JP2018207310A - Amplification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplification device capable of achieving both high sound quality and energy saving. An amplification device (1) includes a switching power supply (3), a ternary pulse density modulation circuit (6), and a microcomputer (2). The switching power supply 3 includes a voltage change circuit 9 that changes the reference voltage input to the reference terminal of the shunt regulator U1. In the ternary pulse density modulation circuit 6, a power supply voltage is supplied from the switching power supply 3. The microcomputer 2 changes the reference voltage by the voltage change circuit 9 according to the maximum output of the ternary pulse density modulation circuit 6. [Selection diagram] Fig. 1

Description

  The present invention relates to an amplifying apparatus that amplifies an audio signal.

  Some audio output devices including an amplifier and a power source variably control the power supply voltage at the time of high output and at the time of low output to suppress power consumption (see Patent Document 1). However, when changing the output voltage of the switching power supply, the setting of the shunt regulator of the feedback unit is not appropriately performed, and thus it may be difficult to change the power supply.

  In order to solve this problem, the inventors have conceived an invention related to Japanese Patent Application No. 2017-000433 (hereinafter referred to as “prior application invention”). FIG. 7 is a diagram showing a circuit configuration of the switching power supply according to the invention of the prior application. In the prior invention, the reference voltage is changed by the switch SW102, and the output voltage of the switching power supply 101 is changed. Further, the current flowing through the photocoupler Q102 (feedback element) is changed by the switch SW101. For this reason, even if the reference voltage is changed by the switch SW102 and the output voltage of the switching power supply 101 is changed, the current flowing through the photocoupler Q102 can be changed by the switch SW101. Thereby, since the electric current which flows into a feedback element can be made appropriate, even if the output voltage of switching power supply is changed, feedback can be performed normally.

  In addition, the power supply voltage at the time of large output and small output can be variably controlled to effectively suppress power consumption.

  In order to change the output voltage by remote control, there is an invention that changes the voltage dividing resistance ratio that creates the input voltage of the feedback error amplifier (see Patent Document 2).

  Here, consider a case where a ternary pulse density modulation circuit (signal modulation circuit) according to Japanese Patent No. 5846194 is used as an amplifier. FIG. 8 is a block diagram showing the configuration of the ternary pulse density modulation circuit. Hereinafter, a ternary pulse density modulation circuit will be described. For details, refer to Japanese Patent No. 5846194. The ternary pulse density modulation circuit includes a subtracter 20, an integrator 22, a phase inversion circuit 23, bias generation circuits 50 and 51, zero reset type DFFs 24 and 25, a clock signal generation source 26, and a delay circuit 28. A switching unit 30, a zero reset signal generation unit 32, and a pulse synthesis circuit 34.

  The clock signal from the clock signal generation source 26 is delayed by the delay circuit 28 and supplied to the clock terminals of the zero reset type DFFs 24 and 25. The subtracter 20 calculates a difference between the input signal and the feedback signal and outputs the difference to the integrator 22. The integrator 22 integrates the difference signal and outputs it to the bias generation circuit 50 and the phase inversion circuit 23. The phase inversion circuit 23 inverts the phase of the output of the integrator 22 and outputs the inverted phase to the switching unit 30 and the bias generation circuit 51. The bias generation circuits 50 and 51 apply predetermined biases to the output of the integrator 22 and the output of the phase inversion circuit 23, respectively, and output to the zero reset type DFFs 24 and 25. The bias generation circuits 50 and 51 increase and adjust the outputs of the integrator 22 and the phase inversion circuit 23. This is achieved by adjusting the level of the no-signal state to zero level, thereby ensuring the zero level in the no-signal state. This is to realize a state where no switching is performed as (zero voltage).

  The switching unit 30 compares the output from the integrator 22 and the output from the phase inverting circuit 23 with a predetermined value, and outputs a switching signal to the zero reset signal generating unit 32 when the predetermined value is exceeded. In other words, the switching unit 30 sets the switching signal to a low level when the output level of the integrator 22 is equal to or lower than a predetermined value, and outputs the switching signal as a high level when the output level of the integrator 22 exceeds a predetermined value. This switching signal functions as a signal for switching from modulation with a fixed pulse width to modulation with an increased pulse width.

