JP3579254B2 - Amplifier circuit - Google Patents

Description

【００７６】
【数２】

【００７７】
【数３】

また、ＶＢＥ１はトランジスタＴＲ１のべース−エミッタ間電圧であって、ＶＢＥ２はトランジスタＴＲ２のべース−エミッタ間電圧である。またＶＲはボリウムＶＲ１１の抵抗値である。
【００７８】
上式より、ボリウムＶＲ１１の抵抗値ＶＲが大きくなってスピーカの音量が小さくなると、直流電源電圧±Ｖｃは低くなり、逆にＶＲが小さくなってスピーカの音量が大きくなると直流電源電圧±Ｖｃが大きくなることがわかる。
【００７９】
本実施形態の回路には、第１の実施形態で説明した作用効果に加えて、比較的簡単な回路構成で実現することができ、コストも比較的に安くすむという利点がある。
【００８０】
（３）第３の実施形態
以下、本発明の第３の実施形態について図１０を参照しながら説明する。尚、第１、第２の実施形態と共通する事項については、重複を避けるため説明を省略する。
【００８１】
本実施形態の特徴は、前記ボリウム連動可変電源回路として、図１０に示すチョッパ電源方式の降圧回路を用いたものであり、以下ではこの構成及び動作について説明する。
【００８２】
本実施形態のボリウム連動可変電源回路は、パワートランジスタＱ３１，Ｑ３２、パルス変調回路２１，２２、コンパレータ２３，２４、連動ボリウムＶＲ２１，ＶＲ２２、ダイオードＤ２１，Ｄ２２、コイルＬ２１，Ｌ２２を有する回路であって、不図示の音量調整用のボリウムの抵抗値に連動して変動する直流電源電圧±Ｖｃを生成してアンプのパワー出力段トランジスタに供給する降圧回路である。
【００８３】
パワートランジスタＱ３１，Ｑ３２は、接地電位ＧＮＤを挟んで正負両側にそれぞれ設けられたスイッチング素子であって、これがＯＮ／ＯＦＦすることにより直流電源電圧±Ｖｃｃから、パワー出力段トランジスタに供給される直流電源電圧±Ｖｃを生成する素子である。
【００８４】
パルス変調回路２１，２２は、後述のコンパレータ２３，２４から出力される信号をＰＷＭ（Ｐｕｌｓｅ Ｗｉｄｔｈ Ｍｏｄｕｌａｔｉｏｎ）変調し、パワートランジスタＱ３１，Ｑ３２のべースにそれぞれ出力する回路である。
【００８５】
コンパレータ２３，２４は、基準電圧Ｖｒ１，Ｖｒ２と連動ボリウムＶＲ２１，ＶＲ２２によって設定される電圧とを比較してその比較結果をパルス変調回路２１，２２にそれぞれ出力する回路である。連動ボリウムＶＲ２１，ＶＲ２２は、第１の実施形態の連動ボリウムＶＲ２と同様に、音量調整をするためのボリウムの抵抗値に連動してその抵抗値が変動するボリウムである。
【００８６】
以下、この回路の動作を説明すると、不図示の音量調整用のボリウムの抵抗値に連動して連動ボリウムＶＲ２１，ＶＲ２２の抵抗値は変動する。例えば、ボリウムの抵抗値が高くなってスピーカの音量が小さくなると連動ボリウムＶＲ２１，ＶＲ２２の抵抗値も高くなり、コンパレータ２３，２４の反転入力−の電位が上昇する。逆にボリウムの抵抗値が低くなってスピーカの音量が大きくなると連動ボリウムＶＲ２１，ＶＲ２２の抵抗値も低くなり、コンパレータ２３，２４の反転入力−の電位が下降する。
【００８７】
反転入力−の電位が上昇して基準電圧Ｖｒ１，Ｖｒ２を上回るとコンパレータ２３，２４の出力は“Ｌ”になる。また、反転入力−の電位が下降して基準電圧Ｖｒ１，Ｖｒ２を下回るとコンパレータ２３，２４の出力は“Ｈ”になる。
【００８８】
このように、コンパレータ２３，２４の出力は連動ボリウムＶＲ２１，ＶＲ２２の抵抗値、即ち音量調整用のボリウムの抵抗値によって変動する。このコンパレータ２３，２４の出力が、パルス変調回路２１，２２によってＰＷＭ変調され、その変調結果がパワートランジスタＱ３１，Ｑ３２のべースに出力される。
【００８９】
これにより、パワートランジスタＱ３１，Ｑ３２はＯＮ／ＯＦＦ動作をし、そのＯＮ／ＯＦＦのデューティ比はパルス変調回路２１，２２の出力によって決まる。このデューティ比が大きければ、不図示のパワー出力段のトランジスタに供給される直流電源電圧±Ｖｃは増大し、デューティ比が小さければ、直流電源電圧±Ｖｃは下降するというように、ボリウムの抵抗値に連動して変動する連動ボリウムＶＲ２１，ＶＲ２２の抵抗値が変動すると、直流電源電圧±Ｖｃも変動する。
【００９０】
以上のようにして、本実施形態では音量に応じて直流電源電圧を可変にするという本発明の回路を実現しているので、第１，第２の実施形態と同様の効果を奏し、更に、第１，第２の実施形態のようなドロッパ電源回路を用いておらず、比較的消費電力のロスが少ないチョッパ電源回路を用いているので、第１，第２の実施形態で説明した回路と異なりパワー出力段における効率の改善のみならず、増幅部と電源部とを合せたシステム全体の効率についても、向上させることが可能になるという利点を有する。
【００９１】
尚、ボリウム連動可変電源回路としてチョッパ電源方式による降圧回路を用いたものについては、図１０に示した回路に限らず、例えば図１１に示すような反転チョッパ電源方式の降圧回路を用いても良い。
【００９２】
この場合は、図１０の回路と異なり、図１１に示すように正の電圧＋ＶｃとＧＮＤだけで正の＋Ｖｃと負の−Ｖｃとを生成することができるので、バッテリーなどの単電源を用いた場合に有効である。
【００９３】
【発明の効果】
本発明によれば、可変電源回路方式の増幅装置の電源部に切換電源方式を採用したことで、電源部の損失と増幅部の実用領域における損失を従来に比べて軽減できるため、電源部と増幅部とのトータルの損失が軽減できる。
【００９４】
従って、従来のようにパワートランジスタについて特別な放熱設計を施さなくても良いので、取扱いが容易になり、今まで使用することが困難であった加熱保護回路内蔵のモノリシックＩＣであっても容易に用いることが可能になる。
【００９５】
また、巻線の巻数が多くなり大型で、コストの高いレギュレーション特性の良いＡＣトランスを用いなくても済むので、コストの低減が可能になる。
【００９６】
更に、ハイブリッドＩＣのように電源部と増幅部とを隣接配置するような場合に、お互いの熱干渉を抑制することができる。
【図面の簡単な説明】
【図１】本発明の増幅回路を説明する構成図である。
【図２】本発明の増幅回路の動作を説明する第１の図である。
【図３】本発明の増幅回路の動作を説明する第２の図である。
