JPH0969732A - Amplifier circuit and audio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the harmful effects of noises which are caused by an amplifier circuit that is used to an audio amplifier, etc., mounted on a vehicle and an audio receiver that contains the amplifier circuit. SOLUTION: An amplifier circuit is provided with a signal amplifier part 11 which amplifies an input signal AS and outputs it as an amplifier signal ZS, an offset voltage generation part 14 which generates the offset voltage Va by adding the voltage of a fixed level to the signal ZS, a signal generation part 19 which generates a drive signal having the prescribed switching frequency based on the voltage Va, a switching circuit SW which performs a switching operation based on the switching frequency, and a chopper power supply 18 which supplies the voltage following the voltage Va to the part 11 as the power voltage Vc. Then the part 19 functions to reduce the switching frequency of the circuit SW while a radio set is working at a place near the amplifier circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit and an audio receiver, and more specifically, an object thereof is to reduce an adverse effect due to noise of an amplifier circuit used for a vehicle audio amplifier or the like and an audio receiver equipped with the amplifier circuit. To do.

[0002]

2. Description of the Related Art An amplifier circuit mounted in a vehicle audio amplifier according to a conventional example will be described below. Conventionally,
In an audio amplifier that uses a constant voltage as a power supply voltage, the amplifier is driven by using a high voltage that can always obtain the maximum output as a power supply voltage.

In such a circuit, even when the output is at a low level, the power supply voltage is such that the maximum output can always be taken out, so that the power consumption in the amplifier becomes unnecessarily large. , The efficiency of the amplifier was low. This problem was particularly serious when applied to a circuit such as an in-vehicle audio amplifier which has a low power supply voltage and a loss of power consumption cannot be ignored.

Therefore, in order to increase the efficiency of the amplifier,
The following amplifier circuits have been proposed. this is,
The power supply voltage is a voltage obtained by multiplying the amplified signal (ZS) by a constant voltage, and the driving is performed while varying the power supply voltage according to the increase or decrease of the amplified signal (ZS). Specifically, this circuit is a circuit as shown in FIG. 10, and has an amplifier (1) and an auxiliary power supply section (2). A power supply having the same configuration as the auxiliary power supply unit (2) shown in FIG. 10 is connected to the negative side of the amplifier (1), but this is the same as the positive side, and the description thereof will be omitted.

According to the above circuit, when the power is turned on, a constant power supply voltage (± Vcc) is applied to the auxiliary power supply section (2). Next, the input signal (AS) is amplified by the amplifier (1) to generate an amplified signal (ZS), which is output to a speaker (not shown) and simultaneously output to the auxiliary power supply unit (2).

Then, a constant voltage is added to the amplified signal (ZS) by the offset voltage generation circuit (4), and the amplified signal (ZS) is input to the inverting input portion (-) of the comparator (7). On the other hand, the power supply voltage (+ Vc) output from the chopper power supply (8) is input to the non-inverting input section (+) of the comparator (7), and the power supply voltage (+ Vc) and the constant voltage are always added. It is compared with the amplified signal (ZS).

The output of the comparator (7) is connected to the switching circuit (SW) of the chopper power supply (8),
The amplified signal (ZS) with the added constant voltage is supplied to the power supply voltage (+
When Vc) falls, the output of the comparator (7) becomes low level (hereinafter referred to as "L"), the switching circuit (SW) is turned on, the power supply voltage (+ Vc) rises, and conversely the constant voltage rises. When the power supply voltage (+ Vc) exceeds the amplified signal (ZS) generated, the output of the comparator (7) becomes a high level (hereinafter referred to as “H”), the switching circuit (SW) is turned off, and the power supply voltage (+ Vc). Rises.

By the above operation, the power supply voltage (+ Vc) changes while following the voltage obtained by adding a constant voltage to the amplified signal (ZS) as shown in FIG.
Is supplied to. Using this power supply voltage (+ Vc), the input signal (AS) is amplified by the amplifier (1), and the amplified signal (ZS) is output to the speaker. By varying the power supply voltage (± Vc) in accordance with the magnitude of the amplified signal (ZS) in this manner, especially in comparison with a case where the amplifier is driven using a high voltage from which the maximum output can always be taken out as the power supply voltage. The power consumption loss at the time of a small level output was reduced, and the efficiency was improved.

