JPH0722860A - Switching amplifier for speaker driving - Google Patents

Abstract

PURPOSE:To provide the switching amplifier for speaker driving which can take out a large power without reducing the impedance of a speaker or using DC-DC converter to raise the supply voltage. CONSTITUTION:A PWM conversion circuit 20 which generates a PWM1 signal from an in-phase signal and a saw tooth wave and generates a PWM2 signal from an anti-phase signal and the saw tooth wave connects the PWM1 signal to a first push-pull circuit 31 and connects the PWM2 signal to a second push- pull circuit 32. The first push-pull circuit 31 is connected to a first smoothing circuit 71 through a first switching circuit 41, a first pulse transformer 51, and a first rectifying circuit 61, and the second push-pull circuit 32 is connected to a second smoothing circuit 72 through a second switching circuit 42, a second pulse transformer 52, and a second rectifying circuit 62, and first and second smoothing circuits 71 and 72 are connected to a speaker 80.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a speaker driving switching amplifier for driving an on-vehicle speaker.

[0002]

2. Description of the Related Art Generally, the output power P ₀ of an amplifier is P ₀ = V, where R is the load impedance and V is the power supply voltage of the amplifier output stage.
² / R ... As can be seen from the equation, there are two methods for increasing the output power P ₀ of the amplifier: (1) increasing the power supply voltage V of the output stage or (2) decreasing the load impedance R. Among these methods (1) and (2), A class, AB class, B class
In the case of a class amplifier, the method (1) is usually adopted. For example, when the amplifier is used as an amplifier for driving an in-vehicle speaker, the battery voltage of the vehicle is low and can be set only up to about 12V.
When the output power P ₀ of the amplifier is increased by the method (1), a method of increasing the battery voltage by the DC-DC converter to increase the power supply voltage V is adopted. However, in this case, there is a problem in that the power supply efficiency is reduced by about 10 to 20% by interposing the DC-DC converter.

However, the first advantage of the PWM amplifier is high power supply efficiency. Therefore, if the power supply efficiency is reduced by using the DC-DC converter as described above, the advantage of the PWM amplifier cannot be fully utilized. On the other hand, even when the method (2) is adopted, there are problems shown in the following (a) and (b).

(A) From the above equation, it seems that the smaller the load (= speaker) impedance R, the larger the output power P ₀ . However, in reality, as the speaker impedance decreases, the damping factor also deteriorates. Therefore, if the speaker impedance is excessively decreased, the power efficiency is rather decreased. That is, even if the speaker impedance is reduced, there is a limit that can be reduced from the viewpoint of power supply efficiency, and the power P that can be taken out by the limit.
The size of ₀ is also limited.

(B) To put it in reverse, the output power
P₀ Of the output power P ₀ Necessary to get out
It is necessary to prepare a speaker with the required impedance value
There will be. That is, load impedance R is small
Output power P₀When trying to increase
Is the output power P₀ Every time you try to upgrade
It is costly because the speaker must be replaced every time.
And it will be troublesome to replace it especially for in-vehicle use
The problem arises.

The present invention has been made in view of the above problems, and it is possible to take out a large output power without reducing the load (= speaker) impedance or boosting the power supply voltage using a DC-DC converter. Switching amplifier for speaker drive (= PWM amplifier)
Is intended to provide.

[0007]

To achieve the above object, a speaker driving switching amplifier according to the present invention comprises:
A PWM conversion circuit is provided that creates a PWM1 signal only on the plus side of the in-phase signal from the in-phase signal and the sawtooth wave, and a PWM2 signal only on the plus side of the anti-phase signal from the in-phase signal and the sawtooth wave. The PWM conversion circuit is composed of a flip-flop, a switching element, etc., and a first push-pull circuit that alternately distributes the PWM1 signal to the push side and the pull side, and the PWM2 signal to the push side and the pull side. The first push-pull circuit is connected to a second push-pull circuit which is alternately distributed, and the first push-pull circuit is composed of a switching element or the like. The signal distributed to the push side and the pull side is distributed between a power supply voltage and a ground level. The second push-pull circuit is connected to a first switching circuit for switching, and the second push-pull circuit is also a switching element or the like. Is connected to a second switching circuit that is formed, the first switching circuit is connected to a first pulse transformer that boosts the output voltage from the first switching circuit, and the second switching circuit is the same. A first pulse transformer connected to a second pulse transformer, wherein the first pulse transformer smooths an output of the first rectifier circuit via a first rectifier circuit which rectifies an output voltage from the first pulse transformer; The second pulse transformer is also connected to the second smoothing circuit via the second rectifying circuit, and the first smoothing circuit and the second smoothing circuit are connected to the speaker. It is characterized by being.

