JP3426824B2 - Amplifier circuit - Google Patents

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 more specifically, it is an object of the present invention to reduce the circuit scale of an amplifier circuit used for an audio amplifier for vehicles.

[0002]

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

In such a circuit, even if the output is at a low level, the power supply voltage is high enough to always take out the maximum output, so that the power consumption in the amplifier becomes unnecessarily large. , The efficiency of the amplifier was low. Therefore, in order to improve the efficiency of the amplifier, the following amplifier circuit has been proposed. In this technique, a voltage obtained by multiplying the amplified signal (ZS) by a constant voltage is used as a power supply voltage, and the power supply voltage is changed while the power supply voltage is changed according to the increase or decrease of the amplified signal (ZS).

This circuit is a circuit as shown in FIG. 3, and has a transformer (1), a bridge circuit (2), a positive side chopper (3), a negative side chopper (4) and an amplifier (5). According to the above circuit, first, the AC voltage is the transformer (1).
Is output to the bridge circuit (2) and is rectified by the bridge circuit (2) to generate a DC voltage (± Vcc). Among them, the positive DC voltage (+ Vcc) is applied to the positive chopper (3), and the negative DC voltage (-Vcc) is applied to the negative chopper (4).

Next, the input signal (AS) is amplified by the amplifier (5) to generate an amplified signal (ZS), which is output to the speaker (SP). This amplified signal (ZS) is simultaneously output to the positive side chopper (3) and the negative side chopper (4). The positive side chopper (3) monitors the amplified signal (ZS) and changes the positive power supply voltage (+ V) so as to follow the voltage obtained by adding a constant voltage to the amplified signal (ZS).
c) is generated from the positive DC voltage (+ Vcc), and at the same time, the negative side chopper (4) monitors this amplified signal (ZS), and a voltage obtained by adding a constant voltage to this amplified signal (ZS) is added. Negative power supply voltage (-Vc) that changes to follow
Is generated from a negative DC voltage (-Vcc).

By the above operation, the positive power supply voltage (+ V
c) The negative power supply voltage (-Vc) is supplied to the amplifier (1) while changing so as to follow the voltage obtained by adding a constant voltage to the amplified signal (ZS) as shown in FIG. The input signal (AS) is amplified by the amplifier (1) using this power supply voltage (+ Vc), and the amplified signal (ZS) is output to the speaker.

By varying the power supply voltage (± Vc) according to the magnitude of the amplified signal (ZS) in this way, as compared with the case where the amplifier is driven by using the high voltage that can always obtain the maximum output as the power supply voltage. In particular, the loss of power consumption was reduced especially at the output of a small level, and the efficiency was improved.

[0008]

However, in the above conventional amplifier circuit, the bridge circuit (2) for rectification is provided on the secondary coil side of the transformer (1) to generate a DC voltage from the AC voltage, and the DC voltage is generated. The voltage is stepped down by the positive side chopper (3) and the negative side chopper (4) and supplied to the amplifier (5), and once the high voltage DC voltage is generated, the DC voltage is stepped down. Since (± Vc) is generated, two types of circuits, that is, a DC power supply and a chopper power supply, are actually needed as a power supply circuit, so the number of parts is large, and when this is mounted, the scale of the device is large. There was a problem that the size became large.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above drawbacks of the prior art. As shown in FIG. 1, a delay circuit for delaying an input signal and an amplifier for amplifying the delayed input signal are provided. An amplification comprising: a signal amplification unit that generates an amplified signal; and a switching power supply that generates a power supply voltage that changes according to a change in the input signal that is not delayed from an AC voltage and supplies the power supply voltage to the signal amplification unit. A circuit, the switching power supply includes a switching element that performs a switching operation to step down the AC voltage, a switching control unit that supplies an AC voltage that changes in accordance with a change in the input signal to a transformer, and the input signal. A transformer for transforming the alternating voltage that changes in accordance with the change of the voltage to the voltage level of the amplified signal, and the signal increasing after converting the transformed alternating voltage to the DC voltage. And a power supply voltage varying in accordance with the change of the input signal is a voltage obtained by adding a constant voltage to the input signal. By the amplifier circuit according to the present invention, which is characterized in that it becomes possible to reduce the scale of the device when the amplifier circuit is mounted in the device, and it is possible to obtain a highly efficient amplifier. is there.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the amplifier circuit according to the exemplary embodiment of the present invention includes a switching power supply (2
0), an amplifier (15) and a delay circuit (16), which amplifies an input signal (AS) such as an audio signal to generate an amplified signal (ZS) and outputs it to a speaker (SP) which is a load. Is.