[0009]

However, the above conventional amplifier circuit uses the chopper power source (8), and the switching frequency of this switching circuit (SW) is
It is about 200 kHz to 500 kHz. This is because the frequency characteristics of the amplifier can be obtained up to the upper limit of the audible band of 20 kHz, the follow-up of the output waveform can be ensured, and the ripple component can be suppressed.

The noise frequency of the switching circuit (SW) is 200 kHz of the fundamental frequency and the second to fifth harmonics, that is, 400 kHz to 1 MHz. This noise is A
Since it falls within the range of 200 kHz to 2 MHz which is the frequency band of the M radio, there is a problem that noise is output from the AM radio when the AM radio is located near this amplifier circuit.

Particularly for in-vehicle applications, since a radio tuner of AM or FM and an audio amplifier are used together, this problem is a serious problem that cannot be ignored.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art. As shown in FIG. 1, a signal amplifier for amplifying an input signal and outputting the amplified signal, and the amplified signal. An offset voltage generating unit for generating an offset voltage by adding a constant voltage to the signal, a signal generating unit generating a drive signal having a predetermined switching frequency based on the offset voltage, and a switching circuit performing a switching operation at the switching frequency. And a chopper power supply that supplies a voltage that follows the offset voltage to the signal amplification unit as a power supply voltage, and the signal generation unit is configured to operate when the radio is operating near the amplification circuit. An amplifier circuit characterized by lowering the switching frequency of the switching circuit, or an amplifier for amplifying and increasing an input signal as illustrated in FIG. A signal amplifying unit for outputting a signal,
A slope detection unit that detects the slope of the amplified signal and outputs it to an offset voltage generation unit, an offset voltage generation unit that generates an offset voltage based on the amplified signal and the slope of the amplified signal, and outputs the offset voltage to a chopper power supply. And a signal generator that generates a drive signal having a predetermined switching frequency based on the offset voltage, and a switching circuit that performs a switching operation at the switching frequency, and supply a voltage that follows the offset voltage to the signal amplifier. An amplifier circuit having a chopper power supply for supplying a voltage, wherein the signal generation unit lowers the switching frequency of the switching circuit when the radio is operating near the amplifier circuit, As illustrated in FIG. 8, a power supply that generates a constant voltage and an input signal that is amplified to output an amplified signal. An amplifying unit, a bypass circuit that supplies the constant voltage to the amplifying unit as a power supply voltage, and a switching circuit, and a booster circuit that boosts the constant voltage to generate a boosted voltage; the amplified signal and the constant voltage; And a selection switching circuit that operates the booster circuit to supply the boosted voltage to the amplification unit as a power supply voltage only when the amplified signal is larger than the constant voltage. The booster circuit is an amplifier circuit characterized by lowering the switching frequency of the switching circuit when the radio is operating near the amplifier circuit,
As illustrated in FIG. 9, an audio receiver including a radio, an amplifier circuit according to the present invention, and a control unit that outputs a signal indicating that the radio is operating to the amplifier circuit. Thus, it is possible to reduce the adverse effect of switching noise of the amplifier circuit particularly on the AM radio and the like.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (1) First Embodiment Hereinafter, an amplifier circuit according to a first embodiment of the present invention will be described with reference to the drawings.

Specifically, this amplifier circuit is a circuit as shown in FIG. 1, which is used in an audio amplifier for vehicles, etc., and is an example of a signal amplifier section (11) and an auxiliary power source section (12). ) And. A power supply having the same configuration as the auxiliary power supply unit (12) shown in FIG. 1 is connected to the negative side of the amplifier (11), but this is an auxiliary power supply that generates a positive power supply voltage (+ Vc). The configuration is the same as that of the section (12), and only the point that a negative power supply voltage (-Vc) is generated is omitted and not illustrated, and the description is also omitted.