[0008]

"Function" will be described with reference to FIGS. 2, 3 and 4. FIG. 2 is a block diagram showing the basic configuration of the speaker driving switching amplifier having the above configuration. Figure 3
3A is a waveform diagram showing an input signal, FIG. 3B shows a relationship between an in-phase signal and a sawtooth wave, and FIG. 3C shows a relationship between an antiphase signal and a sawtooth wave. It is a waveform diagram. 3 (d), (e) and FIG. 4 are waveform diagrams schematically showing output signals output from the blocks shown in FIG.

In the PWM conversion circuit 20, as shown in FIG. 3B, the PWM1 signal (FIG. 3), which is the PWM signal only on the plus side of the in-phase signal and the sawtooth wave, is applied.
(D)) is created and, as shown in FIG. 3 (c), the PWM2 signal (FIG. 3 (e)) is the PWM signal only on the plus side of the anti-phase signal and the sawtooth wave. )
Is created.

Next, after the PWM1 signal is alternately distributed to the push side and the pull side by the first push-pull circuit 31, the primary side coil of the first pulse transformer is powered by the first switching circuit 41. After switching between the voltage (+ B) and the ground level, and similarly, the second push-pull circuit 32 alternately distributes the PWM2 signal to the push side and the pull side, and then the second switching circuit 42. Then, the primary side coil of the second pulse transformer is switched between the power supply voltage (+ B) and the ground level.

Next, due to the switching of the first switching circuit 41, a voltage having the waveform shown in FIG. 4A is induced on the secondary side of the first pulse transformer 51, and similarly, the second voltage is generated.
By the switching of the switching circuit 42, the voltage having the waveform shown in FIG. 4B is induced on the secondary side of the second pulse transformer 52. After that, the signal boosted by the first pulse transformer 51 in the first rectifier circuit 61 is rectified to the plus side, and the signal level is different as shown in FIG. ) PWM with the same waveform as
The signal is created. Similarly, in the second rectifier circuit 62, the second rectifier circuit 62
The signal boosted by the pulse transformer 52 is rectified to the minus side, and as shown in FIG. 4 (d), a PWM signal with the waveform shown in FIG. 3 (e) inverted is created.

Next, in the first smoothing circuit 71, the output signal (FIG. 4 (c)) output from the first rectifying circuit 61 is smoothed, and the first smoothing circuit 71 shows a dotted line in FIG. 4 (c). The signal indicated by is output. On the other hand, in the second smoothing circuit 72, the output signal (FIG. 4D) output from the second rectifying circuit 62 is smoothed, and
The signal shown by the dotted line in (d) is output. Then, these signals are combined and a signal shown by a solid line in FIG. 4E, that is, a signal having a different level but the same waveform as the input signal shown in FIG. 3A is taken out, and the speaker 80 is driven. To be done.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a speaker driving switching amplifier according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram schematically showing a speaker driving switching amplifier according to an embodiment.

In the figure, 11 indicates a buffer and 12 indicates an inverter. Buffer 11 and inverter 1
2, an input signal is input to the buffer 2, and the buffer 11 is a comparator 2 that constitutes the PWM conversion circuit 20.
1, the inverter 12 is connected to the other comparator 22 that constitutes the PWM conversion circuit 20. Further, a sawtooth wave is input to the comparator 21 and the comparator 22, and the sawtooth wave is also input to the flip-flop 13. The comparator 21 is connected to one end of a resistor R ₁₀ and one end of a resistor R ₁₅ which form the first push-pull circuit 31, while the comparator 22 has one end and a resistor R ₂₀ which forms a second push-pull circuit 32. It is connected to one end of R ₂₅ .

