JP2016072877A - Power amplifier and power amplification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To handle, with a simple configuration, a load variation to obtain a satisfactory audio characteristic.SOLUTION: An amplification unit amplifies an input signal and supplies the signal to a load. A current detection circuit provided at an output stage of the amplification unit detects a current of an output signal output from the amplification unit. A variable current feedback circuit feeds back the detected current by a feedback amount switched, depending on the detected current, from among a plurality of feedback amounts. A voltage feedback circuit feeds back a voltage of the output signal by a predetermined feedback amount. An adjustment unit adjusts the input signal by using the fed-back current and fed-back voltage. This makes it possible to handle a load variation with a simple configuration of switching feedback amounts depending on the load variation, and thereby obtain a satisfactory audio characteristic.SELECTED DRAWING: Figure 19

Description

  The present invention relates to a power amplification device and a power amplification method.

  2. Description of the Related Art Today, digital amplifier devices (class D amplifier devices) that perform power amplification with a switching circuit using pulse width modulation (PWM) or pulse density modulation (PDM) are known. The digital amplifier device can perform high-efficiency amplification, for example, 90% or more at the maximum, and has a small amount of heat generation. For this reason, it is used for mini audio components, car audio, portable music players, and the like.

  Here, if the load resistance of a load such as a speaker device connected to the digital amplifier device fluctuates, the current flowing from the digital amplifier device to the load may fluctuate, which may affect audio characteristics and the like.

  Conventionally, the following first to third techniques are known as techniques for making the current flowing from the digital amplifier device to the load constant even when the load resistance fluctuates. First, an FET (Field Effect Transistor) is inserted and connected in series to the output line of the digital amplifier device. Then, when the line load of the speaker device is short-circuited (for example, about 1Ω to 3Ω), the output current is controlled to a constant value by the FET (first technique).

  Japanese Patent Application Laid-Open No. 2011-171967 (Patent Document 1) detects a current in a demodulation circuit (in an LC filter) and controls a stop of an output switch of a digital amplifier device when a current exceeding a predetermined value flows. Has disclosed a technique for interrupting the current flowing through the second (second technique).

  In Japanese Patent No. 3922182 (Patent Document 2), a load current flowing through a load of a speaker device or the like is measured, and when the current amount exceeds a predetermined amount, a limiter is applied to an input audio signal to output a signal. Has been disclosed (third technique) for suppressing the value of the value from exceeding a certain level.

JP 2011-171967 A Japanese Patent No. 3922182

  However, in the case of the first technique, the output current is controlled to a constant value by the FET inserted and connected in series to the output line of the digital amplifier device, which increases the burden on the FET and shortens the life of the FET element. is there. In addition, it is necessary to provide an FET that can handle a large current, which increases the mounting area, which increases the cost.

  In the case of the second technique disclosed in Patent Document 1, since current detection is performed in the demodulation circuit (in the LC filter), there is a problem that current measurement with high accuracy becomes difficult. Moreover, since the output switch of the digital amplifier device is controlled to stop when the current amount exceeds a predetermined amount, there is a problem that the sound quality is deteriorated and the sound is difficult to hear.

  In the case of the third technique disclosed in Patent Document 2, when the amount of current exceeds a predetermined amount, a limiter is applied to the input audio signal, so that the sound is distorted during operation and the audio becomes difficult to hear. There is.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a power amplifying apparatus and a power amplifying method capable of obtaining good audio characteristics corresponding to load fluctuations with a simple configuration. .

  As means for solving the above-described problems, the present invention is provided with an amplifying unit that amplifies an input signal and supplies the amplified signal to a load, and detects the current of the output signal output from the amplifying unit. A current detection circuit that performs feedback, a variable current feedback circuit that feeds back current by a feedback amount that is switched according to the detected current among a plurality of feedback amounts, and voltage feedback that feeds back the voltage of the output signal by a predetermined feedback amount A circuit, and a subtraction processing unit that subtracts the feedback current and the feedback voltage from the input signal.

  As a means for solving the above-described problems, the present invention provides an amplification step in which an amplification unit amplifies an input signal and supplies the amplified signal to a load, and a current detection circuit provided in the output stage of the amplification unit Current detection step for detecting the current of the output signal output from the unit, and a variable current feedback step in which the variable current feedback circuit feeds back the current with a feedback amount switched according to the detected current among a plurality of feedback amounts And a voltage feedback step in which the voltage feedback circuit feeds back the voltage of the output signal by a predetermined feedback amount, and a subtraction processing step in which the subtraction processing unit subtracts the feedback current and the feedback voltage from the input signal. And have.

  The present invention can obtain good audio characteristics corresponding to load fluctuations with a simple configuration.

FIG. 1 is a block diagram of a power amplifying apparatus according to a first embodiment to which the present invention is applied. FIG. 2 is a diagram for explaining the operation principle of the power amplifying apparatus according to the first embodiment. FIG. 3 is a block diagram illustrating a state where the power amplifying devices according to the first embodiment are connected in parallel. FIG. 4 is an equivalent circuit diagram of the power amplifying device according to the first embodiment. FIG. 5 is a diagram illustrating an example of design conditions when the power amplifying device according to the first embodiment is connected in parallel. FIG. 6 is a diagram illustrating design conditions when the power amplifying device according to the first embodiment is connected in parallel. FIG. 7 is a diagram for explaining the dependency of the output resistance on the current feedback amount when the power amplifying device according to the first embodiment is connected in parallel. FIG. 8 is a diagram for explaining the dependency of the gain on the current feedback amount when the power amplifying device according to the first embodiment is connected in parallel. FIG. 9 is a diagram for explaining the dependency of the gain on the output additional resistance when the power amplifying device according to the first embodiment is connected in parallel. FIG. 10 is a diagram for explaining the dependency of the gain on the output current when the power amplifying device according to the first embodiment is connected in parallel. FIG. 11 is a block diagram of a power amplifying apparatus according to a second embodiment to which the present invention is applied. FIG. 12 is an equivalent circuit diagram of the power amplifying device according to the second embodiment. FIG. 13 is an equivalent circuit diagram of a power amplifying device according to a third embodiment to which the present invention is applied. FIG. 14 is an equivalent circuit diagram of a power amplifying device according to a fourth embodiment to which the present invention is applied. FIG. 15 is a flowchart for explaining the operation of the power amplifying device according to the fourth embodiment to which the present invention is applied. FIG. 16 is an equivalent circuit diagram of a power amplifying device according to a fifth embodiment to which the present invention is applied. FIG. 17 is a flowchart for explaining the operation of the power amplifying device according to the fifth embodiment to which the present invention is applied. FIG. 18 is a block diagram of a power amplifying device according to a sixth embodiment to which the present invention is applied. FIG. 19 is a block diagram of a power amplifying apparatus that is a modification of the sixth embodiment to which the present invention is applied. FIG. 20 is a diagram for explaining the operation principle of the power amplifying device according to the sixth embodiment to which the present invention is applied. FIG. 21 is a diagram for explaining the dependence of the gain on the output current before switching the current feedback amount of the power amplification device according to the sixth embodiment to which the present invention is applied. FIG. 22 is a diagram for explaining the dependence of the gain on the output current after switching the current feedback amount of the power amplifying device according to the sixth embodiment to which the present invention is applied.

