JPH07249945A - Audio signal power amplifier circuit and audio device using the same - Google Patents

Abstract

PURPOSE:To reduce the power consumption of an output circuit by controlling a switching period so that feeding power is changed based upon the level of an audio signal in accordance with a difference between either one of audio signal voltage and an audio signal amplifying voltage and feeding voltage. CONSTITUTION:An amplifier 3 amplifies the power of an audio signal B and outputs a signal C. On the other hand, a TR Q50 (a TR above a TR Q52) in a detection circuit 50 in a feeding power control circuit 40 receives the voltage of feeding power D at its emitter and receives the voltage of the output signal C of the amplifier 3 at its base through diodes D51, D52 connected in the forward direction. In the detecting operation of the circuit 50, difference voltage VD-C between the voltage of feeding power D and that of the output signal C depends upon 1Vf (forward drop voltage between the base and emitter). When the voltage VD-C is <1Vf, the TR Q50 is turned on, a current corresponding to the difference voltage VD-C - 1Vf = error voltage is applied to a TR Q61 and amplified divided voltage F is generated. When the voltage VD-C>1Vf, the TR Q50 is turned off and a signal E with fixed voltage is generated. The ON/OFF of a switching TR Q62 is controlled in accordance with the signal E to reduce power consumption.

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 amplifier circuit and an audio apparatus using the same, and more particularly to a radio or cassette for amplifying an audio signal composed of voice or performance sound and outputting it as sound from a speaker. In a device such as a tape player, a video tape recorder, a video camera, a component stereo device, etc. which generates an audio signal (these are collectively referred to as an audio device), it is possible to reduce the power consumption of its output circuit. The present invention relates to a power amplifier circuit suitable for a portable audio device.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a circuit of a signal reproducing system of a conventional portable cassette tape player as an example of an audio device. Reference numeral 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. It is an electrolytic capacitor for output.

At the time of reproduction, a read signal A is obtained as an audio signal from the tape (not shown) on which the audio signal is recorded via the 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, the equalizing process is performed, and the audio signal B is reproduced. The reproduced audio signal B is finally added to the output stage amplifier 3 and amplified. Here, the 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 in the input stage. The audio signal B is amplified by the input stage up 3a to be a pair of signals having phases different from each other by 180 °. These signals are added to the transistors Q1 and Q2 constituting the output stage amplifier and are so-called push-pull amplified, whereby the audio signal B is power-amplified as the output signal C.

To explain the power amplification in detail, the input signal B
Accordingly, the voltage of the power supply line Vcc for supplying power to the output stage amplifier 3 is lowered 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 voltage drop caused by the internal impedance of the transistor Q1 changing according to the waveform of the audio signal B. In the meantime, the transistor Q1 takes charge of the difference voltage between the voltage of the power supply line Vcc and the voltage of the output signal C. As a result,
The transistor Q1 consumes electric power corresponding to the difference voltage.
Note that the output stage amplifier is shown as a simple circuit with only the output transistors Q1 and Q2 for convenience of description, but a peripheral circuit such as a drive circuit may be added as an actual circuit.

Most cassette tape players, like other audio devices, are of the stereo type, and this type of cassette tape player has an L channel system and an L channel system or vice versa. One signal reproduction system (1 ', 2', 3 ', 4', 5 ') is provided. The audio signal B ′ also produces an output signal C ′ by similar signal processing. Therefore, the power consumption of the transistor Q1 is doubled in the stereo device.

[0007]

The power due to the voltage drop of the output transistor is dissipated as heat by the power amplification transistor. Therefore, a power transistor with large power loss is required. Since a large amount of power is consumed here, the power efficiency when generating the output signal C is not good. This is a problem, especially in portable audio devices that operate on a battery with limited power, as the operating time of the device will depend on the power usage efficiency. Moreover, in this type of device, the ability to operate for a long time is extremely important as a product value. Therefore, it is required that the device consumes as little power as possible.

An object of the present invention is to provide an audio signal power amplifier circuit which can reduce the power consumption of the output circuit. Another object of the present invention is to provide an audio signal power amplifier circuit in which a transistor with low power loss can be used by reducing the power consumption of the transistor in the output circuit. Another object of the present invention is to provide an audio device capable of reducing the power consumption of the output circuit of the audio device. Still another object of the present invention is to provide an audio device suitable for carrying.

