JPH11112256A - Amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent heat from concentrating on the transistors of a power output stage by generating low power voltage when the sound volume of a speaker is small, generating high power voltage when the sound volume of the speaker is large and supplying it to a power output part. SOLUTION: An input signal AS1 which is level-adjusted is voltage-amplified in a preamplifier 11 and is supplied to the bases of the transistors Q11 and Q12 of the power output stage. The input signal which is voltage-amplified is power-amplified in the transistors Q11 and Q12 of the power output stage and is outputted to the speaker SP as output voltage Vo. Power voltage ±Vc is generated in variable power sources 12A and 12B, and it fluctuates in cooperation with the resistance value of a volume VR0. Namely, low power voltage ±Vc is generated when the sound volume of the speaker is small and output voltage Vo is low since the resistance value of the volume is large, and high power voltage ±Vc is generated when the sound volume of the speaker is large and output voltage Vo is high since the resistance value of the volume is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit, and more particularly, to heat dissipation design and efficiency improvement of an amplifier circuit used for an audio amplifier or the like.

[0002]

2. Description of the Related Art An amplifier circuit conventionally used generally will be described below with reference to the drawings. FIG.
FIG. 1 is a diagram showing a configuration of a conventional general amplifier circuit, and FIG.
FIG. 5 is a diagram showing a configuration of a conventional BTL (Balanced Transformerless) type amplifier circuit.

The circuit shown in FIG. 14 has a power supply circuit having a transformer 1 and a bridge circuit 2, an amplifying section including a preamplifier and a power output stage transistor, and amplifies an input signal AS and outputs it to a speaker SP. It is. According to this circuit, after an AC voltage is input from a not-shown AC power supply to the transformer 1, it is output to the bridge circuit 2, where it is rectified to generate a power supply voltage ± Vcc and applied to the preamplifier 3. . Using this power supply voltage ± Vcc, preamplifier 3 voltage-amplifies input signal AS and outputs it to power output stage transistors Q1 and Q2. Power output stage transistors Q1 and Q2 further amplify the current to generate an amplified signal. Is output to the speaker SP.

A BTL type amplifier circuit shown in FIG. 15 includes a DC power supply 4 composed of a battery or the like, a first preamplifier 5, and first power output stage transistors Q3 and Q4.
A first amplifying section, a second preamplifier 6 and a second
And a second amplifying section composed of power output stage transistors Q5 and Q6, and the first amplifying section and the second amplifying section
They are L-connected.

According to this circuit, since the first amplifier and the second amplifier are BTL-connected, even if the power supply voltage of the single power supply is low, the voltage is actually about twice that of the single power supply. There is an advantage that a large output can be obtained even when a relatively low voltage such as a battery is used as the power supply voltage because the power can be supplied to the power output stage transistor.

[0006]

According to the conventional amplifier circuit described above, the following problems occur. (1) Problems in heat radiation design In the above circuit, the transistor in the power output stage to which the most current is consumed and to which the high voltage is applied is a monolithic IC
In some cases, and in the future it is desired to do so in the interest of handling. In most cases, such an IC has a built-in overheat protection circuit. However, when such an IC is mounted on the above-described circuit, a high voltage is constantly applied to the IC.
Since the voltage is applied to C, the IC is overheated and the overheat protection circuit is immediately activated, so that the normal heat dissipation design cannot operate as the actual performance. For this reason, there has been a problem that a special heat radiation design has to be performed, for example, a heat radiation plate is laid over the front and back of the IC to increase a heat radiation area.

(2) Problems in Withstand Voltage of Amplifier Also, there is a problem that an amplifier with a high withstand voltage is required in terms of withstand voltage. FIG. 16 is a diagram illustrating regulation characteristics of a transformer for generating a power supply voltage to be supplied to an amplifier. Usually, the regulation characteristics of a transformer are
A downward-sloping curve is drawn as shown in FIG. This means that the voltage generated by the transformer is higher when the power consumption of the amplifier is smaller than when the power consumption is higher. Therefore, it is required to increase the withstand voltage of the amplifier to such an extent that it can cope with a high voltage when the power consumption is small. Therefore, there is a problem that the amplifier becomes large and the cost increases.

In order to reduce this problem, it is conceivable to use a transformer having a good regulation characteristic and a small difference in voltage generated between when the power consumption is small and when the power consumption is large. This is because the withstand voltage of the amplifier can be designed to be lower than that of a transformer having normal regulation characteristics. However, there is another problem that the transformer having such good regulation characteristics has the drawback that the number of windings is large and the cost is high even if the transformer has the same voltage.