【図４】本発明の増幅回路の動作を説明する第３の図である。
【図５】本発明の増幅回路の動作を説明する第４の図である。
【図６】本発明の第１の実施形態の増幅回路を説明する図である。
【図７】本発明の第１の実施形態の増幅回路による出力電力と出力電圧との関係を説明するための図である。
【図８】本発明の第１の実施形態の増幅回路による出力電力と損失との関係を説明するための図である。
【図９】本発明に適用されるボリウム連動可変電源回路の他の実施形態を説明する図である。
【図１０】本発明に適用されるボリウム連動可変電源回路の他の実施形態を説明する図である。
【図１１】本発明に適用されるボリウム連動可変電源回路の他の実施形態を説明する図である。
【図１２】従来の増幅回路の回路構成を示す図である。
【図１３】従来の問題点を説明するための図である。
【符号の説明】
１１…プリアンプ
１２Ａ，１２Ｂ…可変電源回路
１３…トランス
１４Ａ，１４Ｂ…第１，第２のブリッジ回路
１５…ボリウム連動可変電源回路
Ｑ１１，Ｑ１２…パワー出力段トランジスタ
ＳＰ…スピーカ
Ｓ１，Ｓ２…スイッチ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an amplifier circuit, and more particularly, to improvement in heat dissipation design and efficiency of an amplifier circuit used for an audio amplifier or the like.
[0002]
[Prior art]
Hereinafter, an amplifier circuit generally used in the related art will be described with reference to the drawings.
[0003]
FIG. 12 is a diagram showing a configuration of a conventional general amplifier circuit.
[0004]
The circuit in FIG. 12 includes a power supply unit having an AC transformer 1 and a bridge circuit 2, an amplifying unit including a preamplifier 3, and power output stage transistors Q1 and Q2, and amplifies an input signal AS and outputs it to a speaker SP. It is a circuit to make it.
[0005]
According to this circuit, after an AC voltage is input from an AC power supply (not shown) to the AC transformer 1, the AC voltage is input to the bridge circuit 2, where it is rectified to generate a DC power supply voltage ± Vcc and applied to the preamplifier 3. You. Using the DC power supply voltage ± Vcc, the preamplifier 3 amplifies the voltage of the input signal AS and outputs the amplified signal to the power output stage transistors Q1 and Q2. The power output stage transistors Q1 and Q2 further amplify the current to generate an amplified signal. It is generated and output to the speaker SP.
[0006]
However, such an amplifier circuit has the following problems.
[0007]
(1) Problems in heat dissipation design In the above circuit, the power output stage transistor that consumes the most current and is applied with the highest voltage may be mounted on a monolithic IC, and in the future due to handling concerns, it may be necessary to do so in the future. Is desired. In most cases, such an IC has a built-in overheat protection circuit. However, if such an IC is mounted on the above-described circuit, a high voltage is constantly applied to the IC. Then, the overheat protection circuit operates, and the normal heat dissipation design makes it impossible to operate according to the actual performance. For this reason, there has been a problem that a special heat radiation design has to be performed, for example, a heat radiation plate is laid over the front and back of the IC to increase a heat radiation area.