  Hereinafter, a power amplifying apparatus according to an embodiment to which the present invention is applied will be described in detail with reference to the accompanying drawings.

(Overview)
The power amplifying device according to the embodiment has a method in which current feedback and voltage feedback of a demodulated audio signal are fused. The power amplifying device according to the embodiment can easily set the current feedback amount and the voltage feedback amount of the demodulated audio signal, and can absorb variations between amplifiers with high accuracy. Further, there is no need to increase the breakdown voltage, and the circuit can be realized with a simple circuit configuration. In addition, it can automatically cope with load fluctuations and enables good parallel operation.

  Further, the power amplifying apparatus of the embodiment switches the current feedback amount and suppresses the load current when the load resistance is reduced and the output current is increased to reach the threshold current. Thereby, the power amplifying device of the embodiment reduces audio distortion and the like. In addition, the power amplifying device according to the embodiment does not need to insert a power FET in series with the amplifier output, and thus can prevent wasteful heat generation. In addition, the power amplifying device of the embodiment can cope with both a short circuit load and an incomplete load short circuit by calculating the short circuit current and varying the current feedback amount. In addition, even when the output current is controlled, distortion of the audio signal can be suppressed, and the audio can be clearly transmitted to the speaker device. In addition, since the amount of current feedback can be set freely, it is possible to cope with any genre of products, usage environment, and usage location.

(First embodiment)
FIG. 1 shows a block diagram of a power amplifying apparatus 1 according to the first embodiment of the present invention. The power amplifying apparatus 1 shown in FIG. 1 is an example of a single end type. The power amplification device 1 includes an input terminal 2, an operational amplifier circuit 3, a PWM modulation circuit 4, a voltage amplification circuit 5, a low-pass filter (LPF: demodulation circuit) 6, a current detection circuit 7, a voltage feedback circuit 8, a current feedback circuit 9, and an addition And an output terminal 11a, 11b. Such a power amplifying device 1 is connected to a load 12 such as a speaker device. The voltage amplification circuit 5 is an example of an amplification unit. The adder 10 is an example of an adjustment unit.

  An audio signal (Vin) is supplied to the input terminal 2. The operational amplifier circuit 3 amplifies the input audio signal with a predetermined gain and outputs it. The PWM modulation circuit 4 performs pulse width modulation processing on the amplified audio signal. PWM is an abbreviation for “Pulse Width Modulation”. Instead of the PWM modulation circuit 4, a delta sigma modulator (ΔΣ modulator) may be used.

  The voltage amplification circuit 5 amplifies the voltage of the audio signal subjected to the pulse width modulation process by a predetermined amount. Specifically, for example, two output power MOSFETs are used, and a relatively high voltage is switched at the timing of the pulse width of the audio signal subjected to the pulse width modulation process. MOSFET is an abbreviation for “Metal-Oxide-semiconductor Field-Effect Transistor”. As a result, it is possible to obtain an audio signal that has been subjected to pulse width modulation processing with a large voltage amplitude. The LPF 6 has a coil 6R inserted and connected in series to the audio signal line, and a capacitor 6C connected in parallel between the output side of the coil 6R and the ground. The LPF 6 removes a high frequency component from the audio signal subjected to the pulse width modulation process, and supplies it to the load 12 via the output terminals 11a and 11b.

  The voltage feedback circuit 8 negatively feeds back the voltage value (β0) of the audio signal from which the high frequency component has been removed by the LPF 6. The current feedback circuit 9 negatively feeds back the voltage value (β1) detected by the current detection circuit 7 and corresponding to the current value of the audio signal from which the high frequency component has been removed by the LPF 6. The adder 10 adds each negative voltage value (β0, β1) to the input audio signal. As a result, when a plurality of power amplifying devices 1 are connected in parallel, variations in amplifier gain, power supply voltage, and the like between the power amplifying devices 1 are absorbed, and favorable parallel operation is enabled.

  Next, the principle by which the data generator 1 according to the embodiment enables a good parallel operation will be described. FIG. 2 shows the relationship between the output current Io after the LPF 6 (horizontal axis) and the output voltage (Vo) after the LPF 6 when two power amplifying devices 1 are connected in parallel. In FIG. 2, when the voltage feedback amount β0 is large (β1 = 0, β0 >> 0), the audio performance is good, but the parallel operation of the power amplifying devices 1 is hindered. Note that the audio performance is good means that the fluctuation of the voltage of the audio signal is small. On the other hand, when the current feedback amount β1 is large (β1 >> 0, β0 = 0), the parallel operations of the power amplifying devices 1 are good, but the audio performance is hindered.

  Here, in FIG. 2, Vo1 indicates the output voltage of one of the two power amplifying apparatuses 1 connected in parallel. Moreover, Vo2 has shown the output voltage of the other power amplification apparatus 1 among the two power amplification apparatuses 1 connected in parallel. Even if output voltage variations (Vo1> Vo2) such as Vo1 and Vo2 occur between the power amplifying devices 1 connected in parallel, as the slope corresponding to the output voltage difference between Vo1 and Vo2 increases, The output current fluctuation width ΔIo is reduced, and each power amplifying device 1 can be operated in good parallel operation. Then, by adjusting the ratio of the voltage / current feedback ratio β1 / β0, it is possible to allow each power amplifying apparatus 1 to perform a good parallel operation while ensuring audio performance. However, if the slope of the voltage-current feedback ratio β1 / β0 is excessively increased, the audio performance (gain fluctuation, distortion, rated output, PSRR) is significantly lowered and cannot be put into practical use. PSRR is an abbreviation for “Power Supply Rejection Ratio”.