(3) Problem in Efficiency Transistor Q in the power output stage in the circuit of FIG.
1 and Q2, and the power supply voltage ± supplied to the transistors Q3, Q4, Q5 and Q6 in the power output stage in the circuit of FIG.
For Vcc, it is necessary to constantly apply a constant high voltage that can correspond to the maximum output.

This may be the case where the maximum output is always output from the speaker while the volume is maximized, but it is extremely rare that an actual audio amplifier requires such a large output. Therefore, an amplified signal smaller than that is actually output. Then, in order to always obtain a power supply voltage that can support the maximum output, it is necessary to apply a higher voltage, so that the power consumption loss increases,
There has been a problem that the efficiency is reduced.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and provides a voltage amplifier for an input signal, a preamplifier comprising an analog circuit, and a current amplifier for the voltage-amplified input signal. A power output unit that outputs to a speaker serving as a load, a volume for adjusting the volume of the speaker, and a low power supply voltage when the volume of the speaker is low, in conjunction with a change in the resistance value of the volume, An amplifier circuit that has a variable power supply that generates a high power supply voltage and supplies the power output unit when the volume of the speaker is high, and the variable power supply is a dropper power supply that steps down a constant power supply voltage. The amplifier circuit according to the present invention and the variable power supply may include a DC-DC converter including an inverter circuit and a rectifying / smoothing circuit in a part thereof. And an amplifier circuit according to the present invention to symptoms,
The DC-DC converter is a non-insulated DC-DC converter in which the inverter circuit and the rectifying / smoothing circuit are not insulated.
The amplifier circuit according to the present invention, which is a DC converter, or the non-isolated DC-DC converter has a switching element that performs a switching operation, and reduces a constant power supply voltage by a duty ratio of the switching element. The amplifying circuit and the DC-DC converter according to the present invention, wherein the chopper power supply is an insulated DC-DC converter in which the inverter circuit and the rectifying / smoothing circuit are insulated. The amplifier circuit according to the present invention and the isolated DC-DC converter are any one of a flyback, a forward, a center tap, a half bridge, a full bridge, and a ringing choke converter. And the variable power supply are provided with a rectifier circuit for rectifying an AC voltage and a primary coil. And a transformer having a secondary coil and transforming the rectified voltage, a collector connected to the primary coil of the transformer, performing a switching operation, and generating a voltage generated by the primary coil at a duty ratio. A light emitting diode having one end connected to one end of the output of the secondary coil,
A photocoupler including a phototransistor through which a collector current flows when the light emitting diode emits light; a shunt regulator connected between the other end of the secondary output of the transformer and the other end of the light emitting diode; And an interlocking regulator that varies the gate voltage of the shunt regulator in conjunction with the variation of the resistance value of the shunt regulator, and reduces the duty ratio of the switching transistor when a collector current flows through the phototransistor to generate the primary coil. The above problem is solved by an amplifier circuit according to the present invention, which is a switching power supply having a control circuit for lowering a voltage to be applied.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. First, the first of the present invention
Configurations and operations common to the amplifier circuits according to the fourth to fourth embodiments will be described with reference to the drawings. The amplifier circuit according to the embodiment of the present invention includes a preamplifier 11, power output transistors Q11 and Q12, a speaker SP serving as a load, a volume VR0 for adjusting the volume of the speaker SP, and a variable power supply 12A, 12B. This circuit is an audio amplifier that amplifies the input signal AS0 and outputs sound from the speaker SP.

The volume VR0 adjusts the level of an input signal AS0 input to itself and outputs it to the non-inverting input of the preamplifier 11 as AS1. Preamplifier 1
1 is an input signal AS whose level is adjusted by the volume VR0.
1 is amplified by a voltage, and the transistors Q11,
It is a circuit that outputs to Q12. Note that a negative feedback circuit NF is provided from the speaker SP serving as a load to the inverted input of the preamplifier 11.

Power output stage transistors Q11, Q1
2 is a voltage-amplified input signal AS using power supply voltages + Vc and -Vc supplied from the variable power supplies 12A and 12B.
1 is amplified and output to the speaker SP.
The variable power supplies 12A and 12B are each provided with a volume VR0.
Is a circuit that generates a positive power supply voltage + Vc and a negative power supply voltage −Vc, which fluctuate in conjunction with the resistance values of the power output stage, and supplies them to the collectors of the transistors Q11 and Q12 in the power output stage.

The operation of the circuit shown in FIG. 1 will be described below with reference to FIGS. FIG. 2 shows the input signal AS
FIG. 3 is a diagram showing the input signal AS1 adjusted by the volume VR0. FIG. 4 is a diagram showing the relationship between the power supply voltages + Vc, -Vc and the output voltage Vo. First, for example, the input signal AS0 shown in FIG.
Is input to the volume VR0, where the voltage level is adjusted and input to the non-inverting input + of the preamplifier 11.

