JPH07273569A - Audio signal power amplifier circuit and audio equipment using the same - Google Patents

Abstract

PURPOSE:To improve the power utilizing efficiency by providing a switching control circuit and a switching circuit between an amplifier and a power supply line or a ground line and setting either of push-pull outputs for each half cycle. CONSTITUTION:A comparator 44 applies an input audio signal B to a noninverting input and a Vcc/2 reference voltage is applied to an inverting input and provides an output of a pulse signal T corresponding to an upper half cycle of the signal B. The signal T is fed to a base of a transistor(TR) Q4 and inverted by an inverter 45 and the inverted signal is fed to a base of the TR Q2. Either of the pull-side TRs Q2, Q4 is set for each half cycle of the signal B and one terminal of a speaker 4 reaches a voltage higher than a ground level by a collector-emitter voltage of the TR when it is conductive. Thus, a current flowing to coils L70, L71 is commutated respectively via diodes D70, D71 when the switching is released respectively. In this case, since the commutated current does not flow the ground, the voltage is made stable and the power consumption is reduced by the commutated current not via the ground line.

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 device using the same, and more particularly to an output circuit of a BTL (Balanced Tranceformer Less) system which amplifies an audio signal composed of voice or performance sound. In a device such as a radio, a cassette tape player, a video tape recorder, a video camera, or a component stereo device that outputs a sound by driving a speaker by an audio signal (including these, it is referred to as an audio device here), The present invention relates to a power amplifier circuit that can reduce power consumption of an output circuit of a BTL and is particularly suitable for a portable audio device.

[0002]

2. Description of the Related Art FIG. 7A is a simple block diagram showing a circuit of a signal reproducing system of a conventional portable cassette tape player as an example of an audio device using a BTL output circuit. 1 is a reading head, 2 is a signal reproduction processing circuit including a head amplifier, an equalizer circuit, etc., 3 is an output stage amplifier on the positive phase side (non-inverting output side), 4 is a speaker as a load, and 5 is an inverse It is an output stage amplifier on the phase side (inverted output side).

At the time of reproduction, a read signal A is obtained as an input audio signal via the read head 1 from a tape (not shown) on which an audio signal is recorded. The 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 and the like are performed, and the audio signal B is reproduced. The reproduced audio signal B is finally added to and amplified by the output stage amplifiers 3 and 5, respectively. The input signal B becomes output signals C and C * in the respective output stage amplifiers, and the speaker 4 is driven by these outputs. As a result, reproduced sound is generated from the speaker 4.

Normally, the transistor amplifiers 3 and 5 are input stage amplifiers 3 that generate a pair of signals at their respective input stages.
a and 5a. The audio signal B is amplified by the input stage amplifier 3a to be a pair of signals having phases different from each other by 180 °. These signals are amplified by the push-pull transistors Q1 and Q2 forming the output stage amplifier, and the power is amplified as the output signal C. The audio signal B is inverted and amplified by the input stage amplifier 5a and similarly amplified by the push-pull transistors Q3 and Q4 to be power-amplified as the output signal C *.

The power amplification of the output stage amplifier 3 will be described in detail below.
The voltage of the power supply line Vcc for supplying the voltage to V 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. At this time, the transistor Q1
Is responsible for the difference voltage between the voltage of the power supply line Vcc and the voltage of the output signal C. As a result, transistor Q1
The difference voltage is consumed.

For convenience of explanation, the output stage amplifier is shown as a simple circuit with only output transistors Q1 and Q2. However, as an actual circuit, peripheral circuits such as a drive circuit are added. Good. The same applies to the output stage amplifier 5. Especially BT
In the case of the L circuit, the input stage amplifiers 3a and 5a are usually constituted by differential amplifier circuits, and the output terminals of the amplifiers 3 and 5 are connected to the reference voltage (Vcc / 2 of the input stage differential amplifiers 3a and 5a).
Negative feedback is applied to the inverting input side to which the voltage Vcc, Vcc is the power supply voltage), but since it is not directly related to the invention, it is omitted in the figure.

