JPH07240636A - Power amplifier - Google Patents
Power amplifierInfo
- Publication number
- JPH07240636A JPH07240636A JP6056613A JP5661394A JPH07240636A JP H07240636 A JPH07240636 A JP H07240636A JP 6056613 A JP6056613 A JP 6056613A JP 5661394 A JP5661394 A JP 5661394A JP H07240636 A JPH07240636 A JP H07240636A
- Authority
- JP
- Japan
- Prior art keywords
- power supply
- level
- circuit
- power
- output
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は音声信号を増幅してスピ
ーカを駆動する電力増幅器に係り、とくにインピーダン
スの不適正なスピーカが接続される場合の発熱対策とし
て電源電圧を切り替え可能にした電力増幅器に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier for amplifying a voice signal to drive a speaker, and more particularly to a power amplifier capable of switching a power supply voltage as a countermeasure against heat generation when a speaker having an incorrect impedance is connected. Regarding
【０００２】[0002]
【従来の技術】スピーカには標準インピーダンスのもの
のほか標準インピーダンスより小さいインピーダンスの
ものがあり、標準インピーダンス用のパワーアンプに対
しユーザが標準より小さいインピーダンスのスピーカを
接続した場合、駆動電流が増え過ぎて過度の発熱を生
じ、最悪の場合、パワーアンプのトランジスタが破壊し
てしまうことがある。このため、従来からパワーアンプ
の動作電源電圧を切り替え可能とし、標準より小さいイ
ンピーダンスのスピーカ接続時には電源電圧を低くでき
るようにし、駆動電流を抑えて発熱量を抑えられるよう
にしてある。一例として図４に示すホーム用パワーアン
プの如く、電源回路１がＡＣ100V電源を降圧トランス２
で降圧し、二次コイル３の出力側に設けたダイオードブ
リッジ回路４と大容量コンデンサＣ１，Ｃ２により整
流、平滑化して±Ｖccの電源電圧を作成する場合、二次
コイル３にタップ５Ａ，５Ｂ、６Ａ，６Ｂを設け、ダイ
オードブリッジ回路４への入力をスイッチ７と８を連動
してマニュアル操作で５Ａ，５Ｂ側または６Ａ，６Ｂ側
に切り替えて、電源電圧を±Ｖcc（１）と±Ｖcc（２）
の２段階に切り替え可能にしたものがある（但し、Ｖcc
（１）＞Ｖcc（２））。2. Description of the Related Art Some speakers have a standard impedance and others have a smaller impedance than the standard impedance. When a user connects a speaker having an impedance smaller than the standard to a power amplifier for the standard impedance, the driving current increases too much. Excessive heat generation may occur, and in the worst case, the transistor of the power amplifier may be destroyed. For this reason, conventionally, the operating power supply voltage of the power amplifier can be switched, the power supply voltage can be lowered when a speaker having an impedance smaller than the standard is connected, and the drive current can be suppressed to suppress the heat generation amount. As an example, as in the home power amplifier shown in FIG. 4, the power supply circuit 1 converts the AC100V power supply into the step-down transformer 2
When the power supply voltage of ± Vcc is created by rectifying and smoothing with the diode bridge circuit 4 provided on the output side of the secondary coil 3 and the large-capacity capacitors C1 and C2, taps 5A and 5B are applied to the secondary coil 3. , 6A, 6B are provided, and the input to the diode bridge circuit 4 is manually switched to 5A, 5B side or 6A, 6B side by interlocking the switches 7 and 8, and the power supply voltage is ± Vcc (1) and ± Vcc. (2)
There is one that can be switched to two stages (however, Vcc
(1)> Vcc (2)).