Next, as shown in FIG. 3, the input signal AS1 whose level has been adjusted is voltage-amplified by the preamplifier 11 and supplied to the bases of the power output stage transistors Q11 and Q12. Next, the voltage-amplified input signal is current-amplified by the power output stage transistors Q11 and Q12 and output to the speaker SP as an output voltage Vo. The power supply voltage ± Vc supplied to the power output stage transistors Q11 and Q12 is a voltage as shown in FIG. 4. The following describes how this voltage ± Vc is generated and supplied. explain.

The power supply voltage ± Vc is generated by the variable power supplies 12A and 12B, respectively, and fluctuates in conjunction with the resistance value of the volume VR0. That is, when the volume of the speaker is small and the output voltage Vo is low because the resistance of the volume is large, a low power supply voltage ± Vc is generated. In addition, the volume of the speaker is large and the output voltage Vo is small because the resistance of the volume is small. When it is high, a high power supply voltage ± Vc is generated.

The fluctuation of the output voltage Vo and the power supply voltage ± V
FIG. 5 shows the relationship between c and the variation. In FIG. 5, it can be seen that when the output voltage Vo is increased by increasing the resistance value of the volume, the power supply voltage ± Vc also increases in conjunction therewith. As described above, in the present invention, it is not necessary to constantly supply a high constant voltage corresponding to the maximum output of the amplifier to the transistor in the power output stage, so that heat is not concentrated on the transistor in the power output stage.

Therefore, since it is not necessary to design a special heat radiation for the power transistor as in the prior art, the power transistor is easy to handle, and even if it is a monolithic IC with a built-in overheat protection circuit which has been difficult to use until now. It can be used easily. Further, the output voltage Vo of the circuit of the present embodiment draws a curve as shown in FIG. Therefore, even if a transformer having poor regulation characteristics as shown in FIG. 12, for example, is used by generating and supplying a power supply voltage having the characteristics shown in FIG. Since an output voltage that draws a sharply upward-sloping curve is generated, the result is no different from using a transformer having an effective regulation characteristic.

Therefore, the number of windings of the winding is increased and the winding is large.
Since it is not necessary to use a transformer having high cost and good regulation characteristics, it is possible to reduce the cost and the size of the device. Further, since the power supply voltage ± Vc is changed in accordance with the change in the output voltage Vo, the power consumption in the power output stage transistor having the largest power consumption is different from the conventional case where a constant voltage is supplied to the power output stage transistor. Power loss can be reduced.

FIG. 13 is a diagram for explaining the relationship between output power and power consumption loss in the power output stage transistor of the present invention. As shown in FIG. 13, the loss of power consumption in the transistor in the power output stage is significantly reduced as compared with the related art. Therefore, the efficiency of this transistor can be improved, which is also effective.

Based on the above points, an actual circuit configuration will be described below. 6 to 13 are diagrams illustrating the amplifier circuit according to the present embodiment. (1) First Embodiment Hereinafter, a first embodiment will be described with reference to FIG. This circuit includes, as shown in FIG.
The input signal AS is composed of a power supply section having a bridge circuit 14 and a volume-linked variable power supply circuit 15 and an amplification section having a preamplifier 11, power output stage transistors Q11, Q12 and a volume VR1. And outputs the amplified signal to the speaker SP.

First, the configuration of the power supply unit will be described. The transformer 13 transforms the AC voltage and outputs it to the bridge circuit 14. The bridge circuit 14 is a circuit composed of four diodes and rectifying the voltage transformed by the transformer. The volume-linked variable power supply circuit 15 generates a power supply voltage ± Vc that fluctuates in conjunction with the resistance value of a volume VR1 described later, and generates a power output stage transistor Q1 described later.
1 and Q12.

This circuit has a volume V as shown in FIG.
Interlocking volume VR2 whose value fluctuates in conjunction with R1
And comparators CP1 and CP2 provided symmetrically with respect to the ground potential GND.
Power transistors T1,
T2. Next, the configuration of the amplification unit will be described.

The volume VR1 is an element for adjusting the voltage level of the input signal AS. The preamplifier 11 receives the input signal AS whose voltage level has been adjusted by the volume VR1.
Is a circuit for amplifying the voltage. The power output stage transistors Q11 and Q12 are push-pull connected power transistors, and current-amplify the input signal voltage-amplified by the preamplifier 11 and supply the amplified signal to the speaker SP.

The comparators CP11 and CP12 are circuits that compare a fixed reference voltage with a voltage defined by the interlocking regulator VR2, and change the emitter voltages of the power transistors T1 and T2 according to the comparison result.
According to this circuit, first, an AC voltage is applied from an AC power supply (not shown) to the transformer 13, where it is transformed and output to the bridge circuit.

