JP3164136B2 - Audio signal power amplifier circuit and audio device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal power amplifying circuit and an audio apparatus using the same, and more particularly, to a radio or cassette which amplifies an audio signal composed of a sound or performance sound and outputs the amplified signal from a speaker. In a device such as a tape player, a video tape recorder, a video camera, and a component stereo device that generates an audio signal (including the audio device here), the power consumption of an output circuit thereof can be reduced. The present invention relates to a power amplifier circuit suitable for a portable audio device.

[0002]

2. Description of the Related Art FIG . 4 is a simple block diagram showing a signal reproducing system circuit of a conventional portable cassette tape player as an example of an audio apparatus. 1 is a read head, 2 is a signal reproduction processing circuit including a head amplifier, an equalizer circuit, etc., 3 is an output stage amplifier, 4 is a speaker as a load, and 5 is inserted between the amplifier 3 and the speaker 4. Output electrolytic capacitor.

At the time of reproduction, a read signal A is obtained as an audio signal from a tape (not shown) on which an audio signal is recorded via a read head 1. This read signal A
Is input to the signal reproduction processing circuit 2, the high frequency bias component at the time of recording is removed, and an equalizing process or the like is performed to reproduce the audio signal B. The reproduced audio signal B is finally added to the output stage amplifier 3 and amplified. Here, an output signal C is generated and sent to the speaker 4 via the capacitor 5. as a result,
A reproduction sound is generated from the speaker 4.

Normally, in the transistor amplifier 3, an input stage up 3a for generating a pair of signals is provided at the input stage. The audio signal B is amplified by the input stage up 3a to form a pair of signals whose phases are different from each other by 180 °. These signals are added to the transistors Q1 and Q2 constituting the output stage amplifier and subjected to so-called push-pull amplification, whereby the audio signal B is power-amplified as the output signal C.

The power amplification will be described in detail.
Accordingly, the voltage of the power supply line Vcc for supplying power to the output stage amplifier 3 drops to the voltage of the output signal C by the transistor Q1. In other words, the output signal C is generated as a result of the amount of the voltage drop due to the internal impedance of the transistor Q1 changing according to the waveform of the audio signal B. The transistor Q1 is responsible for a voltage difference between the voltage of the power supply line Vcc and the voltage of the output signal C. As a result,
The transistor Q1 consumes power corresponding to the difference voltage.
Although the configuration of the output stage amplifier is a simple circuit including only the output transistors Q1 and Q2 for convenience of explanation, a peripheral circuit such as a drive circuit may be added as an actual circuit.

As with other audio devices, most cassette tape players are of the stereo type, and this type of cassette tape player is no more than an R-channel system or an L-channel system, or vice versa. One signal reproducing system (1 ', 2', 3 ', 4', 5 ') is provided. The audio signal B 'also generates an output signal C' through similar signal processing. Therefore, the power consumption of the transistor Q1 is doubled in a stereo device.

[0007]

The power due to the voltage drop of the output transistor is dissipated as heat by the power amplifying transistor. Therefore, a power transistor having a large power loss is required. Here, since large power is consumed, the power efficiency when generating the output signal C is not good. This is a problem, particularly in portable audio devices that operate on batteries with limited power, as the operating time of the device will depend on power usage efficiency. Moreover, in this type of device, it is extremely important that the device can operate for a long time as a product value. Therefore, it is demanded that the device consume as little power as possible.

An object of the present invention is to provide an audio signal power amplifier circuit capable of reducing power consumption of an output circuit. Another object of the present invention is to provide an audio signal power amplifier circuit that can use a transistor with low power loss by reducing power consumption of a transistor of an output circuit. Another object of the present invention is to provide an audio device capable of reducing power consumption of an output circuit of the audio device. Still another object of the present invention is to provide an audio device suitable for portable use.