The operation of the BTL output stage amplifiers 3 and 5 will be described in detail. When the voltage value of the audio signal B is higher than the reference voltage (Vcc / 2), the input stage amplifier 3a.
The output of Q.sub.1 causes the transistor Q1 on the power supply side to be activated and the transistor Q2 on the ground side to be cut off. Further, the power supply side transistor Q3 is cut off and the ground side transistor Q4 is activated by the output of the input stage amplifier 5a. Then, a current corresponding to the voltage value of the audio signal B flows from the power supply line Vcc through the transistor Q1 to the speaker 4, the transistor Q4, and the ground.

When the voltage value of the audio signal B is lower than the reference voltage, the ON / OFF relation of the transistor is reversed, and a current corresponding to the voltage value of the audio signal B is supplied from the power supply line Vcc to the transistor Q3 and the speaker. 4. Transistor Q2 flows to ground. When the voltage value of the audio signal B is at the reference voltage, each transistor is in the OFF state. At this time, the output terminals of the amplifiers 3 and 5 become Vcc / 2 due to the negative feedback to the input stage amplifiers 3a and 5a.

[0009]

As described above, the pair of output stage amplifiers 3 and 5 which operate in opposite phases are provided to the BTL.
Each transistor Q1, Q2, Q3, when operated
The power consumed by Q4 is shown by the slanted lines in Fig. 7 (b). In addition,
In the figure, the power consumed by each transistor is shown in the range of each diagonal line by changing the direction of the diagonal line. The electric power due to the voltage drop of the output transistor shown by the diagonal line is dissipated as heat by the transistor for power amplification. Therefore, a power transistor with large power loss is required. Since a large amount of power is consumed here, the power efficiency when the output signals C and C * are generated by the BTL output circuit is not good.

This is a problem, especially in a portable audio device that operates on a battery of limited power, since the operating time of the device depends 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 a BTL audio signal power amplifier circuit that can reduce power consumption of an output circuit. Another object of the present invention is to provide a BTL 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. Also,
An object of the present invention is to provide an audio device capable of reducing the power consumption of the BTL output circuit of the audio device. Still another object of the present invention is to provide an audio device suitable for carrying.

[0011]

The features of an audio signal power amplifier circuit of the present invention and an audio apparatus using the same which achieves the above-mentioned object are characterized by a push-pull first circuit for receiving an audio signal, amplifying it, and outputting it. No. 1 amplifier, push-pull second amplifier that receives and amplifies the audio signal and outputs it, and receives power from the power supply line and performs switching operation at a frequency exceeding the audible frequency to supply power to the first amplifier. A first switching circuit for
The voltage of the audio signal and the voltage of the amplified audio signal generated by amplifying the audio signal by the first amplifier are supplied in accordance with the difference between the voltage and the voltage of the power supplied to the first amplifier. A first control circuit for controlling a switching period of the first switching circuit so that the electric power changes corresponding to the level of the audio signal;
The second which receives power from the power supply line and performs a switching operation at a frequency exceeding the audible frequency to supply power to the second amplifier
Of the voltage of the audio signal and the voltage of the amplified audio signal generated by amplifying the audio signal by the second amplifier and the voltage of the power supplied to the second amplifier. And a second control circuit for controlling the switching period of the second switching circuit so that the electric power to be supplied changes in accordance with the level of the audio signal, and the push side of the push-pull of the first amplifier is provided. Is for amplifying a signal of a half cycle of the audio signal, the output of the pull side is maintained in the ON state in response to the signal of the other half cycle of the audio signal, and the push of the second amplifier is performed. The output on the push side of the pull is for amplifying the other half cycle signal, and the output on the pull side corresponds to the half cycle signal. Te is maintained in the ON state, in which the output of the first amplifier and the output of the second amplifier to drive the speakers. As another invention, the first and second switching circuits and the first and second control circuits are respectively arranged on the ground side, and the pull-side output of the first amplifier is a half-cycle audio output. Occurs,
The output on the push side is maintained in the ON state corresponding to the remaining half cycle, and conversely, the output on the pull side of the second amplifier generates the audio output for the remaining half cycle and Is maintained in the ON state in the half cycle. Then, as a more specific invention, a smoothing circuit including a coil is provided in the first and second switching circuits so that the output side of the first and second amplifiers is connected to the first and second switching circuits. A diode is cross-connected to form a commutation passage for a current flowing through the coil when the switching of each circuit is in the OFF state.

