JP4604396B2 - Audio output control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a BTL (balanced transformer less) type amplifier to detect the sound output amplitude, controls the power supply voltage supplied to the BTL amplifier based on this voltage, and keeps the maximum sound output constant. The present invention relates to a control circuit.
[0002]
[Prior art]
In a color television, the load on the deflection circuit varies due to a change in screen brightness, so the voltage of the power supply circuit varies. Along with this, the power supply voltage of the audio circuit also varies. Therefore, in the audio circuit, it is necessary to set the power supply voltage supplied to the BTL amplifier so that the maximum audio output can be obtained even when the power supply voltage supplied to the BTL amplifier changes and becomes small.
[0003]
In setting the power supply voltage to be supplied to the BTL amplifier, there is no problem if the power supply voltage is appropriate. However, the power supply voltage does not match, and a power supply voltage drop resistor is used to adjust the power supply voltage. The means to insert into was common.
[0004]
FIG. 5 is a diagram showing an embodiment of a conventional circuit. In FIG. 5, 1 is a BTL class B audio output IC. 2 is an input audio signal, which is input to the audio output IC 1. Reference numeral 3 denotes a positive-phase and negative-phase amplifier. The positive-phase + output is sent to the bias circuit 4 and the negative-phase -output is sent to the 5 bias circuit. 7, 8, 9, and 10 are transistors of a BTL amplifier, and this output is sent to a speaker 6 to reproduce sound.
Waveforms input to the bias circuit at this time are shown in FIG.
[0005]
As can be seen from Fig. 6, the audio input signal of A passes through the positive and negative phase amplifiers, the positive phase + side waveform becomes B, and the current loop flowing through the BTL amplifier is
Power supply voltage supplied to the BTL amplifier → 7 transistor → 6 speaker → 10 transistor → GND.
[0006]
In addition, the waveform on the negative-phase side is like C, and the current loop flowing through the BTL amplifier is
The power supply voltage supplied to the BTL amplifier → 9 transistors → 6 speakers → 8 transistors → GND.
[0007]
11 is a selector that compares the output of the BTL amplifier and selects a high level. The output selected by this selector is input to the + side of 12 operational amplifiers, and the voltage of 17 smoothing capacitors is input to the − side. This voltage is a voltage that is controlled by a switching power supply from a voltage supplied from 18 audio power supplies. The switching power supply is composed of 14 switching transistors, 15 flyhole diodes, 16 chopper coils, and 17 smoothing capacitors. The voltage is controlled by 13 drive circuits. Reference numeral 19 is a power supply voltage drop resistor inserted to control the maximum audio output.
[0008]
In the above configuration, for example, when the output from 11 high-level selectors increases, the output of 12 operational amplifiers increases, and the drive amount from 13 drive circuits increases, so the ON period of 14 switching transistors Becomes longer and the voltage of the 17 smoothing capacitor rises. That is, the voltage of the 17 smoothing capacitors is always controlled according to the audio signal level of 2.
[0009]
Conversely, when the output from 11 high-level selectors decreases, the output of 12 operational amplifiers decreases and the drive amount from 13 drive circuits decreases, so the ON period of 14 switching transistors is shortened. The voltage of the 17 smoothing capacitor drops. That is, the voltage of the 17 smoothing capacitors is always controlled according to the audio signal level of 2. The input / output signal waveforms of the audio output IC at this time are shown in FIG.
[0010]
Next, when a fine adjustment of the power supply voltage is required, a necessary series of power supply voltage drop resistors will be described. In FIG. 5, reference numeral 19 denotes a power supply voltage drop resistor, which is a resistor inserted to set the maximum audio output.
[0011]
The following relationship exists between the input power supply voltage V1 of the audio circuit and the input voltage V2 of the switching power supply.
When voice load is light V1 = V2
When the audio load is heavy V1> V2 (V1−V2 = voltage across the supply voltage drop resistor)
When a large audio signal is input, since the load on the audio circuit increases, the current flowing through the power supply voltage drop resistor increases, and the voltage across the resistor also increases. That is, it is possible to control the power supply voltage supplied to the BTL amplifier at the time of maximum audio output. The input / output signal waveforms of the audio output IC at this time are shown in FIG.
[0012]
If there is no power supply voltage drop resistor, the output waveform is as shown by a broken line, but if a power supply voltage drop resistor is inserted, the waveform is clipped as shown by a solid line.
[0013]
Further, when the value of the power supply voltage drop resistor of 19 is increased, the capacitor voltage of 17 is lowered, so that the clip point of the speaker output of 6 is further lowered. In this way, the maximum audio output can be set arbitrarily by changing the value of the 19 loss resistance.