[0009]

The audio signal power amplifying circuit and the audio apparatus using the same according to the present invention which achieve the above object are characterized by an amplifier for receiving an audio signal, amplifying and outputting the audio signal, and a power supply. A switching circuit that receives power from the line and performs a switching operation at a frequency exceeding an audible frequency to supply power to the amplifier;
A control circuit that controls a switching period of the switching circuit so that power to be supplied changes in accordance with a level of the audio signal in accordance with a difference between a voltage of the output signal of the amplifier and the voltage of the power to be supplied. I have.

[0010]

By providing a control circuit and a switching circuit for performing the above-described control between the amplifier and the power supply line, power supplied to the amplifier is generated by switching control. In addition, the voltage of the power supplied to the amplifier is fed back according to the voltage of the audio signal. Therefore, it is possible to operate so as to keep the potential difference between the voltage of the power supply and the voltage of the output signal of this amplifier constant,
This constant potential difference is the minimum voltage required for the operation of the amplifier,
Even above that, it is possible to maintain a constant value in a low voltage range. Its operation is to detect the difference voltage
ON between the base and emitter of the transistor
ON / OFF using / OFF, and further OFF
In each case, a detection signal is generated,
1Vf voltage between base and emitter of transistor
And keep it at or near this
It controls the difference between the output voltage and the supply voltage. Also,
When the transistor of the detection circuit is OFF,
By turning off the switching of the switching circuit,
Circuit can be easily separated from other circuits to reduce power consumption.
Suitable for low-voltage driving, the entire control circuit
Road.

The above-mentioned constant potential difference (constant voltage)
Corresponds to a voltage drop for generating an output signal in the amplifier. Therefore, in this case, the amplification operation is performed while the voltage drop in the amplifier is maintained at the above-mentioned minimum voltage or a constant voltage lower than that. The current value of the output signal at this time is determined by the power supplied from the switching circuit, and it is a current corresponding to the input audio signal. The power consumption of the amplifier at this time is substantially determined by the constant voltage. Therefore, the power consumption is lower than the power consumption when an output signal is obtained by directly lowering the voltage from a constant power supply voltage as in the related art.

On the other hand, the power loss of the sum of the switching circuit generated for switching the power supply line Vcc and its control circuit is not always generated due to the low ON resistance of the switching transistor, but is generated transiently during switching. The main thing is to do. The number is extremely small as compared with the conventional one which has always occurred. The increase in power consumption due to this is relatively small in view of the power consumption of the power amplification stage.

Therefore, the power loss consumed for amplifying the audio signal can be reduced as a whole. As a result, power use efficiency can be improved. In the present invention, switching of the power supply line is performed at a high timing exceeding the audible frequency. As a result, even if a distortion component due to switching is included in the amplified audio signal, this component is not finally heard. Therefore,
In practice, the performance of the audio device can be maintained without deteriorating the quality of the audio signal.

[0014]

1, an output stage circuit 30 is an output stage amplifier circuit of the portable cassette tape player 10, and has a supply power control circuit 40 for supplying power to the amplifier 3 in FIG. ing. The same components as those in FIG. 4 are denoted by the same reference numerals. Therefore, the description is omitted. Although not shown, the power supply line Vcc is
As a portable audio device, it is connected to the output power line on the + side of the battery.

The power supply control circuit 40 controls the output power by PWM (pulse wide modulation) control so as to perform switching regulation so that the voltage of this power is maintained at a constant value with respect to the voltage of the output signal of the audio signal. It is a control circuit. The control of the supply current is performed in accordance with a change in the internal impedance of the output transistor Q1 determined according to the signal level of the input signal. For that purpose, the voltage of the output power and the voltage of the output signal C are detected. Then, the power corresponding to these differences is supplied to the transistor Q1 to control the potential difference between the output side of the transistor Q1 and the power supply terminal to be constant. Thereby, at the same time, power corresponding to the input signal (or the output signal) is supplied. This circuit 40 includes a detection circuit 50,
It comprises a switching regulation circuit 60 and a smoothing circuit 70. The capacitor CN shown by the dotted line is
This is for bypassing a high-frequency signal, and its capacity is about 2000P. This capacitor is unnecessary in principle.

