JP3189605B2 - Speaker drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a PA (Public Audio) system or the like, and particularly when the output current exceeds the allowable input current value of the speaker, the speaker is well protected. It relates to a drive circuit.

[0002]

2. Description of the Related Art For example, in a PA (public audio) system, in order to generate a large volume, an output current of an amplifier circuit often exceeds an allowable input current of a speaker, and an accident such as disconnection due to heat generation of a voice coil occurs. There was a risk of occurrence. Therefore, in order to protect the speaker from such an accident, a speaker protection circuit that regulates the output current of the amplifier circuit to an allowable level or less has been studied.

That is, in FIG. 5, an audio signal supplied to an input terminal 71 is amplified by an amplifier 72, and the amplified signal is supplied to a speaker 75 through a resistor 73 and a relay 74. Further, the voltage between both ends of the resistor 73 is supplied to the overcurrent detection circuit 76, and the current flowing through the resistor 73 is detected by the voltage drop generated according to the current.
The detection signal from the overcurrent detection circuit 76 is supplied to the control terminal of the relay 74.

Accordingly, in this circuit, the speaker 75 is driven by the audio signal supplied to the input terminal 71, and a voltage corresponding to the signal current supplied to the speaker 75 is generated between both ends of the resistor 73. Then, the voltage between both ends of the resistor 73 is supplied to an overcurrent detection circuit 76, and an overcurrent exceeding the allowable input current is detected. When the detection signal is obtained, the relay 74 is turned off. The supply of an excessive current exceeding the allowable input current from 72 to the speaker 75 is cut off.

However, in this circuit, since the resistor 73 for detecting an excessive current is in the line of the speaker 75, the voltage drop of the resistor 73 causes the speaker 75 to drop.
, Power may be reduced, efficiency may be reduced, and distortion may occur. Further, since the line of the speaker 75 is disconnected by the relay 74, the generated sound is intermittent, and there is a possibility that the user may feel uncomfortable when listening.

On the other hand, a circuit as disclosed in Japanese Utility Model Laid-Open No. 4-50913 has been proposed. That is, FIG. 6 is a diagram of a circuit proposed in FIG. 1 (FIG. 1). In FIG. 6, an audio signal supplied to an input terminal 81 is supplied to a non-inverting input of an amplifier 82. The output signal of the amplifier 82 is supplied to one end of the voice coil of the speaker 83, and is fed back to the inverting input of the amplifier 82 through the resistors 84 and 85.

The other end of the voice coil of the speaker 83 is grounded through a resistor 86, and the other end is supplied to an inverting input of an amplifier 88 through a resistor 87. The output of the amplifier 88 is supplied to the inverting input of the amplifier 88 through a resistor 89. Further, the output of the amplifier 88 is supplied to the inverting input of the amplifier 82 through the resistors 90 and 91.

Therefore, in the circuit so far, the amplifier 8
The positive feedback 2 is applied to the low frequency band, especially when a small speaker is used. However, in this circuit, when an excessive input is supplied, there is a disadvantage that the linearity is deteriorated by the positive feedback, and distortion is likely to occur. Therefore, in this circuit, a feedback current limiting circuit 92 is provided on the output side of the amplifier 82 as shown in the figure.

That is, in the feedback current limiting circuit 92, the output signal of the amplifier 82 is grounded through resistors 93 and 94, and the connection point is connected to one end of a parallel circuit of a capacitor 96 and a resistor 97 through a diode 95. . Further, the other end of the parallel circuit is grounded, and one end of the parallel circuit is connected to the base of a transistor 99 through a resistor 98. The collector of the transistor 99 is connected to the connection point between the resistors 90 and 91, and the emitter is grounded.

Thus, in this circuit, the amplifier 8
When the output current of (2) becomes excessive, the diode 95 is turned on, and the potential of one end of the parallel circuit of the capacitor 96 and the resistor 97 is increased. When this potential rises, the collector and the emitter of the transistor 99 become conductive, the positive feedback through the resistors 90 and 91 is cut off, and the output current of the amplifier 82 is regulated.

However, in this circuit, although the feedback current limiting circuit 92 detects the output of the amplifier 82, it does not detect the current flowing through the speaker 83, so that the feedback current limiting circuit 92 detects the change in the impedance of the speaker 83. Level is changed, and the amplifier 82
The amount of positive feedback decreases and the output level that is substantially constant also fluctuates. Further, there is a problem that the operation of the amplifier 82 becomes unstable because the feedback amount of the amplifier 82 is changed.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and the problem to be solved is that in the conventional configuration, a resistor for detecting an excessive current is provided with a resistor of a speaker. Because it is in the line, the power applied to the speaker is reduced due to the voltage drop of the resistor, and there is a possibility that the efficiency may decrease or distortion may occur, or the current flowing through the speaker is not detected. However, there is a problem that the level detected by the change in the impedance of the speaker fluctuates.