  For this reason, the power amplifying device 1 of the embodiment increases the ratio of the voltage / current feedback ratio β1 / β0 when the amount of variation between the output voltage Vo1 and the output voltage Vo2 of each power amplifying device 1 connected in parallel is large, Increasing the slope of the output voltage Vo with respect to the output current Io. Thereby, a favorable parallel operation corresponding to various variations is possible.

  Moreover, since the power amplifying apparatus 1 of the embodiment applies feedback from the subsequent stage of the LPF 6 that operates as a demodulation circuit, the values of the current feedback amount β1 and the voltage feedback amount β0 can be adjusted independently and simply.

  2 is an example in which two power amplifying apparatuses 1 are connected in parallel, but FIG. 3 is an example in which three power amplifying apparatuses 1 are connected in parallel. In this example, the audio signal input from the input terminal 2 is supplied to the operational amplifier circuit 3 via the adder 10 of each power amplifying device 1, and the output terminals 11 a and 11 b of each power amplifying device 1 are The three power amplifying devices 1 are connected in parallel so as to be connected to the load 12, respectively. Also in this case, if the range of variation of the output voltage of each power amplifying device 1 is known, the parallel connection of the three power amplifying devices 1 is good by adjusting the slope of the output voltage Vo with respect to the output current Io. It can be. The same applies to the parallel connection of four or more power amplifiers 1.

  Next, how to derive the amplifier gain, loop gain, and output resistance of the power amplifying apparatus 1 will be described. FIG. 4 is an equivalent circuit diagram of the power amplifying apparatus 1 shown in FIG. In FIG. 4, the internal resistance Ro is the on-resistance of the MOSFET of the voltage amplification circuit 5, the DC resistance of the coil 6 </ b> R (Lo) of the LPF 6, and the like. The current detection circuit 7 is replaced with a sense resistor Rs (current detection resistor Rs). The current detection circuit 7 detects the potential difference (voltage) across the current detection resistor Rs as the current value io of the audio signal demodulated by the LPF 6. Note that the current value io of the audio signal = the output voltage Vo / the resistance value RL of the load 12.

  The current feedback circuit 9 negatively feeds back the voltage value of “adjusted current feedback amount β1 × current detection resistor Rs × current value io of the audio signal” to the adder 10. In this example, the current value io of the audio signal demodulated by the LPF 6 is detected by the current detection resistor Rs. However, a transformer may be inserted instead of the current detection resistor Rs and detected by the secondary voltage. The voltage feedback circuit 8 negatively feeds back to the adder 10 the voltage value of “the voltage value Vo of the audio signal output from the LPF 6 × the adjusted voltage feedback amount β0”. 4 indicates the output impedance of the power amplifying device 1 (the output resistance of the power amplifying device 1).

  In such an equivalent circuit of the power amplifying device 1, the amplifier gain (Gain) of the power amplifying device 1 is expressed by the following equation (1), the loop gain (Loop Gain) is expressed by the following equation (2), and the output resistance Zo is expressed by the following equation. These are calculated by the following equation (3). In each equation, “A” indicates an internal gain of the power amplifying apparatus 1 such as a gain of the operational amplifier circuit 3 and the voltage amplifying circuit 5. Further, “A × β0 >> 1” and “A × β1 >> 1” are set.

  Gain = ∂Vo / ∂Vin ≒ A / (1 + A × (β0 + β1 × (Rs / Zo))) ≒ 1 / (β0 + β1 × (Rs / Zo) ・ ・ ・ (Formula 1)

  Loop Gain ≒ A × (β0 + β1 × (Rs / Zo)) (Expression 2)

  Zo ＝ ∂Vo / ∂io ≒ ((((1 + A × β1) / (1 + A × β0)) × Rs) + ((1 / (1 + A × β0)) × Ro) ≒ (β1 / β0 ) X Rs (Expression 3)

  The amplifier gain (Gain), the loop gain (Loop Gain), and the output resistance Zo of the power amplifying apparatus 1 are established by the fusion of the voltage feedback amount β0 and the current feedback amount β1, respectively.

  Next, design conditions for the power amplifying apparatus 1 will be described. FIG. 5 is a diagram schematically showing three power amplifying devices 1 that are connected in parallel and connected to a load 12 such as a speaker device. Thus, when a plurality of power amplifying devices 1 are connected in parallel, in order to exhibit good parallel operation and to obtain good audio performance, the power is set so as to satisfy the following first to seventh conditions. It is necessary to design the amplifying apparatus 1.

(First condition)
The amplifier gain (Gain) is uniformly determined at the time of system design, but is 27 dB as an example here.

(Second condition)
The output power of the power amplifying apparatus 1 is also uniformly determined at the time of system design, but here it is set to 90 W / 4Ω as an example.

(Third condition)
As amplifier operation, Loop Gain ≥ 20dB or more (increase audio performance) to improve sound quality.

(Fourth condition)
The variation of the output voltage of each power amplifying apparatus 1 operating in parallel is set to ± 10% or less as shown in FIG.

(Fifth condition)
As shown in FIG. 5, the circulating current that flows when the maximum voltage variation (± 10%) of the power amplifying devices 1 that operate in parallel is 2.5 A or less.

(Sixth condition)
The output resistance Zo of the power amplifying device 1 for setting the circulating current to 2.5 A is derived.

(Seventh condition)
The gain fluctuation range of the power amplifying apparatus 1 when the load 12 is reduced (at the time of outputting a large current) is set to be within 3 dB.

  The voltage feedback amount β0 and the current feedback amount β1 that satisfy such first to seventh conditions exist within a limited range. If a point satisfying the first to seventh conditions can be found, the voltage feedback amount β0 and the current feedback amount β1 can be emphasized and merged with each other, and good parallel operation and good audio performance can be obtained.