Switching regulation circuit 60
Is a circuit inserted between the power supply line Vcc and a power supply terminal (output terminal 6) to the amplifier 3. It comprises a control voltage value generating circuit 65 and a switching circuit 66. The control voltage value generating circuit 65 has a transistor Q61 and an amplifier 61, and generates a control voltage value for switching control. The switching circuit 66 includes a comparator 62 and a PNP-type switching transistor Q6.
2, and from the triangular wave generating circuit 63, the power supply line Vc
The power supply line connected to c is turned on / off by the transistor Q62, and the resulting power is sent to the output terminal 6 via the smoothing circuit 70. That is the output terminal 6
, The power D to be supplied to the amplifier 3.

The voltage at the output terminal 6 fluctuates following the level of the output signal C under the control of the supply power control circuit 40. The potential difference between this output terminal 6 and the output terminal of the output signal of the transistor Q1 is determined. Is kept constant, the power consumption of the transistor Q1 is reduced as described above. That is, here, when the signal level of the output signal C is low, the voltage of the output terminal 6 is also reduced accordingly. When the signal level of the output signal C is high, the voltage of the output terminal 6 increases accordingly.

The power supply control circuit 40 and the transistor Q1
Must be lower than the power consumption of the conventional transistor Q1. This can be achieved by selecting a high switching frequency, for example 50k.
And a potential difference between the output terminal 6 and the output terminal of the output signal of the transistor Q1 at a constant voltage lower than the average voltage drop from the conventional power supply line Vcc. Can be achieved by As a result, the average power consumption caused by a voltage drop from the power supply voltage Vcc in the conventional transistor Q1 can be suppressed to be smaller.

As described above, the amplifier 3
The audio signal B is received, and this is applied to the transistors Q1, Q
In step 2, power is amplified by push-pull amplification to generate an amplified output signal C. The detection circuit 50 mainly includes an NPN transistor Q50 having a detection terminal between the base and the emitter. The detection signal E is output to the transistor Q61 of the switching regulation circuit 60 to turn on / off the transistor Q62. Transistor Q50 receives the voltage of power supply D at its emitter,
The base receives the voltage of the output signal C output from the amplifier 3 via the forward-connected diodes D51 and D52. As a result, the detecting operation of the detecting circuit 50
The difference voltage VD-C between the voltage of the output signal C and the voltage of the output signal C is 1 Vf.
(Forward voltage drop between base and emitter).

When the difference voltage VD-C is 1 Vf or less, the transistor Q50 is turned on. As a result, the difference voltage VD-
A current corresponding to the detection signal E (= error voltage) of C-1Vf is applied to the transistor Q61. The transistor Q61 generates a voltage obtained by amplifying the error voltage as a divided voltage F (described later) in accordance with the error voltage. On the other hand, when the difference voltage VD-C exceeds 1 Vf, the translator Q50 is turned off. As a result, a detection signal E having a constant voltage (= Vcc) is generated. Reference numeral 51 denotes a constant current source for maintaining the diodes D51 and D52 in the ON state.
A high reference signal G is generated at the base of transistor Q50 (= 2Vf).

The control voltage value generation circuit 65 includes a detection circuit 50
To generate a comparison voltage value P for the comparator 62. This occurs when the transistor Q61 is turned on in response to the detection signal E from the detection circuit 50, in other words, the voltage of the output signal C and the power supply D of the output terminal 6.
When the voltage difference between the two becomes less than 1 Vf, the power supply line V
A voltage value between the voltage of cc and the voltage of the output signal C is generated as a divided voltage F at a connection point N between the series-connected resistance circuits R62 and R63. The amplifier 61 receives the divided voltage F and amplifies the signal of the difference between the divided voltage F and the voltage of the reference signal G to generate the comparison voltage value P. This is output to the (-) input (reference terminal side) of the comparator 62.

