection means when the switching element is conductive, and is detected by the second current detection means when the switching element is turned off.

The outputs of the first and second current detection means are added and applied to the other input of the integrating circuit.

Therefore, even if there are variations in the drive coil, heat generation, or fluctuations in the power supply voltage, the current that flows through the drive coil corresponds to the input electricity No. It is possible to obtain high-fidelity sound reproduction.

Embodiment FIG. 1 shows a drive circuit 2 for a speaker 1 according to an embodiment of the present invention.
FIG. The acoustic signal from the acoustic signal source 3 is
The signal is applied to the amplifier circuit 4. From the amplifier circuit 4, the positive side acoustic signal is given to the duty conversion circuit 6 via the differentiating circuit 5. A negative-pole side acoustic signal is also supplied from the amplification path 4 to a duty conversion circuit 8 via a differentiation circuit 7. The output from the duty conversion circuit 6.8 is on line 9
Voice coil 11°12 of speaker 1 via °10
are given to each.

As shown in FIG. 2, the speaker 1 is constructed by winding a pair of voice coils 11 and 12 around the outer peripheral surface of a right cylindrical bobbin 22, which is disposed at the base end of a diaphragm 21. be done. In this speaker 1, the terminal B of the voice coil 11 is connected to the line 9, and the terminal C of the voice coil 12 is connected to the line 10, as described above. Power from a power source 27 is commonly supplied to the terminal A of the voice coil 11 and the terminal A of the voice coil 12 via a line 25. The power supply 27 also connects the constant voltage circuit 2 via line 25.
6.

The acoustic signal from the acoustic signal source 3 is input to the amplifier circuit 4, and is applied to the base of the transistor Tr3 via the coupling capacitor C3. Also, the voltage from the constant voltage circuit 26 via the line 28 is applied to the base of the transistor Tr3 after being divided by the resistors R11 and R12. The collector of the transistor Tr3 is connected to a line 28 via a resistor R13, and to a duty conversion circuit 8 via a differentiating circuit 7 consisting of a capacitor C6, a resistor R20, and a diode D4.

The emitter of the transistor Tr3 is grounded via a resistor R14 and connected to a duty conversion circuit 6 via a differentiating circuit 5 including a capacitor C5, a resistor R19, and a diode D3. Acoustic signals are derived from the amplifier circuit 4 to the differentiator circuit 5.7 with the same gain.

Power from the constant voltage circuit 26 is also applied to a sawtooth wave generation circuit 30, which is an oscillation circuit. This sawtooth wave generation circuit 30 includes a differential amplifier IC4, resistors R15 to R18,
and a capacitor C4. This sawtooth wave generating circuit 30 oscillates at a frequency of, for example, 20 to 100 kHz.

The output of the sawtooth wave generating circuit 30 is applied to the duty conversion circuits 6 and 8 via a line 29.

The duty conversion circuit 6 includes a deviation integration circuit 31, a comparison circuit 32, and an output transistor 3 which is a switching element.
3, a resistor RIO and an amplifier circuit 40 as a first Th current detection means, and a resistor R5 and a current mirror circuit 41 as a second current detection means.

The acoustic signal given to the duty conversion circuit 6 via the differentiation circuit 5 is transmitted to the differential amplifier I that constitutes the deviation integration circuit 31.
Applied to the non-inverting input terminal of CI. This differential amplifier I
A capacitor C1 is connected between the output terminal of CI and the inverting input terminal, so that the operational amplifier I
The deviation between the signal input to the inverting input terminal via line 34 and the acoustic signal input to the non-inverting input terminal is integrated and derived from CI.

The output from the deviation integration circuit 31 is given to a non-inverting input terminal of a comparator circuit 32, and the output of the aforementioned sawtooth wave generating circuit 30 is connected to the inverting input terminal of the comparator circuit 32 via a line 29. Given.

The comparison circuit 32 compares the output of the deviation integration circuit 31 and the output of the sawtooth wave generation circuit 30, and when the output voltage of the deviation integration circuit 31 is equal to or higher than the output voltage of the sawtooth wave generation circuit 30, a high-level signal is generated. An output is derived, and when the output voltage of the deviation integration circuit 31 is less than the output voltage of the sawtooth wave generation circuit 30, a low level output is derived. That is, when the output shown in FIG. 3 (1) is derived from the sawtooth wave generation circuit 30, the comparison circuit 32 derives the output shown in FIG. A duty signal corresponding to the acoustic signal level is created. In FIG. 3 (1), the output of the deviation integration circuit 31 is
Reference mark! 1.

The output from comparison circuit 32 is applied to output transistor 33 via resistor R7. The output transistor 33 is
The transistor 35 and the transistor 36 are configured in a so-called Darlington connection. In the output transistor 33, the collectors of transistors 35 and 36 are
It is connected to terminal B of voice coil 11 and to line 25 via resistor R5 and diode D2. The emitter of transistor 36 is grounded via resistor R10.

In relation to the resistor RIO, a differential amplifier IC3 and a resistor R8
, R9 and a capacitor C2. As a result, the output transistor 3
A current i3 flowing through the voice coil 11 when the voltage V3 is conductive is detected by the resistor RIO, amplified by the amplifier circuit 40, and derived as an output voltage v2. Thus the current i
It is possible to obtain an output voltage V2 proportional to 3.