  The power amplifying apparatus 1 according to the embodiment obtains good parallel operation and good audio performance by using the voltage feedback amount β0 and the current feedback amount β1 derived as described below. First, FIG. 6 is a table summarizing conditions or set values (representative values) corresponding to each item. As described above, the amplifier gain of the power amplifying apparatus 1 is set to 27 dB as shown in FIG. The maximum output power of the power amplifying apparatus 1 is set to a maximum of 90 W / 4Ω. The internal gain A of the power amplifying apparatus 1 is set to 70 dB. The resistance value of the current detection resistor Rs is set to 50 mΩ. The internal resistance Ro of the power amplifying apparatus 1 is set to 50 mΩ. The loop gain is set to 20 dB or more. The variation of the output voltage of the power amplifying apparatus 1 is set to ± 10% or less. The allowable circulating current shall be ± 2.5A or less. The fluctuation range (load dependence) of the amplifier gain of the power amplification device 1 is 3 dB or less.

  Under such conditions, since the amplifier gain of the power amplifying apparatus 1 of FIG. 6 is 27 dB, the voltage feedback amount β0 = 0.045 is calculated using Equation (1). That is, in the case of only voltage feedback (β1 = 0), β0 = 1 / Gain is obtained by transforming Equation (1). From FIG. 6, since the amplifier Gain is 27 dB (22.4 times), the voltage feedback amount β0 = 1 / 22.4 = 0.045 can be calculated.

  Next, from the respective conditions of the maximum output power of 90 W / 4Ω, the variation of the output voltage of each power amplifying device 1 shown in FIG. 6, ± 10% or less, and the allowable circulating current ± 2.5 A or less, Equation 3 is used. Then, the output resistance Zo of the power amplification device 1 is calculated. Formula 4 of the output resistance Zo corresponding to this condition is as follows.

  Zo = (√90 W × √4Ω × (1.1−0.9)) / 2.5A≈1.5Ω (Expression 4)

  From this equation, it can be seen that the output resistance Zo ≧ 1.5Ω is required. FIG. 7 is a diagram showing the relationship (dependency) between the output resistance Zo and the current feedback amount β1 when the voltage feedback amount β0 is 0.045. As can be seen from FIG. 7, the current feedback amount β1 at which the output resistance Zo ≧ 1.5Ω is β1 ≧ 1.35.

  Next, as shown in FIG. 6, the gain fluctuation width due to the load fluctuation (no load, 4Ω, 8Ω, 20Ω) of the load 12 needs to be 3 dB or less. FIG. 8 is a diagram illustrating a relationship (dependency) between the amplifier gain of the power amplification device 1 and the current feedback amount β1 when the voltage feedback amount β0 is 0.045. As can be seen from the above equation 1 and FIG. 7, the current feedback amount β1 at which the load fluctuation is within 3 dB is β1 ≦ 1.45.

  7 and 8 that the optimum value of the current feedback amount β1 is in the range of “1.35 ≦ β1 ≦ 1.45”. Therefore, the design value of the voltage feedback amount β0 is β0 = 0.045, and the design value of the current feedback amount β1 is β1 = 1.40 (an intermediate value between 1.35 and 1.45). When the design value of the voltage feedback amount β0 and the design value of the current feedback amount β1 are substituted into the above equation 2, a value of 46 dB is calculated as the loop gain. As shown in FIG. 6, the loop gain condition is 20 dB or more. Therefore, the design value of the voltage feedback amount β0 = 0.045 and the design value of the current feedback amount β1 = 1.40 satisfy the loop gain condition.

  Next, the power amplifying device 1 according to the embodiment under the condition that the voltage feedback amount β0 = 0.045, the current feedback amount β1 = 1.40, and the maximum output power of the power amplifying device 1 are 90 W / 4Ω. As a result of verification, the following verification results were obtained.

  FIG. 9 is a diagram illustrating a relationship (amplifier gain load resistance dependency) between the amplifier gain of the power amplifying device 1 set as a condition of 27 dB and the load resistance RL of the load 12. Further, FIG. 10 shows the relationship between the amplifier gain of the power amplifying apparatus 1 set as a condition of 27 dB and the output current Io supplied from the power amplifying apparatus 1 to the load 12 (dependence of the amplifier gain on the output current). FIG.

  By optimizing the voltage feedback amount β0 of the power amplifying apparatus 1 to be β0 = 0.045 and the current feedback amount β1 to be β1 = 1.40, the load 12 becomes voltage feedback with respect to 90Ω as shown in FIG. Current feedback automatically fluctuates. Further, as shown in FIG. 10, the voltage feedback and the current feedback are automatically changed when the output current becomes 1A.

  That is, looking at the characteristic curve of the current feedback amount β1 = 1.40 shown in FIG. 9, when the load resistance RL of the load 12 is 4Ω, the minimum load resistance satisfying the condition that the gain fluctuation range (load dependence) is 3 dB or less. Value. Thereafter, as the load resistance RL gradually increases, the current feedback amount β1 also gradually increases, and the amplifier gain of the power amplifying apparatus 1 changes within a range up to 27 dB, corresponding to fluctuations in the load resistance RL. Then, when the value of the load resistance RL becomes 90Ω, the effect of the voltage feedback amount β0 becomes dominant. The current feedback region shown in FIG. 9 indicates that the effect of the current feedback amount β1 is dominant when the load resistance RL is in the range of 4Ω to 90Ω. Further, the voltage feedback region shown in FIG. 9 indicates that the effect of the voltage feedback amount β0 is dominant in the range where the load resistance RL is 90Ω or more.

  Next, looking at the characteristic curve of the current feedback amount β1 = 1.40 shown in FIG. 10, when the value of the output current Io of the power amplification device 1 is 4.75 A, the gain fluctuation range (load dependence) is 3 dB or less. The current fluctuation maximum satisfying the above condition. That is, the condition that the gain fluctuation range (load dependence) is 3 dB or less is satisfied within the output current fluctuation range where the value of the output current Io of the power amplifying apparatus 1 is 0.1 A to 4.75 A. In addition, within the output current fluctuation range where the value of the output current Io is 0.1 A to 1 A, the effect of the voltage feedback amount β0 becomes dominant. The voltage feedback region shown in FIG. 10 indicates a range where the effect of the voltage feedback amount β0 is dominant. In addition, when the value of the output current Io is within the output current fluctuation range of 1A to 4.75A, the effect of the current feedback amount β1 becomes dominant. The current feedback region shown in FIG. 10 indicates a range where the effect of the current feedback amount β1 is dominant. When the value of the output current Io is within the output current fluctuation range of 1A to 4.75A, the effect of the current feedback amount becomes dominant, and the amplifier gain of the power amplification device 1 is reduced to a predetermined value.