This AC voltage is rectified by the bridge circuit 14 to generate a constant voltage ± Vcc. This constant voltage ± Vcc
, The power supply voltage ± Vc is generated by the volume-linked variable power supply circuit 15 and the power output stage transistor Q
11 and supplied to the collector of Q12. On the other hand, in the amplifying section, the input signal AS is output to the volume VR1,
The voltage level is adjusted by this volume VR1 and input to the non-inverting input + of the preamplifier 16.

The input signal AS whose voltage level has been adjusted is amplified by the preamplifier 16. The voltage-amplified input signal is current-amplified by the power output stage transistors Q11 and Q12 and supplied to the speaker SP.
Sounds more. In the above circuit, the operation of the volume-linked variable power supply circuit 15 is a feature of the present embodiment, and the operation will be described in detail below.

The interlocking regulator VR2 provided in the interlocking variable power supply circuit 15 is set so that its resistance value fluctuates in conjunction with the adjusting resistor VR1. That is,
When the resistance value of the volume VR1 increases, the interlocking volume V
The resistance value of R2 also increases, and as the resistance value of volume VR2 decreases, the resistance value of interlocking volume VR2 also decreases.

Focusing only on the positive side operation, the resistance value of the volume VR1 increases (the volume decreases).
Then, the resistance value of the interlocking regulator VR2 also increases. on the other hand,
The interlocking regulator VR2 defines the voltage of the inverting input of the comparator CP1. Therefore, when the resistance value of the regulator VR1 increases and the resistance value of the interlocking regulator VR2 increases, the voltage of the inverting input of the comparator CP1 increases, so that the output of the comparator CP1 decreases and the emitter voltage of the power transistor T1 decreases. Works.

Therefore, power supply voltage ± Vc generated from constant power supply ± Vcc decreases. This is the same for the operation on the negative side. Conversely, when the resistance value of the volume VR1 decreases and the volume increases, the resistance value of the interlocking volume VR2 also decreases, and the voltage on the inverting input side of the comparators CP1 and CP2 decreases. The power supply voltage ± Vc increases because the transition is made in the direction of increasing the emitter voltage.

As described above, the power supply voltage ± Vc increases when the volume increases due to the fluctuation of the resistance value of the volume, and decreases when the volume decreases. In this manner, in the present embodiment, the power supply voltage supplied to the transistors Q11 and Q12 in the power output stage can be varied in accordance with the loudness of the volume of the speaker. Is not applied.

Therefore, heat is not concentrated on the transistor in the power output stage, and it is not necessary to design a special heat radiation for the power transistor as in the prior art, so that the handling becomes easy and it has been difficult to use it until now. Even a monolithic IC with a built-in overheat protection circuit can be easily used. Further, since the circuit configuration can be realized by using a transformer having poor regulation characteristics, the size and cost can be reduced.

Further, since the power supply voltage ± Vc is varied in accordance with the variation of the output voltage Vo, the loss of power consumption in the power output stage transistor having the largest power consumption can be reduced, and the efficiency of this transistor can be reduced. Can be improved. (2) Second Embodiment Hereinafter, a second embodiment of the present invention will be described with reference to FIG. Note that the description of items common to the first embodiment will be omitted to avoid duplication.

This circuit has substantially the same configuration as that of the first embodiment, but differs from the circuit of FIG. 6 in the configuration and operation of a volume-linked variable power supply circuit which is a feature of the present invention. Hereinafter, only this configuration and operation will be described. The volume-linked variable power supply circuit of the present embodiment includes power transistors Q21 and Q22 and transistors TR1 and TR1.
TR2, first to fifth resistors R1 to R5, interlocking regulator V
This is a step-down circuit having R11.

The power transistors Q21 and Q22 are provided on both the positive and negative sides of the ground potential GND, and operate to generate the power supply voltage ± Vc supplied to the power output stage transistor from the constant voltage ± Vcc. is there. The interlocking volume VR11 is a volume whose resistance value fluctuates in conjunction with the resistance value of the volume for adjusting the volume, similarly to the interlocking volume VR2 of the first embodiment.

In the above circuit, when the resistance value of the interlocking regulator VR11 fluctuates, the first resistor R1 and the second resistor R
2, the base potential of the transistor TR1 determined by the fifth resistor R5 fluctuates, and the collector current of the transistor TR1 fluctuates according to the fluctuation. That is, for the positive output voltage + Vc, the voltage Vz of the Zener diode is
And the voltage V between the base and the emitter of the transistor TR1.
The sum with BE is a reference voltage, and this voltage is compared with the base potential of the transistor TR1 determined by the first resistor R1, the second resistor R2, the fifth resistor R5, and the interlocking volume VR11.