[0008]
(2) Problems with the Withstand Voltage of the Amplifier Also, there is a problem that an amplifier with a high withstand voltage is required in terms of the withstand voltage. FIG. 13 is a diagram illustrating regulation characteristics of an AC transformer for generating a DC power supply voltage to be supplied to an amplifier.
[0009]
Normally, the regulation characteristic of the AC transformer draws a downward-sloping curve as shown in FIG. 13, and the voltage generated by the AC transformer is smaller when the power consumption of the amplifier is smaller than when the power consumption is larger. Will be higher. Therefore, it is required to increase the withstand voltage of the amplifier to such an extent that it can cope with a high voltage when the power consumption is small, and there is a problem that the amplifier becomes large and the cost increases.
[0010]
To reduce this problem, it is conceivable to use a transformer having a small difference in voltage generated between when the power consumption is small and when the power consumption is large, and which has good regulation characteristics. In this way, the withstand voltage of the amplifier can be designed to be lower than that of a transformer having normal regulation characteristics.
[0011]
However, there is another problem that the transformer having such good regulation characteristics has the drawback that the number of turns of the winding is increased even at the same voltage, the size is increased, and the cost is high.
[0012]
(3) Problems in Efficiency The DC power supply voltage supplied to the power output stage transistors Q1 and Q2 in the circuit of FIG. 12 needs to always apply a constant high voltage that can correspond to the maximum output.
[0013]
This may be the case where the volume is maximized and the maximum output is always output from the speaker. However, it is rare that the actual audio amplifier requires such a large output.
[0014]
Therefore, an amplified signal smaller than that is actually output. Even in such a case, since the DC power supply voltage capable of coping with the maximum output is always applied to the power output stage transistors Q1 and Q2, there is a problem that the power consumption is increased and the efficiency is reduced. .
[0015]
Therefore, the present inventor has invented a technique disclosed in the specification attached to Japanese Patent Application No. 9-266676 in order to solve the above problem. An example of the present invention will be described. For example, an input signal AS as shown in FIG. 1 is power-amplified, and a preamplifier 11 composed of an analog circuit and a voltage-amplified input signal are current amplified and output to a speaker SP serving as a load. Power output units Q11 and Q12, a volume VR0 for adjusting the volume of the speaker SP, and a low DC power supply voltage is generated when the volume of the speaker SP is low, and the volume is high, in conjunction with the resistance value of the volume VR0. This is a variable power supply circuit system that includes variable power supply circuits 12A and 12B that sometimes generate a high DC power supply voltage and supply it to the power output units Q11 and Q12.
[0016]
Thus, conventionally, a high constant voltage was always supplied to the power output stage transistor so as to correspond to the maximum output even when the volume was low, but according to the above-described technology, it is possible to reduce the loss of power consumption in the power transistor. This eliminates the need for a special heat dissipation design, making it easier to handle and making it easy to use even a monolithic IC with a built-in heating protection circuit, which has been difficult to use until now. become.
[0017]
Further, since it is not necessary to use a transformer having a large number of windings and a large size which is expensive and has good regulation characteristics, it is possible to reduce the size and cost.
[0018]
Furthermore, since the DC power supply voltage is fluctuated in conjunction with the resistance value of the volume, the power consumption of the power output stage transistor, which consumes the largest amount of power, differs from the conventional case where a voltage higher than necessary is supplied to the transistor of the power output stage. Since the power loss can be reduced, the efficiency of the transistor can be improved.
[0019]
[Problems to be solved by the invention]
According to the above-described variable power supply circuit system, the volume resistance of the signal input and the DC power supply voltage of the amplifying unit are interlocked and varied, and a voltage according to the volume is supplied, so that the loss (Pd) of the amplifying unit can be reduced. In this case, the loss (Pd) in the conventional amplifying unit is borne by the power supply unit. In this case, when a circuit of a dropper power supply system is used in the power supply unit, Since the total loss (Pd) of the power supply section and the amplification section does not change, when this section is formed as a HIC (hybrid IC) and both are arranged adjacent to each other, there is no conventional variable power supply circuit due to thermal interference or the like. There was a problem that it would not be different from the case.
[0020]
Therefore, an object of the present invention is to provide an amplifier circuit that reduces the total loss of the power supply unit and the amplifier unit.
[0021]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional disadvantages, and as shown in FIG. 6, a first bridge circuit for generating a DC power supply voltage ± VccL for supplying a voltage to a volume-linked variable power supply circuit 15 via an AC transformer 13. 14A and a second bridge circuit 14B for generating a second DC power supply voltage ± VccH higher than the DC power supply voltage ± VccL, and the second bridge circuit 14B and the variable power supply circuit are provided. 15, switches S1 and S2 for separating the two are provided.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same components as those in the related art are denoted by the same reference numerals, and the description is simplified.
[0023]
(1) First Embodiment The feature of the amplifier circuit of the present invention is that a DC power supply voltage supplied to a variable power supply circuit via a switch mechanism driven in response to a volume change in a conventional variable power supply circuit type amplifier circuit. ± Vcc can be switched and supplied to a first DC power supply voltage (± VccL) and a second DC power supply voltage (± VccH).