The structure of each part will be described below. The switching power supply (20) includes a smoothing circuit (11), a bridge circuit (12), a switching control unit (13), a transformer (14), a frequency control circuit (17) and a rectifying circuit (1).
8), which is a circuit that generates a DC power supply voltage (± Vc) described below from an AC voltage (AC) and supplies the DC power supply voltage to the amplifier (15).

The smoothing circuit (11) comprises a choke coil and a capacitor, and is a circuit for smoothing an alternating voltage (AC) and outputting it to the bridge circuit (12). The bridge circuit (12) is a circuit that rectifies the smoothed AC voltage (AC) and supplies it to the switching control unit (13). The switching control unit (13) has switching transistors (SW1, SW2) and a control IC (13A), and the switching transistors (SW1, SW2) perform ON / OFF operations under the control of the control IC (13A). , A circuit for stepping down and varying the smoothed AC voltage (AC). This control I
The control of C (13A) is performed by the frequency control circuit (17) described later.
The switching control unit (1
The block 3) is a hybrid IC block.

The transformer (14) is a circuit for transforming the AC voltage (AC) stepped down by the switching controller (13). The rectifier circuit (18) is a circuit that converts the AC voltage transformed by the transformer (14) into a DC voltage, generates a DC power supply voltage (± Vcc), and supplies the DC power supply voltage to the amplifier (15).

The frequency control circuit (17) receives the input signal (A
S) is compared with the DC power supply voltage (± Vcc) to generate a DC power supply voltage (± Vcc) that follows the voltage obtained by adding a constant voltage to the input signal (AS). A circuit for controlling the control IC (13A). The delay circuit (16) delays the input signal (AS) to generate a delayed input signal (AS ') and outputs the delayed input signal (AS') to the amplifier (15), and at the same time outputs the undelayed input signal (AS) to the frequency of the switching power supply (20). This is a circuit for outputting to the control circuit (17).

The amplifier (15) is an example of a signal amplifying unit, which amplifies the delayed input signal (AS ') to obtain an amplified signal (Z
S) is generated and output to the speaker (SP) that is a load. The operation of the above circuit will be described below.
First, when an AC voltage (AC) is applied, the smoothing circuit (11)
AC voltage (AC) smoothed by the bridge circuit (12) and output by the bridge circuit (12).
Is rectified and supplied to the switching controller (13).

Next, the smoothing AC voltage (AC) is stepped down by the ON / OFF operation of the switching transistors (SW1, SW2) under the control of the control IC (13A) of the switching control section (13). To be done. The control of the control IC (13A) operates under the control of a frequency control circuit (17) described later. The AC voltage stepped down by the operation of the switching control unit (13) is transformed by the transformer (14) to the voltage level of the amplified signal (ZS), which is converted into a DC voltage by the rectifier circuit (18) to generate a DC power supply voltage. (+ Vcc) is generated and supplied to the amplifier (15).

On the other hand, an input signal (AS) such as an audio signal is input to the above circuit, delayed by a delay circuit (16) to generate a delayed input signal (AS ') and output to an amplifier (15). . At the same time, the delay circuit (16) outputs a signal obtained by adding twice the delay time to the input signal (AS) to the frequency control circuit (17). Then
DC power supply voltage (± Vcc) in the frequency control circuit (17)
Is attenuated to the voltage level of the input signal (AS), and at the same time, a constant voltage is added to the input signal (AS). The attenuated DC power supply voltage (± Vcc) is compared with the input signal (AS) on which a constant voltage is added, and the comparison result is output to the control IC (13A).

Based on the comparison result, the control IC (13A) switches the switching transistors (SW1, SW2) so that a voltage that follows the voltage obtained by adding a constant voltage to the input signal (AS) is generated. ON / OF
The F motion is controlled. Under this control, the switching transistors (SW1, SW2) are turned on / off, the AC voltage (AC) is stepped down, and a voltage (V1) that fluctuates in accordance with the change of the input signal is generated to generate the voltage of the transformer (14). Supplied to the primary side.