[0009]

The features of an audio signal power amplifier circuit of the present invention and an audio device using the same which achieves the above-mentioned object are characterized by an amplifier for receiving an audio signal, amplifying and outputting the same, and a power supply. A switching circuit that receives power from a line and performs a switching operation at a frequency exceeding an audible frequency to supply power to the amplifier, a voltage of an audio signal and a voltage of an amplified audio signal generated by amplifying the audio signal by the amplifier. A control circuit that controls the switching period of the switching circuit so that the power to be supplied changes in accordance with the level of the audio signal in accordance with the difference between any one of the voltages and the voltage of the power to be supplied. .

[0010]

By providing the control circuit and the switching circuit for performing the above control between the amplifier and the power supply line, the power supplied to the amplifier is generated by the switching control. Moreover, 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,
Is this constant potential difference the minimum voltage required to operate the amplifier,
It is possible to maintain a constant value in the range of low voltage even if it is higher than that.

This constant potential difference (constant voltage) corresponds to the voltage drop in the amplifier for generating the output signal. Therefore, in this case, the voltage drop in the amplifier is maintained at the above-mentioned minimum voltage or a constant voltage lower than the minimum voltage, and the amplification operation is performed. The current value of the output signal at this time is determined by the power supplied from the switching circuit, and it becomes a current according to the input audio signal. The power consumption of the amplifier at this time is almost determined by the constant voltage. Therefore, the power consumption is lower than the power consumption when the 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 and the control circuit for switching the power supply line Vcc does not always occur because the ON resistance of the switching transistor is low, but it occurs transiently during switching. What you do is the main subject. The number is extremely small compared to the conventional one which was always generated. The increase in power consumption due to this is relatively small in view of the power consumption of the power amplification stage.

Therefore, as a whole, the power loss consumed for amplifying the audio signal can be reduced. As a result, power usage efficiency can be improved. In the present invention, switching of the power supply line is performed at a fast 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 will not be heard in the end. Therefore,
Practically, the performance of the audio device can be maintained without impairing the quality of the audio signal.

[0014]

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

The power supply control circuit 40 controls the switching of the output power by PWM (pulse wide modulation) control 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 according to the change of the internal impedance of the output transistor Q1 which is determined according to the signal level of the input signal. Therefore, the voltage of the output power and the voltage of the output signal C are detected. Then, power corresponding to these differences is supplied to the transistor Q1 so that the potential difference between the output side of the transistor Q1 and the power supply terminal is controlled to be constant. As a result, power corresponding to the input signal (or output signal) is supplied at the same time. This circuit 40 includes a detection circuit 50,
It includes a switching regulation circuit 60 and a smoothing circuit 70. The capacitor CN shown by the dotted line is
It is for bypassing a high frequency signal, and its capacity is about 2000P. This capacitor is not necessary 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 generation circuit 65 and a switching circuit 66. The control voltage value generation 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 the triangular wave generation 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 output terminal 6
The power supply D to the amplifier 3 is generated.

The voltage of the output terminal 6 varies according to the level of the output signal C under the control of the power supply control circuit 40. However, the potential difference between the output terminal 6 and the output terminal of the output signal of the transistor Q1. Is maintained 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 also decreases accordingly. When the signal level of the output signal C is high, the voltage of the output terminal 6 also increases accordingly.

Supply power control circuit 40 and transistor Q1
And the total power consumption of the transistor Q1 must be less than that of the conventional transistor Q1. This is done by choosing a high switching frequency, eg 50k.
To a high frequency of about Hz to 800 kHz, and to maintain the 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. As a result, the average power consumption generated by the voltage drop from the power supply voltage Vcc in the conventional transistor Q1 can be suppressed to be smaller than the average power consumption.

As described above, the amplifier 3 is
It receives the audio signal B and outputs it to the transistors Q1 and Q.
The output signal C is amplified by push-pull amplification and power amplification at 2. The detection circuit 50 mainly comprises an NPN transistor Q50 having a base-emitter detection terminal. The detection signal E is output to the transistor Q61 of the switching regulation circuit 60 to turn on / off the transistor Q62. The transistor Q50 receives the voltage of the power supply D at its emitter,
The base receives the voltage of the output signal C output from the amplifier 3 via the diodes D51 and D52 connected in the forward direction. As a result, the detection operation of the detection circuit 50 is the power supply D
Difference voltage VD-C between the output voltage and the output signal C is 1Vf
It differs depending on whether it is larger than (forward drop voltage 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) according to the error voltage. On the other hand, when the difference voltage VD-C exceeds 1Vf, the transter Q50 is turned off. As a result, the detection signal E having a constant voltage (= Vcc) is generated. Reference numeral 51 is a constant current source for maintaining the diodes D51 and D52 in the ON state, and 2 × 1 Vf from the output signal C.
A (= 2Vf) high reference signal G is generated at the base of transistor Q50.