[0024]
FIG. 1 is a diagram showing an amplifying unit applied to the amplifying circuit of the present invention. The basic configuration and operation will be described. The amplifying unit serves as a preamplifier 11, power output transistors Q11 and Q12, and a load. An audio amplifier that includes a speaker SP, a volume VR0 for adjusting the volume of the speaker SP, and variable power circuits 12A and 12B, and amplifies the input signal AS0 and outputs sound from the speaker SP.
[0025]
The volume VR0 adjusts the level of the input signal AS0 input to itself and outputs it to the non-inverting input + of the preamplifier 11 as AS1.
[0026]
The preamplifier 11 is a circuit that amplifies the voltage of the input signal AS1 whose level has been adjusted by the volume VR0 and outputs the amplified signal to the power output stage transistors Q11 and Q12. Note that a negative feedback circuit NF is provided from the speaker SP serving as a load to the inverted input − of the preamplifier 11.
[0027]
The power output stage transistors Q11 and Q12 use the DC power supply voltages + Vc and -Vc supplied from the variable power supply circuits 12A and 12B to current-amplify the voltage-amplified input signal AS1 and output the amplified signal to the speaker SP. .
[0028]
The variable power supply circuits 12A and 12B generate a positive DC power supply voltage + Vc and a negative DC power supply voltage -Vc, respectively, which fluctuate in accordance with the resistance value of the volume VR0, and are connected to collectors of the power output stage transistors Q11 and Q12. It is a circuit to supply each.
[0029]
Hereinafter, the operation of the circuit shown in FIG. 1 will be described with reference to FIGS.
[0030]
FIG. 2 is a diagram showing the input signal AS0, and FIG. 3 is a diagram showing the input signal AS1 adjusted by the volume VR0. FIG. 4 is a diagram showing the relationship between the DC power supply voltages + Vc, -Vc and the output voltage Vo.
[0031]
First, for example, an input signal AS0 as shown in FIG. 2 is input to the volume VR0, where the voltage level is adjusted and input to the non-inverting input + of the preamplifier 11.
[0032]
Next, as shown in FIG. 3, the input signal AS1 whose level has been adjusted is voltage-amplified by the preamplifier 11 and supplied to the bases of the power output stage transistors Q11 and Q12.
[0033]
Next, the voltage-amplified input signal is current-amplified by the power output stage transistors Q11 and Q12, and output to the speaker SP as an output voltage Vo. The DC power supply voltage ± Vc supplied to the power output stage transistors Q11 and Q12 is a voltage as shown in FIG. 4. The following describes how this voltage ± Vc is generated and supplied. explain.
[0034]
This DC power supply voltage ± Vc is generated by variable power supply circuits 12A and 12B, respectively, and varies in conjunction with the resistance value of volume VR0.
[0035]
That is, when the volume of the speaker is small and the output voltage Vo is low, a low DC power supply voltage ± Vc (± VcL) is generated. When the volume of the speaker is large and the output voltage Vo is high, the high DC power supply voltage ± Vc (± VcL) is generated. VcH) will be generated.
[0036]
FIG. 5 shows the relationship between the fluctuation of the output voltage Vo and the fluctuation of the DC power supply voltage ± Vc. In FIG. 5, when the resistance value of the volume is changed so as to increase the output voltage Vo, it is understood that the DC power supply voltage ± Vc increases in conjunction therewith.
[0037]
Conventionally, a high constant voltage due to the regulation characteristics of the AC transformer has always been supplied to the power output stage transistor. However, by varying the DC power supply voltage in this way, the loss of the power output stage transistor is reduced. The configuration up to this point is the same as that of the conventional amplification unit.
[0038]
The feature of the present invention is that, as shown in FIG. 6, the AC voltage is reduced to a low DC power supply voltage ± VccL and a high DC power supply voltage ± VccH by an AC transformer 13 and first and second bridge circuits 14A and 14B described later. Rectification is performed, and these are used as a supply voltage of a volume-linked variable power supply circuit 15 (corresponding to the above-described variable power supply circuits 12A and 12B), and the first and second bridge circuits 14A and 14B can be switched. Switches S1 and S2 are provided.
[0039]
The switches S1 and S2 are opened and closed according to the position (resistance value) of the volume VR1. When the volume of the speaker SP is small and the output voltage Vo is small, the switches S1 and S2 are opened. In operation, the low DC power supply voltage ± VccL rectified by the first bridge circuit 14A is supplied to the volume-linked variable power supply circuit 15. When the volume of the speaker SP is large and the output voltage Vo is large, the switches S1 and S2 are closed, and the high DC power supply voltage ± VccH rectified by the second bridge circuit 14B is applied to the volume-linked variable power supply. It is supplied to the circuit 15.
[0040]
Hereinafter, the configuration of the power supply unit, which is a feature of the amplifier circuit of the present invention, will be described with reference to FIG.
[0041]
The power supply unit includes an AC transformer 13, first and second bridge circuits 14A and 14B, a smoothing circuit (in the present embodiment, a smoothing capacitor is used as shown in FIG. 6), as shown in FIG. The AC transformer 13 further has a volume-linked variable power supply circuit 15 for transforming the AC voltage and outputting it to the first and second bridge circuits 14A and 14B, respectively. Each of the bridge circuits 14A and 14B is composed of four diodes and is a circuit for rectifying the voltage transformed by the AC transformer 13, and when the switches S1 and S2 are opened, the first bridge circuits 14A and 14B A low DC power supply voltage ± VccL is supplied to the volume-linked variable power supply circuit 15 via the smoothing circuit, and when the switches S1 and S2 are closed, the high DC power supply voltage is supplied via the second bridge circuit 14B and the smoothing circuit. The voltage ± VccH is supplied to the volume-linked variable power supply circuit 15.