For example, the attenuated DC power supply voltage (± Vc
When c) is larger than the input signal (AS) on which a constant voltage is added, the voltage (V1) that fluctuates following the change of the input signal is increased and attenuated by the control of the control IC (13A). Power supply voltage (± Vcc) of
When the DC power supply voltage (± Vcc) is smaller than the input signal (AS) on which a constant voltage is added, the voltage (V1) that changes in accordance with the change of the input signal drops and is attenuated. The voltage (± Vcc) decreases, and the constantly attenuated DC power supply voltage (± Vcc) operates so as to follow the input signal (AS) on which a constant voltage is added.

Next, the transformer (14) transforms the voltage (V1), which changes in accordance with the change of the input signal, to the voltage level of the amplified signal (ZS) and transforms it into the rectifier circuit (18) connected to the secondary side. Is output. After that, the rectifier circuit (1
By 8), the transformed AC voltage (AC) is converted into a DC voltage to generate a DC power supply voltage (± Vcc),
It is supplied to the amplifier (15).

This power supply voltage (± Vcc) is a voltage (V1) which changes following the input signal (AS) on which a constant voltage is added is transformed to the voltage level of the amplified signal (ZS). Therefore, it is a voltage that changes so as to follow the voltage obtained by adding a constant voltage to the amplified signal (ZS) whose phase is almost the same as that of the input signal (AS). The amplifier (15) uses the DC power supply voltage (± Vcc) to delay the delay circuit (1
The delayed input signal (AS ') delayed by 6) is amplified to generate an amplified signal (ZS), which is output to the speaker (SP) which is a load.

By varying the power supply voltage (+ Vc) according to the magnitude of the amplified signal (ZS) in this way, as compared with the case where the amplifier is driven with the high voltage that can always obtain the maximum output as the power supply voltage. In particular, it is possible to reduce the loss of power consumption at the time of low-level output and achieve high efficiency. As described above, according to the amplifier circuit of the present embodiment, the voltage (V1) that has already changed following the change of the input signal (AS) on the primary side of the transformer (14).
To generate a transformer directly from AC voltage (AC) (14)
The switching power supply (20) is used which transforms into a DC voltage in the rectifier circuit (18) and then generates a power supply voltage that changes corresponding to the amplified signal (ZS) after being transformed by.

Therefore, unlike the prior art in which two kinds of power supplies, that is, a DC power supply and a chopper power supply, are actually required as a power supply system circuit, only one type of switching power supply (20) is required for the power supply system circuit. Since the circuit configuration is simplified and the number of parts can be reduced, and since the switching power supply has a high switching frequency, the size of the transformer (14) can be reduced to about a fraction of that of the conventional transformer. It is possible to significantly reduce the scale.

Here, the reason why the input signal (AS) is delayed by the delay circuit (16) and the delayed input signal (AS ') is amplified to generate the amplified signal (ZS) is referred to FIG. However, it will be described below. As described above, in the circuit, the switching control unit (13) has the transformer (1
4) is provided in the primary side coil (L11), attenuates the DC power supply voltage (± Vcc) to the level of the input signal (AS), compares it with the input signal (AS), and compares it with the transformer (1
Although the voltage (V1) that fluctuates following the change of the input signal (AS) has already been generated on the primary side of 4), this control is performed on the primary side of the transformer (14). Therefore, the transformer (14) transforms the secondary coil (L
There is a delay in control when transmitted to 12).

For example, when the control IC (13A) tries to raise the DC power supply voltage (± Vcc) by raising the voltage (V1) which changes in accordance with the change of the input signal, the change of the input signal. Voltage (V
Even if 1) is raised, a delay occurs when the rise of this voltage (V1) is transmitted to the secondary side of the transformer (14), so the DC power supply voltage (+ Vcc) does not rise immediately,
It finally rises after the delay time peculiar to the transformer (14) has elapsed.

In this way, the switching power supply (2
0) is used to control the amplified signal (ZS) having substantially the same phase as the input signal (AS), the transmission of control is delayed by the transformer (14), so the input signal is directly input to the amplifier (15). When you input (AS), amplifier (15)
The output of will be distorted.