The amplifier (11) is an example of a signal amplifier, and amplifies the input signal (AS) by using a power supply voltage (+ Vc) described later and outputs an amplified signal (ZS). Each of them has a voltage amplifying unit for amplifying the voltage of the input signal (AS) and a current amplifying unit for amplifying the current of the output of the voltage amplifying unit. The auxiliary power supply unit (12) is a circuit having an offset voltage generation circuit (14), a signal generation unit (19), and a chopper power supply (18), and a constant DC voltage (+ Vcc) amplified signal (Z).
S) is changed and supplied to the amplifier (11). Specifically, the amplified voltage (ZS) is multiplied by the offset voltage generated by the offset voltage generation circuit (14), and a positive power supply voltage (+ Vc) that changes so as to follow this voltage is supplied. There is.

The offset voltage generator (14) is for multiplying the amplified signal (ZS) by a constant voltage. The signal generator (19) includes a comparator (17) and a modulation circuit (1
5) and an oscillation circuit (16), and is a circuit that generates a PWM signal that drives a switching circuit (SW) described later.

The comparator (17) compares the amplified signal (ZS) multiplied by a constant voltage with the positive power supply voltage (+ Vc), and outputs the comparison result to the modulation circuit (15). . The oscillator circuit (16) is a circuit that generates a clock having a predetermined frequency. This frequency matches the switching frequency of the switching circuit (SW) of the chopper power supply (18). The frequency of the clock generated by the oscillator circuit (16) is usually 200 to 500 kHz, but the radio operation signal (AM) output when the AM radio near the amplifier circuit is ON. When input, this frequency is set to drop to 30-80 kHz.

The modulation circuit (15) includes a comparator (1
Based on the comparison result of 7), the clock from the oscillation circuit (16) is PWM (Pulse Width Modulation) modulated to generate a PWM signal, which is output to the switching circuit (SW). Switching circuit (S
W) is turned on / off by this PWM signal, and an amplifier (1) is operated while increasing / decreasing a constant direct current voltage (+ Vcc).
It is supplied to 1).

The operation of the above amplifier circuit will be described below. First, a fixed power supply voltage (±
Vcc) is applied. Next, the input signal (AS) is amplified by the amplifier (11) to generate an amplified signal (ZS), which is output to a speaker (not shown), and is also output to the auxiliary power supply unit (12).

Then, a constant voltage is added to the amplified signal (ZS) by the offset voltage generation circuit (14), and the amplified signal (ZS) is input to the inverting input section (-) of the comparator (17). On the other hand, the power supply voltage (+ Vc) output from the chopper power supply (18) is applied to the non-inverting input section (+) of the comparator (17).
Is input, and the power supply voltage (+ Vc) is always compared with the amplified signal (ZS) on which a constant voltage is added.

The result of this comparison by the comparator (17) is output to the modulation circuit (15). The modulation circuit (15) is simultaneously input with a clock of 200 to 500 kHz from the oscillation circuit (16), and this clock is PWM-modulated by the output signal of the comparator (17) to perform PWM.
A signal is generated, this PWM signal is output to the switching circuit (SW), and the switching circuit (SW) performs ON / OFF operation at a switching frequency of 200 to 500 kHz.

Thus, when the power supply voltage (+ Vc) falls below the amplified signal (ZS) on which the constant voltage is added, the output of the comparator (17) becomes low level (hereinafter referred to as "L") and the switching circuit (SW). ) Is turned on and the power supply voltage (+ Vc) rises, and conversely, when the power supply voltage (+ Vc) exceeds the amplified signal (ZS) on which a constant voltage is added, the output of the comparator (17) is at a high level (hereinafter referred to as “H "")
Then, the switching circuit (SW) is turned off and the power supply voltage (+ Vc) rises.

By the above operation, the power supply voltage (+ Vc) changes while following the voltage obtained by multiplying the amplified signal (ZS) by a constant voltage as shown in FIG.
Is supplied to. Using the power supply voltage (+ Vc), the input signal (AS) is amplified by the amplifier (11) and the amplified signal (ZS) is output to the speaker. Therefore, the efficiency is higher than when a constant voltage is used as the power supply voltage. Will be better.