When the base current of the transistor TR1 also decreases due to a decrease in the resistance value of the interlocking regulator VR11,
Since the collector current of the transistor TR1 also decreases and the base current of the power transistor Q21 increases, the output voltage + Vc also increases. Conversely, when the base current of the transistor TR1 increases, the output voltage becomes + Vc.
Will decrease. Therefore, the positive output voltage + Vc
Fluctuates in conjunction with the resistance value of the interlocking regulator VR11.

On the negative side, the emitter voltage of power transistor Q22 is defined by transistor TR2, and the base potential of transistor TR2 is
It is determined by the potential difference between the positive output voltage + Vc and the negative output voltage -Vc and the bleeder ratio of the resistors R3 and R4. On the negative side, the positive output voltage +
When Vc decreases, the base potential of the transistor TR2 also decreases (the absolute value of the base potential decreases) by the reduced bleeder ratio, and when the positive output voltage + Vc increases, the transistor TR2 increases by the increased bleeder ratio. Also increases (the absolute value of the base potential increases).

When the base potential of the transistor TR2 rises, the emitter voltage of the power transistor Q22 increases, and the negative output voltage -Vc also increases.
2 lowers the base potential of power transistor Q22.
And the negative output voltage -Vc also decreases. In short, the negative output voltage −Vc varies according to the variation of the positive output voltage + Vc by the variation of the + Vc, so that the bleeder ratio of the resistors R3 and R4 is 1
In this case, the positive output voltage + Vc and the negative output voltage -Vc are symmetrical voltages.

Usually, in order to obtain a symmetrical voltage between positive and negative, it is a general circuit configuration to configure a circuit symmetrical with respect to the ground potential. However, in the above circuit, first, a positive output voltage + Vc Is controlled by the resistance value of the interlocking regulator VR11, and then the positive output voltage + Vc and the negative output voltage −
Since the negative side circuit is controlled by the voltage between Vc and Vc, there is no need to configure a positive and negative symmetrical circuit as shown in FIG.

Accordingly, on the negative side, a zener diode Vz, a resistor, and the like, which are necessary elements on the positive side, are not required, so that a symmetrical output voltage ± Vc can be generated with a simpler circuit configuration. It is also effective in point. The values of the voltage ± Vc obtained by the above circuit are + Vc = (Vz + Vbe1) · (1 + R1 / RA) −Vc = | + Vc | − (| + Vc | + Vbe2) · (1+
R3 / R4). In the above equation, 1 / RA = 1 / R2 + 1 / (R5 + VR).

Vbe1 is the base-emitter voltage of the transistor TR1, and Vbe2 is the transistor T1.
This is the base-emitter voltage of R2. VR is the resistance value of the volume VR11. From the above formula, the volume VR
11, the power supply voltage ± Vc decreases when the resistance value VR increases and the speaker volume decreases, and conversely, when the VR decreases and the speaker volume increases, the power supply voltage ± Vc decreases.
Is larger.

The circuit of this embodiment has the advantages that it can be realized with a relatively simple circuit configuration and that the cost is relatively low, in addition to the functions and effects described in the first embodiment. (3) Third Embodiment Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. Note that the description of items common to the first and second embodiments will be omitted to avoid duplication.

This circuit has substantially the same configuration as that of the first embodiment, but differs from the circuit of FIG. 6 in the configuration and operation of the volume-linked variable power supply circuit, which is a feature of the present invention. Hereinafter, only this configuration and operation will be described. FIG. 8 shows the configuration of this volume-linked variable power supply circuit. This circuit comprises power transistors Q31, Q32,
Pulse modulation circuits 21, 22, comparators 23, 24,
Interlocking regulators VR21, VR22, diode D21,
D22, a circuit having coils L21 and L22,
This is a step-down chopper power supply that generates a power supply voltage ± Vc that fluctuates in accordance with the resistance value of a volume control volume (not shown) and supplies the power supply voltage ± Vc to the power output stage transistor of the amplifier.

The power transistors Q31 and Q32 are switching elements provided on both the positive and negative sides with respect to the ground potential GND. The power transistors Q31 and Q32 are supplied with power from the constant voltage ± Vcc to the power output stage transistors by turning on / off. This is an element for generating the voltage ± Vc. The pulse modulation circuits 21 and 22 include comparators 23 and 2 described later.
4 is converted to PWM (Pulse Width Modulati)
on) A circuit that modulates and outputs the modulated signals to the bases of the power transistors Q31 and Q32.

The comparators 23 and 24 output the reference voltage Vr
1 and Vr2 are compared with voltages set by the interlocking regulators VR21 and VR22, and the comparison result is output to the pulse modulation circuits 21 and 22, respectively. The interlocking regulators VR21 and VR22 are, like the interlocking regulator VR2 of the first embodiment, the resistors whose resistance values fluctuate in conjunction with the resistance value of the volume for adjusting the volume.