  The zero reset signal generation unit 32 is supplied with the clock signal from the clock signal generation source 26 and the switching signal from the switching unit 30. The zero reset signal generation unit 32 outputs the clock signal to the reset terminals of the zero reset type DFFs 24 and 25 when the switching signal from the switching unit 30 is at the Low level, and outputs the clock signal when the switching signal is at the Hi level. Shut off and do not output to the reset terminals of the zero reset type DFFs 24 and 25.

  The zero reset type DFF 24 converts the output of the bias generation circuit 50 into a 1-bit digital signal and outputs it. At this time, if the output of the bias generation circuit 24 is less than or equal to a predetermined value, a zero level is inserted at a timing synchronized with the clock signal and output as a signal having a fixed pulse width, and the output of the bias generation circuit 50 exceeds the predetermined value. In this case, a zero level is not inserted and a signal with an extended pulse width is output.

  Similarly, the zero reset type DFF 25 converts the output of the bias generation circuit 51 into a 1-bit digital signal and outputs it. At this time, if the output of the bias generation circuit 51 is less than or equal to a predetermined value, a zero level is inserted at a timing synchronized with the clock signal and output as a signal having a fixed pulse width, and the output of the bias generation circuit 51 exceeds the predetermined value. In this case, a zero level is not inserted and a signal with an extended pulse width is output.

  The pulse synthesis circuit 34 synthesizes and outputs the outputs of the zero reset type DFFs 24 and 25. The output of the zero reset type DFF 24 is a binary signal of +1, 0. On the other hand, the output of the zero reset type DFF 25 is a binary signal of −1 and 0 because the signal whose phase is inverted by the phase inverting circuit 23 is modulated. The pulse synthesizing circuit 34 synthesizes these two binary signals to generate and output a +1, 0, −1 ternary signal. As the pulse synthesis circuit 34, any circuit capable of synthesizing two 1-bit digital signals can be used. As an example, a first potential and a second potential, and a third potential that is a midpoint between the first potential and the second potential and serves as a reference potential, the output is the first potential, A switch group for fixing the second potential and the third potential is provided, and these switch groups are controlled to be turned on and off by the output signals of the zero reset type DFFs 24 and 25, and the first potential, the second potential, and the third potential are controlled. A circuit configuration that selectively outputs one of them may be used.

  FIG. 9 is a diagram showing the relationship between the input signal waveform and the output waveform of the pulse synthesis circuit 34. The output waveform of the pulse synthesizing circuit 34 is a ternary waveform of +1, 0, −1. However, when the amplitude of the input signal is small, it is a PDM signal with a fixed pulse width, and the amplitude of the input signal has a predetermined value. When it exceeds, a combined signal of a PDM with an expanded pulse width and a PDM with a fixed pulse width is obtained. When the amplitude of the input signal is particularly large, all the pulse widths are expanded.

  In the circuit configuration of FIG. 8, the outputs of the zero reset DFFs 24 and 25 are synthesized by the pulse synthesis circuit 34 to generate +1, 0, and −1 ternary signals. In order to obtain an output, it is necessary to drive the speaker with a voltage VB higher than the modulator power supply Vdd. However, if the speaker is driven with the ternary signal, it is necessary to provide not only the high voltage VB but also a midpoint voltage source (VB / 2) and a midpoint voltage holding circuit separately, which increases the circuit scale.

  Therefore, as shown in FIG. 10, even if the monovalent ternary waveform generation circuit 40 generates a single power source three-state speaker drive signal and outputs it to the driver circuit 42, the driver circuit 42 drives the speaker as the load 44. Good.

  The monovalent ternary waveform generation circuit 40 converts the +1, 0 binary signal from the zero reset type DFF 24 and the −1, 0 binary signal from the zero reset type DFF 25 into a monovalent ternary waveform signal. Here, the “monovalent ternary value” refers to a state in which a speaker driven by a single power source is driven by a positive current (positive on), a state driven by a negative current (negative on), and an off state by a short circuit. It means to realize two driving states. A positive current and a negative current mean that the directions of the currents flowing through the speakers are opposite to each other.

  As described above, in the ternary pulse density changing circuit, the pulse width fixed mode, the mixed pulse width and pulse width expansion (hybrid) mode, and the pulse width are obtained at the time of low power, medium power, and high power, respectively. As in the extended mode, the operation of the amplifier is switched. Furthermore, from the viewpoint of sound quality, there is a case where it is desired to enlarge the operation region in the fixed pulse width mode.