【０００３】また、他の例として図５に示す車載用パワ
ーアンプの如く、電源回路９がバッテリ電圧＋Ｂを昇圧
トランス１０の一次コイル１１に印加し、一次コイル両
端とアース間に設けたスイッチング用のトランジスタＱ
１，Ｑ２をコントローラ１２によりスイッチング制御
し、二次コイル１３に大きな交流電圧を発生させ、二次
コイル１３の出力側に設けたダイオードブリッジ回路１
４と大容量コンデンサＣ３，Ｃ４により整流、平滑化し
て±Ｖccを作成し、＋Ｖccを抵抗Ｒ１，Ｒ２で分圧した
電圧が一定となるようにコントローラ１２でＰＷＭ制御
して定電圧とする場合、直列接続した抵抗Ｒ３とスイッ
チ１５を抵抗Ｒ１と並列に設け、スイッチ１５を開くか
閉じることで電源電圧を±Ｖcc（１）´と±Ｖcc（２）
´の２段階に切り替え可能にしたものがある（但し、Ｖ
cc（１）´＞Ｖcc（２）´）。As another example, as in a vehicle power amplifier shown in FIG. 5, a power supply circuit 9 applies a battery voltage + B to a primary coil 11 of a step-up transformer 10 for switching provided between both ends of the primary coil and ground. Transistor Q
The diode bridge circuit 1 provided on the output side of the secondary coil 13 controls the switching of 1 and Q2 by the controller 12 to generate a large AC voltage in the secondary coil 13.
In the case where ± Vcc is created by rectifying and smoothing with 4 and the large-capacity capacitors C3 and C4, and the voltage obtained by dividing + Vcc by the resistors R1 and R2 is PWM controlled by the controller 12 to be a constant voltage, A resistor R3 and a switch 15 connected in series are provided in parallel with the resistor R1, and the power supply voltage is ± Vcc (1) 'and ± Vcc (2) by opening or closing the switch 15.
There is one that can be switched to two stages of '(However, V
cc (1) '> Vcc (2)').
【０００４】[0004]
【発明が解決しようとする課題】けれども、スイッチ
７，８や１５はマニュアルで操作を行うため、ユーザが
スイッチを開とするか閉とするか間違えることがあり、
かかるとき、加熱対策をとれず、特に、小インピーダン
ススピーカを接続しているのに、スイッチ７，８をタッ
プ５Ａ，５Ｂ側に切り替えたり、スイッチ１５を開いた
りしたときパワーアンプを破壊してしまう恐れがある。
この点につき、温度センサでパワーアンプの温度を検出
し、設定値以下の温度のときは電源電圧を大きくし、電
源電圧を小さくさせて負荷インピーダンスの大小に対応
するようにした発明がある（特開平3-123108号）。しか
しながら、負荷インピーダンスが小さいときに音量を大
きくして聴取していた場合、トランジスタが発熱してか
らケースが昇温し、温度センサの温度が上がって検出温
度が設定値を越えるまでにはどうしても時間的な遅れが
生じることから、給電電圧の切り替えが間に合わず、ト
ランジスタを熱破壊してしまう恐れがある。この発明
は、上記した従来技術の問題に鑑み、確実に負荷インピ
ーダンスの大小を判別でき、電源電圧を適正に切り替え
て加熱の防止を図ることのできる電力増幅器を提供する
ことを目的とする。However, since the switches 7, 8 and 15 are manually operated, the user may mistakenly open or close the switch.
In such a case, it is not possible to take measures against heating, and particularly when the switches 7 and 8 are switched to the taps 5A and 5B side or the switch 15 is opened even if the small impedance speaker is connected, the power amplifier is destroyed. There is a fear.
With respect to this point, there is an invention in which the temperature of the power amplifier is detected by a temperature sensor, and when the temperature is lower than a set value, the power supply voltage is increased and the power supply voltage is decreased to respond to the load impedance. Kaihei 3-123108). However, when listening with a high volume when the load impedance is low, it takes time for the temperature of the temperature sensor to rise and the detected temperature to exceed the set value after the transistor heats up. However, there is a risk that the switching of the power supply voltage will not be in time and the transistor will be thermally destroyed. The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a power amplifier that can reliably determine the magnitude of the load impedance and appropriately switch the power supply voltage to prevent heating.
【０００５】[0005]
【課題を解決するための手段】本発明は、音声信号を電
力増幅して出力側に接続されたスピーカ負荷を駆動する
電力増幅手段と、電力増幅手段に動作電源を供給する電
源手段を備えた電力増幅器において、電力増幅器の入力
電圧レベルまたは出力電圧レベルを検出する第１の検出
手段と、電力増幅器の出力電流レベルを検出する第２の
検出手段と、電力増幅器の入力電圧レベルまたは出力電
圧レベルに対する電力増幅器の出力電流レベルの大きさ
から負荷のインピーダンスの大小を判別する判別手段
と、判別手段での判別結果に基づき電源手段の発生する
電源電圧を切り替えさせる切り替え手段とを備えたこと
を特徴としている。The present invention comprises power amplification means for power-amplifying an audio signal to drive a speaker load connected to the output side, and power supply means for supplying operating power to the power amplification means. In a power amplifier, a first detecting means for detecting an input voltage level or an output voltage level of the power amplifier, a second detecting means for detecting an output current level of the power amplifier, and an input voltage level or an output voltage level of the power amplifier. And a switching unit that switches the power supply voltage generated by the power supply unit based on the determination result of the determination unit. I am trying.