[0042]
Further, the volume-linked variable power supply circuit 15 is a circuit that generates a DC power supply voltage ± Vc that fluctuates in accordance with the resistance value of a volume VR1 described later and supplies the generated DC power supply voltage ± Vc to the power output stage transistors Q11 and Q12 described later.
[0043]
As shown in FIG. 6, this circuit includes an interlocking regulator VR2 whose value fluctuates in conjunction with the volume VR1, comparators CP1 and CP2 provided symmetrically with respect to the ground potential GND, and outputs of the comparators CP1 and CP2. And power transistors T1 and T2 respectively connected to the power transistors T1 and T2.
[0044]
Next, the configuration of the amplification unit of the amplification circuit of the present invention will be described.
[0045]
The volume VR1 is an element for adjusting the voltage level of the input signal AS.
[0046]
The preamplifier 11 is a circuit that amplifies the voltage of the input signal AS whose voltage level has been adjusted by the volume VR1.
[0047]
The power output stage transistors Q11 and Q12 are push-pull connected power transistors, and current-amplify the input signal voltage-amplified by the preamplifier 11 and supply the amplified signal to the speaker SP.
[0048]
The comparators CP11 and CP12 are circuits that compare a fixed reference voltage with a voltage defined by the interlocking regulator VR2, and change the emitter voltages of the power transistors T1 and T2 according to the comparison result. According to this circuit, first, an AC voltage is applied from an AC power supply (not shown) to the AC transformer 13, where it is transformed and output to the bridge circuit.
[0049]
This AC voltage is rectified by the first and second bridge circuits 14A and 14B, and the DC power supply voltage (± VccL, ± VccH) selected by the opening and closing operations of the switches S1 and S2 is adjusted by the volume-linked variable power supply circuit 15. Supplied to
[0050]
Here, as shown in FIG. 6, when the output is low, the switches S1 and S2 are open, and based on the DC power supply voltage ± VccL rectified by the first bridge circuit 14A, the DC-linked variable power supply circuit 15 Power supply voltage ± VcL is generated and supplied to the collectors of power output stage transistors Q11 and Q12. When the output is high, the switches S1 and S2 are closed, and the DC power supply voltage ± VcH is generated by the volume-linked variable power supply circuit 15 based on the DC power supply voltage ± VccH rectified by the second bridge circuit 14B. It is supplied to the collectors of the power output stage transistors Q11 and Q12. The diodes D1 and D2 are diodes for preventing backflow when the switches S1 and S2 are closed.
[0051]
On the other hand, in the amplifying unit, the input signal AS is output to the volume VR1, and the voltage level is adjusted by the volume VR1 and input to the non-inverting input + of the preamplifier 11.
[0052]
The input signal AS whose voltage level has been adjusted is amplified by the preamplifier 11. The voltage-amplified input signal is current-amplified by the power output stage transistors Q11 and Q12 and supplied to the speaker SP, and a sound is output from the speaker SP.
[0053]
Here, the operation of the volume-linked variable power supply circuit 15 will be described. The linked volume VR2 provided in the volume-linked variable power supply circuit 15 is set so that its resistance value fluctuates in conjunction with the volume VR1.
[0054]
That is, the resistance of the interlocking regulator VR2 increases as the resistance of the regulator VR1 increases, and the resistance of the interlocking regulator VR2 decreases as the resistance of the regulator VR2 decreases.
[0055]
Focusing only on the positive side operation, as the resistance value of the volume VR1 increases (the volume decreases), the resistance value of the interlocking volume VR2 also increases. On the other hand, the interlocking regulator VR2 defines the voltage of the inverting input of the comparator CP1. Therefore, when the resistance value of the regulator VR1 increases and the resistance value of the interlocking regulator VR2 increases, the voltage of the inverting input of the comparator CP1 increases, so that the output of the comparator CP1 decreases and the emitter voltage of the power transistor T1 decreases. Works.
[0056]
Therefore, the DC power supply voltage ± VcL generated from the power supply ± VccL decreases. This is the same for the operation on the negative side.
[0057]
Conversely, when the resistance value of the volume VR1 decreases and the volume increases, the resistance value of the interlocking volume VR2 also decreases, and the voltage on the inverting input side of the comparators CP1 and CP2 decreases. Since the transition is made to increase the emitter voltage, the DC power supply voltage ± VcH increases.
[0058]
As described above, the DC power supply voltage ± Vc increases when the volume increases due to the fluctuation in the resistance value of the volume, and decreases when the volume decreases. In this manner, in the present embodiment, the DC power supply voltage supplied to the power output stage transistors Q11 and Q12 can be varied in accordance with the volume of the speaker, so that the power output stage transistors The variable power supply circuit 15 is driven at ± VccL at the time of low output by applying the switching power supply method in the power supply section without applying a high voltage that can always cope with the maximum output. By driving the amplifier and driving the variable power supply circuit 15 at ± VccH at high output and driving the amplifier with a controlled voltage, the total loss (Pd) in the power supply circuit and the amplifier circuit is reduced. be able to.