JP-A-4-275707 Japanese Patent No. 2579069

  When the variable power source shown in FIG. 7 and the ternary pulse density modulation circuit amplifier shown in FIG. 8 or FIG. 10 are used, if the power source voltage is varied only from the viewpoint of energy saving, In order to reduce the voltage, there is a problem that the operation in the pulse width expansion mode increases as shown in FIG. Here, by changing the power supply voltage supplied from the switching power supply to the amplifier in accordance with the maximum output of the amplifier, both high sound quality and energy saving can be achieved.

  An object of the present invention is to provide an amplifying device capable of achieving both high sound quality and energy saving.

  An amplifying device according to a first aspect of the present invention is an amplifying device comprising a switching power supply, an amplifier, and a control unit, wherein the switching power supply is connected to the feedback element and the feedback element on the primary side, A switching element control unit for controlling, a shunt regulator having a cathode connected to the feedback element and an anode connected to a ground potential, and a voltage changing unit for changing a reference voltage input to a reference terminal of the shunt regulator; The amplifier is supplied with a power supply voltage from the switching power supply, and the control unit changes the reference voltage by the voltage changing unit according to a maximum output of the amplifier.

  In the present invention, the control unit changes the reference voltage by the voltage changing unit according to the maximum output of the amplifier. As a result, the power supply voltage supplied from the switching power supply to the amplifier changes according to the maximum output of the amplifier. For this reason, it is possible to achieve both high sound quality and energy saving.

  According to a second aspect of the present invention, there is provided the amplification device according to the first aspect, wherein the control unit increases the reference voltage by the voltage changing unit as the maximum output increases.

  The amplifying device according to a third aspect is the amplifying device according to the first or second aspect, wherein the switching power supply further includes a current changing unit that changes a current flowing through the feedback element.

  In the present invention, the current changing unit changes the current flowing through the feedback element. For this reason, even if the reference voltage is changed by the voltage changing unit and the output voltage of the switching power supply is changed, the current flowing through the feedback element can be changed by the current changing unit. Thereby, since the electric current which flows into a feedback element can be made appropriate, even if the output voltage of switching power supply is changed, feedback can be performed normally.

  An amplifying device according to a fourth invention is the amplifying device according to any one of the first to third inventions, wherein the voltage changing section includes a first variable resistor connected to an output of the switching power supply, and the first variable resistor. A first resistor and a second resistor connected in series to each other, and the reference terminal of the shunt regulator is connected between the first resistor and the second resistor, and the control unit Is characterized in that the reference voltage is changed by changing a resistance value of the first variable resistor.

  An amplifying device according to a fifth invention is the amplifying device according to the third invention, wherein the current changing portion is a third resistor connected in parallel to the feedback element and a second resistor connected in series to the third resistor. A variable resistor and a fourth resistor; the second variable resistor is connected to an output of the switching power supply; and the control unit changes the resistance value of the second variable resistor to thereby change the feedback. It is characterized in that the current flowing through the element is changed.

  An amplifying device according to a sixth invention is the amplifying device according to any one of the first to fifth inventions, wherein the amplifier has three values of positive current on, negative current on, and off for a speaker connected to a single power source. When the signal level output from the amplifier is equal to or lower than a predetermined value of the maximum output, and operates in a pulse width fixed mode for outputting a pulse width fixed PDM signal, When the level is equal to or greater than the predetermined value of the maximum output, the pulse width expansion mode is used to output a PDM signal in which all pulse widths are expanded.

  An amplifying device according to a seventh invention is the amplifying device according to the sixth invention, wherein, when the maximum output is equal to or less than a predetermined value of the first maximum output, the control unit causes the reference voltage to be changed by the voltage changing unit. The reference voltage is increased by the voltage changing unit when the maximum output is equal to or greater than a predetermined value of the first maximum output.

For example, assume that the amplifier operates as follows.
Low signal level (up to 1/4 power of maximum output (below the predetermined value)): Fixed pulse width mode High signal level (from 1/4 power of maximum output to maximum output): Pulse width expansion mode In the case of 40 W (first maximum output) (power supply voltage is small), the amplifier is
0-10W: Pulse width fixed mode 10-40W: Operates in pulse width expansion mode.