The operation that is a characteristic operation of this embodiment when the AM radio is ON near the amplifier circuit will be described below. In this case, it is detected that the AM radio is operating by some means, and the radio operating signal (AM) as shown in FIG. 1 causes the oscillation circuit (16).
Is input to Then, the frequency of the clock generated by the oscillation circuit (16) is changed from 200 to 500 kHz to 30 to 80 kHz.
The switching circuit (SW) turns ON / O at this switching frequency of about 30 to 80 kHz.
The FF operation is performed, and thereafter, the same operation is performed as when the AM radio is not turned on near the amplifier circuit.

According to the amplifier circuit of this embodiment, the AM
Since the switching frequency of the switching circuit (SW) is lowered to about 30 to 80 kHz when the radio is operating in the vicinity, the switching noise frequency in the case of 30 kHz includes the secondary frequency including the basic frequency of 30 kHz. ~ This is the frequency band of AM radio because it is the range up to 60 to 150 kHz of the 5th harmonic.
It does not fall within the range of 00 kHz to 2 MHz.

For this reason, the switching noise that has occurred conventionally is 200 kHz to 2 which is the frequency band of AM radio.
It becomes possible to suppress the problem that noise is output from this AM radio when it is in the MHz range and there is an AM radio nearby. In particular, for in-vehicle applications, a radio tuner of AM or FM and an audio amplifier are often used together, so that particularly effective effects can be obtained in such a case.

Although the amplifier circuit having the circuit configuration shown in FIG. 1 has been described in the present embodiment, the present invention is not limited to this, and a voltage obtained by adding a constant voltage to the amplified signal (ZS) is added. The same effect can be obtained with any circuit as long as it is an amplifier circuit that operates with a power supply voltage that changes so as to follow and has a chopper power supply that includes a switching circuit.

(2) Second Embodiment Before explaining the amplifier circuit according to the second embodiment of the present invention, the reason why the following configuration is adopted in the present embodiment will be briefly explained. explain. In the amplifier circuit having the circuit configuration of the first embodiment, when an amplified signal (ZS) having a steep rise is generated as shown in FIG. 4, the auxiliary power supply unit cannot follow the steep change. As shown in the figure, the power supply voltage (+ Vc), which should be always higher than the amplified signal (ZS), is lower than the amplified signal (ZS), and the amplified signal (ZS) is distorted. The amplifier circuit according to the embodiment has improved this drawback.

A second embodiment of the present invention will be described below with reference to the drawings. Note that the description of items common to the first embodiment will be omitted to avoid duplication. The difference of this circuit from the first embodiment is not that the amplified signal (ZS) is simply superposed with a constant voltage and the power supply voltage follows this, but the slope detection section (2
1) The gradient of the amplified signal (ZS) is detected by 1), and the sum of the detection result and a constant voltage is added to the amplified signal (ZS).

The amplifier circuit according to the present embodiment is used for an on-vehicle audio amplifier or the like, and as shown in FIG. 3, a gradient detecting section (21), an offset voltage generating section (22), a chopper power source (24) and The circuit includes an auxiliary power supply unit (27) having a signal generation unit (30) and an amplification unit (25) including a preamplifier (25A) and a power amplifier (25B).

The gradient detecting section (21) has a differentiating circuit and is a circuit for obtaining the differential of the amplified signal (ZS). The offset voltage generation unit (22) includes an offset unit (22A) that adds a constant voltage to the amplified signal (ZS) and an addition circuit (22B).
And a circuit that generates an offset voltage (Va) as a differential result of the amplified signal (ZS), a constant voltage, and an addition result of the amplified signal.

The signal generator (30) has a first comparator (23A), a second comparator (23B), a modulation circuit (28) and an oscillation circuit (29), and a PWM signal for driving a switching circuit described later. Is a circuit for generating.
The operation of the amplifier circuit according to the present embodiment will be described below. First, the amplified signal (ZS) output from the power amplifier (25B) is differentiated by the gradient detection unit (21) which is a differentiation circuit. On the other hand, a constant voltage is added to the amplified signal (ZS) by the offset voltage generator (22), and the addition result of the differential of the amplified signal (ZS) and the amplified signal (ZS) to which the constant voltage is added is added by the addition circuit. A voltage (hereinafter referred to as offset voltage (Va)) is generated.

