JP3360419B2 - Amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a high-efficiency amplifier circuit used for amplifying power of an audio signal or the like.

[0002]

2. Description of the Related Art A conventional audio power amplifier circuit generally drives an output stage element for power amplification with a fixed power supply voltage (a voltage corresponding to a maximum output). However, in such a case, a high voltage is applied between the collector and the emitter of the output stage element at the time of a small level input.
There is a drawback that power loss (heat generation) is large and efficiency is poor.

In order to solve such a problem, the applicant of the present invention has proposed a device described in Japanese Patent Application Laid-Open No. Hei 4-372212. This is because the power supply voltage is switched according to each cycle change of the input signal waveform to change the power supply voltage waveform (collector voltage waveform) for driving the output stage element, so that the collector-emitter voltage V of the output stage element is changed. _{The CE} is driven while being kept substantially constant regardless of changes in the input signal.

[0004] In such an amplifier circuit, in addition to the power loss being reduced and the efficiency being improved, there is an advantage that a larger output can be taken out than an ordinary amplifier circuit by using an output stage element having the same withstand voltage. . That is, generally, in an amplifier circuit, a dynamic power of 20% to 30% higher than the continuous maximum output can be obtained due to the influence of power supply regulation. In a normal amplifier circuit, as shown in FIG. 2, a power supply voltage supply terminal (collector) of an output stage element according to an input signal waveform
And the applied voltage V _CE between the output terminal (emitter) and the output terminal (emitter) changes. Therefore, when V _CE of the output stage element during continuous output to set the breakdown voltage barely To become as its driving power source voltage, exceeds the breakdown voltage by the dynamic power. For this reason, the power supply voltage must be set to a voltage corresponding to a power 20 to 30% lower than the withstand voltage of the output stage element, and the maximum power during continuous output is a value corresponding to a voltage 20 to 30% lower than the withstand voltage. Was restricted to

[0005] In contrast, according to the high efficiency amplifier circuit, as shown in FIG. 3, the output since V _CE of stage elements is maintained at a low value, and a power supply voltage higher than for normal amplifier circuit However, the dynamic power does not cause the _VCE of the output stage element to exceed the withstand voltage. Accordingly, it is possible to drive the power supply voltage higher than that of a normal amplifier circuit, and to increase the maximum power accordingly.

[0006]

In the high efficiency amplifier circuit, in order to obtain the maximum efficiency in actual use, the input signal frequency is shown in FIG. 4 (a) from a low band to a middle band of about several kHz. Thus, the switching circuit is made to follow the input signal (the switching frequency is, for example, 50 to 100 kHz),
The input signal frequency e.g. 10kHz or more high-frequency, as shown in FIG. 4 (b), the collector voltage V _C of the output stage element
It is desirable to hold the peak. This is because, in order to make the switching circuit follow up to a high-frequency input signal frequency, it is necessary to increase the switching frequency, so that the switching loss increases and the efficiency in actual use decreases.

[0007] However, when such peak hold against high frequency signal, because the V _CE as shown in FIG. 4 (b) increases, the V _CE of the output stage element for dynamic power of the high frequency signal Exceeds withstand voltage.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned point, and by changing a power supply voltage waveform for driving an output stage element by switching a power supply voltage in accordance with each period change of an input signal waveform, In a high-efficiency amplifier circuit that is driven while keeping the voltage between the power supply voltage supply terminal of the output stage element and its output terminal substantially constant irrespective of changes in the input signal, the output stage for the high-frequency signal Provided is an amplifier circuit that prevents the voltage between the power supply terminal and the output terminal of the output stage element from exceeding the withstand voltage due to the dynamic power of the high-frequency signal when the voltage at the power supply terminal of the device is peak-held. What you want to do.