[0012]

By providing the switching control circuit and the switching circuit for performing the above-mentioned control between the first and second amplifiers 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 maintain the potential difference between the voltage of the power supply and the voltage of the output signal of the amplifier constant. Therefore, this constant potential difference can be maintained at a constant value in the range of the minimum voltage required for the operation of the amplifier or a voltage lower than the minimum voltage.

This constant potential difference (constant voltage) corresponds to the drop voltage for generating the output signal in the amplifier. 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. Therefore, the power consumption of the amplifier at this time is
It is almost determined by the constant voltage. Furthermore, here, one of the push-pull outputs is turned on every half cycle.
Since the state is set, the power consumed by the output circuit on the ON side is further reduced. As a result, the power consumption becomes 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 conventional case. The above is the same when the current flowing from the amplifier to the ground is switched.

By the way, 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 amplification of the audio signal can be reduced. As a result, power usage efficiency can be improved.

In the present invention, the 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 deteriorating the quality of the audio signal.

[0016]

DETAILED 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 power supply control circuits 40 and 41 for supplying power to the amplifiers 3 and 5 of FIG. Each is provided for each amplifier. The same components as those in FIG. 7 are designated by the same reference numerals. Therefore, the explanation is omitted. Although not shown, the power supply line Vcc is connected to the + side output power line of the battery as a portable audio device.

The output stage circuit 30 is obtained by replacing the input stage amplifiers 3a and 5a in FIG. 7 with differential amplifiers 3b and 5b, respectively. The differential amplifier 3b has an input audio signal at its (+) input side. B, a reference voltage of Vcc / 2 is applied to the (-) input side thereof, and only the upper half cycle of the input audio signal B is amplified and output. The differential amplifier 5b is
The input audio signal B is applied to the (-) input side, and the input audio signal B is applied to the (+) input side with a reference voltage of Vcc / 2.
Amplifies and outputs only the lower half cycle of. The comparator 44 receives the input audio signal B on its (+) input side and the reference voltage of Vcc / 2 on its (-) input side, and outputs the pulse signal T corresponding to the upper half cycle of the input signal B. Occur. The signal T is applied to the base of the transistor Q4, while being inverted by the inverter 45 and applied to the base of the transistor Q2.

Therefore, the pull-side transistors Q2 and Q4
Is O for each half cycle of the audio signal B.
In the N state, one end of the speaker 4 has a voltage higher than the ground level by the voltage when the collector-emitter of the transistor is ON. With this configuration, the currents flowing through the coils L70 and L71 when the switching is OFF are commutated through the diodes D70 and D71, respectively. In this case, since these commutation currents do not flow to the ground side, this voltage has a stable value, and power consumption is reduced by the amount that the commutation current does not pass through the ground line.

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 supply power 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.

In the output stage circuit 30 of this embodiment, the push-side (ejection-side) transistors Q1 and Q3 of the push-pull output amplifiers 3 and 5 have a half cycle on the positive side of the audio signal B with respect to the reference voltage. An output signal corresponding to the negative half cycle is generated, and the pull side (sink side) transistors Q2 and Q4 are maintained in the ON state at each half cycle timing to operate. In such an operation, the detection circuit 50 is mainly composed of 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. Transistor Q50 is
The voltage of the power supply power D is received by its emitter, and the voltage of the output signal C output from the amplifier 3 is received by its base via the diodes D51 and D52 connected in the forward direction. As a result, the detection operation of the detection circuit 50 depends on whether or not the difference voltage VD-C between the voltage of the power supply D and the voltage of the output signal C is larger than 1 Vf (the forward drop voltage between the base and the emitter). Will be different.