The control voltage value generation circuit 65 includes a detection circuit 50.
In response to the detection signal E, the comparison voltage value P for the comparator 62 is generated. This is because 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 power D of the output terminal 6 are set.
When the voltage difference between the two becomes less than 1Vf, the power supply line V
A voltage value between the voltage of cc and the voltage of the output signal C is generated as the divided voltage F at the connection point N of the resistance circuits R62 and R63 connected in series. The amplifier 61 receives the divided voltage F, amplifies the difference signal between the divided voltage F and the voltage of the reference signal G, and generates the comparison voltage value P. Then, 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, the difference between the voltage of the output signal C and the voltage of the power supply D of the output terminal 6 is 1.
When it exceeds Vf, the voltage (= 2Vf) of the difference between the output signal C and the reference signal G is amplified by the amplifier 61, so that the comparison voltage value P is generated. This is a constant value (a value lower than the signal level of the triangular wave, as will be described later). The comparator 62 receives a triangular wave signal S having a constant frequency whose frequency exceeds the audible frequency from the triangular wave generation circuit 63 at the (+) input. Then, the voltage of the comparison voltage value P and the voltage of the signal S are compared, and when the voltage of the signal S exceeds the voltage of the comparison voltage value P, the PNP transistor Q62 is turned off.
The IGH level signal is output as the 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 its output power. This circuit is a circuit mainly composed of 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.
The switched power is smoothed through the coil L70, and the smoothed power supply D is generated at the output terminal 6. The input end 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. As a result, 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 side as an inertial current and returns to the coil L70.

Next, the feed power 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 between the control voltage and VD-C to about 1 Vf will be described. As shown in FIG. 2, the comparator 62 has a triangular wave signal S (FIG.
(see (a) and (c)) is input, and the comparison voltage value P
Is entered. When the difference voltage VD-C is less than 1Vf,
As shown in FIG. 2 (a), the comparator 62 uses a binary drive pulse H (see the figure) corresponding to the result of comparison between the signal level of the triangular wave (waveform S) and the level of the output signal of the amplifier 61 (waveform P). 2 (b) H) is generated 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 1Vf and is almost 1
It is in the state of Vf. Level P of the latter half of signal P
b is above the reference signal G. At this time, the difference voltage VD-C becomes lower than 1Vf. At this time, the period in which the drive pulse H is at the HIGH level is shortened so that the amount of the power supply D is increased. As a result, the power supply D increases and its voltage rises, resulting in a difference voltage VD-
It is controlled so that C becomes 1 Vf.

As a result, when the difference voltage VD-C is 1 Vf or less, the level of the comparison voltage value P changes in such a direction that the difference is substantially equal to 1 Vf, and a current corresponding to this change is sent to the amplifier 3. Supplied. And the difference voltage VD-C
Becomes almost 1Vf. That is, PWM is performed according to the result of comparison between the comparison voltage value P and the triangular wave S, and the switching transistor Q62 is turned on / off by the drive pulse H. Then, 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 electric power D supplied to the output terminal 6 exceeds 1 Vf, the transistor Q50 is turned off. The detection voltage E becomes the power supply voltage Vcc at this time. Then, the transistor Q61 turns off,
A voltage difference of 2 Vf is generated. As a result, the comparison voltage value P
Becomes the level of Pc shown in FIG. 2 (c), and a constant voltage lower than the reference signal G by 2Vf 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, the power is supplied to the amplifier 3 so that the difference voltage VD-C substantially matches 1Vf, and the comparison voltage value P returns to the level of Pa.

The level of 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 this is also selectable. Further, the response speed to the change of the level of the comparison voltage value P is
It's fast enough for audio signal changes,
It can be selected on the circuit design.

As a concrete operation, for example, when the voltage level of the input signal B is significantly lowered, the internal impedance of the transistor Q1 is rapidly increased, and the voltage of the output signal C and the power supply D of the output terminal 6 are increased. Voltage difference is 1V
exceeds f. As a result, the comparison voltage value P becomes a level lower than the triangular wave S as shown 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 electric power D supplied to the output terminal 6 becomes close to 1 Vf.