[0009]

According to the first aspect of the present invention,
A positive-side and a negative-side output stage element for amplifying an audio signal and supplying the amplified signal to a load, and a change in the signal waveform in each cycle with respect to a relatively middle and low frequency component of the audio signal. The power supply voltage waveform for driving the output stage element is changed so that the applied voltage between the power supply voltage supply end of the output stage element and the output end thereof is kept substantially constant. A peak hold type power supply voltage for performing control and changing a power supply voltage waveform for driving the output stage element in accordance with a peak hold value of a signal waveform to be amplified for a relatively high frequency component of the audio signal. Positive and negative to control
The output stage element power supply voltage control means on the positive side and the signal of the positive side output stage element in the peak hold type power supply voltage control.
Signal input terminal and the power supply voltage supply terminal of the negative side output stage element.
The applied voltage is monitored during the
From a voltage corresponding to a predetermined value within the rated withstand voltage value of the power stage element
When trying to increase, the input of the positive output stage element
Reduce the level of the signal to be amplified supplied to the force end
Negative side amplitude limiting means, and the peak hold type power supply voltage
In the control, the signal input terminal of the negative output stage element is
Applied voltage between the positive side output stage element and the power supply terminal
Is monitored, and the applied voltage is fixed to the positive output stage element.
Will be higher than the voltage corresponding to the specified value within the rated withstand voltage
Is supplied to the input terminal of the negative output stage element.
And positive-side amplitude limiting means for reducing the level of the signal to be amplified .

[0010]

According to a second aspect of the present invention, there is provided a positive and negative output stage element for driving a load in accordance with an input audio signal, and a positive and negative power supply voltage for supplying each of the output stage elements. Side and negative side main power supply paths, positive and negative switching elements inserted into each of these main power supply paths to turn on and off each of the main power supply paths, respectively, and inserted into each of the main power supply paths. Positive-side and negative-side smoothing circuits for smoothing the output of the switching elements and supplying the output elements to the output stage elements; and turning on and off the switching elements in response to changes in each cycle of the audio signal. The switching ratio is variably switched, and the positive and negative switching control means for supplying the power required by the load mainly from the main power supply path, and to each of the output stage elements separately from the main power supply path. Positive and negative power supply Positive and negative auxiliary power supply paths for supplying a voltage, and capable of supplying power in response to a change in the audio signal with a faster response than the main power supply path; A positive-side and negative-side auxiliary power supply amount adjusting element inserted into the auxiliary power supply path to adjust the amount of power supply to the load, and the auxiliary power supply amount adjusting element with a signal obtained by shifting an input signal. And controls the auxiliary power supply amount adjusting elements for relatively middle and low frequency components of the audio signal by following changes in the signal waveform in each cycle, thereby controlling the audio signal. For a relatively high-frequency component of the signal, the respective auxiliary power supply amount adjusting elements are controlled in accordance with the peak hold value of the signal waveform, and the power supply amount to the load by the main power supply paths is insufficient. Supply from each auxiliary power supply path An auxiliary power supply amount control means side and the negative side, by monitoring the voltage applied between the power supply voltage supply terminal of the output stage elements of the positive side of the signal input terminal of the output stage element and the negative side, the applied When the voltage is going to be higher than a voltage corresponding to a predetermined value within the rated withstand voltage value of the negative output stage element, the level of the signal to be amplified supplied to the input terminal of the positive output stage element is changed. Monitoring the applied voltage between the signal input terminal of the negative output stage element and the power supply terminal of the positive output stage element, and When the voltage becomes higher than a voltage corresponding to a predetermined value within the rated withstand voltage of the positive output stage element, the level of the signal to be amplified supplied to the input terminal of the negative output stage element is reduced. Side auxiliary power supply path, It is driven by a power supply voltage capable of supplying a substantially maximum output to the load regardless of the amount of power supply to the load by the main power supply path.