When the transistor Q61 is turned off in response to the detection signal E from the detection circuit 50, that is, when the difference between the voltage of the output signal C and the voltage of the power supply D at the output terminal 6 is 1
When the voltage exceeds Vf, the voltage of the difference between the output signal C and the reference signal G (= 2Vf) is amplified by the amplifier 61 to generate the comparison voltage value P. This is a constant value (a value lower than the signal level of the triangular wave, as described later). The comparator 62 receives a triangular wave signal S of a constant frequency whose frequency exceeds the audible frequency from the triangular wave generating circuit 63 at the (+) input. Then, the voltage of the comparison voltage value P is compared with the voltage of the signal S, and when the voltage of the signal S exceeds the voltage of the comparison voltage value P, the PNP transistor Q62 is turned off.
An IGH level signal is output as a drive pulse H. This drive pulse H is applied to the transistor Q62. However, the triangular wave signal S here is based on the voltage of the reference signal G, and the reference signal G and the signal S are combined by the combining circuit 64 before being input to the comparator 62.

The smoothing circuit 70 is connected to the output of the transistor Q62 of the switching circuit 66 and smoothes the output power. This circuit is mainly a coil L70 inserted in series between the output of the transistor Q62 and the power supply line (output terminal 6) to the amplifier 3.
Through the coil L70, the switched power is smoothed, and the smoothed power supply D is generated at the output terminal 6. The input terminal of the coil L70 and the ground GN
A flywheel diode is connected between D.
This diode forms a return path for the current flowing through the coil L70. Thus, when the power supply line is cut off by the switching transistor Q62, the energy stored in the coil L70 is supplied to the amplifier 3 as an inertial current and returns to the coil L70.

Next, the power supply D and the output signal C of the amplifier 3
The operation of the switching regulation circuit 60 for controlling the difference voltage VD-C to about 1 Vf will be described. As shown in FIG. 2, the comparator 62 outputs a triangular wave signal S (see FIG.
(a) and (c)), and the comparison voltage value P
Is entered. When the difference voltage VD-C is 1 Vf or less,
As shown in FIG. 2A, the comparator 62 outputs a binary drive pulse H (see FIG. 2) according to the result of comparison between the signal level of the triangular wave (waveform S) and the level of the output signal (waveform P) of the amplifier 61. 2 (b), H) to turn on / off the transistor Q62. Here, the level Pa of the first half of the signal P is lower than the reference signal G. This is because the difference voltage VD-C is maintained slightly below 1 Vf, and
Vf. Level P in the latter half of signal P
b is above the reference signal G. At this time, the difference voltage VD-C becomes lower than 1 Vf. At this time, the period during which the drive pulse H is at the HIGH level is shortened so as to increase the amount of the power supply D. As a result, the supply power D increases, the voltage increases, and the difference voltage VD−
C is controlled to 1 Vf.

Thus, when the difference voltage VD-C is equal to or less than 1 Vf, the level of the comparison voltage value P changes in a direction to make the difference substantially equal to 1 Vf, and a current corresponding to the change is supplied to the amplifier 3. Supplied. And the difference voltage VD-C
Becomes approximately 1 Vf. That is, PWM is performed in accordance with the comparison result between the comparison voltage value P and the triangular wave S, and the ON / OFF of the switching transistor Q62 is controlled by the drive pulse H. Such control is performed according to the value of the detection signal E.

When the difference between the voltage of the output signal C and the voltage of the power supply D at the output terminal 6 exceeds 1 Vf, the transistor Q50 is turned off. At this time, the detection voltage E becomes the power supply voltage Vcc. Then, the transistor Q61 turns off,
A voltage of 2Vf difference is generated. As a result, the comparison voltage value P
Is at the level of Pc shown in FIG. 2C, and a constant voltage lower than the reference signal G by 2 Vf is applied to the comparator 62. As a result, HIGH as shown by the waveform H in FIG.
The drive pulse H maintained at the level is generated to turn off the switching transistor Q62. As a result, power is supplied to the amplifier 3 so that the difference voltage VD-C becomes substantially equal to 1 Vf, and the comparison voltage value P returns to the level of Pa.