Next, the first comparator (23A) outputs the power supply voltage (+) which is the output of the chopper power supply (24).
Vc) and the offset voltage (Va) are compared and output to the inverting input side of the second comparator (23B),
The output result compared with the reference voltage of the non-inverting input of the second comparator (23B) is output to the modulation circuit (28). The second comparator (23B) is provided for stable operation, and its output is the same as the output of the first comparator (23A).

At the same time, the modulation circuit (28) has an oscillation circuit (2
The clock of 200-500 kHz from 9) is input, this clock is PWM-modulated by the output of the second comparator (28), the PWM signal is output to the switching circuit (SW), and the switching of 200-500 kHz is performed. Switching circuit (SW) is ON / at frequency
Turns off.

That is, when the power supply voltage (+ Vc) falls below the offset voltage (Va), the first comparator (23
The output of A) becomes "L", and the second comparator (23
This "L" is input to the non-inverting input (-) of B). Then, the output of the second comparator (23B) becomes "H", and the switching circuit (SW) of the chopper power supply (24).
Turns on and the power supply voltage (+ Vcc) rises.

On the contrary, when the power supply voltage (+ Vc) exceeds the offset voltage (Va), the output of the first comparator (23A) becomes "H" and the non-inverting input (-) of the second comparator (23B). This "H" is input. Then, the output of the second comparator (23B) becomes "L", and the switching circuit (SW) of the chopper power supply (24) becomes OF.
After F, the power supply voltage (+ Vcc) drops.

As a result of the above operation, the power supply voltage (+ Vc) operates so as to follow the offset voltage (Va). In this way, the above-described amplifier circuit always generates the offset voltage (Va) which is the sum of the voltage obtained by adding a constant voltage to the amplified signal (ZS) and the differential of the amplified signal (ZS).
The final stage transistor (TR of the power amplifier (25B)
It operates so that the power supply voltage (+ Vc) applied to the collector of 11) follows.

Considering an amplified signal (ZS) having a steep rise as shown in FIG. 4 in which distortion has occurred in the amplifier circuit of the first embodiment, the amplified signal (ZS).
, And at the same time, the differential of the amplified signal (ZS) as shown in FIG. 6 is taken, and the sum of the amplified signal with the added constant and the differential of the amplified signal (ZS) is taken. , The offset voltage (Va) as shown in FIG. 7 is generated, and the power supply voltage (+ Vc) is changed and generated so as to follow this offset voltage (Va).

Therefore, when the change of the amplified signal (ZS) is steep, the differential increases, and the increased amplified signal (ZS)
Since the power supply voltage (+ Vc) is supplied so as to follow the offset voltage (Va) with the differential of the added power, the power supply voltage is always increased as shown in FIG. 7 even when there is a sharp signal change. , The amplified signal (Z
The power supply voltage (+ Vc) can follow the change of S) with a margin, and it is possible to suppress the distortion of the output of the amplifier which occurs in the amplifier circuit of the first embodiment.

The operation when the AM radio is operating near the amplifier circuit will be described below. In this case, as in the first embodiment, the radio operation signal (AM) is input to the oscillator circuit (29) as shown in FIG. Then, when this radio operation signal (AM) is input, the frequency of the clock generated by the oscillation circuit (29) is reduced from 200 to 500 kHz to about 30 to 80 kHz, and the switching circuit (SW) is ~ 80k
ON / OFF operation at a switching frequency of about Hz,
After that, the operation is similar to the case where the AM radio is not turned on near the amplifier circuit.

Therefore, for example, the switching frequency is 30
When the frequency drops to kHz, the frequency of the switching noise is in the range of 60 to 150 kHz of the second to fifth harmonics, including the fundamental frequency of 30 kHz, and is 200 kHz to the AM radio frequency band. Since it does not fall within the range of 2 MHz, switching noise enters the range of 200 kHz to 2 MHz, which is the frequency band of the AM radio, and there is an AM radio nearby, as in the first embodiment. It is possible to obtain the effect that it is possible to suppress the problem that has occurred in the past, that noise is output, as much as possible.