[0012]

According to the first aspect of the present invention, in the peak hold power supply voltage control, the signal input of the positive side output stage element is controlled.
Voltage between the terminal and the power supply terminal of the negative output stage element.
The applied voltage is monitored for the negative side output stage element.
Should be greater than the voltage corresponding to the specified value within the rated withstand voltage
To the input terminal of the positive output stage element
While reducing the level of the signal to be amplified,
The signal input terminal of the negative output stage element and the power of the positive output stage element
Monitor the applied voltage between the power supply terminal and the
Pressure to a specified value within the rated withstand voltage of the positive output stage element.
When trying to become larger than the corresponding voltage,
Of the signal to be amplified supplied to the input terminals of the
Since the bell is reduced, it is possible to prevent the voltage applied between the power supply voltage supply terminal of the output stage element and the output terminal from exceeding the withstand voltage due to the dynamic power of the high band signal. Therefore, the maximum power can be increased by increasing the power supply voltage accordingly.

[0013]

According to the second aspect of the present invention, an applied voltage between the signal input terminal of the positive-side output stage element and the power supply voltage supply end of the negative-side output stage element or the voltage applied to the negative-side output stage element. By limiting the amplitude according to the applied voltage between the signal input terminal and the power supply voltage supply terminal of the positive output stage element, the power supply voltage supply terminal and the output terminal of the output stage element can be controlled by the dynamic power of the high-frequency signal. Can be prevented from exceeding the withstand voltage.

[0015]

FIG. 1 shows an embodiment of the present invention. FIG. 1 shows only the + side circuit. The negative side circuit 12 '(output stage element power supply voltage control means) is configured in the same manner as the positive side,
It is driven by a power supply 46 (power supply voltage -B). The following description is made only on the + side.

The audio input signal output from the voltage amplifying stage is supplied to the drive stage transistors Qd and Qd 'via the bias circuit 40, and drives the output stage transistors Qa and Qa' to load the load (speed). F) Supply necessary power to 10.

In the output stage element power supply voltage control means 12, a main power supply path 42 for mainly supplying power to the load 10 is provided.
Is a power supply 44 (power supply voltage + B), a switching transistor Qs (switching element), a smoothing coil L1 (smoothing circuit), an output transistor Qa, and a resistor Ra (= R
a '). The auxiliary power supply path 48 for supplying the power supply shortage by the main power supply path 42 includes a power supply 44 and a resistor R.
s, transistor Qb (element for adjusting auxiliary power supply),
The output stage transistor Qa includes a resistor Ra.

The resistance Rs is a current I flowing through the auxiliary power supply path 48.
_This is a small resistor for detecting _Qb . R by the current I _Qb
The voltage V _Rs generated at both ends of s is input to the hysteresis comparator 50. Hysteresis comparator 50
Constitutes switching control means together with the resistor Rs, and when the voltage _VRs becomes higher than a predetermined upper limit value V _HCH , "0"
Turning the transistor Qs and output, once "0" after reaching the until the voltage V _Rs drops to a predetermined lower limit value V _HCL holds "0", the voltage V _Rs than the lower limit value V _HCL and outputs the composed and "1" low to turn off the transistor Qs, once the voltage V _Rs once they become "1" holds "1" until becomes higher than a predetermined upper limit value V _HCH. Thus, the transistor Qs performs a switching operation. Smoothing coil L1
Is to smooth the output waveform of the transistor Qs by this switching operation and supply it to the load. The diode D3 is a flywheel diode that forms a current path for a current flowing out of the smoothing coil L1 when the transistor Qs is turned off.

A DC power supply 52 and a high-frequency peak hold circuit 53 are connected between the base of the transistor Qd and the base of the transistor Qb. This signal path 51 corresponds to auxiliary power supply control means. DC power supply 52
A potential obtained by shifting the base potential of the transistor Qd by V1 is applied to the base of the transistor Qb. As a result, the collector-emitter voltage V _Qa of the output stage transistor Qa is maintained at a predetermined low voltage determined by the value of the DC voltage V1 (the minimum voltage at which the output stage transistor Qa can ensure linearity, usually 2-3 V). It is.

The high-frequency peak hold circuit 53 outputs the input signal waveform as it is for an input signal in the middle and low frequency (for example, several kHz or less), and outputs the input signal waveform for a high frequency (for example, 10 kHz or more). , And peak-holds and outputs the input signal waveform.