Further, in relation to the resistor R5, a current mirror circuit 41 including a transistor Tri, resistors R1, R2, and R4, and a diode D1 is provided. As a result, the current i4 due to the back electromotive force when the output transistor 33 is cut off is detected and absorbed by the resistor R5, and in proportion to this current i4, the emitter current 11 flows through the transistor T r 1, and thus the collector current 12 generates an output voltage v1. Collector current 12 is approximately equal to emitter current 11 and is therefore proportional to said current i4. Thus, the output voltage v proportional to the current i4
1 can be obtained.

In the amplifier circuit 40 and current mirror circuit 41 described above, when the output transistor 33 is turned on, the voice coil 1
When the current i3 flowing through the output transistor 33 is equal to the current i4 flowing when the output transistor 33 is cut off, the output voltages Vl and V
The gain of the amplifier circuit 40 or the output of the current mirror circuit 41 is adjusted to wJMi so that 2 becomes equal. The output of the amplifier circuit 40 and the output of the current mirror circuit 41 are added to the line 34 via resistors R6 and R3, respectively, and then fed back negatively to the differential amplifier ICI of the deviation integration circuit 31 described above. Note that the time constant τ of the deviation integration circuit 31 is
When resistors R3 and R6 are equal, τ-CIX0.5R
It is expressed as 3. This time constant τ increases the frequency of the acoustic signal by 20
If it is about Hz to 10kHz, the minimum period is 50 to 1
00 μs and the aforementioned sawtooth wave generation circuit 30
The pulse period from 10 to 50 μs is selected.

The duty conversion circuit 8 is the duty conversion circuit 6 described above.
Corresponding parts are indicated by the same reference numerals with the suffix a added.

In the drive circuit 2 configured as described above, for example, the resistance and inductance of the voice coils 11, 12 are reduced, and the output current i3. If i4 becomes excessive, the output voltage ■2 of the amplifier circuit 40 or the current mirror circuit 41
The output voltage V1 of increases, the output from the deviation integration circuit 31 decreases, the conduction time of the output transistor 33 by the comparator circuit 32 shortens, and the output current [3 or i4
is lowered. In this way, the duty signal shown by the broken line in FIG. Control is performed so that the load current becomes the same, so that the output sound pressure level corresponding to the sound signal level can be obtained from the speaker 1, and high-fidelity sound reproduction can be performed.

FIG. 4 (1) shows a case where the duty is 25%, FIG. 4 (2) shows a case where the duty is 50%, and FIG. 4 (3) shows a case where the duty is 75%.

Effects As described above, according to the present invention, the current flowing through the drive coil of the speaker is detected by the first and second i-current detection means, and the outputs thereof are added together and given to the integrating circuit, where they are subtracted from the input electrical signal. As a result, the duty signal from the comparator circuit, which changes in response to the output from the integrating circuit, can cause the current flowing through the speaker drive coil to correspond to the input electrical signal, thereby reducing variations in the drive coil and heat generation. Even if variations in the power supply voltage or the like occur, the speaker can obtain an accurate output sound pressure level corresponding to the input electrical signal, and high-fidelity reproduction can be performed.

[Brief explanation of the drawing]

1 is an electric circuit diagram of a drive circuit 2 of a speaker 1 according to an embodiment of the present invention, FIG. 2 is a simplified perspective view of the speaker 1, and FIG. 3 is an electric circuit diagram for explaining the operation of a comparison circuit 32. FIG. 4 is a waveform diagram showing the load current corresponding to each duty, and FIG. 5 is a block diagram showing the configuration of the prior art. DESCRIPTION OF SYMBOLS 1...Speaker, 2...Drive circuit, 3...Acoustic signal source, 4.40.40a...Amplification circuit, 5.7...
Differentiation circuit, 6.8...Duty conversion circuit, 11.1
2...Voice coil, 21...Diaphragm, 26...
Constant voltage circuit, 27... Power supply, 30... Sawtooth wave generation circuit, 31, 31a... Deviation integration circuit, 32.32a
...Comparison circuit, 33.33a...Output transistor, 41,41a...Current mirror circuit Agent Patent attorney Kei Saikyo Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] An integration circuit that receives an input electrical signal at one input and subtracts the integral value of the electrical signal that is assigned to the other input and outputs the result, and a period in which the output voltage changes over time. an oscillator circuit for deriving a voltage waveform; the output of the integrating circuit is given to one input, the output of the oscillator circuit is given to the other input, and the voltage of one of these inputs is greater than or equal to the voltage of the other; a comparator circuit that derives a high-level output at a certain time and a low-level output when one voltage is less than the other; a switching element that conducts/cuts off in response to an output; a first current detection means that detects a current flowing through the drive coil when the switching element is turned on; and a second current detection means that detects a current that flows through the drive coil when the switching element is turned off. A speaker drive circuit comprising: current detection means; and means that responds to the outputs of the first and second current detection means, adds the outputs, and applies the sum to the other input of an integrating circuit.