When the difference voltage VD-C is 1 Vf or less, the transistor Q50 is turned on. As a result, the difference voltage of 1V
A current corresponding to the detection signal E (= error voltage) of f-VD-C 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. In addition,
Reference numeral 51 is a constant current source for keeping the diodes D51 and D52 in the ON state, and 2 × 1 Vf (= 2) from the output signal C.
Vf) Generate a high reference signal G 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,
The signal of the difference between this and the voltage of the reference signal G is amplified to generate the comparison voltage value P. Then, this is output to the (-) input (reference terminal side) of the comparator 62. Upon receiving the detection signal E from the detection circuit 50, the transistor Q61 turns off.
When F, 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 exceeds 1 Vf, the voltage of the difference between the output signal C and the reference signal G (= 2 Vf)
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 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 Q
The drive pulse H is a HIGH level signal that turns OFF 62.
Output as. This drive pulse H is applied to the transistor Q
Added to 62. However, the triangular wave signal S here is
The voltage of the reference signal G is used as a reference, 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 amplifier 5
A flywheel diode D70 is connected to the output terminal of the. This diode D70 allows coil L7
A return path for the current flowing to 0 is formed. 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 the coil L70 is supplied.
Return to.

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 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. Therefore, the transistor Q61 turns off and 2
A voltage having a difference of 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, 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 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 sufficiently fast to the change of the audio signal, and can be selected in the design of the circuit.

As a concrete operation, for example, when the voltage level of the input signal B is greatly reduced, the internal impedance of the transistor Q1 is rapidly increased, and the voltage of the output signal C and the power supply power 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 2Vf (about 1.4V).
It is said that Specifically, another diode is further inserted in series with respect to the diodes D51 and D52.

The internal structure of the supply power control circuit 41 provided on the amplifier 5 side is the same as that of the supply power control circuit 40. The output terminal 6a corresponds to the output terminal 6, and the supplied power D'corresponds to the supplied power D. Coil L71,
The diode D71 is the coil L7 of the supply power control circuit 40.
0 and diode D70, respectively. The flywheel diode D71 is connected between the input end of the coil L71 and the output terminal of the amplifier 3. The diode D71 forms a return path for the current flowing through the coil L71, as described above. The other internal configuration of the supply power control circuit 41 and its operation description are omitted.

As a result, the output waveforms of the amplifiers 3 and 5 become the waveforms shown in (f) of FIG. Waveform 3c shown by solid line
Is the output of the amplifier 3, and the part of the chain line is the supply power D
Is a voltage waveform of. A waveform 5c shown by a dotted line is the output of the amplifier 5, and a portion indicated by a chain double-dashed line is a voltage waveform of the supplied power D '. The level of VODC is the DC voltage level of the output terminal when the transistors Q2 and Q4 on the sing side are turned on.

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. The positive half cycle of the audio signal B is push-pull amplified by the transistors Q1 and Q4 of the amplifiers 3 and 5, respectively, and the negative half cycle is push-pull amplified by the transistors Q3 and Q2 of the amplifiers 3 and 5, respectively. To be done. At this time, the transistor Q2 on the sink side
, Q4 turn on at the timing of each half cycle
Maintained in a state. As a result, the input signal B is power-amplified and output signals C and C * are generated to drive the speaker 4. At this time, for the upper half cycle, the amplifier 3
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 controlled to be maintained at a value of 1Vf, which is close to the minimum value required for the operation of the amplifier 3.
Similarly, in the lower half cycle, the difference voltage VD'-C * between the voltage of the power supply D'to the amplifier 5 and the voltage of the output signal C * of this amplifier 5 is the minimum value required for the operation of the amplifier 5. It is controlled so as to be maintained at a value of 1 Vf close to.