The level Pa of the comparison voltage value P is determined by the values of the resistors R62 and R63 and can be selected. The level of Pc of the comparison voltage value P is determined in relation to the amplitude of the triangular wave, and can be selected. The response speed to the change in the level of the comparison voltage value P is
It is fast enough for changes in the audio signal,
It can be selected in circuit design.

As a specific operation, for example, when the voltage level of the input signal B is greatly reduced, the internal impedance of the transistor Q1 rises sharply, and the voltage of the output signal C and the power supply D of the output terminal 6 are reduced. Voltage difference is 1V
exceeds f. As a result, the comparison voltage value P becomes lower than the triangular wave S as indicated by Pc, the drive pulse H of the comparator 62 is maintained at the HIGH level, and the transistor Q62 is maintained in the OFF state. Such control is continued until the difference between the output signal C and the voltage of the power supply D at the output terminal 6 becomes close to 1 Vf.

Further, for example, when the voltage level of the input signal B rises significantly, the internal impedance of the transistor Q1 drops sharply, and the difference between the voltage of the output signal C and the voltage of the power supply D at the output terminal 6 becomes 1 Vf. Less than. At this time, the comparison voltage value Pb corresponding to the error lower than 1 Vf is added. As a result, control is performed to increase the voltage of the power supply power D and set the target value of the difference voltage VD-C to 1 Vf. With respect to a gradual change in the level of the input signal B, two controls are performed alternately in a short time when the voltage is 1 Vf or more and 1 Vf or less in accordance with the change in the internal impedance of the transistor Q1. And Figure 2
As shown in (e), a pulse having a pulse width and a pulse having a short pulse width over a plurality of cycles of the triangular wave signal S appear alternately.

The upper limit of the audible frequency of the triangular wave is generally set at 20 KHz,
Considering the ease of adjustment of the oscillation circuit and power efficiency, etc.
A range of about 0 kHz to 500 kHz is preferable. Here, 1Vf of the difference voltage VD-C, which is the control target value (about 0.
7V) is a value determined corresponding to the fact that the transistor Q1 of the amplifier 3 has a single stage. That is, the amplifier 3
The difference VD-C between the voltage of the power supply D to the power supply and the voltage of the output signal C of the amplifier 3 is a minimum value required for the amplifier 3 to perform an amplifying operation from values which do not impair the response performance of the transistor Q1. The value is selected as close as possible to the ON-time voltage between the collector and the emitter, which is the minimum voltage. Therefore, if the transistor Q1 is a Darlington transistor, the difference voltage VD-C is 2 Vf (about 1.4 V). Specifically, for diodes D51 and D52,
Another diode is further inserted in series.

Next, the overall operation of the tape player will be described. At the time of reproduction, a read signal A of an audio signal is obtained via a read head 1 from a tape (not shown) on which the audio signal is recorded. An audio signal B is obtained by the signal reproduction processing circuit 2 for the read signal A. This audio signal B is supplied to the transistors Q 1 and Q
2 is push-pull amplified. At this time, the supply power control circuit 40 supplies a current corresponding to the level of the input signal B for the upper half cycle of the reference level of the audio signal B. In the lower half cycle, the current supplied to the capacitor 5 is sunk via the transistor Q2. As a result, the input signal B is power-amplified and the output signal C is generated, whereby the speaker 4 is driven.
At this time, for the upper half cycle, the difference voltage VD-C between the voltage of the power supply D to the amplifier 3 and the voltage of the output signal C of the amplifier 3 is 1 Vf close to the minimum value required for the operation of the amplifier 3. It is controlled to be maintained at the value.

As a result, the power loss in the amplifier 3 becomes a voltage drop of about 1 Vf corresponding to the difference voltage VD-C, and the power consumption is reduced as compared with the conventional case. The power loss generated by switching the power supply line is
As described above, mainly the resistance at the time of ON of the transistor Q62 is used. However, since the ON resistance value is low, the actual power consumption can be suppressed low. In particular, a PWM-controlled drive circuit that switches the transistor Q62
Since it can be constituted by an IC circuit having a differential amplifier configuration, its power consumption can be suppressed smaller than the power consumption of the power amplification stage.