  Thereby, when a plurality of power amplifying devices 1 are connected in parallel and operated, if a voltage difference occurs between the power amplifying devices 1, the difference voltage is absorbed by the effect of current feedback, and each power amplifying device 1 The parallel operation can be stabilized. In addition, when the value of the output current Io is 1 A or less and small, the audio performance can be sufficiently obtained by the effect of voltage feedback. With respect to the set voltage feedback amount β0, the range of the current feedback amount β1 is preferably a large value when considering the sound quality, and a small value is preferable when the stability of the parallel operation of each power amplifying apparatus 1 is intended.

  As is clear from the above description, the power amplifying apparatus 1 according to the first embodiment negatively feeds back the current value of the audio signal demodulated by the LPF 6 by a predetermined amount by the current feedback circuit 9 and demodulates the audio signal by the LPF 6. Is negatively fed back by the voltage feedback circuit 8 by a predetermined amount. Then, the adder 10 adds the input audio signal. Since the current feedback amount β1 and the voltage feedback amount β0 of the current value detected from the demodulated audio signal can be freely set, variations in output voltage between the plurality of power amplifying devices 1 connected in parallel can be absorbed with high accuracy. In addition, since variations in output voltage between the plurality of power amplifying devices 1 connected in parallel can be absorbed with high accuracy, it is not necessary to vary the power supply voltage highly in order to operate the power amplifying devices 1 in parallel. For this reason, it is not necessary to use a high voltage | pressure-resistant element, and cost reduction of the power amplification apparatus 1 is realizable.

  Further, it is possible to automatically cope with a load fluctuation of the load 12 connected to each power amplifying apparatus 1 operating in parallel. For this reason, it is not necessary to measure the load in advance, and a simple circuit configuration with a small number of elements can be realized.

  Since the output power and the load fluctuation range of the power amplifying apparatus 1 are different depending on the product genre, usage environment, usage location, and the like, it is necessary to optimize the ratio of the current feedback amount β1 and the voltage feedback amount β0 for each product. However, in the case of the power amplifying apparatus 1 of the embodiment, the ratio of the current feedback amount β1 and the voltage feedback amount β0 can be freely set. For this reason, it has a high degree of freedom that can be applied to any type of power amplifying apparatus 1.

  In addition, the woofer which is a speaker unit that reproduces the bass is divided into a current feedback type and a voltage feedback type. If the current feedback and voltage feedback described above are applied, the sound quality and the large current drive can be optimized, and the sound quality ( It is possible to easily adjust the tightening feeling.

  Further, the power amplifying apparatus 1 of the first embodiment inputs an audio signal in a normal phase to one channel, inputs an audio signal in an opposite phase to the other channel, and connects the positive electrodes of the respective outputs to a speaker device. By connecting to the two, it is also applicable to BTL connection in which two outputs of a stereo amplifier are bridge-connected and used as a monaural amplifier. BTL is an abbreviation for “Bridged Transless”.

(Second Embodiment)
Next, a power amplifying apparatus according to the second embodiment of the present invention will be described. The power amplifying apparatus 1 of the first embodiment described above. The current detection circuit 7 is provided at the output stage of the LPF 6. In the power amplifying apparatus 1 of the second embodiment, as shown in FIG. 11, a current detection circuit 7 is provided between the output terminal 11b and the ground. Hereinafter, only such differences will be described, and redundant description will be omitted.

  FIG. 12 shows an equivalent circuit diagram of the power amplifying apparatus 1 according to the second embodiment. As shown in FIG. 12, in the case of the power amplifying apparatus 1 of the second embodiment, the current detection resistor Rs of the current detection circuit 7 is inserted and connected between the output terminal 11b and the ground. Then, the voltage across the current detection resistor Rs is detected as the current value of the output current Io, and negatively fed back to the adder 10 via the current feedback circuit 9. Thereby, the same effect as the power amplification device 1 of the first embodiment described above can be obtained.

(Third embodiment)
Next, a power amplifying device according to a third embodiment of the present invention will be described. The power amplifying apparatus 1 according to the third embodiment is provided with a filter that removes switching noise peculiar to a digital amplifier from the current detection output from the current detection circuit 7. Hereinafter, only such differences will be described, and redundant description will be omitted.

  FIG. 13 is an equivalent circuit diagram of the power amplifying apparatus 1 according to the third embodiment. In the case of the power amplifying apparatus 1 according to the third embodiment, as shown in FIG. 13, a filter 20 is provided that removes switching noise peculiar to a digital amplifier from the current detection output detected by the current detection resistor Rs of the current detection circuit 7. doing.

  In the power amplifying apparatus 1, as described above, the voltage amplifying circuit 5 uses, for example, two output power MOSFETs, and switches a relatively high voltage at the timing of the pulse width of the audio signal subjected to the pulse width modulation processing. For this reason, spike noise-like switching noise is superimposed on the audio signal. The filter 20 removes switching noise from the current detection output detected by the current detection resistor Rs, and supplies the switching noise to the current feedback circuit 9.

  As a result, malfunction of the current feedback circuit 9 can be prevented, the stability of the output current io can be increased, and the same effects as those of the above-described embodiments can be obtained. Note that the filter 20 may be incorporated in the current feedback circuit 9.

(Fourth embodiment)
Next, a power amplifying apparatus according to the fourth embodiment of the present invention will be described. In the power amplifying apparatus 1 of the fourth embodiment, the determination of the voltage feedback amount β0 and the current feedback amount β1 is automatically performed under the control of a microcomputer device (microcomputer). Hereinafter, only such differences will be described, and redundant description will be omitted.

  FIG. 14 is an equivalent circuit diagram of the power amplifying apparatus 1 according to the fourth embodiment. In the case of the power amplifying apparatus 1 according to the fourth embodiment, the microcomputer 25 as an example of a control unit controls the voltage feedback amount β0 and the current feedback amount β1.

  Specifically, the microcomputer 25 sets the voltage feedback amount β0 optimized as described above corresponding to the desired amplifier gain input by the user for the voltage feedback circuit 8. Next, the microcomputer 25 optimizes the current feedback amount β1 with respect to the preset output resistance Zo of the power amplifying device 1 from the optimized voltage feedback amount β0. Note that the microcomputer 25 may automatically optimize the current feedback amount β1 when the user inputs a desired output resistance Zo.