Therefore, the input signal (AS) necessary for the control of the switching control section (13) is left as it is, and the input signal (AS) is supplied to the amplifier (15) by the delay time (Δt) as shown in FIG. A delayed input signal (AS ') is generated by delaying, and the delayed input signal (AS') is amplified to generate an amplified signal (ZS). This delay time (Δ
t) is the same as the above-mentioned delay time generated on the primary side and the secondary side of the transformer (14).

By doing so, even if a delay occurs when the control is transmitted to the secondary side of the transformer (14), the input signal (AS) is delayed in advance by the delay amount (Δt), and the delayed input signal is delayed. (AS ') is generated and the amplified signal (Z
Since S) is generated, it is possible to prevent the inconvenience that the output of the amplifier is distorted when controlling the amplified signal (ZS) having substantially the same phase as the delayed input signal (AS ') as shown in FIG. can do. For this reason, the delay circuit (16) is provided in the circuit.

In this embodiment, the input signal (AS) which is not delayed is output to the switching power supply (20) through the delay circuit (16), but the present invention is not limited to this, and the delay circuit (16) is used. Switching power supply (2
Even if it is input to 0), the same effect can be obtained.

[0030]

As described above, according to the amplifier circuit of the present invention, the delay circuit for delaying the input signal, the signal amplifier section for amplifying the delayed input signal to generate the amplified signal, and the AC voltage And a switching power supply that generates a power supply voltage that varies in accordance with the change of the input signal and supplies the power supply voltage to the signal amplification unit.

Therefore, the circuit of the power supply system is different from the conventional one in which two kinds of power supplies, that is, the direct current power supply and the chopper power supply are practically required, and the circuit of the power supply system is one of the switching power supplies.
Since only the type is required, the circuit configuration is simple and the number of parts can be reduced. Also, since the switching power supply has a high switching frequency, the size of the transformer can be reduced to a fraction of that of the conventional transformer. In this case, the scale of the device can be significantly reduced.

Furthermore, the adverse effect of the delay in control transmission between the primary side and the secondary side of the transformer, which occurs when a switching power supply is used, is also provided with a delay circuit at the input of the signal amplification section, so that the switching power supply can be controlled. This can be solved by using an undelayed input signal and delaying the input signal to be input to the signal amplification unit and then inputting it to the signal amplification unit.

[Brief description of drawings]

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

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

FIG. 3 is a circuit diagram of an amplifier circuit according to a conventional example.

FIG. 4 is a diagram illustrating an operation of an amplifier circuit according to a conventional example.

[Explanation of symbols] (11) Smoothing circuit (12) Bridge circuit (13) Switching control unit (13A) Control IC (14) Transformer (15) Amplifier (Signal amplifier) (16) Delay circuit (17) Frequency control circuit (18) Rectifier circuit (20) Switching power supply (AS) Input signal (AS ') Delayed input signal (ZS) Amplified signal (SW1, SW2) Switching transistor element (± Vc) DC power supply voltage

Continued Front Page (56) References 62-80417 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03F 1/00-3/72 H02M 3/335

Claims (3)

(57) [Claims] 1. A delay circuit for delaying an input signal, a signal amplifying section for amplifying the delayed input signal to generate an amplified signal, and a delay circuit for changing the input signal from an AC power supply voltage.
And a change of the input signal supplied from the switching control unit that generates an alternating voltage
The AC voltage that fluctuates according to the
And a transformer for changing the transformed AC voltage to a DC voltage after converting the transformed AC voltage to a DC voltage.
A rectifying circuit that supplies the signal to the signal amplifying section . 2. The switching control unit is a signal amplification unit.
DC signal supplied and input signal with a constant voltage added
, And the input signal with a constant DC voltage added
When it is larger, the first switching element is turned off and the second switching element is turned off.
Turn on the switching element of and input from the AC power supply voltage.
The AC voltage that fluctuates following a signal change is reduced
When the voltage is less than the input signal with a constant voltage added,
Turn on the first switching element and turn on the second switching
Turn off the element and follow the change of the input signal from the AC power supply voltage.
The amplifier circuit according to claim 1, wherein the alternating voltage that fluctuates accordingly is increased . 3. The first and second switching elements are
Amplifier circuit according to claim 2, characterized in that it is a transistor.