[0014]
[Problems to be solved by the invention]
When the power supply voltage drop resistor of the series is inserted in this way, the loss in the resistor increases as the audio output is increased, and this is a drawback of reducing the efficiency of the circuit, and there is a problem from the viewpoint of energy saving. In addition, when the screen is dark and the load is light, and the screen is bright and the load is heavy, the input power supply voltage of the voice circuit increases, so that a voice larger than the value shown in the voice maximum rating is output. For this reason, since the voltage applied to the circuit element rises, there are problems such as heat generation and withstand voltage. In some cases, means for providing a limit circuit for the input signal is necessary.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the audio output control circuit of the present invention controls the power supply voltage supplied to the BTL amplifier with the switching power supply even when the input power supply voltage of the audio circuit changes, and makes the maximum audio output constant. It is characterized by being able to keep.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The audio output control circuit according to claim 1 of the present invention is an audio output circuit using a switching power supply to drive a BTL audio amplifier, and the maximum audio output even if the input power supply voltage of the audio circuit changes. In order to keep the power supply voltage constant to the BTL amplifier, a zener diode is provided on the + side of the op-amp, which is the output of the high level selector, to set the maximum audio output. is there.
[0017]
(Embodiment 1)
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0018]
An embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is used about the same structure as the prior art example mentioned above, and description is abbreviate | omitted.
[0019]
20 is a Zener diode for keeping the voltage constant, and 21 is a resistor for controlling the current flowing through the Zener diode.
According to such a configuration, since 20 Zener diodes are inserted in the output of the 11 high level selectors, for example, even if the audio signal of 2 becomes large, the voltage input to the 12 operational amplifiers + side is Because it is clipped with a zener voltage of 20, the voltage will not rise any further.
In other words, the maximum audio output can be arbitrarily set by changing 20 Zener voltages. Because of this, it is also possible to delete the 19 loss resistances that were previously inserted to set the maximum audio output.
The input / output signal waveforms of the audio output IC at this time are shown in FIG.
As can be seen from FIG. 9, there is an improvement effect similar to that when clipping with the power supply voltage drop resistor. Further, in this configuration, since the power supply voltage drop resistor is not used, the power loss can be reduced, and there is also an energy saving effect.
[0020]
(Embodiment 2)
Next, another embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is used about the same structure as embodiment mentioned above, and description is abbreviate | omitted.
[0021]
In the case of the configuration shown in (Embodiment 1), since the predetermined Zener voltage which is 20 Zener diodes is set, the maximum audio output can only be set to a predetermined value. Embodiment 2 has improved this point.
[0022]
23 is a transistor, and 22 is an emitter resistance of the transistor. The bases of 23 transistors are connected to 24 microcomputers, and the base voltage can be arbitrarily varied according to the output of the microcomputer. By changing the base voltage, the emitter voltage changes in the same manner, and a constant voltage can be output. For example, even if the audio signal of 2 becomes large, the voltage input to the 12 operational amplifiers + side is clipped by the emitter voltage of 23 transistors, and therefore does not increase any more. That is, the maximum audio output can be arbitrarily set by the microcomputer. FIG. 10 shows input / output signal waveforms of the audio output IC at this time.
[0023]
As can be seen from FIG. 10, the audio output waveform can be clipped with an arbitrary voltage corresponding to the output of the microcomputer. For example, since the power consumption of the audio circuit can be reduced by reducing the maximum audio output setting, the added value can be increased by selecting from the menu and adding the energy saving mode function.
[0024]
(Embodiment 3)
Next, another embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is used about the same structure as embodiment mentioned above, and description is abbreviate | omitted.
[0025]
In the case of the configuration shown in (Embodiment 1), the maximum audio output can be set with a predetermined Zener voltage, which is 20 Zener diodes. However, when the audio signal of 2 is large, the audio output waveform is distorted. Embodiment 3 has improved this point.
[0026]
Reference numeral 25 denotes a gain adjustment circuit, and reference numeral 26 denotes an audio signal preamplifier. The input of the 25 gain adjustment circuit is connected to the anode of the 20 Zener diodes. When a current flows through the 20 Zener diodes, a current also flows through the 21 resistor, so that a potential difference occurs in the 21 resistor.