[0059]
FIG. 7 is a diagram for explaining the relationship between the output power (Po) and the output voltage (Vo), and FIG. 8 is a diagram for explaining the relationship between the output power (Po) and the loss (Pd). .
[0060]
In the present invention, as shown in FIG. 7, the first regulation characteristic (A) and the second regulation characteristic (B) are switched and used (see the slope of the voltage ± Vc) as shown in FIG. The total loss (Pd) can be reduced by the loss (Pd) corresponding to the shaded portion shown. That is, in response to a change in output power (Po) (a change in volume), the variable power supply circuit 15 is driven with the DC power supply voltage ± VccL as described above, and the amplifier is driven with the controlled voltage (the volume is small). The variable power supply circuit 15 is driven by the DC power supply voltage ± VccH, and the amplifier is driven by the controlled voltage (the volume is large). The switches S1 and S2 are opened and closed according to the position (resistance value) of the volume VR1 as described above. Specifically, when an electronic volume is used, a microcomputer is used. The switches S1 and S2 may be opened and closed in response to a signal, and the switches S1 and S2 may be opened and closed when a voltage value compared with a certain reference voltage value exceeds the reference voltage.
[0061]
Further, the loss (Pd) of the power supply unit of the present invention shown by the solid line (A) in FIG. 8 is significantly reduced as compared with the loss (Pd) of the conventional power supply unit shown by the dashed line (B). , The total loss (Pd) of the present invention shown by the solid line (C) is also smaller than the conventional total loss (Pd) shown by the dashed line (D). Note that the two-dot chain line (E) shows the loss (Pd) of the amplifying unit according to the conventional and the present invention using the variable power supply system.
[0062]
(2) Second Embodiment Hereinafter, a second embodiment of the present invention will be described with reference to FIG. The description of the same configuration as that of the first embodiment will be omitted to avoid duplication.
[0063]
The feature of this embodiment is that a circuit of a dropper power supply system shown in FIG. 9 is used as the volume-linked variable power supply circuit, and the configuration and operation will be described below.
[0064]
The volume-linked variable power supply circuit according to the present embodiment includes power transistors Q21 and Q22, transistors TR1 and TR2, first, second, third, fourth, and fifth resistors R1, R2, R3, R4, and R5. This is a step-down circuit having a volume VR11.
[0065]
The power transistors Q21 and Q22 are provided on both the positive and negative sides of the ground potential GND, and operate to generate a DC power supply voltage ± Vc to be supplied to the power output stage transistor from the DC power supply voltage ± Vcc. It is. Similar to the interlocking regulator VR2 of the first embodiment, the interlocking volume VR11 is a volume whose resistance value changes in conjunction with the resistance value of the volume for adjusting the volume.
[0066]
In the above circuit, when the resistance value of the interlocking regulator VR11 changes, the base potential of the transistor TR1 determined by the first resistor R1, the second resistor R2, and the fifth resistor R5 changes, and the collector of the transistor TR1 changes. The current fluctuates according to the fluctuation.
[0067]
That is, for the positive output voltage + Vc, the sum of the voltage Vz of the Zener diode and the voltage VBE between the base and the emitter of the transistor TR1 becomes a reference voltage, and this voltage is used as the first resistance R1, This is compared with the base potential of the transistor TR1 determined by the second resistor R2, the fifth resistor R5, and the interlocking volume VR11.
[0068]
When the base current of the transistor TR1 decreases due to a decrease in the resistance value of the interlocking regulator VR11, the collector current of the transistor TR1 also decreases, and the base current of the power transistor Q21 increases. It also increases. Conversely, when the base current of the transistor TR1 increases, the output voltage + Vc decreases. Therefore, the positive output voltage + Vc fluctuates in conjunction with the resistance value of the interlocking regulator VR11.
[0069]
On the negative side, the emitter voltage of the power transistor Q22 is defined by the transistor TR2, and the base potential of the transistor TR2 is the potential difference between the positive output voltage + Vc and the negative output voltage -Vc, It is determined by the bleeder ratio of the resistors R3 and R4. On the negative side, when the positive output voltage + Vc decreases due to the operation of the positive side circuit, the base potential of the transistor TR2 also decreases by the bleeder ratio corresponding to the decrease (absolute value of the base potential decreases). When the positive output voltage + Vc increases, the base potential of the transistor TR2 also increases (the absolute value of the base potential increases) by the increased bleeder ratio.
[0070]
When the base potential of the transistor TR2 increases, the emitter voltage of the power transistor Q22 increases and the negative output voltage −Vc also increases. Conversely, when the base potential of the transistor TR2 decreases, the emitter voltage of the power transistor Q22 increases. As a result, the negative output voltage −Vc also decreases.
[0071]
As described above, the negative output voltage -Vc varies according to the variation of + Vc in accordance with the variation range of the positive output voltage + Vc. Therefore, when the bleeder ratio of the resistors R3 and R4 is 1, the positive output voltage -Vc is changed. + Vc and the negative output voltage -Vc are symmetric voltages.