[0013]

First means according to the invention According to an aspect of the control the level of the input audio signal volume control circuit 2
And amplify the audio signal supplied from this volume control circuit.
And an audio amplifier circuit 3 for supplying the audio signal to the speaker .
Becomes from 37), the spin from the output terminal of the output resistor
Output terminal for extracting the audio signal supplied to the
Gain control from the output terminal of the amplifier to the amplifier (resistor 38)
With multiplying, the current detection circuit (differential amplifier circuit for detecting a signal current flowing through the output resistor of the audio amplifier circuit
5) and the signal current detected by the current detection circuit
In response, the volume control circuit adjusts the level of the input audio signal.
A speaker driving circuit which is characterized by being configured by adding a current control means for controlling <br/> the output current of the audio amplifier circuit by controlling.

[0014] A second means according to the present invention is the above-mentioned current detection.
Circuit is a speaker driving circuit of the first means, wherein the structure <br/> formed by a differential amplifier 5 for detecting the signal current flowing through the potential difference is supplied the output resistance across the output resistor.
According to a third aspect of the present invention, in the above-mentioned current control means,
Peak hold the output of the current detection circuit for a predetermined time.
The hold circuit 6 is further provided.
The volume control circuit controls the input audio signal according to the output of the road.
The first means configured to control the level of
It is a speaker drive circuit.

According to a fourth aspect of the present invention, there is provided the above-mentioned current control device.
Means, the output resistance of the audio amplifier circuit 3 (resistor 3
6, 37) is detected (differential amplifier circuit 5)
Then, the value of the detected signal current is compared with a value (reference voltage source 9) corresponding to the allowable input current value of the speaker (circuit 8), and the value of the signal current is determined as the allowable input current value.
When the value exceeds the value corresponding to the above, the volume control circuit lowers the level of the input audio signal in accordance with the detected signal current, thereby reducing the output current of the audio amplifier circuit.
The speaker driving circuit according to the first to third means , configured to control the speaker driving circuit.

The fifth means according to the present invention, the upper Symbol detected signal current through the switch 7 is supplied to the volume control circuit 2, the current control means, the value of the detected signal current A comparison circuit 8 compares a value (reference voltage source 9) corresponding to the allowable input current value of the speaker with a value corresponding to the allowable input current value.
When the value exceeds the value corresponding to the above, the switch is turned on, and the volume control circuit according to the detected signal current.
Above by but reducing the level of the input speech signal
The audio amplifier circuit is configured to control an output current .
A speaker drive circuit according to a fourth means .

[0017]

According to this, the signal current flowing through the output resistance of the output stage in the feedback loop of the audio amplification circuit is detected, and the volume of the volume control circuit is controlled by the detected signal current to make the output current constant. As a result, the output resistance of the output stage of the audio amplifier circuit does not reduce the power applied to the speaker, and the level detected by the change in the impedance of the speaker does not fluctuate. It is possible to always provide good speaker protection without instability due to a change in the feedback amount of the amplifier.

[0018]

FIG. 1 is a block diagram showing the configuration of an embodiment of a speaker drive circuit according to the present invention. In FIG. 1, an audio signal supplied to an input terminal 1 is supplied to an audio amplifier circuit 3 through a volume control circuit 2 constituting a speaker drive circuit 10 according to the present invention. This audio amplification circuit 3
Is supplied to one end of the voice coil of the speaker 4. The other end of the voice coil of the speaker 4 is grounded.

In the audio amplifier circuit 3, the output of the volume control circuit 2 is connected to the non-inverting input of the amplifier 31, and the output of the amplifier 31 is supplied to the complementary transistors 34 and 35 through bias voltages 32 and 33, respectively. Connected to base. The collectors of these transistors 34 and 35 are connected to the power supply and the ground, respectively. The emitters of these transistors 34 and 35 are connected to a resistor 3
6 and 37, and the connection midpoint is connected to one end of the voice coil of the speaker 4.

Further, the connection midpoint between the above-described resistors 36 and 37 is connected to the inverting input of the amplifier 31 through the resistors 38 and 39. As a result, feedback is applied to the amplifier 31, the signal from the volume control circuit 2 is amplified and supplied to the speaker 4, and the transistors 34 and 35 are pushed at the connection point between the resistors 36 and 37. With the pull configuration, a signal proportional to the output terminal of the amplifier 31 is extracted.

Therefore, the potentials at both ends of the resistors 36 and 37 (emitters of the transistors 34 and 35) are respectively applied to the inverting input and the non-inverting input of the differential amplifier 53 through the resistors 51 and 52 constituting the differential amplifying circuit 5. And the non-inverting input of the differential amplifier 53 is grounded through a resistor 54, and the output of the differential amplifier 53 is fed back to an inverting input through a resistor 55. This allows the resistor 36,
The positive potential and the negative potential from both ends of 37 are converted to the ground center potential.