The operation of the above circuit will be described below. In this circuit, the resistance values of the interlocking regulators VR21 and VR22 fluctuate in conjunction with the resistance value of an unillustrated volume adjusting volume. For example, when the resistance value of the volume increases and the volume of the speaker decreases, the resistance values of the interlocking volumes VR21 and VR22 also increase, and the inverting inputs of the comparators 23 and 24-
Potential rises. Conversely, when the resistance value of the volume decreases and the volume of the speaker increases, the interlocking volume VR21,
The resistance value of VR22 also decreases, and comparators 23 and 24
, The potential of the inverting input-of the input terminal falls.

The potential of the inverting input-rises and the reference voltage Vr
When the voltage exceeds 1, Vr2, the outputs of the comparators 23 and 24 become "L". When the potential of the inverting input-falls below the reference voltages Vr1, Vr2, the comparators 23, 24
Becomes "H". Thus, the comparator 2
The outputs 3 and 24 vary depending on the resistance values of the interlocking regulators VR21 and VR22, that is, the resistance values of the volume adjustment volume. The outputs of the comparators 23 and 24 are PWM-modulated by the pulse modulation circuits 21 and 22, and the modulation results are output to the bases of the power transistors Q31 and Q32.

Thus, the power transistors Q31,
Q32 performs an ON / OFF operation, and the ON / OFF duty ratio is determined by the outputs of the pulse modulation circuits 21 and 22. If the duty ratio is large, the power supply voltage ± Vc supplied to the transistor in the power output stage (not shown) increases, and if the duty ratio is small, the power supply voltage ± Vc decreases, so that the power supply voltage ± Vc decreases. When the resistance values of the interlocking regulators VR21 and VR22 fluctuate, the power supply voltage ± Vc also fluctuates.

As described above, in the present embodiment, the circuit of the present invention in which the power supply voltage is made variable in accordance with the sound volume is realized, so that the same effects as those of the first and second embodiments are obtained. Further, since the dropper circuit as in the first and second embodiments is not used and the chopper circuit with relatively small power consumption loss is used, the circuit described in the first and second embodiments is the same as that in the first and second embodiments. On the contrary, there is an advantage that not only the efficiency in the power output stage can be improved, but also the efficiency of the entire system including the amplifier circuit and the power supply unit can be improved.

The circuit using the step-down chopper as the volume-linked variable power supply circuit is not limited to the circuit shown in FIG. 8, but may be a circuit such as that shown in FIG. In this case, unlike the circuit of FIG. 7, as shown in FIG. 8, only the positive voltage + Vc and GND are used, and the positive + Vc and negative −
Vc can be generated, which is effective when a single power supply such as a battery is used.

(4) Fourth Embodiment Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings. Note that the description of items common to the first, second, and third embodiments will be omitted to avoid duplication. FIG. 10 is a diagram showing the configuration of a flyback type power supply unit that generates a power supply voltage ± Vc to be supplied to a transistor in a power output stage of an amplifier (not shown) in the circuit according to the present embodiment.

This circuit comprises a line filter 31, a bridge circuit 32, a pulse transformer 33, a control IC 3
4, light emitting diode 35A, phototransistor 35B
This is a circuit having a photocoupler 35 and an interlocking regulator VR31. The line filter 31 is a circuit that removes noise of the AC voltage. The bridge circuit 32 is a circuit that rectifies the AC voltage input via the line filter 31.

The pulse transformer 33 is a high-frequency (several hundred kHz) transformer that inputs a rectified AC voltage to its primary side and thereby induces an electromotive force on the secondary side. The switching transistor TR31 is ON / OF
F operation, and the pulse transformer 33
Is a switching element for fluctuating the voltage on the primary side.

The control IC 34 is an example of a control circuit, and turns on / off the switching transistor TR31.
This is an IC that controls the FF. The photocoupler 35 including the light emitting diode 35A and the phototransistor 35B is
This element is necessary to insulate the secondary side from the primary side while providing feedback from the secondary side to the primary side.

The light emitting diode 35A is connected in series to the output of the secondary side of the pulse transformer 33 together with the shunt regulator TA. The phototransistor 35B is connected to the control IC 34, is turned on when the light emitting diode 35A emits light, and a current flows,
The control IC 34 is a detecting element for detecting the current and changing the switching duty ratio of the switching transistor TR31.