  As an example, the microcomputer 25 sets the current feedback amount β1 to a large value when considering the sound quality, and sets the current feedback amount β1 to a small value when considering the stability of the parallel operation of the power amplifiers 1 connected in parallel. The current feedback circuit 9 is set. When the power amplifying apparatus 1 is not operated in parallel, the microcomputer 25 may set the current feedback amount β1 having a small value or a zero value for the current feedback circuit 9.

  The flowchart of FIG. 15 shows the operation flow of the microcomputer 25 in the power amplifying apparatus 1 of the third embodiment. First, in step S1, the user inputs whether or not to switch the amplifier gain. When an input operation indicating that the amplifier gain is not switched is performed (step S1: No), the microcomputer 25 proceeds to step S7, reads a preset amplifier gain value, and performs the process in step S3. Proceed to

  On the other hand, when an input operation indicating that the amplifier gain is switched is performed (step S1: Yes), the microcomputer 25 acquires the value of the amplifier gain input from the user in step S2, and the process proceeds to step S3. Proceed with the process.

  In step S <b> 3, the microcomputer 25 determines whether or not an input operation for instructing switching of the output resistance Zo of the power amplification device 1 has been performed by the user. When an input operation for instructing switching of the output resistance Zo of the power amplifying device 1 is not detected (step S3: No), the microcomputer 25 reads a preset value of the output resistance Zo in step S8 and performs processing. Proceed to S5.

  On the other hand, when detecting an input operation instructing switching of the output resistance Zo of the power amplifying device 1 (step S3: Yes), the microcomputer 25 determines the value of the output resistance Zo input by the user in step S4. Acquire and proceed to step S5.

  In step S5, the microcomputer 25 calculates the voltage feedback amount β0 and the current feedback amount β1 using the amplifier gain and the output resistance Zo. In step S 6, the microcomputer 25 sets the calculated voltage feedback amount β 0 in the voltage feedback circuit 8 as shown in FIG. 14 and sets the calculated current feedback amount β 1 in the current feedback circuit 9.

  As a result, the voltage feedback amount β0 for the voltage feedback circuit 8 and the current feedback amount β1 for the current feedback circuit 9 can be automatically set, and the same effects as those of the above-described embodiments can be obtained. it can.

(Fifth embodiment)
Next, a power amplifying device according to a fifth embodiment of the present invention will be described. In the above-described fourth embodiment, the microcomputer 25 automatically sets the voltage feedback amount β0 and the current feedback amount β1 for the power amplifying apparatus 1 in which the microcomputer 25 is provided. In contrast, the power amplifying apparatus according to the fifth embodiment performs communication between microcomputers provided in the power amplifying apparatuses 1 connected in parallel. Then, each microcomputer automatically supplies the voltage feedback amount β0 and the current feedback amount β1 that enable good parallel operation and good audio performance to each power amplification device 1 provided with the microcomputer. It is something that is set. Hereinafter, only such differences will be described, and redundant description will be omitted.

  FIG. 16 is an equivalent circuit diagram of the power amplifying device 1 according to the fifth embodiment. As shown in FIG. 16, in the case of the power amplifying apparatus 1 according to the fifth embodiment, the microcomputer 25a and the microcomputer 25b provided in each of the power amplifying apparatuses 1 connected in parallel have their own voltage feedback amounts. β0 is detected and notified to the microcomputer of another power amplifying apparatus 1 connected in parallel. The microcomputer 25a and microcomputer 25b of each power amplifying device 1 compares the voltage feedback amount β0 of its own device with the voltage feedback amount β0 notified from the other power amplifying devices 1. The microcomputer 25a and the microcomputer 25b of each power amplifying apparatus 1 determine the voltage feedback amount β0 used for calculation by communicating the comparison results. Then, the microcomputer 25a and the microcomputer 25b of each power amplifying device 1 calculate the current feedback amount β1 using the determined voltage feedback amount β0 and the output resistance Zo of the power amplifying device 1 serving as its own device, and the current feedback amount β1 and The voltage feedback amount β0 is automatically set.

  The flowchart of FIG. 17 shows the flow of the automatic setting operation of the current feedback amount β1 and the voltage feedback amount β0 in the power amplifying device 1 of the fifth embodiment. In step S11 of the flowchart of FIG. 17, the microcomputer 25a and the microcomputer 25b of each power amplifying device 1 detect the current voltage feedback amount β0 and the current feedback amount β1 of the power amplifying device 1 serving as its own device. Then, the microcomputer 25a transmits the voltage feedback amount β0 of its own power amplifying apparatus 1 to the microcomputer 25b, the microcomputer 25b transmits the voltage feedback amount β0 of its own power amplifying apparatus 1 to the microcomputer 26a, and the processing is step S12. Proceed to

  In step S12, the microcomputer 25a and the microcomputer 25b compare the voltage feedback amount β0 of the own device with the voltage feedback amount β0 of the other power amplifying apparatus 1 acquired through communication. Then, it is determined whether or not the comparison result is, for example, 0.5 or more and 2 or less (0.5 ≦ β0 (A) / β0 (B) ≦ 2). Note that β0 (A) is the voltage feedback amount of the own device. Further, β0 (B) is a voltage feedback amount of another power amplifying apparatus 1 acquired by communication.

  That the ratio of each voltage feedback amount β0 is not less than 2 and not more than 2 means that the ratio of each voltage feedback amount β0 is not less than a predetermined value. In this case (step S12: No), the microcomputer 25a and the microcomputer 25b proceed to step S18, and determine an intermediate value of each voltage feedback amount β0 as the voltage feedback amount β0 set in the own device ((β0 ( A) + β0 (B)) / 2 = β0 to be set).

  On the other hand, when the ratio of each voltage feedback amount β0 is 0.5 or more and 2 or less (step S12: Yes), the microcomputer 25a and the microcomputer 25b advance the process to step S13. In step S13, the microcomputer 25a and the microcomputer 25b determine whether or not the voltage feedback amount β0 of the own device is larger than the voltage feedback amount β0 of the other power amplifying devices 1 (β0 (A)> β0 ( B)).