Next, a configuration suitable for a stereotype will be described with reference to FIG. In FIG. 3, a speaker 4,
The configuration of the supply power control circuit 40 (the detection circuit 50, the switching regulation circuit 60, and the smoothing circuit 70) is the same as that of the above-described embodiment, but in FIG.
Is provided with a feedback circuit 31 as an output stage amplifier 32. The amplifier 3 'shown in FIG.
3 is provided.

The amplifier 34 is connected to the supply power control circuit 40 via a detection circuit 55. The detection circuit 55
This is a circuit similar to the detection circuit 50, and is connected in parallel with the detection circuit 50. In this figure, circuits before and after the amplifier 3 'are omitted. The current source 56 of the detection circuit 55 is a circuit corresponding to the current source 51 of the detection circuit 50. The detection circuit 55 generates a detection signal E 'having a value according to whether or not a difference voltage VD-C' between the voltage of the power supply power D and the output signal voltage C 'is greater than 1 Vf. The detection signal E ′ is wired-ORed with the detection signal E and sent to the transistor Q61 of the switching regulation circuit 60.

Thus, the PWM control in the switching regulation circuit 60 depends not only on the difference voltage VD-C but also on the difference voltage VD-C 'on the amplifier 34 side. The current supply operation of each of the amplifiers 32 and 34 is the same as described above, except that the supply power control circuit 40
A current is supplied in parallel to. Therefore, one of the amplifiers 3
When the output signal C of the other amplifier 3 'rises greatly and the output signal C' of the other amplifier 3 'rises or decreases slightly and the voltages of these output signals become different levels, the voltage of the power supply power D becomes It follows the higher level of the signal. The reason is that, since the detection circuits 50 and 55 are connected in parallel, the operation of the transistor which is turned on among the transistors has priority. Of the transistors Q50 of the detection circuit 50 and the transistor Q55 of the detection circuit 55, the ON state is the higher of the output signals C and C '. When both transistors are in the ON state, the sum of their currents causes P
WM control is performed.

By the way, when a stereo signal is reproduced, a signal in a low band, for example, a signal having a frequency of 200 Hz or less often has the same level on both the left and right sides. The signal of the band bears. Therefore, even if the supply power control circuit 40 is commonly connected to the left and right output stage amplifiers, the distortion of the output signal is almost small.
Particularly, when the feedback circuits 31 and 33 are provided as shown in FIG.
Voltage forcibly follows the voltage of the higher output signal, but even if this occurs, the level of the output signal on the lower side of the output signal is affected by it. And the distortion of the output signal is reduced. Of course, the supply power control circuit 4 is provided for each of the left and right output stage amplifiers.
If 0 is provided, the signal distortion can be further reduced. However, in order to reduce power consumption as much as possible, it is better to use a common signal as shown in FIG. By doing so, the plurality of detection circuits 50, 55
Of the plurality of difference voltages VD-C and VD-C ', the difference voltage on the side where the difference voltage is lower than 1 Vf is substantially equal to 1 Vf.

The operation and power consumption will be specifically described. The voltage value of the output signal C of the amplifier 32 is equal to that of the amplifier 3 '.
When the output signal C 'is equal to or higher than the voltage value of the output signal C', the voltage drop VD-C at the amplifier 32 is maintained at a small value of 1 Vf. On the other hand, the drop voltage VD-C 'in the amplifier 34 is 1 V
The value is maintained at f or higher. Since the voltage of the power supply line Vcc> the voltage of the power supply power D, the conventional voltage drop value = Vcc−C ′ (where Vcc is the voltage of the power supply line Vcc,
C 'is higher than Vcc-D (however, the voltage of the output signal C').
D is the voltage of the supply power D), and the power consumption is small.
Conversely, when the voltage value of the output signal C of the amplifier 32 is equal to or less than the voltage value of the output signal C 'of the amplifier 34, the voltage drop in the amplifier 34 is maintained at a small value of 1 Vf, which is opposite to the above.