[0072]
Usually, in order to obtain a symmetrical voltage between positive and negative, it is a general circuit configuration to configure a circuit symmetrical with respect to the ground potential. However, in the above circuit, first, a positive output voltage + Vc is linked. Since the negative side circuit is controlled by controlling the resistance value of the resistor VR11 and then controlling the voltage between the positive output voltage + Vc and the negative output voltage -Vc, as shown in FIG. There is no need to configure a symmetrical circuit.
[0073]
Therefore, on the negative side, a zener diode Vz, a resistor, and the like, which are necessary elements on the positive side, become unnecessary, and a symmetrical output voltage ± Vc can be generated with a simpler circuit configuration. It is.
[0074]
The values of the voltage ± Vc obtained by the above circuit are respectively
[0075]
(Equation 1)

[0076]
(Equation 2)

[0077]
(Equation 3)

VBE1 is a base-emitter voltage of the transistor TR1, and VBE2 is a base-emitter voltage of the transistor TR2. VR is the resistance value of the volume VR11.
[0078]
From the above equation, when the resistance value VR of the volume VR11 increases and the volume of the speaker decreases, the DC power supply voltage ± Vc decreases. Conversely, when the VR decreases and the volume of the speaker increases, the DC power supply voltage ± Vc increases. It turns out that it becomes.
[0079]
The circuit according to the present embodiment has the advantages that it can be realized with a relatively simple circuit configuration and that the cost is relatively low, in addition to the functions and effects described in the first embodiment.
[0080]
(3) Third Embodiment Hereinafter, a third embodiment of the present invention will be described with reference to FIG. Note that the description of items common to the first and second embodiments will be omitted to avoid duplication.
[0081]
The feature of this embodiment is that a step-down circuit of a chopper power supply type shown in FIG. 10 is used as the volume-linked variable power supply circuit, and the configuration and operation will be described below.
[0082]
The volume-linked variable power supply circuit of the present embodiment is a circuit having power transistors Q31 and Q32, pulse modulation circuits 21 and 22, comparators 23 and 24, linked volumes VR21 and VR22, diodes D21 and D22, and coils L21 and L22. , A voltage step-down circuit that generates a DC power supply voltage ± Vc that fluctuates in conjunction with the resistance value of a volume control volume (not shown) and supplies it to the power output stage transistor of the amplifier.
[0083]
The power transistors Q31 and Q32 are switching elements provided on both the positive and negative sides of the ground potential GND, and are turned on / off so that the DC power supply supplied to the power output stage transistor from the DC power supply voltage ± Vcc. This is an element for generating the voltage ± Vc.
[0084]
The pulse modulation circuits 21 and 22 are circuits that perform PWM (Pulse Width Modulation) modulation of signals output from comparators 23 and 24 described below and output the signals to the bases of the power transistors Q31 and Q32.
[0085]
The comparators 23 and 24 are circuits that compare the reference voltages Vr1 and Vr2 with the voltages set by the interlocking regulators VR21 and VR22, and output the comparison results to the pulse modulation circuits 21 and 22, respectively. The interlocking regulators VR21 and VR22 are, like the interlocking regulator VR2 of the first embodiment, variable in resistance in conjunction with the resistance of the volume for volume adjustment.
[0086]
Hereinafter, the operation of this circuit will be described. The resistance values of the interlocking regulators VR21 and VR22 fluctuate in conjunction with the resistance value of a volume control regulator (not shown). For example, when the resistance value of the volume increases and the volume of the speaker decreases, the resistance values of the interlocking volumes VR21 and VR22 also increase, and the potential of the inverting input − of the comparators 23 and 24 increases. Conversely, when the resistance value of the volume decreases and the volume of the speaker increases, the resistance values of the interlocking volumes VR21 and VR22 also decrease, and the potential of the inverting input of the comparators 23 and 24 decreases.
[0087]
When the potential of the inverting input-rises and exceeds the reference voltages Vr1 and Vr2, the outputs of the comparators 23 and 24 become "L". Also, when the potential of the inverting input − falls below the reference voltages Vr1 and Vr2, the outputs of the comparators 23 and 24 become “H”.
[0088]
As described above, the outputs of the comparators 23 and 24 fluctuate according to the resistance values of the interlocking regulators VR21 and VR22, that is, the resistance values of the volume adjusting volume. The outputs of the comparators 23 and 24 are PWM-modulated by the pulse modulation circuits 21 and 22, and the modulation results are output to the bases of the power transistors Q31 and Q32.
[0089]
Thus, the power transistors Q31 and Q32 perform an ON / OFF operation, and the ON / OFF duty ratio is determined by the outputs of the pulse modulation circuits 21 and 22. If the duty ratio is large, the DC power supply voltage ± Vc supplied to the transistor of the power output stage (not shown) increases, and if the duty ratio is small, the DC power supply voltage ± Vc decreases. When the resistance values of the interlocking regulators VR21 and VR22 which fluctuate in response to the fluctuations, the DC power supply voltage ± Vc also fluctuates.