When the maximum power is 100 W (power supply voltage is large), the amplifier
0 to 25 W: pulse width fixed mode 25 to 100 W: operate in pulse width expansion mode.

Conventionally, an amplifier is operated with a power supply voltage as low as possible for SN and energy saving. That is,
0 to 40 W: Low power supply voltage 40 to 100 W: High power supply voltage In this case, the amplifier has many regions that operate in the pulse width fixed mode. However, there is a problem of using the pulse width fixed mode as much as possible in order to improve the sound quality and operating the amplifier with a power supply voltage as low as possible in order to save SN and energy.

  Therefore, in the present invention, the power supply voltage from the switching power supply is varied by changing the reference voltage by the voltage changing unit according to the maximum output of the amplifier. For example, when the maximum output of the amplifier is 10 W or less (1/4 (predetermined value) or less of 40 W (first maximum output)), the control unit reduces the reference voltage to reduce the power supply voltage from the switching power supply. Make it smaller. Therefore, since the signal level is up to 1/4 power of the maximum output, the amplifier operates in the fixed pulse width mode.

  When the maximum output of the amplifier is 10 W or more, the control unit increases the power supply voltage from the switching power supply by increasing the reference voltage by the voltage changing unit. Therefore, the amplifier operates in a fixed pulse width mode up to a signal level of 25W. The amplifier operates in a pulse width expansion mode with a signal level of 25 to 100 W.

That is, the amplifier
0 to 10 W: Pulse width fixed mode when power supply voltage is small 10 to 25 W: Pulse width fixed mode when power supply voltage is large 25 to 100 W: Pulse width expansion mode when power supply voltage is large.

  For this reason, the energy saving performance at 25 to 40 W is somewhat sacrificed, but there is an advantage that both sound quality and energy saving can be achieved. That is, when the output power is small, energy saving can be realized, and the use range of the pulse width fixed mode of the amplifier can be increased.

  An amplifying device according to an eighth aspect of the present invention is the amplifying device according to any one of the first to seventh aspects, further comprising an operation unit for receiving an instruction of a volume value, wherein the control unit determines the maximum output. The reference voltage is changed by the voltage changing unit in accordance with a volume value received by the operation unit.

  An amplifying device according to a ninth aspect is the amplifying device according to the fourth aspect, wherein the first variable resistor is a digital potentiometer.

  An amplifying device according to a tenth aspect is the amplifying device according to the fifth aspect, wherein the second variable resistor is a digital potentiometer.

  An amplifying device according to an eleventh aspect of the invention is the amplifying device according to any one of the first to tenth aspects, further comprising a step-down circuit for stepping down a power supply voltage from the switching power supply to a predetermined potential, and a power supply from the step-down circuit. The voltage is supplied to the control unit, and the control unit is activated by the power supply voltage from the step-down circuit, and then the power supply voltage from the switching power supply is increased to the power supply voltage at which the amplifier is activated by the voltage changing unit. It is characterized by gradually increasing.

  In the present invention, the step-down circuit steps down the power supply voltage from the switching power supply to a predetermined potential. In addition, after the control unit is activated by the power supply voltage from the step-down circuit, the voltage changing unit gradually increases the power supply voltage from the switching power supply to the power supply voltage at which the amplifier is activated. Thereby, inrush current and pop noise to the secondary side capacitor are prevented.

  According to the present invention, both high sound quality and energy saving can be achieved.

It is a figure which shows the structure of the amplifier which concerns on 1st Embodiment of this invention. It is a figure which shows the relationship between a power supply voltage and the audio | voice level output from a speaker. It is a figure which shows the relationship between an input signal waveform, the output waveform of a ternary pulse density modulation circuit, and a power supply voltage. It is a figure which shows the structure of the amplifier which concerns on 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the amplifier after AC power supply activation. (A) is a figure which shows the conventional power supply control. (B) is a figure which shows the power supply control in 2nd Embodiment. It is a figure which shows the circuit structure of the switching power supply of prior invention. It is a block diagram which shows the structure of a ternary pulse density modulation circuit. It is a figure which shows the relationship between an input signal waveform and the output waveform of a pulse synthetic | combination circuit. It is a block diagram which shows the structure of a ternary pulse density modulation circuit. It is a figure which shows the relationship between an input signal waveform, the output waveform of a ternary pulse density modulation circuit, and a power supply voltage.