Further, for example, when the voltage level of the input signal B is greatly increased, the internal impedance of the transistor Q1 is drastically decreased, and the difference between the voltage of the output signal C and the voltage of the power supply D of the output terminal 6 is 1 Vf. Less than At this time, the comparison voltage value Pb corresponding to the error amount lower than 1 Vf is added. As a result, the voltage of the power supply D is increased and the target value of the differential voltage VD-C is controlled to 1Vf. Then, with respect to the gradual change of the level of the input signal B, two controls are alternately performed in a short time depending on the change of the internal impedance of the transistor Q1 in the case of 1 Vf or more and the case of 1 Vf or less. Fig. 2
As shown in (e), a pulse having a pulse width and a pulse having a short pulse width alternately appear over a plurality of cycles of the triangular wave signal S.

By the way, as the frequency of the triangular wave, the upper limit of the audible frequency is generally set to 20 KHz,
Considering the ease of adjustment of the oscillator circuit and power efficiency, 10
A range of about 0 kHz to 500 KHz is preferable. It should be noted that here, 1 Vf of the difference voltage VD-C (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 amplifier 3 and the voltage of the output signal C of the amplifier 3 is the minimum value required for the amplifier 3 to perform the amplifying operation from the value that does not impair the response performance of the transistor Q1. It is selected as a value as close as possible to the ON-state voltage between the collector and the emitter, which is the limit voltage. Therefore, if the transistor Q1 is a Darlington transistor, the difference voltage VD-C is set to 2Vf (about 1.4V). Specifically, for the diodes D51 and D52,
Another diode is further inserted in series.

Next, the overall operation of this tape player will be described. At the time of reproduction, a read signal A of an audio signal is obtained via the read head 1 from a tape (not shown) on which an audio signal is recorded. An audio signal B is obtained from the read signal A by the signal reproduction processing circuit 2. This audio signal B is the transistors Q1 and Q of the amplifier 3.
2 is push-pull amplified. At this time, the power supply control circuit 40 supplies a current according 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 through the transistor Q2. As a result, the input signal B is power-amplified to generate the output signal C, which drives the speaker 4.
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 1Vf which is close to the minimum value required for the operation of the amplifier 3. It is controlled to maintain the value.

As a result, the power loss in the amplifier 3 becomes a voltage drop of about 1 Vf corresponding to this difference voltage VD-C, and the power consumption is reduced as compared with the conventional one. The power loss caused by switching the power supply line is
As described above, the main factor is the resistance when the transistor Q62 is ON, but since the ON resistance value is low, the actual power consumption can be kept low. In particular, the PWM control drive circuit that switches the transistor Q62 is
Since it can be configured 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 the stereotype will be described with reference to FIG. In FIG. 3, the speaker 4,
The configuration of the supply power control circuit 40 (detection circuit 50, switching regulation circuit 60, smoothing circuit 70) is the same as that of the above-mentioned embodiment, but in FIG.
Is provided with a feedback circuit 31 as an output stage amplifier 32. Further, the amplifier 3 ′ shown in FIG.
3 is provided.

The amplifier 34 is connected to the power supply control circuit 40 via a detection circuit 55. The detection circuit 55 is
It is a circuit similar to the detection circuit 50 and is connected in parallel with the detection circuit 50. In this figure, the 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 the detection signal E ′ having a value depending on whether the difference voltage VD−C ′ between the voltage of the power supply D and the output signal voltage C ′ is larger than 1Vf. The detection signal E ′ is wired-ORed with the detection signal E and sent to the transistor Q61 of the switching regulation circuit 60.

As a result, 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 that described above, but the supply power control circuit 40 controls the amplifier 32,
Current is supplied to 34 in parallel. Therefore, one amplifier 3
When the output signal C of the output signal C of the other amplifier 3'is greatly increased and the output signal C'of the other amplifier 3'is slightly increased or decreased to the voltages of these output signals at different levels, the voltage of the feeding power D is It follows the higher signal level. The reason is that since the detection circuits 50 and 55 are connected in parallel, the operation of the turned-on transistor side of any of the transistors is prioritized. The transistor Q50 of the detection circuit 50 and the transistor Q55 of the detection circuit 55 are turned on when the level of the output signals C and C'is higher. Then, when both transistors are in the ON state, P due to the sum current of them.
WM control is performed.