As a result, the power loss in the amplifiers 3 and 5 becomes a voltage drop of about 1 Vf corresponding to the difference voltage VD-C and the difference voltage VD'-C *, and the power consumption is reduced as compared with the conventional case. To be done. As described above, the power loss caused by switching the power supply line is mainly due to the resistance when the transistor Q62 is turned on.
Since the resistance value is low, the actual power consumption can be kept low. In particular, since the PWM control drive circuit for switching the transistor Q62 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.

FIG. 3 shows an example in which a half cycle signal generating circuit 2a for individually generating upper and lower half cycles of the audio signal B is provided between the amplifiers 3 and 5 and the signal reproduction processing circuit 2. Its internal structure is composed of so-called positive-side and negative-side half-wave rectification circuits, and only a voltage of Vcc / 2 is given as a voltage that serves as a rectification reference. In this way, the differential amplifiers 3b and 5b of the amplifiers 3 and 5 can be replaced with the input stage amplifiers 3a and 5a similar to the conventional one, and it is necessary to set the reference level side of the input stage to Vcc / 2. There is no. Since the operation is the same as that in FIG. 1, its explanation is omitted.

FIG. 4 shows an embodiment of the supply power control circuit 40a which obtains a detection signal by changing the detection target of one of the voltages of the detection circuit to the voltage of the output signal C to obtain the voltage of the input signal B. In FIG. 4, the power supply control circuit 40a 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 set to the base bias potential of the transistor Q1. This is the point that
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 power supply 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. The output signal and the input signal have the same phase. 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.

According to the input signal B, the triangular wave S and the reference signal P
, And the PWM pulse corresponding to the width of the triangular wave exceeding the reference signal P is obtained by the transistor Q (see FIG. 5 (a)).
Added to 62. As a result, in relation to the output signal C,
PWM control is performed in the waveform relationship shown in FIG.

In the above embodiments, the reproduction signal in the tape player has been described as an example, but it 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 preamplifier 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.

The transistor Q50 of the detection circuit 50 is NP
Although it is an N transistor, it may be a PNP transistor. 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 needed,
The capacitor CN between the output terminal 6 of the power supply D and the ground GND may be a smoothing capacitor having a larger capacity than that for a simple high frequency bypass.

FIG. 6 shows an embodiment corresponding to FIG. 1 in which supply power control circuits 42 and 43 are respectively provided between the transistors Q2 and Q4 and the ground. Supply power control circuit 4
Reference numerals 2 and 43 are circuits having the same configuration, and the difference from the supply power control circuit 40 is that the supply power control circuit 40 has N
The PN (PNP) transistor was replaced with the PNP (NPN) transistor, the input side terminal of the comparator was connected to the opposite side, the input side terminal of the operational amplifier was connected to the opposite side, and the power supply line Vcc and the ground line GND were replaced. Circuit. Reference numeral 57 denotes the detection circuit, which corresponds to the detection circuit 50. The NPN transistor Q63 is
It is a switching transistor and corresponds to the PNP transistor Q62. The amplifier 61a is an amplifier 61
The comparator 62a corresponds to the comparator 62, and the triangular wave generating circuit 63a corresponds to the triangular wave generating circuit 63. The operation is the same as the above except that the polarity is reversed, and the details thereof will be omitted.

The power supply control circuit 40a shown in FIG.
Similarly, if the connection of the input side terminals of the comparator 62 and the operational amplifier 67 is exchanged and the power supply line Vcc and the ground line GND are exchanged, the circuit can be used similarly to the supply power control circuits 42 and 43. .

By the way, it is possible to replace the transistors Q2 and Q4 on the side of the transistors, for example, the sinks in FIG. 1 which are kept ON every half cycle with N-type MOS transistors. As a result, the circuit can be made less susceptible to temperature. If the discharge side transistors Q1 and Q3 in FIG. 6 are replaced, a P-type MOS transistor is used.