The amplitude limiting means 14 is connected between the collector of the output transistor Qa and the base of the negative transistor Qd '. Voltage between the base of the output stage transistor Qa collector and the negative-side transistor Qd 'will vary depending on the collector-emitter voltage V _Qa of the output stage transistor Qa, the amplitude limiting means 14 monitors the meantime the voltage Then, when it tries to become larger than the voltage corresponding to the rated withstand voltage of the collector-emitter voltage of the output stage transistor Qa (during a negative cycle of the input signal), the amplitude of the input signal is limited and Q
Do not exceed the rated withstand voltage of a.

The operation of the circuit shown in FIG. 1 will be described. First,
It is assumed that the output of the hysteresis comparator 50 is “1” and the switching transistor Qs is off. The audio input signal is supplied to the output transistor Qa via the transistor Qd. As a result, the current I _Qb flows through the auxiliary power supply path 48 to the transistor Qa and is supplied to the load 10. This current I _Qb generates a voltage V _Rs across the resistor Rs. This voltage _VRs is a predetermined upper limit value V
_When the signal reaches _HCH , the output of the hysteresis comparator 50 is inverted to "0" to turn on the transistor Qs. Thus, current is supplied from the main power supply path 42.

When the transistor Qs is turned on, the resistance of the main power supply path 42 is smaller than the resistance of the auxiliary power supply path 48. Therefore, once the transistor Qs is turned on, the current I _L1 from the main power supply path 42 increases, The current I _Qb from the auxiliary power supply path 48 decreases accordingly. The currents I _L1 and I _Qb are _equal to the summation point 49.
Are supplied to the load 10 via the transistor Qa as the load current I _RL , thereby supplying necessary electric power to the load 10.

_Shortly before the current I _Qb of the auxiliary power supply path 48 becomes 0, the voltage V _Rs across the resistor Rs reaches a predetermined lower limit V _HCL , the output of the comparator 50 is inverted to “1”, and the transistor Qs is turned off. Turn off. When the transistor Qs is turned off, the current I _L1 of the smoothing coil L1 flows through the diode D3. As the current I _L1 gradually decreases, the current I _Qb of the auxiliary power supply path 48 increases, and when the voltage V _Rs reaches a predetermined upper limit value V _HCH , the output of the comparator 50 is again inverted to “0” and the transistor Qs is turned on, and the same operation is repeated thereafter. As described above, the transistor Qs is switched by self-excited oscillation with the ratio of the ON period and the OFF period being variably set according to the input signal level.

According to such an operation, the transistor Q
b is always in an active state, and a load 1
The current I _RL flowing to 0 is supplied from both the main power supply path 42 and the auxiliary power supply path 48. Transistor Qs of main power supply path 42
Is a switching drive, so the loss is small. Although the auxiliary power supply path 48 causes a loss in the transistor Qb, the current I _Qb flowing through the transistor _Qb depends on the value of the resistor Rs and the setting of the reference voltages V _HCH and V _HCL of the hysteresis comparator 50. Since it can be reduced to almost the same as the ripple current of the output current _IL1 ,
_L1 >> I _Qb, and the loss in the transistor Qb can be reduced.

The transistor Qb is always on during the positive cycle, and the collector-emitter voltage V _Qa of the output stage transistor _Qa is always low (for example, 2 to 2).
3V). Therefore, the output stage transistor Q
a can be minimized.

When a high-frequency signal is input, a high-frequency peak hold circuit 53 peak-holds the input signal and applies it to the base of the transistor Qb. When a large signal exceeding the withstand voltage of the output stage transistor Qa is input during the peak hold, the amplitude limiting means 14 limits the output of the voltage amplification stage Qd '. Driving beyond the withstand voltage is prevented. Therefore, the power supply voltage ±
B can be increased similarly to the case where the high-frequency peak hold circuit 53 is not provided, and the maximum output can be set high. The amplitude is limited to, for example, 10 kHz.
Only for the above high-frequency signals, for example, for a signal in the middle and low frequency range of several kHz or less, it is possible to extract dynamic power exceeding the withstand voltage of the output stage element in a normal amplifier circuit. Since an actual music signal requires a large amplitude at a low frequency of several hundred Hz or less, there is no practical problem at all even if the amplitude of a band of several kHz to 10 kHz or more is limited.