  Hereinafter, embodiments of the present invention will be described.

(First embodiment)
FIG. 1 is a diagram showing a configuration of an amplifying apparatus according to the first embodiment of the present invention. The amplification device 1 includes a microcomputer 2, a switching power supply 3, an operation unit 4, a volume adjustment circuit 5, and a ternary pulse density modulation circuit 6. The microcomputer 2 (control unit) includes hardware such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input / output interface. The microcomputer 2 controls each part constituting the amplification device 1.

  The operation unit 4 is for receiving an instruction for a volume value. The microcomputer 2 receives a volume value instruction through the operation unit 4. The microcomputer 2 outputs the received volume value to the volume adjustment circuit 5. The volume adjustment circuit 5 adjusts the volume of the input audio signal based on the volume value output from the microcomputer 2. The volume adjustment circuit 5 outputs the volume-adjusted audio signal to the ternary pulse density modulation circuit 6.

  The ternary pulse density modulation circuit 6 (amplifier) selectively drives the speaker 7 connected to a single power supply in a ternary state of positive current on, negative current on, and off. Further, the ternary pulse density modulation circuit 6 is configured to output a pulse when the signal level output from the ternary pulse density modulation circuit 6 is up to 1/4 power of the maximum output (below a predetermined value) (signal level is small). It operates in a fixed pulse width mode that outputs a fixed width PDM signal. In addition, the ternary pulse density modulation circuit 6 outputs a PDM signal in which all pulse widths are expanded when the signal level is from 1/4 power of the maximum output to the maximum output (high signal level). Operates in width expansion mode. The ternary pulse density modulation circuit 6 is the same as the ternary pulse density modulation circuit shown in FIG. 8 and FIG.

  The switching power supply 3 supplies a power supply voltage to the ternary pulse density modulation circuit 6. The switching power supply 3 includes a transformer T1, a diode D1, a capacitor C2, a photocoupler Q1, a shunt regulator U1, a current change circuit 8, and a voltage change circuit 9.

  On the primary side of the switching power supply 3, the rectifier circuit rectifies the AC voltage input from the AC power supply. The capacitor smoothes the voltage rectified by the rectifier circuit. The smoothed voltage is supplied to the switching element. The control IC (switching element control unit) controls the switching element. The switching element is controlled by the control IC, and switches at an arbitrary frequency to supply an alternating voltage of an arbitrary frequency to the primary winding T2 of the transformer T1. The switching element is, for example, an n-type MOSFET. The switching element supplies a voltage from a capacitor or a ground potential voltage to the primary winding T2. The transformer T1 transforms the voltage supplied to the primary winding T2 and outputs it from the secondary winding T3. The diode D1 rectifies the AC voltage from the secondary winding T3. The capacitor C1 smoothes the voltage rectified by the diode D1. The voltage smoothed by the capacitor C1 is the output voltage of the switching power supply 3.

  The shunt regulator U1 is connected to the photocoupler Q1 on the secondary side of the switching power supply 3. Further, the shunt regulator U1 changes the current flowing through the photocoupler Q1 according to the output voltage of the switching power supply 3. The reference terminal of the shunt regulator U1 is connected between the resistor R3 and the resistor R4. The cathode of the shunt regulator U1 is connected to the photocoupler Q1 (the cathode of the light emitting diode).

  The photocoupler Q1 (feedback element) includes a light emitting diode and a phototransistor. The anode of the light emitting diode is connected between the resistor R1 and the resistor R2. The cathode of the light emitting diode is connected between the resistor R2 and the shunt regulator U1. The collector of the phototransistor is connected to the feedback terminal of the control IC. The emitter of the phototransistor is connected to the ground potential.

  In the shunt regulator U1, the sink current of the cathode increases / decreases in accordance with the voltage division by the digital potentiometer DP1 of the output voltage of the switching power supply 3 input to the reference terminal, the resistor R3, and the resistor R4. In the shunt regulator U1, the higher the voltage at the reference terminal, the higher the sink current of the cathode. In the shunt regulator U1, the sink current of the cathode decreases as the voltage at the reference terminal is lower.