Incidentally, the supply power control circuit 40 shown in FIG.
It is, instead of the one of the voltage of the output signal C of the detected voltage of the detection circuit 50 may be a power supply control circuit for obtaining a detection signal to the voltage of the input signal B.

In the above embodiment, the reproduction signal of the tape player has been described as an example. However, this may be another audio signal such as a microphone input or a broadcast reception input. In such a case, the signal reproduction processing circuit is often a front-stage amplifier inserted before the output-stage amplifier. Also, an example has been described in which an amplified signal is sent to a speaker, but the output destination of this signal is not limited to this. For example, it may be output as an input to a recording circuit, or may be output as an input to a power amplifier of higher capacity. Although the transistors Q50 and Q55 of the detection circuit 50 are NPN transistors, they may be PNP transistors. In this case, the emitter receives the output signal C, and the base receives the voltage signal of the power supply D. By the way, when more current capacity is required, the output terminal 6 of the power supply D and the ground G
The capacitor CN between the ND and the ND is not a mere high frequency bypass, and may be a smoothing capacitor having a larger capacity.

[0040]

According to the present invention, by providing a control circuit and a switching circuit for controlling as described above between an amplifier and a power supply line, power supplied to the amplifier can be controlled by switching control. The voltage of the generated power supplied to the amplifier is fed back according to the voltage of the audio signal. Therefore, the operation can be performed so as to maintain a constant potential difference between the voltage of the power supply and the voltage of the output signal of the amplifier, and the constant potential difference is set to the minimum voltage required for the operation of the amplifier or a voltage lower than the minimum voltage required for operation of the amplifier. It can be maintained at a constant value in the range.

As a result, the power consumption is lower than the power consumption when an output signal is obtained by directly lowering the voltage from a constant power supply voltage as in the related art. On the other hand, the power loss of the sum of the switching circuit generated for switching the power supply line Vcc and the control circuit thereof does not always occur due to the low ON resistance of the switching transistor, but rather occurs transiently during switching. Be the subject. The number is extremely small as compared with the conventional one which has always occurred. The increase in power consumption due to this is relatively small in view of the power consumption of the power amplification stage. Therefore, power loss consumed for amplifying the audio signal can be reduced as a whole. As a result, power use efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment in which the audio apparatus of the present invention is applied to a portable cassette tape player.

FIG. 2 is a waveform chart for explaining an operation of the supply power control circuit in FIG. 1;

FIG. 3 is a block diagram of an embodiment in which the audio apparatus of the present invention is applied to a stereo portable cassette tape player.

FIG . 4 is a conventional stereo portable cassette card.
It is a block diagram of a loop player.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Read head, 2 ... Signal reproduction processing circuit, 3 ... Output stage amplifier, 4 ... Speaker, 5 ... Electrolytic capacitor for output, 6 ... Output terminal, 10 ... Portable cassette tape player 30 ... Output stage circuit, 40 ... Supply Power control circuit, 50,5
Reference numeral 5: detection circuit, 60: switching regulation circuit, 65: control voltage value generation circuit, 61: amplifier, 62: comparator, 63: triangular wave generation circuit, 66: switching circuit, 70: smoothing circuit, Q1, Q2, Q50, Q61 , Q62: transistor, B: audio input signal, C: audio output signal.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-372212 (JP, A) JP-A-56-136010 (JP, A) JP-A-60-14516 (JP, U) JP-A-5-136 70017 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03F 1/00-3/72

Claims (5)