FIG. 5 shows a specific example of the amplitude limiting circuit of FIG. 1 are denoted by the same reference numerals. FIG. 5 shows the amplitude limiting means 14 'for the negative output stage transistor Qa'. The amplitude limiting means 14 for the positive-side output stage transistor Qa is similarly configured.

The audio signal output from the voltage output stage 39 is input to the transistors Q1 and Q1 'of the predrive stage, where the audio signal is amplified. The signal amplified by the transistor Q1 drives the output transistor Qa via the drive transistor Qd.

The main power supply path 42 supplies the main current to the output stage transistor Qa via the switching transistor Qs → coil L1 → current addition point 49. Capacitor C1
2 is for ripple absorption. The auxiliary power supply path 48 supplies an auxiliary current to the output transistor Qa via the resistor Rs → the transistor Qb. The path 51 in FIG. 1 for controlling the base potential of the transistor Qb is shown in FIG. 5 as: the base of the transistor Qd → the DC power supply 52 → the diode D1
It corresponds to a path from the base of the transistor Q11 to the emitter to the base of the transistor Qb. As a result, when the input rises rapidly, the base potential of the transistor Qb immediately rises, and the auxiliary current increases to follow this.
Thereafter, the main current gradually increases, and the auxiliary current decreases.

The collector potential V _C of the output stage transistor Qa at the positive cycle of the input signal, _{V b} Then the base potential of the transistor _{Qd, V C = V b +} V1-0.6-0.6-0.6 Becomes On the other hand, the emitter potential V _E at the output stage capacitors Qa at this time is _{V E} = V b -0.6-0.6. Therefore, the collector-emitter voltage V of the output stage transistor Qa in the positive cycle of the input signal
_Qa is given by V _Qa = V _C -V _E = V1-0.6. The value of V1 is V _Qa during the positive cycle of the input signal.
Is 2 to 3 V (the lowest voltage at which the output stage transistor Qa can ensure linearity).

The high-frequency peak hold circuit 53 includes a diode D1 and a capacitor C11. Capacitor C
11 is charged by the current flowing through the diode D1 (however, the voltage across the capacitor C11 decreases), and discharged by the base current flowing from the capacitor C11 to the transistor Q11 (however, the voltage across the capacitor C11 increases). In the high-frequency peak hold circuit 53, for example, the charge and discharge of the capacitor C11 follows an input signal in the middle and low frequency range of several kHz or less. . On the other hand, for a high frequency input signal of, for example, 10 kHz or more, the discharge of the capacitor (due to the current from the capacitor C11 to the base of the transistor Q11) cannot catch up, and the peak-held value is applied to the base of the transistor Q11. Is done. In this way, the peak hold for the high frequency signal is performed.

The 'amplitude limiting means 14 for' the negative side of the output stage transistor Qa is diode D2 between the base and the negative output stage the collector of the transistor Qa 'of the transistor Qd, the transistor Q _L, zener diode Z
D and a constant voltage circuit 16 composed of resistors R1 and R2 are connected. The resistor R3 is for adjusting the bias of the Zener diode ZD. The constant voltage circuit 16 includes a base of the transistor Qd and a negative output stage transistor Qa ′.
When the voltage between the first and second collectors is smaller than the voltage Vs set by the constant voltage circuit 16, the transistor is turned off. On the other hand, when the voltage becomes higher than the voltage Vs, the transistor becomes conductive (at this time, the input is in a positive cycle and the output transistor Qa 'is off), and a part of the drive current Ii of the drive transistor Qd is turned off. Is sucked into the transistor side so that the output stage transistor Qa cannot be driven any more. That, is limited the output of the pre-drive stage Q1 is the output voltage V ₀ is clipped. As a result, the voltage between the base of the drive stage transistor Qd and the collector of the output stage transistor Qa 'is maintained at Vs, and the voltage V _Qa ' between the collector and the emitter of the output stage transistor Qa 'exceeds its breakdown voltage. Is prevented. To realize such an operation, the value of Vs is 'collector-emitter voltage V _Qa' of the output stage transistor Qa is set to a value that the constant voltage circuit 16 becomes conductive before exceeding the breakdown voltage.