Further, the output of the differential amplifier circuit 5 is connected to one end of a parallel circuit of a capacitor 62 and a resistor 63 through a diode 61 constituting a peak hold circuit 6. The other end of this parallel circuit is grounded. As a result, the output signal from the differential amplifier circuit 5 is peak-held, and the signal of the held peak value is supplied to the control terminal of the volume control circuit 2 through the switch 7.

A signal from the peak hold circuit 6 is supplied to one input of a comparison circuit 8 and a reference voltage source 9
Is supplied to the other input of the comparison circuit 8. As a result, when the signal from the peak hold circuit 6 exceeds the voltage corresponding to the allowable input current value of the speaker 4, an output is taken out of the comparison circuit 8, and the switch 7 is turned on by this output.

That is, in this circuit, the current flowing through the feedback resistor 38 of the amplifier 31 is negligible compared to the current flowing through the speaker 4. Therefore speaker 4
Can be considered to be equal to the current flowing to the output resistor 36 when the amplifier 31 outputs a positive voltage, and to the current flowing to the output resistor 37 when the amplifier 31 outputs a negative voltage.

The idling current flowing through the output resistors 36 and 37 is negligible compared to the current flowing through the speaker 4 at a level where the protection of the speaker 4 is required. The flowing current can be considered to be equal to the current flowing to the output resistor 36 when the amplifier 31 outputs a positive voltage, and to the current flowing to the output resistor 37 when the amplifier 31 outputs a negative voltage.

Therefore, the output resistors 36 and 37 of the amplifier 31
The voltage across converted into a voltage of a ground reference in the differential amplifier circuit 5 performs predetermined time voltage held by the peak hold circuit 6, controls the volume control circuit 2 in this voltage. Thus, for example, when a current larger than the set value flows through the speaker 4, the voltage between both ends of the output resistors 36 and 37 of the amplifier 31 increases, the voltage appearing in the peak hold circuit 6 also increases, and the volume increases. The control circuit 2 is controlled to lower the signal level and protect the speaker 4.

Thus, according to the above-described device, the output resistance (the resistors 36, 3
7) is detected (differential amplification circuit 5), and the volume of the volume control circuit 2 is controlled by the detected signal current to keep the output current constant. The output resistors (resistors 36 and 37) of the output stage do not reduce the power applied to the speaker 4 and the detected level does not fluctuate due to the change in the impedance of the speaker 4; The operation of the speaker 4 can always be satisfactorily protected without the operation becoming unstable due to the change in the feedback amount of the amplifier 31.

In the above-described configuration, for example, when the volume control circuit 2 is directly controlled by the voltage appearing in the peak hold circuit 6, the control of the volume control circuit 2 is performed by the feedback control even at a level where the speaker 4 does not need to be protected. Is performed, amplitude modulation by the current flowing through the speaker 4 is always applied, and sound quality is deteriorated.

Therefore, in the above-described configuration, the voltage appearing in the peak hold circuit 6 and the voltage corresponding to the allowable input current value of the speaker 4 from the reference voltage source 9 are compared by the comparison circuit 8,
Only when the voltage appearing in the peak hold circuit 6 is higher than the voltage corresponding to the allowable input current value of the speaker 4, the switch 7 is turned on to perform the feedback control.

Thus, when the voltage appearing in the peak hold circuit 6 is smaller than the voltage corresponding to the allowable input current value of the speaker 4, the feedback control can be cut off to prevent the sound quality from being deteriorated due to the amplitude modulation. However, the invention of the present application can operate even when the feedback control is always performed by omitting the switch 7, the comparison circuit 8, the reference voltage source 9, and the like.

Therefore, in this circuit: 1 There is no disconnection in the circuit by the relay as compared with the prior art, so that a sense of incongruity due to intermittent sound does not occur. (2) Since the overcurrent detection resistor is provided in the feedback loop as compared with the related art, there is no reduction in the power supplied to the speaker 4 due to the overcurrent detection resistor. 3. The operation of the amplifier 31 is stable because the amount of feedback of the amplifier 31 is not changed as compared with the conventional case. 4. Since the current flowing through the speaker 4 is detected as compared with the conventional case, the relationship between the level at which the feedback control is started and the output current that is made constant by the volume control is constant.

In the circuit described above, the audio amplification circuit 3
Is, for example, as shown in FIG.
A BT system in which an inverted signal is supplied through an inverter 30 to one of them (indicated by the symbol [']) and the outputs of both are supplied to both ends of a voice coil of the speaker 4
It may be used as an L connection. In this case, the detection of the signal current may be performed from any of the two systems of amplifier circuits.

In the above-described circuit, the audio amplification circuit 3
The amplifier 31 is not limited to the above-described non-inverting amplification, and can obtain the same operation and effect by inverting amplification as shown in FIG. 3, for example.