[0049]

According to the present invention, the switching control circuit and the switching circuit for performing the above-described control are provided between the amplifier and the power supply line or the ground line, and any one of the push-pull outputs is provided. One of them is turned on every half cycle. 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. Moreover, since either one of the push-pull outputs is turned on every half cycle, the power consumed by the output on the ON side is further reduced. As a result, the power loss consumed for amplifying the audio signal can be reduced as a whole. 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 another embodiment in which the audio device of the present invention is applied to a portable cassette tape player.

FIG. 4 is a block diagram centering on a power supply control circuit 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 an embodiment corresponding to the embodiment of FIG. 1 in which the power supply control circuit is provided on the ground side.

7A and 7B are explanatory diagrams of a portable cassette tape player using a BTL output circuit, in which FIG. 7A is a block diagram thereof, and FIG. 7B is an explanatory diagram of power consumption of an output stage transistor thereof. .

[Explanation of symbols]

1 ... Read head, 2 ... Signal reproduction processing circuit, 3, 5 ... Output stage amplifier, 4 ... Speaker, 6 ... Output terminal, 10 ... Portable cassette tape player, 30 ... Output stage circuit, 4
0, 40a, 41, 42, 43 ... Supply power control circuit, 4
4, 62, 62a ... Comparator, 50, 55, 57,
58 ... 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, L70, L71 ... Coil, D
70, D71 ... Diode, Q1, Q2, Q50, Q61, Q6
2, Q63 ... Transistor, B ... Audio input signal, C
… Audio output signal.

Claims (5)