[0090]
As described above, in the present embodiment, the circuit of the present invention in which the DC power supply voltage is made variable in accordance with the sound volume is realized, so that the same effects as those of the first and second embodiments are obtained. Since the dropper power supply circuit as in the first and second embodiments is not used and the chopper power supply circuit with relatively small power consumption loss is used, the circuit described in the first and second embodiments is the same as that in the first and second embodiments. Differently, there is an advantage that not only the efficiency in the power output stage can be improved, but also the efficiency of the entire system including the amplifying unit and the power supply unit can be improved.
[0091]
The circuit using the step-down circuit based on the chopper power supply system as the volume-linked variable power supply circuit is not limited to the circuit shown in FIG. 10, but may be a step-down circuit based on the inverted chopper power supply system as shown in FIG. .
[0092]
In this case, unlike the circuit of FIG. 10, as shown in FIG. 11, positive + Vc and negative −Vc can be generated only by the positive voltage + Vc and GND, so that a single power source such as a battery is used. It is effective in the case.
[0093]
【The invention's effect】
According to the present invention, by employing the switching power supply system for the power supply unit of the variable power supply circuit-type amplifying device, the loss of the power supply unit and the loss in the practical area of the amplifier unit can be reduced as compared with the prior art. The total loss with the amplifier can be reduced.
[0094]
Therefore, it is not necessary to provide a special heat radiation design for the power transistor as in the prior art, so that the power transistor is easy to handle, and even if it is a monolithic IC with a built-in heating protection circuit, which has been difficult to use until now, it is easy. It can be used.
[0095]
Further, since the number of windings of the winding is increased and a large-sized AC transformer having a high cost and good regulation characteristics is not required, the cost can be reduced.
[0096]
Furthermore, when the power supply unit and the amplifier unit are arranged adjacent to each other as in a hybrid IC, thermal interference between them can be suppressed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an amplifier circuit of the present invention.
FIG. 2 is a first diagram illustrating the operation of the amplifier circuit of the present invention.
FIG. 3 is a second diagram illustrating the operation of the amplifier circuit of the present invention.
FIG. 4 is a third diagram illustrating the operation of the amplifier circuit of the present invention.
FIG. 5 is a fourth diagram illustrating the operation of the amplifier circuit of the present invention.
FIG. 6 is a diagram illustrating an amplifier circuit according to the first embodiment of the present invention.
FIG. 7 is a diagram for explaining a relationship between output power and output voltage by the amplifier circuit according to the first embodiment of the present invention.
FIG. 8 is a diagram for explaining a relationship between output power and loss by the amplifier circuit according to the first embodiment of the present invention.
FIG. 9 is a diagram illustrating another embodiment of a volume-linked variable power supply circuit applied to the present invention.
FIG. 10 is a diagram illustrating another embodiment of a volume-linked variable power supply circuit applied to the present invention.
FIG. 11 is a diagram illustrating another embodiment of a volume-linked variable power supply circuit applied to the present invention.
FIG. 12 is a diagram illustrating a circuit configuration of a conventional amplifier circuit.
FIG. 13 is a diagram for explaining a conventional problem.
[Explanation of symbols]
11 Preamplifiers 12A and 12B Variable power supply circuit 13 Transformers 14A and 14B First and second bridge circuits 15 Volume-variable variable power supply circuits Q11 and Q12 Power output stage transistors SP Speakers S1 and S2 Switches

Claims (3)

A preamplifier that amplifies the voltage of the input signal,
A power output unit that current-amplifies the voltage-amplified input signal and outputs the amplified signal to a speaker serving as a load.
An amplifier comprising a first volume for adjusting the volume of the speaker;
In conjunction with the variation of the first resistance value of the first volume, a second volume to change the second resistance value, and when the volume of the speaker is small low level in response to the change of the second resistance value It generates a DC power supply voltage, a variable power supply circuit for supplying to said power output section to generate a high level of the DC power supply voltage in accordance with a change in the second resistance value when the volume of the speaker is large,
A first power supply circuit connected to an intermediate terminal of the AC transformer, rectifying the AC voltage transformed by the AC transformer and generating a first DC power supply voltage to be supplied to the variable power supply circuit;
A second DC power supply connected to both terminals of the AC transformer, rectifying the AC voltage transformed by the AC transformer and generating a second DC power supply voltage higher than the first DC power supply voltage supplied to the variable power supply circuit; A power supply unit comprising a power supply circuit ;
The power supply unit is provided with a switching circuit capable of switching the first and second DC power supply voltages in accordance with the first or second volume position, and the first and second DC power supply voltages are switched when the output voltage of the power output unit is small. Wherein the DC power supply voltage is supplied and the second DC power supply voltage is supplied when the output voltage of the power output section is large. The variable power supply circuit includes a transistor that varies a collector potential according to the second volume that is interlocked with the first volume that adjusts a volume, and a transistor that varies a collector potential of the transistor. 2. The amplifier circuit according to claim 1, further comprising a power transistor that generates an output voltage that fluctuates in conjunction with said second volume. The variable power supply circuit includes a comparator to which a voltage fluctuating with the second volume and a reference voltage interlocked with the first volume for adjusting a volume are input, and a pulse modulation circuit that performs pulse width modulation on an output signal of the comparator. 2. The amplifier circuit according to claim 1, further comprising: a power transistor controlled by a pulse signal from the pulse modulation circuit to generate an output voltage that varies in conjunction with the second volume.

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