Further, in the above-mentioned circuit, the present invention is not limited to an amplifier circuit having an output stage of a push-pull configuration, but can be implemented with a configuration as shown in FIG. That is, in FIG. 4, the output of the amplifier 31 is connected to the base of the transistor 34. The collector of the transistor 34 is connected to the power supply, and the transistor 3
4 is connected to one end of the voice coil of the speaker 4 through the output resistor 36. Further, one end of the voice coil of the speaker 4 is connected to the inverting input of the amplifier 31 through resistors 38 and 39. And output resistor 3
6 are connected to a differential amplifier 53 through resistors 51 and 52, respectively.

Thus, also in this circuit, the amplifier 31 is fed back in the same manner as the above-mentioned circuit, the signal from the volume control circuit 2 is amplified and supplied to the speaker 4, and the other end of the resistor 36 , A signal exactly equivalent to the output terminal of the amplifier 31 is taken out. And this resistor 36
Of the speaker 4 by detecting the potential between both ends of the
The current flowing through the speaker 4 is directly detected, and good detection of the speaker 4 can be performed using the detected value.

[0036]

According to the present invention, the signal current flowing through the output resistance of the output stage in the feedback loop of the audio amplifier circuit is detected,
Since the volume of the volume control circuit is controlled by the detected signal current to keep the output current constant, the output resistance of the output stage of the audio amplifier circuit does not reduce the power applied to the speaker, and Therefore, the level detected by the change in the impedance of the speaker does not fluctuate, and the operation does not become unstable due to the change in the feedback amount of the amplifier. It became so.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of a speaker drive circuit according to the present invention.

FIG. 2 is a configuration diagram of another example of a speaker drive circuit according to the present invention.

FIG. 3 is a configuration diagram of another example of the speaker drive circuit according to the present invention.

FIG. 4 is a configuration diagram of another example of the speaker drive circuit according to the present invention.

FIG. 5 is a configuration diagram of a conventional speaker drive circuit.

FIG. 6 is a configuration diagram of a conventional speaker drive circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Speaker drive circuit 1 Input terminal 2 Volume control circuit 3 Audio amplifier circuit 4 Speaker 31 Amplifier 32, 33 Bias voltage 34, 35 Complementary transistor 36, 37 Resistor 38, 39 Resistor 5 Differential amplifier circuit 51, 52 Resistance Device 53 Differential amplifier 54, 55 Resistor 6 Peak hold circuit 61 Diode 62 Capacitor 63 Resistor 7 Switch 8 Comparison circuit 9 Reference voltage source

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04R 3/00 310 H03F 1/34 H04R 27/00

Claims (5)

(57) [Claims] 1. A and level braking Gosuru volume control circuit of the input audio signal, scan amplifies the audio signal supplied from the volume control circuit
An audio amplifier circuit for supplying to a speaker ; the audio amplifier circuit includes an amplifier and an output resistor, and an audio signal supplied to the speaker from an output terminal of the output resistor.
Provided an output terminal for taking out an item, with multiplying the feedback gain control to the amplifier from the output terminal, a current detection circuit for detecting the signal current flowing through the output resistor of the audio amplifier circuit, which is detected by the current detection circuit The volume control circuit controls the input sound according to the signal current.
Speaker driving circuit, characterized in that configured by adding a current control means for controlling the <br/> output current of the audio amplifier circuit by controlling the level of the signal. Wherein said current detection circuit, spin <br/> manufacturers according to claim 1, which is composed of a differential amplifier for detecting the signal current flowing through the potential difference supplied the output resistor across the output resistor Drive circuit. 3. The current detection circuit according to claim 2, wherein
Peak hold times to hold the output of the
And a volume control circuit according to the output of the peak hold circuit.
Path is configured to control the level of the input audio signal.
The speaker drive circuit according to claim 1, wherein Wherein said current control means detects the signal current flowing through the output resistor of the audio amplifier circuit, the allowable input current value of the value and the speaker of the detected signal current
When the value of the signal current exceeds the value corresponding to the permissible input current value , the volume control circuit responds to the input audio signal according to the detected signal current.
<br/> speaker driving circuit configured claims 1-3, wherein to control the output <br/> output current of the audio amplifier circuit by reducing the level of. 5. A top Symbol detected signal current is supplied to the volume control circuit via a switch, said current control means corresponds to the allowable input current value of the value of the detected signal current and the speaker a value to be compared in the comparison circuit, the value of the signal current by the comparator output turns on the switch when it exceeds a value corresponding to the allowable input current value, in response to the detected signal current upper <br/> Symbol volume control circuit controls the output current of the audio amplifier circuit by reducing the level of the input speech signal
5. The speaker driving circuit according to claim 4, wherein the driving circuit is configured as follows .