FIG. 6 shows the operation of the amplifier circuit of FIG.
(A) is an operation for a middle-low range input (1 kHz), and the collector potentials of the output stage transistors Qa and Qa 'change following the input signal waveform. (B) is a high-frequency input (10 kHz)
z) The operation at the time of the low level, the output stage transistors Qa, Q
The collector potential of a 'is peak-held.
(C) is an operation at the time of high-level input high level, in which the constant voltage circuit 16 conducts near the peak of the waveform and the pre-drive stage Q1,
The output signal V ₀ for limiting the output of Q1 'itself is clipped. In this way, it is possible to prevent the output stage transistors Qa and Qa 'from being driven beyond the withstand voltage by the peak hold operation in the high band while securing a large dynamic power in the low and middle band.

[0035]

As described above, according to the first aspect of the present invention, in the peak hold type power supply voltage control,
The signal input terminal of the positive output stage element and the power of the negative output stage element
Monitor the applied voltage between the power supply terminal and the
To a specified value within the rated withstand voltage of the negative output stage element.
When trying to exceed the corresponding voltage, the positive side
Of the signal to be amplified supplied to the input terminals of the
Signal level of the negative output stage
Between the power terminal and the power supply terminal of the positive output stage element
The voltage is monitored, and the applied voltage is changed to the positive side output stage element.
Above the voltage corresponding to the specified value within the rated withstand voltage of
When trying to connect to the input terminal of the negative output stage element,
Since the level of the signal to be amplified is reduced, the dynamic voltage of the high-frequency signal prevents the applied voltage between the power supply voltage supply terminal of the output stage element and its output terminal from exceeding its withstand voltage. can do. Therefore, the maximum power can be increased by increasing the power supply voltage accordingly.

[0036]

According to the second aspect of the present invention, the voltage applied between the signal input terminal of the positive output stage element and the power supply voltage supply terminal of the negative output stage element or the negative output stage element is applied. By limiting the amplitude according to the applied voltage between the signal input terminal and the power supply voltage supply terminal of the positive output stage element, the power supply voltage supply terminal and the output terminal of the output stage element can be controlled by the dynamic power of the high-frequency signal. Can be prevented from exceeding the withstand voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a waveform diagram showing an operation of a general amplifier circuit.

FIG. 3 is a waveform diagram showing an operation of the high efficiency amplifier circuit.

FIG. 4 is a waveform chart showing a difference in operation of the high efficiency amplifier circuit due to a difference in input signal frequency.

FIG. 5 is a circuit diagram showing a specific example of the circuit of FIG. 1;

FIG. 6 is an operation waveform diagram of the circuit of FIG. 5;

[Explanation of symbols]

10 Load 12, 12 'Output stage element power supply voltage control means 14, 14' Amplitude limiting means 42, 42 'Main power supply path 44, 46 Power supply 48, 48' Auxiliary power supply path 49, 51 Addition point, signal path (auxiliary power supply Amount control means) 53, 53 'High-frequency peak hold circuit Rs, Rs', 50, 50 'Auxiliary current detection resistor, hysteresis comparator (switching control means) L1, L1' Smoothing coil (smoothing circuit) 74 Smoothing circuit Qa , Qa 'Output stage transistor (output stage element) Qs, Qs' Switching transistor (switching element) Qb, Qb' Transistor (element for adjusting auxiliary power supply)

Claims (2)