Similar to the interlocking regulator VR2 described in the first embodiment, the interlocking volume VR31 is a volume whose resistance value fluctuates in conjunction with the resistance value of the volume for adjusting the volume. The operation of the above circuit will be described below. First, when the transistor TR31 is ON, the flyback converter stores in the pulse transformer 33 the current determined by the inductance of the primary coil of the pulse transformer 33 and the input voltage, that is, the energy generated by the collector current of the transistor TR31. When TR31 is OFF, the pulse transformer 33
Is supplied (output) as a current flowing through the diode through the secondary side coil to the load. The AC voltage from which noise has been cut by the line filter 31 is rectified by the bridge circuit 32 and supplied to the primary coil of the pulse transformer 33. Then, an electromotive force is induced on the secondary side to generate the power supply voltage ± Vc.

The light-emitting diode 35A and the shunt regulator TA are connected to this output as described above, and the gate of the shunt regulator is connected to the resistors R31 and R3.
2 and the interlocking regulator VR31. Therefore, when the resistance value of the interlocking regulator VR31 changes, the potential VA at the connection between the resistors R31 and R32 also changes, so that the gate voltage of the shunt regulator also changes due to the change in the resistance value of the interlocking resistor VR31.

Therefore, the constant voltage generated by the shunt regulator also varies according to the resistance value of the interlocking regulator VR31, and the light emission amount of the light emitting diode 35A also varies according to the constant voltage. When the resistance value of the interlocking regulator VR31 is small and the volume of the speaker is large, the above-described potential VA is used.
Therefore, the amount of current flowing through the shunt regulator TA increases, and the amount of light emitted from the light emitting diode 35A increases.

Then, the phototransistor 35 constituting the photocoupler 35 together with the light emitting diode 35A
The amount of current flowing through B increases. Control IC
34 detects this and switches the switching transistor TR3
It operates in the direction of changing the duty ratio of 1 to increase the collector current. Accordingly, the current flowing through the primary side coil is large, and the primary side electromotive force is large, so that the voltage induced on the secondary side, that is, the power supply voltage ± Vc also increases.

Conversely, when the resistance value of the interlocking regulator VR31 is large and the volume of the speaker is low, the potential VA
Therefore, the amount of current flowing through the shunt regulator TA decreases, and the effective amount of light emission of the light emitting diode 35A also decreases. Then, a phototransistor 35B constituting a photocoupler 35 together with the light emitting diode 35A
The amount of current flowing through the device also decreases. The control IC 34 detects this and changes the duty ratio of the switching transistor TR31 to reduce the collector current.

Accordingly, the current flowing through the primary side coil is small, and the primary side electromotive force is small, so that the voltage induced on the secondary side, that is, the power supply voltage ± Vc is also low. Thus, in the circuit of the present embodiment, the power supply voltage ± Vc is changed by changing the resistance value of the interlocking regulator VR31. Further, in the circuits of the first and second embodiments, although the efficiency in the power output stage is improved, the efficiency of the whole amplifier is not changed. However, according to the circuit of the present embodiment, one of the pulse transformers 33 is used. The power supply voltage ± Vc is controlled by controlling the voltage on the next side with the interlocking regulator VR31.
, The power consumption loss of the amplifier as a whole can be greatly reduced, and there is an advantage that the efficiency can be improved.

Although the chopper circuit of the third embodiment has a similar effect in terms of improvement in efficiency, the use of the switching power supply of the present embodiment has a lower power consumption than the circuit of the third embodiment. Since the loss can be reduced, the efficiency can be further improved. Needless to say, the effects of the present invention described in the first to third embodiments can be obtained.

In this embodiment, the circuit as shown in FIG. 10 has been described, and the configuration and connection of the interlocking regulator VR31 have been described using the configuration as shown in FIG. 11B. Is not limited to this.
Even if the configuration as shown in (a), (c), (d) is used,
A similar effect is achieved. 11 (a) to 11 (d), the resistance Rh is such that the resistance value of the interlocking regulator VR31 is 0.
It is the protection resistance when it becomes.

In the above embodiment, the dropper power supply is used as the variable power supply in the first and second embodiments, the step-down chopper power supply and the inverting chopper power supply are used in the third embodiment, and the flyback power supply is used in the fourth embodiment. Although a buck converter is used, the present invention is not limited to this. For example, when using a non-insulated DC-DC converter for a variable power supply, a boost chopper may be used, or an isolated DC-DC converter may be used.
When using a converter, for example, forward,
Center tap, half bridge, full bridge, RC
Similar effects can be obtained by using C (Ringing Choke Converter) or the like.

[0067]

As described above, according to the present invention,
Since it is not necessary to always supply a high constant voltage corresponding to the maximum output to the transistor in the power output stage, heat generation does not concentrate on the transistor in the power output stage. Therefore, it is not necessary to design a special heat radiation for the power transistor as in the prior art, so that the power transistor is easy to handle, and even a monolithic IC with a built-in overheat protection circuit, which has been difficult to use until now, is easily used. It becomes possible.