(57) [Claims] An amplifier that receives an audio signal, amplifies and outputs the audio signal, a switching circuit that receives power from a power supply line, performs a switching operation at a frequency exceeding an audible frequency, and supplies power to the amplifier, and The transistor is turned on / off according to the difference between the voltage of the output signal and the voltage of the power to be supplied between the base and the emitter of the transistor.
A detection circuit that generates a detection signal in response to each of the ON and OFF states, and controls a switching period of the switching circuit when the transistor is ON in accordance with the respective detection signals, so that the transistor is turned OFF. An audio signal power amplifier circuit, comprising: a control circuit for turning off the switching of the switching circuit to control the supplied power to change in accordance with the level of the audio signal. 2. The audio signal power amplifier circuit according to claim 1, wherein during the switching period, PWM control is performed so that a difference between a voltage of an output signal of the amplifier and a voltage of the power to be supplied becomes constant. 3. The switching circuit has a frequency of 50 kHz to 800 kHz.
a triangular wave generating circuit that oscillates at a certain frequency in the range of kHz, a comparator that receives the output of the triangular wave generating circuit on one side and receives a control signal on the other side, and turns on the power received from the power supply line according to the output signal of the comparator. /
A smoothing circuit is provided between an output of the switching circuit and a terminal of the amplifier for receiving the power to be supplied, the smoothing circuit being configured to switch a coil and a current flowing through the coil by the switching transistor. 3. The audio signal power amplifier circuit according to claim 2, further comprising: a diode forming a return path for supplying power to said amplifier during a period in which the transistor is off. 4. A amplifies the audio signal in an audio device for outputting the amplified signal to the load, and the pre-stage amplifier circuit for amplifying receiving said audio signal, the audio signal amplified by the preamplifier circuit an output stage amplifier to be output to the load it amplifies the power receiving, a switching circuit for supplying power to the output stage amplifier by a switching operation at a frequency exceeding an audible frequency by receiving power from a power source line, said output The transistor is turned on / off in response to a difference between the voltage of the output signal of the stage amplifier and the voltage of the power to be fed between the base and the emitter of the transistor.
A detection circuit that generates a detection signal in response to each of when the transistor is turned off and when the transistor is off, and controls a switching period of the switching circuit when the transistor is on in response to the detection signal. A control circuit for turning off the switching circuit when OFF, and controlling the power to be supplied to change in accordance with the level of the audio signal; An audio device that is PWM-controlled so that a difference between a voltage of an output signal of the first embodiment and a voltage of the power to be supplied becomes constant. 5. A audio device for outputting to the load a corresponding signal thereof amplified by amplifying the left and right stereo audio signals to the channels independently of the left and right to left and right channels, the right of the stereo audio signal A first pre-amplifier circuit for receiving and amplifying an audio signal corresponding to a channel; a first for receiving the audio signal amplified by the first pre-amplifier circuit, power-amplifying the audio signal, and outputting the amplified signal to the load An output stage amplifier; a second preamplifier circuit for receiving and amplifying an audio signal corresponding to a left channel of the stereo audio signal; and receiving and amplifying the audio signal amplified by the second preamplifier circuit. A second output stage amplifier for amplifying the power and outputting the amplified power to the load; A switching circuit at frequencies above wavenumber by a switching operation to supply power to the first and second output-stage amplifier, a difference between the voltage and the power voltage to the power supply of the output signal of the first output-stage amplifier The first transistor is turned on / off according to the voltage of the difference received between the base and the emitter of the first transistor, and a first detection signal is generated according to each of the ON and OFF states of the first transistor.
A control circuit for controlling the switching period of the switching circuit when the transistor is ON according to the respective detection signals of the first detection circuit, and turning off the switching of the switching circuit when the transistor is OFF. A first control circuit for controlling the power to be supplied so as to change in accordance with the level of the audio signal of the right channel; and a voltage of an output signal of the second output stage amplifier and a power of the power to be supplied. A voltage difference is received between the base and the emitter of the second transistor, and the second transistor is turned on / off in accordance with the voltage of the difference received between the base and the emitter. The second to generate
A control circuit for controlling the switching period of the switching circuit when the transistor is ON according to the respective detection signals of the second detection circuit, and setting the switching of the switching circuit to OFF when the transistor is OFF. And a second control circuit for controlling the power to be supplied so as to change in accordance with the level of the audio signal of the left channel.