In the first push-pull circuit 31, the resistance is reduced.
Anti-R_TenThe other end of the transistor Q₁₁Connected to the collector of
Resistance R₁₅The other end of the transistor Q₁₂Contact the collector of
Continued, transistor Q₁₁And transistor Q
₁₂The emitters of are both connected to ground. Trang
Dista Q₁₁The base is resistance R₁₁Flip through
It is connected to the Q output side of₁₂Through
Connected to ground, and transistor Q₁₂The
Resistance is resistance R₁₄Q of flip-flop 13 via
_INV It is connected to the output side and has a resistance R₁₃Via gra
Connected to the Transistor Q₁₁Collector of
Resistor configuring the first switching circuit 41 ₁₆At one end of
Connected, transistor Q₁₂Is the first collector
Resistor R that constitutes the switching circuit 41₁₉Connect to one end of
Has been done.

[0016] In the second push-pull circuit 32, the other end of the resistor R ₂₀ is connected to the collector of the transistor Q _21, the other end of the resistor R ₂₅ is connected to the collector of the transistor Q _22, the transistors Q ₂₁ and Transistor Q
_{The 22} emitters are both connected to ground. The base of the transistor Q ₂₁ is connected to the Q output side of the flip-flop 13 via the resistor R ₂₁ and is also connected to the ground via the resistor R _22, and the base of the transistor Q ₂₂ is the resistor R _24. Q of flip-flop 13 via
It is connected to the _INV output side and also connected to the ground via a resistor R ₂₃ . The collector of the transistor Q ₂₁ is connected to one end of the resistor R ₂₆ that constitutes the second switching circuit 42, and the collector of the transistor Q ₂₂ is the second
Is connected to one end of a resistor R ₂₉ which forms the switching circuit 42.

In the first switching circuit 41, the other end of the resistor R ₁₆ is connected to the base of the transistor Q ₁₃ , and the other end of the resistor R ₁₉ is connected to the base of the transistor Q ₁₄ . The base of the transistor Q ₁₃ is connected to the ground through the resistor R ₁₇ , the base of the transistor Q ₁₄ is connected to the ground through the resistor R ₁₈ , and the emitters of the transistor Q ₁₃ and the transistor Q ₁₄ are both connected to the ground. . The collector of the transistor Q ₁₃ is connected to the + side of the primary coil L ₁₁ of the first pulse transformer 51, and the collector of the transistor Q ₁₄ is connected to the − side of the primary coil L ₁₂ of the first pulse transformer 51. Has been done.

In the second switching circuit 42, the other end of the resistor R ₂₆ is connected to the base of the transistor Q ₂₃ , and the other end of the resistor R ₂₉ is connected to the base of the transistor Q ₂₄ . The base of the transistor Q ₂₃ is connected to the ground through the resistor R ₂₇ , the base of the transistor Q ₂₄ is connected to the ground through the resistor R ₂₈ , and the emitters of the transistor Q ₂₃ and the transistor Q ₂₄ are both connected to the ground. . The collector of the transistor Q ₂₃ is connected to the + side of the primary coil L ₂₁ of the second pulse transformer 52, and the collector of the transistor Q ₂₄ is connected to the − side of the primary coil L ₂₂ of the second pulse transformer 52. Has been done.

The first pulse transformer 51 has a coil L ₁₁ and a coil L _{12 on} the primary side, and a coil L ₁₃ on the secondary side. Both the − side of the coil L ₁₁ and the + side of the coil L ₁₂ are connected to the + B power source, and one end L _13a of the coil L ₁₃ is connected to the anode of the diode D ₁₁ forming the first rectifying circuit 61.
The other end L _13b of the coil L ₁₃ is connected to the anode side of the diode D ₁₂ which constitutes the first rectifying circuit 61. Further, the central terminal A ₁ of the coil L ₁₃ is connected to one end of the capacitor C ₁ which constitutes the first smoothing circuit 71. The cathode side of the diode D _{11 and} the cathode side of the diode D ₁₂ are both connected to one end of a coil L ₁ that constitutes the first smoothing circuit 71, and the other end of the coil L ₁ is a capacitor C ₁ Is connected to the other end of
Both ends of C ₁ are connected to the speaker 80.