Further, since it is not necessary to use a transformer having a large number of windings and a large size, which is expensive and has good regulation characteristics, it is possible to reduce the size and cost. Furthermore, since the power supply voltage is changed in accordance with the fluctuation of the resistance value of the volume, unlike the conventional case where a constant voltage is supplied to the transistor in the power output stage, the power consumption in the transistor in the power output stage having the largest power consumption is different. Can be reduced, so that the efficiency of this transistor can be improved, which is also effective.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a first diagram illustrating the operation of the amplifier circuit of the present invention.

FIG. 3 is a second diagram illustrating the operation of the amplifier circuit of the present invention.

FIG. 4 is a third diagram illustrating the operation of the amplifier circuit of the present invention.

FIG. 5 is a fourth diagram illustrating the operation of the amplifier circuit of the present invention.

FIG. 6 is a diagram illustrating an amplifier circuit according to the first embodiment of the present invention.

FIG. 7 is a diagram illustrating an amplifier circuit according to a second embodiment of the present invention.

FIG. 8 is a first diagram illustrating an amplifier circuit according to a third embodiment of the present invention.

FIG. 9 is a second diagram illustrating an amplifier circuit according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating an amplifier circuit according to a fourth embodiment of the present invention.

FIG. 11 is a diagram illustrating a configuration of an interlocking volume according to the present embodiment.

FIG. 12 is a diagram illustrating the operation and effect of the amplifier circuit of the present invention.

FIG. 13 is a diagram illustrating the operation and effect of the amplifier circuit according to the fourth embodiment of the present invention.

FIG. 14 is a diagram illustrating a circuit configuration of a conventional amplifier circuit.

FIG. 15 is a diagram illustrating a configuration of a conventional amplifier circuit having a BTL-type power supply.

FIG. 16 is a diagram illustrating a conventional problem.

[Explanation of symbols]

 11 Preamplifier 12A, 12B Variable power supply 13 Transformer 14 Bridge circuit 15 Variable power supply Q11, Q12 Power output stage transistor SP Speaker AS, AS0, AS1 Input signal

Claims (8)

[Claims] 1. A preamplifier comprising an analog circuit for voltage-amplifying an input signal, a power output unit for current-amplifying the voltage-amplified input signal and outputting the amplified signal to a load speaker, and adjusting a volume of the speaker. A low power supply voltage is generated when the volume of the speaker is low, and a high power supply voltage is generated and supplied to the power output unit when the volume of the speaker is high, in conjunction with the fluctuation of the resistance value of the volume and the volume of the volume. An amplifier circuit having a variable power supply. 2. The amplifier circuit according to claim 1, wherein said variable power supply is a dropper power supply for lowering a constant power supply voltage. 3. The amplifier circuit according to claim 1, wherein said variable power supply has a DC-DC converter including an inverter circuit and a rectifying / smoothing circuit in a part thereof. 4. The amplifier circuit according to claim 3, wherein said DC-DC converter is a non-insulated DC-DC converter in which said inverter circuit and said rectifying / smoothing circuit are not insulated. 5. The non-insulated DC-DC converter includes a switching element that performs a switching operation, and is a chopper power supply that steps down a constant power supply voltage at a duty ratio of the switching element. 2. The amplifier circuit according to 1. 6. The amplifier circuit according to claim 3, wherein the DC-DC converter is an insulation type DC-DC converter in which the inverter circuit and the rectifying / smoothing circuit are insulated. 7. The insulated DC-DC converter,
7. The amplifier circuit according to claim 6, wherein the amplifier circuit is one of a flyback, a forward tap, a center tap, a half bridge, a full bridge, and a ringing choke converter. 8. The variable power supply includes a rectifier circuit for rectifying an AC voltage, a primary coil and a secondary coil, a transformer for transforming the rectified voltage, and a primary side of the transformer. A switching transistor that has a collector connected to the coil and performs a switching operation to vary the voltage generated by the primary coil at a duty ratio thereof; a light emitting diode having one end connected to one end of an output of the secondary coil; A photocoupler including a phototransistor through which a collector current having a current amount corresponding to the light emission amount of the light emitting diode flows; and a shunt connected between the other end of the secondary output of the transformer and the other end of the light emitting diode. A regulator, and an interlocking regulator that fluctuates a constant voltage generated by the shunt regulator in conjunction with a change in the resistance value of the regulator. A switching power supply comprising: a control circuit that changes a duty ratio of the switching transistor when a collector current flowing through the phototransistor changes and controls a voltage generated by the primary coil. 2. The amplifier circuit according to 1.