  In the photocoupler Q1, the current of the light emitting diode increases or decreases according to the increase or decrease of the sink current of the shunt regulator U1. The current of the phototransistor increases or decreases according to the increase or decrease of the current of the light emitting diode. Increasing or decreasing the current of the phototransistor changes the voltage at the feedback terminal of the control IC. Here, a power supply is connected to the feedback terminal of the control IC via a resistor. For this reason, the voltage at the feedback terminal decreases as the current of the photransistor increases. The control IC adjusts the output voltage of the switching power supply 3 by changing the on / off duty of the switching element according to the voltage of the feedback terminal.

  The voltage change circuit 9 (voltage change unit) changes the reference voltage input to the reference terminal of the shunt regulator U1. The voltage change circuit 9 includes a digital potentiometer DP2, a resistor R3, and a resistor R4. The digital potentiometer DP2 (first variable resistor) is connected to the output (capacitor C1) of the switching power supply 1. The resistor R3 (first resistor) and the resistor R4 (second resistor) are connected in series to the digital potentiometer DP2. The digital potentiometer DP2 is controlled by the microcomputer 2, and the resistance value changes. As the resistance value of the digital potentiometer DP2 changes, the reference voltage input to the reference terminal of the shunt regulator U1 changes.

  The current change circuit 8 (current change unit) changes the current flowing through the photocoupler Q1. The current change circuit 8 includes a digital potentiometer DP1, a resistor R1, and a resistor R2. The resistor R2 (third resistor) is connected in parallel to the photocoupler Q1. The digital potentiometer DP1 (second variable resistor) and the resistor R1 (fourth resistor) are connected in series to the resistor R2. The digital potentiometer DP1 is connected to the output (capacitor C1) of the switching power supply 1. The digital potentiometer DP1 is controlled by the microcomputer 2 and the resistance value changes. As the resistance value of the digital potentiometer DP1 changes, the current flowing through the photocoupler Q1 changes.

The relationship between the mode of the ternary pulse density modulation circuit 6 and the power supply voltage from the switching power supply 3 is as follows.
Low signal level (up to 1/4 power of maximum output): Fixed pulse width mode High signal level (from 1/4 power of maximum output to maximum output): Pulse width expansion mode, that is, Case A: Maximum power set to 40W In the case (power supply voltage is small), the ternary pulse density modulation circuit 6
0-10W: Pulse width fixed mode 10-40W: Operates in pulse width expansion mode.

Case B: When the maximum power is 100 W (power supply voltage is large), the ternary pulse density modulation circuit 6 is
0 to 25 W: pulse width fixed mode 25 to 100 W: operate in pulse width expansion mode.

Conventionally, a ternary pulse density modulation circuit is operated with a power supply voltage as low as possible for SN and energy saving. That is,
0 to 40 W: Low power supply voltage 40 to 100 W: High power supply voltage In this case, the ternary pulse density modulation circuit has many regions that operate in the pulse width expansion mode. However, there is a problem of using the pulse width fixed mode as much as possible to improve the sound quality and operating the ternary pulse density modulation circuit with as low a power supply voltage as possible for SN and energy saving.

  For this reason, in the present embodiment, the microcomputer 2 changes the reference voltage by the digital potentiometer DP2 (voltage change circuit 9) according to the maximum output of the ternary pulse density modulation circuit 6, so that the switching power supply 3 Vary the power supply voltage. Here, the maximum output of the ternary pulse density modulation times 6 is determined by the volume value. For this reason, the microcomputer 2 varies the power supply voltage from the switching power supply 3 in accordance with the volume value received by the operation unit 3. When the maximum output of the ternary pulse density modulation circuit 6 is a volume value corresponding to 10 W or less (1/4 (predetermined value) or less of 40 W (first maximum output)), the microcomputer 2 reduces the reference voltage. As a result, the power supply voltage from the switching power supply 3 is reduced. Accordingly, since the signal level is ¼ power of the maximum output, the ternary pulse density modulation circuit 6 operates in the pulse width fixed mode.

  When the maximum output of the ternary pulse density modulation circuit 6 is a volume value corresponding to 10 W or more, the microcomputer 2 increases the reference voltage with the digital potentiometer DP2 (voltage change circuit 9), thereby switching power supply. Increase the power supply voltage from 3. Therefore, the ternary pulse density modulation circuit 6 operates in the pulse width fixed mode up to a signal level of 25 W. Further, the ternary pulse density modulation circuit 6 operates in the pulse width expansion mode from a signal level of 25 to 100 W.