The second pulse transformer 52 has a coil L ₂₁ and a coil L _{22 on} the primary side and a coil L ₂₃ on the secondary side. Both the − side of the coil L ₂₁ and the + side of the coil L ₂₂ are connected to the + B power source, and one end L _23a of the coil L ₂₃ is connected to the cathode of the diode D ₂₁ forming the second rectifier circuit 62.
The other end L _23b of the coil L ₂₃ is connected to the cathode side of the diode D ₂₂ that constitutes the second rectifying circuit 62. Further, the central terminal A ₂ of the coil L ₂₃ is connected to one end of a capacitor C ₂ which constitutes the second smoothing circuit 72. The anodic side of the diode D _{21 and} the anodic side of the diode D ₂₂ are both connected to one end of a coil L ₂ that constitutes the second smoothing circuit 72, and the other end of the coil L ₂ is a capacitor C ₂ Of the condenser C ₂ and both ends of the condenser C ₂ are connected to the speaker 80.

The operation of the speaker driving switching amplifier constructed as described above will be described with reference to FIGS.
When the input signal shown in FIG. 3A is input to the buffer 11 and the inverter 12, the buffer 11 outputs an in-phase signal to the comparator 21, and the inverter 1
From 2, a reverse phase signal is output to the comparator 22. Then, as shown in FIG. 3B, the in-phase signal is compared with the sawtooth wave in the comparator 21,
The PWM1 signal shown in FIG. 3D is output from the comparator 21 to the first push-pull circuit 31. Further, in the comparator 22, the reverse phase signal and the sawtooth wave are compared (FIG. 3 (c)), and the PWM2 signal shown in FIG. 3 (e) from the comparator 22 to the second push-pull circuit 32. Is output.

The sawtooth wave is a flip-flop 13
Is also input to, and the states of the Q output and the Q _INV output of the flip-flop 13 change each time the sawtooth wave falls. Then, since the Q output of the flip-flop 13 is input to the base of the transistor Q ₁₁ and the Q _INV output is input to the base of the transistor Q ₁₂ , eventually, every time the sawtooth wave falls, the transistor Q ₁₁ and the transistor Q ₁₂ are output. And turn on and off alternately. Therefore, when the transistor Q ₁₁ (or the transistor Q ₁₂ ) is on, the PWM1 signal which is about to be input to the transistor Q ₁₃ side (or the transistor Q ₁₄ side) of the first push-pull circuit 31 is the transistor of Q ₁₁ (or transistor Q ₁₂₎ is the collector current is absorbed in the transistor Q ₁₁ (or transistor Q _12), the transistor Q ₁₃ (or transistor Q ₁₄₎
Is not transmitted to. On the other hand, the PW that is about to be input to the transistor Q ₁₄ side (or the transistor Q ₁₃ side)
The M1 signal is applied to transistor Q ₁₂ (or transistor Q
_{Since 11} ) is off, it is transmitted to the transistor Q ₁₄ (or transistor Q ₁₃ ) without being absorbed by the transistor Q ₁₂ (or transistor Q ₁₁ ). When the PWM1 signal is input to the transistor Q ₁₃ (or the transistor Q ₁₄ ), a current flows from the + B power supply through the coil L ₁₁ and the transistor Q ₁₃ (or from the + B power supply through the coil L ₁₂ and the transistor Q ₁₄ ). Then, the + B voltage is applied to the primary side coil L ₁₁ (or the coil L ₁₂ ) forming the first pulse transformer 51.

As described above, each time the PWM1 signal is input, the transistors Q ₁₃ and Q ₁₄ forming the first switching circuit 41 are alternately turned on / off.
When turned off, a current flows from the + B power supply through the coil L ₁₁ and the transistor Q ₁₃ on the primary side of the first pulse transformer 51 (or the coil L ₁₂ and the transistor Q ₁₄ on the primary side). As described above, the direction of the + B power source applied to the primary coil L ₁₁ and the direction of the + B power source applied to the coil L ₁₂ are opposite to each other, and thus the first pulse transformer 51
The waveform of the voltage induced in the secondary coil L ₁₃ of FIG.
As shown in (a), a waveform in which the PWM1 signal shown in FIG. 3 (d) is alternately distributed to the plus side and the minus side with reference to the potential of the center terminal A ₁ of the secondary coil L ₁₃ Become.

The above description is the same for the case of the PWM2 signal, and the waveform of the voltage induced in the secondary coil L ₂₃ of the second pulse transformer 52 is as shown in FIG. 4 (b). The PWM2 signal shown in FIG. 3 (e) has a waveform which is alternately distributed to the plus side and the minus side with reference to the potential of the central terminal A ₂ of the secondary coil L ₂₃ .