  When it is determined that the voltage feedback amount β0 of the own device is larger than the voltage feedback amount β0 of the other power amplifying apparatus 1 (step S13: Yes), the microcomputer 25a and the microcomputer 25b The voltage feedback amount β0 of the own device is determined as the voltage feedback amount β0 set in the own device. On the other hand, when it is determined that the voltage feedback amount β0 of the own device is smaller than the voltage feedback amount β0 of the other power amplification device 1 (step S13: No), the microcomputer 25a and the microcomputer 25b In S19 and step S15, the voltage feedback amount β0 of the other power amplifying apparatus 1 acquired by communication is determined as the voltage feedback amount β0 set in the own device. That is, the microcomputer 25a and the microcomputer 25b employ the larger voltage feedback amount β0. This is because the sound quality improves when the value of the voltage feedback amount β0 is large.

  Next, in step S16, the microcomputer 25a and the microcomputer 25b calculate the current feedback amount β1 as described above by using the output resistance Zo set in the own device and the determined voltage feedback amount β0. In step S17, the microcomputer 25a and the microcomputer 25b set the determined voltage feedback amount β0 in the voltage feedback circuit 8 of the own device and set the calculated current feedback amount β1 in the current feedback circuit 9 of the own device. Then, the process of the flowchart of FIG. As a result, the power amplifying devices 1 connected in parallel can automatically determine the current feedback amount β1 and the voltage feedback amount β0 by communication and set them in their own devices. In addition, the same effects as those of the above embodiments can be obtained. Can be obtained.

(Sixth embodiment)
Next, a power amplifying device according to a sixth embodiment of the present invention will be described. In the power amplifying device of each of the above-described embodiments, when the load resistance decreases due to the fluctuation of the load 12, the amount of current flowing from the power amplifying device to the load 12 changes, which hinders good parallel operation and audio characteristics. There is a risk of causing. For this reason, the power amplifying apparatus 1 of the sixth embodiment controls the current feedback circuit to increase the amount of current feedback when the load resistance becomes small and the output current becomes equal to or greater than the threshold current, and the load The amount of current flowing through 12 is suppressed. Hereinafter, only such differences will be described, and redundant description will be omitted.

  FIG. 18 is a block diagram of a power amplifying device according to the sixth embodiment. As shown in FIG. 18, the power amplifying apparatus according to the sixth embodiment has a variable current feedback circuit 30 having a function of switching the current feedback amount β1. The variable current feedback circuit 30 has a current feedback amount β1 (small current feedback amount) ← → current feedback amount β2 (current feedback amount) according to the current current amount of the audio signal detected by the current detection circuit 7 after the LPF 6. The amount of current feedback is switched between (large amount).

  In the following description, switching of the current feedback amount will be described as switching in two steps between the current feedback amount β1 and the current feedback amount β2. However, switching of the current feedback amount may be performed in three or more steps, or analog stepless switching may be performed. Further, although the current detection circuit 7 is provided in the subsequent stage of the LPF 6, as shown in FIG. 19, the current detection circuit 7 may be provided between the output terminal 11b and the installation. In either case, the same effects as described later can be obtained.

  The principle of such a power amplifying device according to the sixth embodiment will be described. FIG. 20 is a diagram illustrating a relationship between the output current Io and the output voltage Vo of the power amplifying device 1. When the load resistance of the load 12 connected to the power amplifying device fluctuates and decreases, the output current Io1 increases (Io1 →) while maintaining the slope of the current feedback amount β1 / voltage feedback amount β0 shown in FIG. Io1 (large)), good parallel operation and audio characteristics may be hindered.

  Therefore, the variable current feedback circuit 30 compares the current output current value detected by the current detection circuit 7 with a predetermined threshold value (threshold current) while performing current feedback control. When the load resistance is reduced and the output current Io is increased so that the current amount of the output current Io becomes equal to or greater than a threshold value (threshold current), the current feedback amount β1 (current feedback amount is small) to the current feedback amount β2 ( The current feedback amount is switched to (large current feedback amount). As a result, as shown in FIG. 20, the output current Io (large) that increases in the amount flowing to the load 12 side can be suppressed to the current amount of the output current Io2. As a result, when the load resistance fluctuates and decreases, the output current Io1 increases, and it is possible to prevent inconveniences that hinder good parallel operation and audio characteristics, as well as the above-described embodiments. The effect of can be obtained.

  When the current amount of the output current Io becomes less than the threshold value (threshold current) by performing such current suppression control, the variable current feedback circuit 30 determines the current from the current feedback amount β2 (large current feedback amount). The current feedback amount is returned to the feedback amount β1 (small current feedback amount).

  The current feedback amount β1 (small current feedback amount) and the current feedback amount β2 (large current feedback amount) of the variable current feedback circuit 30 are derived as follows. First, the voltage feedback amount β0 is calculated from the amplifier gain specification (27 dB: see FIG. 6) of the power amplification device and the loop gain (sound quality improvement). In this example, as described with reference to FIG. 7, the voltage feedback amount β0 = 0.045.

  Next, the current feedback amount β1 (small current feedback amount) is calculated from the calculated voltage feedback amount β0, the circulating current between the power amplifying devices during the parallel operation due to the variation in the output voltage of the power amplifying device, and the gain fluctuation range. Detect a limited range. Then, the current feedback amount β2 (large current feedback amount) is derived from the calculated voltage feedback amount β0 and the necessary amount of decrease in the amplifier gain.

  An example of the current feedback amount β1 and the current feedback amount β2 derived in this way is shown in FIG. FIG. 21 is a diagram illustrating a relationship between the amplifier gain and the output current of the power amplification device 1 (dependence of the amplifier gain on the output current). In this example, as described with reference to FIG. 6, the maximum output power is 90 W / 4Ω, the voltage feedback amount β0 = 0.045, the current feedback amount β1 (small current feedback amount) = 1.4, and the current feedback amount β2. (Large current feedback amount) = 17.

  In this example, as shown in FIG. 21, the maximum amount of output current is 4.75A, and the range of 0A to 4.75A is an allowable variation range of the output current (output current variation range). The threshold current amount of the variable current feedback circuit 30 is set to 4.75A.