Further, it is possible to suppress the distortion of the output of the amplifier as much as possible even when an amplified signal having a sharp rise which is difficult to follow in the first embodiment is generated. Although the amplifier circuit having the circuit configuration shown in FIG. 3 has been described in the present embodiment, the present invention is not limited to this, and the differentiation of the amplified signal (ZS) and the amplified signal (ZS) are performed.
The same effect can be obtained with almost any circuit configuration as long as it is a circuit that operates with a power supply voltage that changes by following a voltage generated by adding a constant voltage to the addition result of S).

(3) Third Embodiment An amplifier circuit according to the third embodiment of the present invention will be described below with reference to the drawings. Note that the description of items common to the first and second embodiments will be omitted to avoid duplication. The amplifier circuit according to the present embodiment is used in a vehicle audio amplifier or the like, and as shown in FIG.
It has a voltage doubler generation circuit (32D), an amplifier (33), a bypass circuit (34), and a comparator (35).

The voltage doubler generation circuit (12
D) is, as shown in FIG. 8, an oscillator circuit (OS), a first circuit,
A circuit including a second switching transistor (M1 and M2), a capacitor (Co), a diode (D21), and a capacitor (C21), which does not require a coil unlike the step-up chopper and is the first when no boost is applied. When the switching transistor (M1) of the above is turned off and the second switching transistor (M2) is turned on to charge the capacitor (Co), and when boosting is applied, the first
Is a circuit for turning on the switching transistor (M1) and turning off the second switching transistor (M2) to discharge the electric charge stored in the capacitor (Co) to boost the power supply voltage.

The bypass circuit (34) comprises a diode (D22) connected in parallel with the boost chopper (32) and is a circuit for transmitting the constant voltage (+ Vb) as it is to the amplifier (33). The amplifier (33) is an example of an amplifier, and is a circuit that amplifies an input signal (AS) input to itself to generate an amplified signal (ZS) and outputs the amplified signal (ZS) to a speaker (SP) of 4Ω.

The comparator (35) is an example of a selection switching circuit, and constantly detects the amplified signal (ZS) and the potential (Va) at point a in FIG. 1, and detects the potential difference (Va-ZS) between them.
Becomes a predetermined voltage (5V) or less, the oscillation circuit (OS) is activated to start the ON / OFF operation of the first and second switching transistors (M1, M2),
When this difference exceeds a predetermined voltage, the oscillation circuit (O
The operation of S) is stopped to stop the ON / OFF operation of the first and second switching transistors (M1, M2).

The operation of the circuit will be described below.
First, when the power is turned on, a constant voltage (+ Vb) is supplied to the circuit. At this time, the constant voltage generated by the battery is supplied to the amplifier (33) as a power supply voltage via the bypass circuit (34), and the constant voltage generated by the battery is used to input the input signal (A
S) is amplified, and the amplified signal (Z
S) is generated.

The comparator (35) uses the potential difference (Va) between the potential (Va) at point a in FIG. 8 and the amplified signal (ZS).
-ZS) is always detected, and this potential difference (Va-Z
S) is a predetermined voltage (5 in this embodiment)
The operation of the circuit differs depending on whether it is V) or more.
That is, when the amplified signal (ZS) is at a relatively small level and the potential difference (Va-ZS) between the potential (Va) at point a in FIG. 8 and the amplified signal (ZS) is equal to or greater than the predetermined voltage (5V). ,
The comparator (35) turns off the first switching transistor (M1) with respect to the oscillation circuit (OS),
Outputs a command to turn on the switching transistor (M2) of the oscillator, and the oscillator circuit (OS) accordingly.
Turns off the first switching transistor (M1) and turns on the second switching transistor (M2).

As a result, the capacitor (Co) is charged, and at the same time, the constant voltage (Vb) is supplied to the amplifier (33) via the bypass circuit (34), and this is supplied to the amplifier (3).
It becomes the power supply voltage of 3). The level of the amplified signal (ZS) becomes a large output, and the potential difference (Va-ZS) between the potential (Va) at the point a in FIG. 8 and the amplified signal (ZS) becomes a predetermined voltage (5
V) or less, the first switching transistor (M1) is turned on and the second switching transistor (M) is turned on from the comparator (35) to the oscillation circuit (OS).
A command to turn off 2) is output, and accordingly, the oscillation circuit (OS) turns on the first switching transistor (M1) and turns off the second switching transistor (M2).