(57) [Claims] 1. A positive side for amplifying an audio signal and supplying it to a load .
And a negative-side output stage element, and for a relatively middle-low frequency component of the audio signal, change a power supply voltage waveform for driving the output stage element by following a change in each cycle of the signal waveform. By doing so, a waveform-following power supply voltage control that keeps the applied voltage between the power supply voltage supply end of the output stage element and the output end substantially constant is performed, and a relatively high-frequency component of the audio signal is controlled. Positive and negative output stage element power supply voltage control means for performing peak hold type power supply voltage control for changing a power supply voltage waveform for driving the output stage element in accordance with the peak hold value of the signal waveform to be amplified; and In the peak hold type power supply voltage control, the positive side
The signal input terminal of the output stage element and the power of the negative output stage element
Monitor the applied voltage between the power supply terminal and the
To a specified value within the rated withstand voltage of the negative output stage element.
When trying to exceed the corresponding voltage, the positive side
Of the signal to be amplified supplied to the input terminals of the
And amplitude limiting means of the negative side to reduce the level, in the peak-hold-type power supply voltage control, the negative side
The signal input terminal of the output stage element and the power supply of the positive side output stage element.
Monitor the applied voltage between the power supply terminal and the
Pressure to a specified value within the rated withstand voltage of the positive output stage element.
When trying to become larger than the corresponding voltage,
Of the signal to be amplified supplied to the input terminals of the
An amplifier circuit comprising: a positive-side amplitude limiter for reducing a bell . 2. A positive-side and negative-side output stage element for driving a load in accordance with an input audio signal, and a positive-side and negative-side main unit for supplying a positive and negative power supply voltage to each of the output stage elements. A power path, a positive-side and a negative-side switching element that is inserted into each of the main power paths to switch on and off the respective main power path, and an output of each of the switching elements that is inserted into each of the main power paths. A positive side and a negative side smoothing circuit that supplies the output signal to each output stage element, and variably switches a ratio between an ON period and an OFF period of each switching element according to a change in each cycle of the audio signal. Positive-side and negative-side switching control means for supplying mainly the power required by the load from the main power supply path; and positive and negative power supply voltages for the output stage elements separately from the main power supply path. Power supply path A positive-side and a negative-side auxiliary power supply path that can supply power in response to a change in the audio signal with a higher speed response than the main power supply path; A positive-side and a negative-side auxiliary power supply amount adjusting element for adjusting the amount of power supply from the power supply path to the load, and controlling each of the auxiliary power supply amount adjusting elements with a signal obtained by shifting an input signal. For each of the relatively middle and low frequency components of the audio signal, the auxiliary power supply amount adjusting element is controlled by following a change in each cycle of the signal waveform, and the relatively high frequency component of the audio signal is controlled. For each component, the auxiliary power supply amount adjusting element is controlled in accordance with the peak hold value of the signal waveform, and the shortage of the power supply amount to the load by each of the main power supply paths is calculated by the auxiliary power supply. Positive and negative supplements supplied from the road Monitoring a power supply amount control means, the voltage applied between the power supply voltage supply terminal of the output stage elements of the positive side of the signal input terminal of the output stage element and the negative side, those
When the applied voltage is going to be higher than a voltage corresponding to a predetermined value within the rated withstand voltage value of the negative output stage element,
Negative-side amplitude limiting means for reducing the level of the signal to be amplified supplied to the input terminal of the positive-side output stage element; signal input terminal of the negative-side output stage element and the positive-side output stage element Monitor the applied voltage to the power supply
When the applied voltage is going to be higher than a voltage corresponding to a predetermined value within the rated withstand voltage value of the positive side output stage element,
Positive-side amplitude limiting means for reducing the level of a signal to be amplified supplied to the input terminal of the negative-side output stage element, wherein each of the auxiliary power paths is the load of each of the main power paths. An amplifier circuit driven by a power supply voltage capable of supplying substantially the maximum output to the load regardless of the amount of power supply to the load.