That is, the ternary pulse density modulation circuit 6
0 to 10 W: Pulse width fixed mode when power supply voltage is small 10 to 25 W: Pulse width fixed mode when power supply voltage is large 25 to 100 W: Pulse width expansion mode when power supply voltage is large.
For this reason, the energy saving performance at 25 to 40 W is somewhat sacrificed, but there is an advantage that both sound quality and energy saving can be achieved. That is, when the output power is small, energy saving can be realized and the use range of the pulse width fixed mode of the ternary pulse density modulation circuit 6 can be increased (see FIGS. 2 and 3). Further, when the volume adjustment circuit 5 is a digital attenuator, there is an effect that an increase in noise can be suppressed.

  The microcomputer 2 changes the current flowing through the photocoupler Q1 by the current change circuit 8 in accordance with the change in the power supply voltage from the switching power supply 3. Specifically, the microcomputer 2 changes the current flowing through the photocoupler Q1 by changing the resistance value of the digital potentiometer DP1.

  As described above, in the present embodiment, the microcomputer 2 changes the reference voltage by the voltage changing circuit 9 according to the maximum output of the ternary pulse density modulation circuit 6. Thereby, the power supply voltage supplied from the switching power supply 3 to the ternary pulse density modulation circuit 6 changes according to the maximum output of the ternary pulse density modulation circuit 6. For this reason, it is possible to achieve both high sound quality and energy saving.

  In the present embodiment, the current change circuit 8 changes the current flowing through the photocoupler Q1. For this reason, even if the reference voltage is changed by the voltage change circuit 9 and the output voltage of the switching power supply 3 is changed, the current flowing through the photocoupler Q1 can be changed by the current change circuit 8. Thereby, since the current flowing through the photocoupler Q1 can be made appropriate, feedback can be normally performed even if the output voltage of the switching power supply 3 is changed.

(Second Embodiment)
The first embodiment has the following problems.
(A) Inrush current to the secondary capacitor C1 when energized.
Since a current that is much larger than the current that is originally output temporarily flows, it is a limit to miniaturization of components such as diodes in the power supply line.
(B) Since the power supply voltage rises too early, voltage fluctuations cause pop noise.
In order to avoid this, it is necessary to attach a semiconductor switch (having a large rating) for slowing the rise on the amplifier substrate side.

  FIG. 4 is a diagram showing a configuration of an amplifying apparatus according to the second embodiment of the present invention. Compared to the first embodiment, a DC / DC converter 10 is added. The DC / DC converter 10 (step-down circuit) steps down the voltage of 20V output from the switching power supply 3 to 5V.

  FIG. 5 is a flowchart showing the operation of the amplifying apparatus 1 after the AC power is turned on. After the AC power is turned on, the DC / DC converter 10 steps down the voltage 20V from the switching power supply 3 to 5V and outputs an initial set value 5V (S1). Next, the microcomputer 2 is activated (S2). Next, the microcomputer 2 starts control of the digital potentiometer DP2 (S3). The microcomputer 2 changes the setting of the digital potentiometer DP2 according to the table so that the voltage from the switching power supply 3 changes at regular intervals (S4). Specifically, the microcomputer 2 changes the setting of the digital potentiometer DP2 so that the voltage from the switching power supply 3 changes every 6, 7,..., 20V and 1V. When the microcomputer 2 completes the output of the voltage 20V (S5), the process is terminated.

  FIG. 6A is a diagram showing conventional power supply control. In FIG. 6A, since the voltage rise is too steep, there are the problems (a) and (b) described above. FIG. 6B is a diagram illustrating power control in the present embodiment. When the voltage becomes 5V after the power is turned on, the microcomputer 2 is started. Thereafter, the microcomputer 2 controls the digital potentiometer DP2 and starts a soft start. When the voltage reaches 20 V, the ternary pulse density modulation circuit 6 (amplifier) is activated.

  As described above, in this embodiment, the DC / DC converter 10 steps down the power supply voltage 20V from the switching power supply 3 to 5V. Further, the microcomputer 2 is activated by the power supply voltage from the DC / DC converter 10, and then the power supply voltage from the switching power supply 3 is increased by the voltage changing circuit 9 to the power supply voltage 20 V at which the ternary pulse density modulation circuit 6 is activated. Increase gradually. Thereby, since a large current does not flow, an inrush current to the secondary side capacitor C1 is prevented. Further, since the rise of the power supply voltage is not accelerated, pop noise can be prevented without providing a semiconductor switch.