[0025] In the first pulse transformer 51, when the + B power to the coil L ₁₁ transistors Q ₁₃ is turned on is applied, the other end L _{13 b} of the coil L ₁₃ in the coil L ₁₃ of the secondary side Positive electromotive force is generated. At this time, the diode D ₁₂ is forward-biased, and a current flows through the path of the diode D ₁₂ , the coil L ₁ , the capacitor C ₁ , and the central terminal A ₁ , and the diode D ₁₂ and the coil L
_The load current flows through the path of ₁ , the speaker 80, and the central terminal A ₁ . On the other hand, when the + B power to the coil L ₁₂ transistor Q ₁₄ is turned on is applied, the electromotive force of the end L _13a of the coil L ₁₃ and the positive direction is generated in the coil L ₁₃ on the secondary side. At this time, the diode D ₁₁ is forward biased, and the diode D ₁₁ , the coil L ₁ , and the capacitor C
_1, the current flows in the path of the central terminals A _1, diode D _11, a coil L _1, a speaker 80, a load current flows through a path of the central terminal A _1. As described above, when the + B power source is applied to the coil L ₁₁ or the coil L ₁₂ on the primary side,
Regardless of the direction of the electromotive force induced in the secondary coil L ₁₃ , the first smoothing circuit 71 is connected to the first rectifying circuit 61.
The current flowing from the coil L ₁ to the capacitor C ₁ and the load current flowing from the terminals 80a to 80b of the speaker 80 flow. As can be seen from this, the output voltage waveform of the first rectifier circuit 61 is a voltage waveform obtained by rectifying the voltage waveform induced in the secondary coil L ₁₃ to the plus side.
The voltage waveform is shown in FIG.

On the other hand, in the second pulse transformer 52
And transistor Q_{twenty three}Turns on and coil L_{twenty one}+ B power supply
Is applied, the secondary side coil L_{twenty three}To coil L
_{twenty three}One end of L_23a Is generated in the negative direction.
It At this time diode D_{twenty one}Is forward biased
Central terminal A₂ , Condenser C₂ , Coil L₂ , Da
Iodo D_{twenty one}Current flows through the route of and the central terminal A
₂ , Speaker 80, coil L ₂ , Diode D_{twenty one}The route
The load current flows. Also, the transistor Q_{twenty four}Turns on
Coil C_{twenty two}If + B power is applied to the
Coil of_{twenty three}To coil L_{twenty three}The other end of L_23b In the negative direction
Electromotive force is generated. At this time, the diode D_{twenty two}
Is forward-biased and the central terminal A₂ , Condenser
C₂ , Coil L ₂ , Diode D_{twenty two}Current flows through the path
And the central terminal A₂ , Speaker 80, coil L₂ ,
Diode D_{twenty two}The load current flows through the path. I mentioned above
Sea urchin coil L_{twenty one}Or coil L_{twenty two}+ B power supply
Is applied, the secondary coil L_{twenty three}Induced electromotive force
The second smoothing circuit 72 is configured regardless of the direction of force.
Condenser C₂ And coil L₂ Second adjustment through
The secondary side coil L from the flow circuit 62_{twenty three}Charging current flowing into the
And the central terminal A₂ From speaker 80 (speech
The load current from terminal 80b of the
Flowing. As can be seen, the output of the second rectifier circuit 62
The force voltage waveform is the coil L on the secondary side._{twenty three}Induced voltage waveform
Is a voltage waveform rectified to the minus side. The voltage waveform
It is shown in FIG.

The output voltage of the first rectifier circuit 61 described above is smoothed by the first smoothing circuit 71 into the signal waveform shown by the dotted line in FIG. 4C, while the output of the second rectifier circuit 62 is output. The voltage is smoothed by the second smoothing circuit 72, and then the voltage is generated as shown in FIG.
The signal waveform is shown by the dotted line. Then, the outputs of these smoothing circuits are combined and the signal shown by the solid line in FIG.
That is, a signal obtained by greatly amplifying the input signal is extracted,
The speaker 80 is driven by the signal.

As described above, if the speaker driving switching amplifier according to the embodiment is used, a large output can be obtained without reducing the impedance of the speaker 80 or boosting the power supply voltage using the DC-DC converter. Power can be taken out. That is, by using the speaker drive switching amplifier according to the embodiment, it is possible to configure a speaker drive amplifier that does not deteriorate efficiency and does not deteriorate the damping factor.