  Note that the range of the output current from 0 A to 1.0 A indicates a voltage feedback region in which the effect of the voltage feedback amount β0 is dominant. The range where the output current is 1.0 A or more indicates a current feedback region where the effect of the current feedback amount β1 (and the current feedback amount β2) becomes dominant. In the current feedback region, the output current of 1.0 A or more indicates the overload region.

  As described above, when the current feedback amount β1 (small current feedback amount) of the variable current feedback amount circuit 30 is set to 1.4 and the current feedback amount β2 (large current feedback amount) is set to 17, the output current Io is, for example, 6A. Then (when the current threshold value exceeds 4.75 A), the variable current feedback circuit 30 switches the current feedback amount from the current feedback amount β1 to the current feedback amount β2. Thereby, in this example, as shown in FIG. 22, the amount of decrease in the amplifier gain of the power amplification device can be decreased by 10 dB, and the amount of output current can be suppressed. Therefore, the power amplifying device of the sixth embodiment can automatically suppress the amount of current flowing through the load even when the load resistance is reduced due to a short circuit of the speaker device or the line, etc. In addition, it is possible to prevent inconveniences that hinder the audio characteristics, and to obtain the same effects as those of the above-described embodiments.

  Further, in the power amplifying device of the sixth embodiment, when the current exceeding the threshold current flows to the load, the current amount is automatically suppressed by the variable current feedback circuit 30, thereby preventing the inconvenience that the audio distortion or the like occurs. it can. Further, since it is not necessary to insert a power FET in series with respect to the output of the power amplifying device, any useless heat generation can be prevented.

  Moreover, it can respond to both the load of a line short circuit (for example, 2Ω-6Ω) and the incomplete load short circuit (6Ω or more) in a high impedance line. In the case of a low impedance line, it is possible to cope with both a load of a line short circuit (for example, 1Ω to 3Ω) and an incomplete load short circuit (for example, 12Ω or more). In either case, calculation is performed from the short-circuit current, and the current feedback amount is made variable (β1 → β2).

  That is, the power amplifying device of the sixth embodiment can cope with various load short circuits with a simple circuit and does not generate unnecessary heat. Further, even when the output current is controlled, distortion of the audio signal can be suppressed and the audio can be clearly transmitted to the speaker device. In addition, since the amount of current feedback can also be set freely, it can be optimized regardless of the product genre, usage environment, and usage location.

  Also, an audio signal is input in the normal phase to one channel, an audio signal is input in the opposite phase to the other channel, and the two outputs of the stereo amplifier are connected to the speaker device by connecting + of each output to each other. The present invention can also be applied to a BTL connection used as a monaural amplifier by bridge connection.

  In the power amplification device according to the sixth embodiment, the current feedback amount β1 and the current feedback amount β2 are switched. However, the current feedback amount β1 and the current feedback amount β2 may be provided separately as current feedback loops. In this case, the current feedback amount β1 → the current feedback amount β1 and the current feedback amount β2 are superposed (superposition operation: β1 + β2).

  Each above-mentioned embodiment is shown as an example and is not intending limiting the range of the present invention. Each of the novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. For example, the power amplifying apparatus 1 of each of the above embodiments is an example in which the present invention is applied to a so-called digital amplifier, but the present invention may be applied to an analog amplifier. Even in this case, the same effect as described above can be obtained. Further, the present invention may be applied to either a high impedance output amplifier or a low impedance output amplifier. Furthermore, the present invention may be applied to parallel operation of motor drive control amplifiers. Each embodiment and modifications of each embodiment are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Power amplifier 2 Input terminal 3 Operational amplifier circuit 4 PWM modulation circuit 5 Voltage amplification circuit 6 Low pass filter (LPF)
6R coil 6C capacitor 7 current detection circuit 8 voltage feedback circuit 9 current feedback circuit 10 adder 11a output terminal 11b output terminal 12 load 15 internal resistance 20 filter 25 microcomputer (microcomputer: CPU)
25a Microcomputer (microcomputer: CPU)
25b Microcomputer (microcomputer: CPU)
30 Variable current feedback circuit

Claims (8)

An amplification unit that amplifies the input signal and supplies it to the load;
A current detection circuit provided at an output stage of the amplifying unit and detecting a current of an output signal output from the amplifying unit;
A variable current feedback circuit that feeds back the current by a feedback amount switched according to the detected current among a plurality of feedback amounts;
A voltage feedback circuit that feeds back the voltage of the output signal with a predetermined feedback amount;
A power amplifying apparatus comprising: an adjustment unit that adjusts the input signal using the fed back current and the fed back voltage. A modulation circuit that digitally modulates the input signal and supplies the modulated signal to the amplifier;
The power amplification device according to claim 1, further comprising: a demodulation circuit that digitally demodulates and outputs the input signal from the amplification unit. The power amplification device according to claim 1, wherein the current detection circuit is provided on a line between an output terminal of the output signal and ground. The feedback amount of the variable current feedback circuit and the feedback amount of the voltage feedback circuit absorb variations in output voltage between the power amplifying devices when the power amplifying device and another power amplifying device are connected in parallel. The power amplification device according to any one of claims 1 to 3, wherein the power amplification device is adjusted to each feedback amount. The power amplifying device according to any one of claims 2 to 4, further comprising a filter that removes noise superimposed on a detection output of a current detected by the current detection circuit. The voltage feedback amount is optimized from the input amplifier gain of the power amplification device and set in the voltage feedback circuit, and the optimized voltage feedback amount corresponds to the output resistance of the power amplification device. The power amplifying device according to claim 1, further comprising: a control unit that optimizes a current feedback amount and sets the current feedback amount in the variable current feedback circuit. The control unit communicates with a control unit provided in the other power amplifying device connected in parallel to determine an optimized feedback amount of the voltage and set it in the voltage feedback circuit. The power amplification device according to claim 6, wherein the optimized feedback amount of the current is determined and set in the variable current feedback circuit. An amplification unit amplifies an input signal and supplies the amplified signal to a load;
A current detection circuit provided at an output stage of the amplifying unit detects a current of an output signal output from the amplifying unit; and
A variable current feedback circuit, a variable current feedback step of feeding back the current by a feedback amount switched according to the detected current among a plurality of feedback amounts;
A voltage feedback step in which the voltage feedback circuit feeds back the voltage of the output signal by a predetermined feedback amount; and
An adjustment step in which an adjustment unit adjusts the input signal using the fed back current and the fed back voltage.

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