[0027]
According to such a configuration, when the audio signal of 2 becomes large, the output of 11 high-level selectors becomes large, and when clipping with 20 Zener diodes, the voltage of 21 resistance rises, and this voltage has a gain of 25 Input to the adjustment circuit. The gain adjustment circuit of 25 is configured to lower the output when the input voltage is large, and conversely increase the output when the input voltage is small, so the audio signal of 2 becomes large and the BTL amplifiers 7, 8, 9 When 10 transistors are clipped, the input to 25 gain adjustment circuits is increased, reducing the 26 preamplifier gain. In other words, since the input signal of the positive and negative phase amplifiers of 3 becomes small, the output amplitude of the transistors 7, 8, 9, and 10 of the BTL amplifier also becomes small and the clipping is reduced, thereby reducing the distortion of the audio signal. can do. FIG. 11 shows input / output signal waveforms of the audio output IC at this time.
[0028]
As can be seen from FIG. 11, when the output amplitude is increased, the input amplitude is controlled to be reduced, so that the output amplitude can be reduced and the distortion rate can be kept constant without changing the maximum audio output. .
[0029]
(Embodiment 4)
Next, another embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is used about the same structure as embodiment mentioned above, and description is abbreviate | omitted.
[0030]
This embodiment is characterized in that control of gain adjustment shown in (Embodiment 3) can be turned on and off by 27 microcomputers.
[0031]
In (Embodiment 3), when the music source is played at a high volume and the audio signal of 2 becomes large, the maximum audio output is controlled, so there is an advantage that distortion is reduced, but conversely it is powerful There was the fault that it became a sound without.
[0032]
According to such a configuration, since the control of the 25 gain adjustment circuits is cut using 27 microcomputers, it is possible to prevent the gain adjustment from being controlled. In other words, it is possible to play powerful music with distortion.
[0033]
【The invention's effect】
As described above, according to the present invention, the potential difference between the output terminals can be detected by the BTL type amplifier and the power supply voltage of the amplifier can be controlled, so that the maximum audio output can be kept constant even if the power supply voltage changes. In addition, the series power supply voltage drop resistor is not required, and there is an advantage that the efficiency of the circuit can be improved.
[Brief description of the drawings]
1 is a circuit diagram of an audio output circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram of an audio output circuit according to an embodiment of the present invention. FIG. 3 is a circuit of an audio output circuit according to an embodiment of the present invention. FIG. 4 is a circuit diagram of an audio output circuit in one embodiment of the present invention. FIG. 5 is a circuit diagram of an audio output circuit in a conventional example. FIG. 6 shows input signal waveforms of a bias circuit in one embodiment of the present invention. FIG. 7 is a diagram showing input / output signal waveforms of an audio output IC according to an embodiment of the present invention. FIG. 8 is a diagram showing input / output signal waveforms of an audio output IC according to an embodiment of the present invention. FIG. 10 is a diagram showing input / output signal waveforms of the audio output IC in one embodiment. FIG. 10 is a diagram showing input / output signal waveforms of the audio output IC in one embodiment of the present invention. Diagram showing I / O signal waveforms [Explanation of symbols]
1 Audio output IC
2 Audio signal 3 Normal phase, negative phase amplifier 4, 5 Bias circuit 6 Speaker 7, 8, 9, 10 Transistor 11 High level selector 12 Operational amplifier 13 Drive circuit 14 Switching transistor 15 Diode 16 Coil 17 Capacitor 18 Audio power supply 19 Power supply voltage drop Resistor 20 Zener diode 21 Resistor 22 Resistor 23 Transistor 24 Microcomputer 25 Gain adjustment circuit 26 Preamplifier 27 Microcomputer

Claims (3)

First amplifying means for amplifying a first audio signal based on an input audio signal;
Second amplification means for amplifying a second audio signal obtained by inverting the first audio signal;
BTL type amplifying means for driving a load based on a potential difference between the output of the first amplifying means and the output of the second amplifying means, using an output of a switching power supply described later as a power supply voltage;
A high level selection means for selecting a high level signal in the potential across the load of the BTL amplification means;
A Zener diode in which the output of the high level selection means is provided on the cathode side and ground is provided on the anode side;
A switching power supply for switching and smoothing the input power supply voltage of the audio circuit by a switching transistor whose conduction period is controlled based on the potential difference between the output potential of the high-level selection means and the output potential of the switching power supply;
An audio output control circuit. A resistor having one end connected to the anode of the Zener diode and the other end connected to ground;
A gain adjustment circuit that reduces the amplification factor of the preamplifier described later as the potential difference between both ends of the resistor is larger;
A preamplifier for amplifying the input audio signal based on an output of the gain adjustment circuit and outputting the first audio signal;
The audio output control circuit according to claim 1 , further comprising: 3. The audio output control circuit according to claim 2, further comprising control means for controlling on / off of the gain adjustment circuit.

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