As a result, the electric charge charged in the capacitor (Co) is discharged, the potential (Va) at point a in FIG. 8 rises, and the high voltage generated by the voltage doubler generation circuit (32D) is supplied to the amplifier ( 13) is supplied as a power supply voltage.
When the level of the amplified signal (ZS) becomes a small output again and the potential difference (Va-ZS) between the potential (Va) at the point a in FIG. 8 and the amplified signal (ZS) becomes a predetermined voltage (5V) or more, The comparator (35) stops the ON / OFF operation of the switching circuit (SW11), and the power supply voltage supplied to the amplifier (33) becomes the constant voltage supplied again via the bypass circuit (34). The efficiency is improved as compared with the case where a constant voltage of is used as the power supply voltage.

The operation when the AM radio is turned on near the amplifier circuit will be described below. In this case, similarly to the first and second embodiments, the radio operation signal (AM) is input to the oscillator circuit (OS). Then, the frequency of the clock generated by the oscillation circuit (OS) is 2
The frequency drops from 00 to 500 kHz to about 30 to 80 kHz, and the first and second switching transistors (M1, M
2) performs the ON / OFF operation at the switching frequency of about 30 to 80 kHz, and thereafter operates in the same manner as when the AM radio is not turned on near the amplification circuit. Therefore, the first and second embodiments Similar to the amplifier circuit described in 1., when the switching frequency is reduced to 30 kHz, the frequency of the switching noise is 60 to 1 of the second to fifth harmonics including the fundamental frequency of 30 kHz.
The range is up to 50 kHz and does not fall within the range of 200 kHz to 2 MHz which is the frequency band of AM radio.

As described above, similar to the first and second embodiments, the switching noise enters the range of 200 kHz to 2 MHz which is the frequency band of the AM radio. It is possible to suppress the problem that has occurred conventionally, that noise is output from the computer. Further, the circuit of the present embodiment does not use the boost chopper, so that the coil is unnecessary. This coil was also a source of noise, but by eliminating the need for this coil, it is possible to prevent noise from flying to devices such as radios that are closer to the device than in the first and second embodiments. It becomes possible to do.

(4) Fourth Embodiment An audio receiver according to the fourth embodiment of the present invention will be described below with reference to FIG. FIG. 9 is a circuit diagram illustrating a main part of the audio receiver according to the present embodiment. The audio receiver according to the present embodiment,
As shown in FIG. 9, it is composed of at least an AM radio (AR), a microcomputer, etc., and has a control unit (SB) which controls all of the audio receiver, an amplifier circuit (HE) and a speaker (SP). This receiver is another CD not shown
It has a player, a cassette deck, an FM tuner, and the like.

The amplifier circuit (HE) of the audio receiver according to the present embodiment is equipped with any one of the amplifier circuits described in the first to third embodiments of the present invention, and is usually not shown. An audio signal (AS) input from a CD player or the like is amplified to generate an amplified signal (ZS), which is output to a speaker (SP). User is AM radio (A
R) wanting to listen, and when switching to this and operating the AM radio (AR), the control unit (SB) switches the mode and the radio operation signal (AM) indicating that the AM radio (AR) is operating. ) Is output from the control unit (SB) to the amplifier circuit (HE). As a result, as described in the first to third embodiments, the switching circuit (SW)
Switching frequency of 200 to 500 kHz, 3
AM radio (A
It is possible to prevent the switching noise from jumping into R).

[0055]

As described above, according to the amplifier circuit of the present invention, the operation of the radio having the signal amplifying section, the offset voltage generating section, the signal generating section, and the chopper power supply, is performed in the vicinity. Since the switching frequency of the switching circuit is lowered, the basic frequency of the switching frequency of the switching element and the frequency band of harmonics do not overlap with the frequency band of the radio, so switching noise jumps into the radio. It is possible to suppress adverse effects as much as possible.

The audio receiver according to the present invention includes the radio, the amplifier circuit according to the present invention, and the control unit. Therefore, when the radio is operating, it indicates that the radio is operating. By outputting the signal from the control unit to the amplifier circuit according to the present invention, it becomes possible to suppress switching noise of the amplifier circuit from jumping into the radio as much as possible.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation of the amplifier circuit according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of an amplifier circuit according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating advantages of the amplifier circuit according to the second embodiment of the present invention.