[Claims] 1. A push-pull first amplifier which receives an audio signal and amplifies and outputs the same, a push-pull second amplifier which receives the audio signal and amplifies and outputs the same, and a power supply line A first switching circuit which receives electric power from the device and performs a switching operation at a frequency exceeding an audible frequency to supply power to the first amplifier; and amplifying the voltage of the audio signal and the audio signal by the first amplifier. So that the power to be supplied changes in accordance with the level of the audio signal in accordance with the difference between any of the voltages of the amplified audio signal generated in step 1 and the voltage of the power to be supplied to the first amplifier. A first control circuit that controls a switching period of the first switching circuit; and a frequency that receives power from the power supply line and exceeds an audible frequency. A second switching circuit that performs a switching operation at a wave number to supply power to the second amplifier; and a voltage of the audio signal and a voltage of an amplified audio signal generated by amplifying the audio signal by the second amplifier. The switching period of the second 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 to the second amplifier. And a second control circuit for controlling the audio signal, wherein the push-side output of the push-pull of the first amplifier amplifies a half cycle signal of the audio signal, and the pull-side output is the audio signal. The signal is maintained in the ON state in response to the signal in the other half cycle of the signal, and the output on the push side of the push-pull of the second amplifier is The other half cycle signal is amplified, the output on the pull side is maintained in the ON state in response to the half cycle signal, and the output of the first amplifier and the second amplifier are maintained. An audio signal power amplifier circuit that drives a speaker according to the output of. 2. A first smoothing circuit having a first coil and a first diode is provided between the output of the first switching circuit and the terminal of the first amplifier which receives the power to be fed. A second smoothing circuit having a second coil and a second diode is provided between the output of the second switching circuit and the terminal of the second amplifier that receives the power to be supplied, One end of the first diode is connected to the output of the second amplifier, and the current flowing through the first coil is supplied to the first amplifier while the switching of the first switching circuit is OFF. To form a return path for connecting the second coil to the second coil during a period in which one end of the second diode is connected to the output of the first amplifier and the switching of the second switching circuit is OFF. The current forms the return path for supplying power to said second amplifier, said one of the voltage, the audio signal power amplifier circuit according to claim 1, wherein the voltage of the output signal of the amplifier. 3. A push-pull first amplifier which receives an audio signal and amplifies and outputs the same, and a push-pull second amplifier which receives the audio signal and amplifies and outputs the same. A first switching circuit that receives a current flowing out from one amplifier and performs a switching operation at a frequency exceeding an audible frequency to flow the current to the ground; and the audio signal and the audio signal in the first amplifier. Depending on the difference between the voltage of any one of the amplified audio signals generated by amplification and the voltage of the current flowing out from the first stage amplifier, the flowing out current is made to correspond to the level of the audio signal. Outflow from the first control circuit that controls the switching period of the first switching circuit so as to sink to the ground, and the second amplifier. A second switching circuit that receives a current that is generated and performs a switching operation at a frequency that exceeds the audible frequency to cause the current to flow to ground, and a frequency that exceeds the audible frequency that is received by the current that is output from the second amplifier. A second switching circuit that performs a switching operation to flow the current to the ground; a voltage of any one of the audio signal and an amplified audio signal generated by amplifying the audio signal by the second amplifier; The switching period of the second switching circuit is controlled so as to sink the outflowing current to the ground corresponding to the level of the audio signal according to the difference between the current flowing out from the second amplifier and the voltage. A second control circuit, wherein the pull-side output of the push-pull of the first amplifier is the audio signal. A half-cycle signal is amplified, and the output on the push side is maintained in the ON state in correspondence with the other half-cycle signal of the audio signal, and the pull side of the push-pull of the second amplifier. Output of the other half cycle is amplified, the output of the push side is maintained in the ON state in response to the signal of the half cycle, and the output of the first amplifier and the An audio signal power amplifier circuit that drives a speaker based on the output of the second amplifier. 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. And a push-pull first output stage amplifier that receives and amplifies the power of the audio signal and outputs the amplified audio signal to the load by receiving the audio signal amplified by the pre-stage amplifier circuit. A push-pull second output stage amplifier; a first 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 first amplifier; One of the voltages of the amplified audio signal generated by amplifying the audio signal by the first amplifier is supplied. And a switching period of the first switching circuit so that the supplied electric power changes in accordance with the level of the audio signal in accordance with the difference between the electric power supplied to the first amplifier and the voltage of the electric power supplied to the first amplifier. A second switching circuit that receives power from the power supply line and performs a switching operation at a frequency exceeding an audible frequency to supply power to the second amplifier; and a voltage of the audio signal and the audio signal. The level of the supplied audio power is the level of the audio signal depending on the difference between any of the voltages of the amplified audio signal generated by the amplification by the second amplifier and the voltage of the power supplied to the second amplifier. A second control circuit for controlling the switching period of the second switching circuit so as to change in accordance with A speaker provided between the output and the output of the second amplifier, and the push-side output of the push-pull of the first amplifier amplifies a half cycle signal of the audio signal. The output on the pull side of the second amplifier is maintained in the ON state in response to the signal of the other half cycle of the audio signal, and the output of the push side of the push-pull of the second amplifier is on the other half cycle of the other. The audio device for amplifying the signal of 1. and the output on the pull side thereof is maintained in the ON state corresponding to the signal of the half cycle. 5. A first smoothing circuit having a first coil and a first diode is provided between the output of the first switching circuit and the terminal of the first amplifier which receives the power to be fed. A second smoothing circuit having a second coil and a second diode is provided between the output of the second switching circuit and the terminal of the second amplifier that receives the power to be supplied, One end of the first diode is connected to the output of the second amplifier, and the current flowing through the first coil is supplied to the first amplifier while the switching of the first switching circuit is OFF. To form a return path for connecting the second coil to the second coil during a period in which one end of the second diode is connected to the output of the first amplifier and the switching of the second switching circuit is OFF. Current to form a return path for supplying power to said second amplifier to said one of the voltage, the audio apparatus according to claim 4, wherein the voltage of the output signal of the amplifier.