Further, in the embodiment, the PWM signal is amplified by using the pulse transformer 51 and the pulse transformer 52.
Even if the two signals are to be amplified by the pulse transformer 51 and the pulse transformer 52 as they are, the modulation frequency (sound frequency) is as low as 20 Hz to 20 KHz, so that residual magnetism is generated between the primary side input and the secondary side output. There is a possibility that the linearity cannot be secured. Considering this point, the embodiment has a sufficiently high frequency (for example, 100K).
The PWM1 signal and the PWM2 signal (Hz or more) are alternately distributed to the push side and the pull side, respectively, and the distributed signal is distributed to the pulse transformer 51 and the pulse transformer 5.
It is amplified by 2 and then rectified. Since the switching frequency is sufficiently higher than the modulation frequency (voice frequency), the pulse widths of adjacent PWM signals are almost the same, so by allocating to the push side and pull side as described above, the polarities are opposite. , PWM pulses having the same level and substantially the same pulse width are input to the pulse transformer 51 and the pulse transformer 52. As a result, the residual magnetism can be canceled and linearity can be secured between the primary side input and the secondary side output of the pulse transformer 51 and the pulse transformer 52.

[0030]

As described above in detail, by using the speaker driving switching amplifier according to the present invention, it is possible to reduce the impedance of the speaker or boost the power supply voltage by using the DC-DC converter. A large output power can be taken out.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram schematically showing a speaker driving switching amplifier according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a basic configuration of a speaker driving switching amplifier according to the present invention.

3A is an input signal input to a speaker driving switching amplifier according to an embodiment, FIG. 3B is a positional relationship between an in-phase signal and a sawtooth wave, and FIG. It is a waveform diagram schematically showing the positional relationship with the sawtooth wave,
FIG. 7D is a waveform diagram schematically showing the PWM1 signal, and FIG. 8E is a waveform diagram schematically showing the PWM2 signal.

FIG. 4 (a) is a waveform diagram schematically showing the secondary output of the first pulse transformer, and FIG. 4 (b) is a waveform diagram schematically showing the secondary output of the second pulse transformer. In the figure (c), the solid line is a waveform diagram schematically showing the output of the first rectifier circuit, and the dotted line is a waveform diagram schematically showing the output of the first smoothing circuit. Similarly, the solid line in the figure (d) is the waveform of the second rectifier circuit. The output and the dotted line are waveform diagrams schematically showing the output of the second smoothing circuit. FIG. 7E is a waveform diagram schematically showing a signal obtained by combining the output of the first smoothing circuit and the output of the second smoothing circuit.

[Explanation of symbols]

 20 PWM conversion circuit 31 1st push-pull circuit 32 2nd push-pull circuit 41 1st switching circuit 42 2nd switching circuit 51 1st pulse transformer 52 2nd pulse transformer 61 1st rectification circuit 62 6th 2 Rectifier circuit 71 First smoothing circuit 72 Second smoothing circuit 80 Speaker

Claims (1)

[Claims] 1. A PWM1 signal of only the plus side of the in-phase signal from the in-phase signal and the sawtooth wave, and a PWM1 signal of only the plus side of the anti-phase signal from the in-phase signal and the sawtooth wave.
A first push-pull circuit that includes a PWM conversion circuit that creates two signals, the PWM conversion circuit including a flip-flop and a switching element, and that alternately distributes the PWM1 signal to a push side and a pull side;
The first push-pull circuit is connected to a second push-pull circuit that alternately distributes the PWM2 signal to the push side and the pull side, and the first push-pull circuit is composed of a switching element or the like, and is distributed to the push side and the pull side. The second push-pull circuit is connected to a first switching circuit that switches a signal between a power supply voltage and a ground level, and the second push-pull circuit is connected to a second switching circuit that is also composed of a switching element or the like. The first switching circuit is connected to a first pulse transformer that boosts an output voltage from the first switching circuit, and the second switching circuit is also connected to a second pulse transformer, and the first pulse transformer is connected to the first pulse transformer. The transformer uses a first rectifier circuit that rectifies the output voltage from the first pulse transformer, Is connected to a first smoothing circuit for smoothing force, and the second pulse transformer is similarly connected to a second smoothing circuit via a second rectifying circuit, and the first smoothing circuit and the second smoothing circuit are connected. A switching amplifier for driving a speaker, wherein the circuit is connected to the speaker.