FIG. 5 is a first diagram illustrating an operation of the amplifier circuit according to the second embodiment of the present invention.

FIG. 6 is a second diagram illustrating the operation of the amplifier circuit according to the second embodiment of the present invention.

FIG. 7 is a third diagram illustrating the operation of the amplifier circuit according to the second embodiment of the present invention.

FIG. 8 is a circuit diagram of an amplifier circuit according to a third embodiment of the present invention.

FIG. 9 is a configuration diagram illustrating a main part of an audio receiver according to a fourth embodiment of the present invention.

FIG. 10 is a circuit diagram of an amplifier circuit according to a conventional example.

FIG. 11 is a diagram illustrating an operation of an amplifier circuit according to a conventional example.

[Explanation of symbols]

 (11) Amplifier (Signal Amplifying Unit) (12) Auxiliary Power Supply Unit (14) Offset Voltage Generation Circuit (15) Modulation Circuit (16) Oscillation Circuit (17) Comparator (18) Chopper Power Supply (19) Signal Generation Unit (AM) Radio operation signal (AS) Input signal (ZS) Amplified signal (SW) Switching circuit (21) Gradient detection unit (22) Offset voltage generation unit (23A) First comparator (23B) Second comparator (24) Chopper power supply Circuit (25) Signal amplification section (25A) Preamplifier (25B) Power amplifier (27) Auxiliary power supply section (28) Modulation circuit (29) Oscillation circuit (30) Signal generation section (Va) Offset voltage (Vb) Constant voltage (32D) ) Double voltage generation circuit (33) Amplifier (amplifier) (34) Bypass circuit (35) Comparator (O ) Oscillation circuit (M1) a first switching transistor (M2) a second switching transistor

Claims (5)

[Claims] 1. A signal amplification unit that amplifies an input signal and outputs the amplified signal as an amplified signal, an offset voltage generation unit that adds a constant voltage to the amplified signal to generate an offset voltage, and a predetermined unit based on the offset voltage. A signal generator that generates a drive signal having a switching frequency, a switching circuit that performs a switching operation at the switching frequency, and a chopper power supply that supplies a voltage that follows the offset voltage to the signal amplifier as a power supply voltage. The signal generation unit lowers the switching frequency of the switching circuit when the radio is operating near the amplification circuit. 2. A signal amplifier for amplifying an input signal and outputting the amplified signal, a gradient detector for detecting a gradient of the amplified signal and outputting it to an offset voltage generator, the amplified signal, and the amplified signal. An offset voltage generation unit that generates an offset voltage based on the gradient of the output voltage and outputs the offset voltage to a chopper power supply; a signal generation unit that generates a drive signal having a predetermined switching frequency based on the offset voltage; A chopper power supply that supplies a voltage that follows the offset voltage to the signal amplification unit as a power supply voltage, and the signal generation unit has a radio operating near the amplification circuit. At times, the amplifier circuit is characterized in that the switching frequency of the switching circuit is lowered. 3. A power supply for generating a constant voltage, an amplification section for amplifying an input signal and outputting an amplified signal, a bypass circuit for supplying the constant voltage to the amplification section as a power supply voltage, and a switching circuit, A booster circuit that boosts the constant voltage to generate a boosted voltage, constantly detects the amplified signal and the constant voltage, and operates the booster circuit only when the amplified signal is larger than the constant voltage. And a selection switching circuit for supplying the boosted voltage to the amplification unit as a power supply voltage. The boosting circuit lowers the switching frequency of the switching circuit when the radio is operating near the amplification circuit. An amplifier circuit characterized in that. 4. The frequency of the switching circuit is set to 30 when an AM radio is operating near the amplifier circuit.
4. The amplifier circuit according to claim 1, wherein the amplifier circuit is lowered to a range of not less than kHz and not more than 80 kHz. 5. A radio, an amplifier circuit according to claim 1, claim 2, claim 3, or claim 4, and a control unit that outputs a signal indicating that the radio is operating to the amplifier circuit. An audio receiver characterized by having.