By the way, when reproducing a stereo signal, a signal in a low band, for example, a signal having a frequency of 200 Hz or less is often at the same level on the left and right, and a large change in the output current is caused by such a low frequency. In-band signal 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.
In particular, when the feedback circuit 31.33 is provided as shown in FIG.
Voltage of the output signal forcibly follows the voltage of the output signal on the higher side, but the level of the output signal on the low side of the output signal is affected by this even if this happens. And the distortion of the output signal is reduced. Of course, the power supply control circuit 4 is supplied to the left and right output stage amplifiers respectively.
If 0 is provided, signal distortion can be further reduced, but in order to suppress power consumption as much as possible, it is better to make them common as shown in FIG. In this way, the plurality of detection circuits 50, 55
Of the plurality of difference voltages VD-C and VD-C 'according to the above, the supply voltage D of a smoothed voltage is generated so that the difference voltage on the side where the difference voltage VD-C' changes below 1Vf is substantially equal to 1Vf.

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

FIG. 3 shows an embodiment of the supply power control circuit 41 which obtains a detection signal by changing the detection target of one voltage of the detection circuit to the voltage of the output signal C and setting it as the voltage of the input signal B.
In FIG. 3, the supply power control circuit 41 controls the voltage of the output signal C and the voltage of the power supply D to be constant according to the voltage of the input signal B and the voltage of the power supply D. The same components as those in FIG. 1 are designated by the same reference numerals. The difference from FIG. 1 is that the circuit from the detection circuit 50 to the amplifier 61 is replaced with a detection / amplification circuit 67 composed of an inverting amplification type operational amplifier, and the reference signal G is a transistor Q1.
This is the point where the base bias potential of is set. Therefore, the triangular wave generating circuit 63 also operates by taking the base of the transistor Q1 as the reference potential.

The detection / amplification circuit 67 receives the voltage of the feeding power D at the (-) input terminal, and the (+) input terminal receives the input signal B obtained from the base of the transistor Q1 via the resistor RS as the reference side potential. Is input. That is, the resistor RS converts the current value of the input signal B into a voltage value. It also has a feedback resistor Rf from the output to the (+) input terminal. Then, the voltage of the output signal P is sent to the (−) input terminal which is the reference input terminal of the comparator 62. The output of the triangular wave generation circuit 63 is supplied to the (+) input terminal of the comparator 62. In such a circuit, the divided voltage signal F generated by the detection signal and the feed power D match, and the reference signal G also becomes the same level because the input terminal of the operational amplifier is a virtual short circuit.

The difference between the voltage of the output signal of the output stage amplifier and the voltage of the input signal is that there is a level difference between them that corresponds to the amplification factor of the output stage amplifier and that the phases differ by 180 °. . Considering this point, even if the input signal B is to be detected, the same operation as the power supply control circuit 40 of the above-described embodiment is performed, and this can be replaced. Since the difference in frequency between the triangular wave signal S and the input signal B is large, the operation of the operation with respect to the input signal B with the frequency of the triangular wave S lowered will be described in principle as shown in FIG. A waveform of the triangular wave S and the reference signal P (see FIG. 5A) is obtained according to the input signal B, and a PWM pulse corresponding to the width of the triangular wave exceeding the reference signal P is applied to the transistor Q62. As a result, in relation to the output signal C, the PWM control is performed in the waveform relationship as shown in FIG.

In the above embodiments, the reproduction signal in the tape player has been described as an example, but 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 pre-stage amplifier that is inserted before the output stage amplifier. Further, the example in which the amplified signal is sent to the speaker has been described, but the output destination of this signal is not limited to that. For example, it may be output as its input to the recording circuit or may be output as its 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 side receives the output signal C and the base side receives the voltage signal of the feeding power 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 ND and ND may be a smoothing capacitor having a larger capacity than that for a simple high frequency bypass.

[0042]

According to the present invention, by providing the control circuit and the switching circuit for performing the above-described control between the amplifier and the power supply line, the power supplied to the amplifier is controlled by the switching control. The voltage of the power generated and 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, and this constant potential difference is the minimum voltage required for the operation of the amplifier, or a voltage lower than that. The range can be kept constant.

As a result, the power consumption is lower than the power consumption when an output signal is obtained by directly dropping the voltage from a constant power supply voltage as in the conventional case. 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 because the ON resistance of the switching transistor is low, but may occur transiently during switching. Be the subject. The number is extremely small compared to the conventional one which was always generated. The increase in power consumption due to this is relatively small in view of the power consumption of the power amplification stage. Therefore, as a whole, the power loss consumed for amplification of the audio signal can be reduced. As a result, power usage efficiency can be improved.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram for explaining the operation of the supply power control circuit in FIG.