  As mentioned above, although embodiment of this invention was described, the form which can apply this invention is not restricted to the above-mentioned embodiment, As suitably illustrated in the range which does not deviate from the meaning of this invention so that it may illustrate below. It is possible to make changes.

  In the above-described embodiment, the ternary pulse density modulation circuit is exemplified as the amplifier. Not only this but other amplifiers may be sufficient.

  The present invention can be suitably employed in an amplifying apparatus that amplifies an audio signal.

1 Switching power supply 2 Microcomputer (control unit)
3 switching power supply 4 operation unit 5 volume adjustment circuit 6 ternary pulse density modulation circuit (amplifier)
7 Speaker 8 Current change circuit (current change part)
9 Voltage change circuit (voltage change part)
10 DC / DC converter (step-down circuit)
DP1 Digital potentiometer (second variable resistor)
DP2 Digital potentiometer (first variable resistor)
R1 resistance (4th resistance)
R2 resistance (third resistance)
R3 resistance (first resistance)
R4 resistance (second resistance)
Q1 Photocoupler (Feedback element)
U1 shunt regulator

Claims (11)

An amplification device comprising a switching power supply, an amplifier, and a control unit,
The switching power supply is
A feedback element;
A switching element control unit which is connected to the feedback element on the primary side and controls the switching element;
A shunt regulator having a cathode connected to the feedback element and an anode connected to a ground potential;
A voltage changing unit that changes a reference voltage input to a reference terminal of the shunt regulator;
With
The amplifier is supplied with a power supply voltage from the switching power supply,
The control unit changes the reference voltage by the voltage changing unit according to a maximum output of the amplifier.   The amplifying apparatus according to claim 1, wherein the control unit increases the reference voltage by the voltage changing unit as the maximum output increases.   The amplification device according to claim 1, wherein the switching power supply further includes a current changing unit that changes a current flowing through the feedback element. The voltage changing unit is
A first variable resistor connected to the output of the switching power supply;
A first resistor connected in series to the first variable resistor; and a second resistor;
The reference terminal of the shunt regulator is connected between the first resistor and the second resistor,
The amplifying apparatus according to claim 1, wherein the control unit changes the reference voltage by changing a resistance value of the first variable resistor. The current changing portion is
A third resistor connected in parallel to the feedback element;
A second variable resistor connected in series to the third resistor, and a fourth resistor;
The second variable resistor is connected to the output of the switching power supply,
The amplifying apparatus according to claim 3, wherein the control unit changes a current flowing through the feedback element by changing a resistance value of the second variable resistor. The amplifier is
A speaker connected to a single power source is selectively driven in a ternary state of positive current on, negative current on, and off,
When the signal level output from the amplifier is equal to or less than a predetermined value of the maximum output, it operates in a fixed pulse width mode that outputs a fixed pulse width PDM signal,
6. The device according to claim 1, wherein when the signal level is equal to or greater than the predetermined value of the maximum output, the pulse level expansion mode is performed in which a PDM signal in which all pulse widths are expanded is output. The amplification device according to claim 1. The control unit reduces the reference voltage by the voltage changing unit when the maximum output is equal to or less than a predetermined value of the first maximum output,
The amplifying apparatus according to claim 6, wherein the reference voltage is increased by the voltage changing unit when the maximum output is equal to or greater than a predetermined value of the first maximum output. It further includes an operation unit for receiving an instruction of the volume value,
The said control part changes the said reference voltage by the said voltage change part according to the volume value received by the said operation part which determines the said maximum output, The any one of Claims 1-7 characterized by the above-mentioned. The amplification device according to item.   The amplifying apparatus according to claim 4, wherein the first variable resistor is a digital potentiometer.   The amplifying apparatus according to claim 5, wherein the second variable resistor is a digital potentiometer. Further comprising a step-down circuit for stepping down the power supply voltage from the switching power supply to a predetermined potential;
The power supply voltage from the step-down circuit is supplied to the control unit,
The control unit is configured to gradually increase the power supply voltage from the switching power supply to the power supply voltage at which the amplifier is activated by the voltage changing unit after being activated by the power supply voltage from the step-down circuit. Item 11. The amplification device according to any one of Items 1 to 10.