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

FIG. 4 is a block diagram of another embodiment in which the audio device of the present invention is applied to a portable cassette tape player.

5 is a waveform diagram for explaining the operation of the supply power control circuit in FIG.

FIG. 6 is a block diagram of a conventional stereo portable cassette tape player.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Read head, 2 ... Signal reproduction processing circuit, 3 ... Output stage amplifier, 4 ... Speaker, 5 ... Output electrolytic capacitor, 6
... output terminal, 10 ... portable cassette tape player 30 ... output stage circuit, 40 ... supply power control circuit, 50, 5
5 ... Detection circuit, 60 ... Switching regulation circuit, 65 ... Control voltage value generation circuit, 61 ... Amplifier, 62 ...
Comparator, 63 ... Triangle wave generating circuit, 66 ... Switching circuit, 70 ... Smoothing circuit, Q1, Q2, Q50, Q61,
Q62 ... Transistor, B ... Audio input signal, C ... Audio output signal.

Claims (5)

[Claims] 1. An amplifier that receives an audio signal, amplifies and outputs the audio signal, a switching circuit that receives power from a power supply line and performs a switching operation at a frequency exceeding an audible frequency to supply power to the amplifier, and the audio signal. Of the voltage of the audio signal and the voltage of the amplified audio signal generated by amplifying the audio signal with the amplifier, and the level of the audio signal is the level of the audio signal supplied according to the difference between the voltage of the supplied power and the voltage of the supplied power. A control circuit for controlling the switching period of the switching circuit so as to change in accordance with the above. 2. The audio signal power amplification circuit according to claim 1, wherein PWM control is performed during the switching period such that a difference between a voltage of an output signal of the amplifier and a voltage of the power to be fed is constant. 3. The switching circuit comprises 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 this triangular wave generating circuit on one side and a control signal on the other side, and the power received from the power supply line according to the output signal of this comparator are turned on. /
A switching transistor that turns off is provided, and a smoothing circuit is provided between the output of the switching circuit and a terminal of the amplifier that receives the power to be supplied, and the smoothing circuit switches a coil and a current flowing through the coil to the switching circuit. The audio signal power amplifier circuit according to claim 2, further comprising a diode that forms a return path for supplying power to the amplifier while the transistor is off. 4. An audio device for amplifying an audio signal and outputting the amplified signal to a load or the like, and a pre-stage amplifier circuit for receiving and amplifying the audio signal, and the audio signal amplified by the pre-stage amplifier circuit. An output stage amplifier that receives the power and outputs it to the load; a switching circuit that receives power from a power supply line and performs a switching operation at a frequency exceeding an audible frequency to supply power to the output stage amplifier; Signal and the amplified audio signal generated by amplifying the audio signal by the amplifier, and the power changes in accordance with the level of the audio signal according to the difference between the voltage of any of the supplied power and the voltage of the power to be supplied. A control circuit for controlling the switching period of the switching circuit so that Etching period, the audio device the difference between the voltage and the power voltage to the power supply of the output signal of the output stage amplifier is PWM controlled to be constant. 5. An audio device that amplifies left and right stereo audio signals independently of the left and right channels and outputs the amplified signals to loads corresponding to the left and right channels, respectively. A first pre-stage amplifier circuit that receives and amplifies an audio signal corresponding to a channel, and a first pre-stage amplifier circuit that receives the audio signal amplified by the first pre-stage amplifier circuit, power-amplifies it, and outputs it to the load. An output stage amplifier, a second pre-stage amplifier circuit for receiving and amplifying an audio signal corresponding to the left channel of the stereo audio signal, and receiving the audio signal amplified by the second pre-stage amplifier circuit The second output stage amplifier that amplifies the power to output to the load, and receives power from the power line A switching circuit that performs a switching operation at a frequency exceeding the frequency to supply power to the first and second output stage amplifiers, and an audio signal voltage of the right channel and the audio signal generated by amplifying the audio signal by the first amplifier Of the switching circuit so that the power to be fed changes in accordance with the level of the audio signal of the right channel in accordance with the difference between any one of the voltages of the amplified audio signal and the voltage of the power to be fed. A first control circuit for performing PWM control of a switching period; a voltage of the left channel audio signal and a voltage of an amplified audio signal generated by amplifying the audio signal by the second amplifier; Depending on the difference between the voltage of the power to be supplied and the voltage of the power to be supplied, the power to be supplied is turned on in the left channel. Audio device and a second control circuit for PWM controlling the switching period of the switching circuit so as to change in response to the level of the audio signal.