【０００６】[0006]
【作用】本発明によれば、電力増幅器の入力電圧レベル
または出力電圧レベルと、出力電流レベルを検出し、入
力電圧レベルまたは出力電圧レベルに対する出力電流レ
ベルの大きさから負荷のインピーダンスの大小を判別
し、判別結果に基づき電源手段の発生する電源電圧を切
り替える。これにより、確実に負荷インピーダンスの大
小を判別することができ、電源電圧の適正切り替えが可
能となる。よって、負荷インピーダンスの小さいスピー
カを接続した場合でも確実に加熱による熱破壊を防止で
きる。According to the present invention, the input voltage level or output voltage level of the power amplifier and the output current level are detected, and the magnitude of the impedance of the load is discriminated from the magnitude of the input current level or the output current level with respect to the output voltage level. Then, the power supply voltage generated by the power supply means is switched based on the determination result. As a result, the magnitude of the load impedance can be reliably determined, and the power supply voltage can be appropriately switched. Therefore, even when a speaker with a small load impedance is connected, it is possible to reliably prevent thermal destruction due to heating.
【０００７】また、他の発明によれば、第２の検出手段
の入力を電力増幅手段の出力段を構成するトランジスタ
のエミッタ抵抗両端から取り出すようにしたので、出力
電流レベルの検出の為に特別な検出抵抗を設ける必要が
ない。また、更に他の発明によれば、判別手段に入力の
立ち上がりを検出する立ち上がり検出手段を設け、判別
手段は負荷のインピーダンスの大小判別を立ち上がり検
出手段が入力の立ち上がりを検出した時点で行うように
したので、無入力時に電源電圧が変動し異音を発するの
を防止できる。According to another aspect of the invention, since the input of the second detecting means is taken out from both ends of the emitter resistance of the transistor forming the output stage of the power amplifying means, it is special for detecting the output current level. It is not necessary to provide a special detection resistor. According to still another aspect of the invention, the discriminating means is provided with a rising edge detecting means for detecting the rising edge of the input, and the discriminating means judges the magnitude of the impedance of the load when the rising edge detecting means detects the rising edge of the input. Therefore, it is possible to prevent the generation of abnormal noise due to the fluctuation of the power supply voltage when there is no input.
【０００８】また、更に他の発明によれば、判別手段は
負荷のインピーダンスの大小を判別したのち、判別結果
を保持して切り替え手段に出力するようにしたので、一
旦、適正な電源電圧に切り替えられたあと、不用意に不
適正な電源電圧に変わってしまうのを防止できる。According to still another aspect of the present invention, the discriminating means discriminates the magnitude of the impedance of the load, and then holds the discrimination result and outputs it to the switching means. It is possible to prevent the power supply voltage from being inadvertently changed to an improper power supply voltage.
【０００９】[0009]
【実施例】図１は本発明の一実施例に係る車載用パワー
アンプの回路図である。なお、図５と同一の構成部分に
は同一の符号が付してある。この実施例では図１のアン
プは標準の４Ωスピーカ用であるが、４Ωスピーカまた
は標準より小さい２Ωスピーカが接続されるものとす
る。また、Ｂ級動作をするものとする。１９は電源スイ
ッチ、９ＡはＰＷＭフィードバック制御方式で電源電圧
±Ｖccを発生する電源回路であり、スイッチ１５を外部
制御できるアナログスイッチ１５Ａに置き換えたほかは
図５に示した電源回路９と同様に構成されており、アナ
ログスイッチ１５Ａの開状態と閉状態とで±Ｖcc＝±Ｖ
cc（１）´と±Ｖcc＝±Ｖcc（２）´を発生する（但
し、Ｖcc（１）´＞Ｖcc（２）´）。２０は電源回路９
から供給された電源電圧±Ｖccに基づき作動し、端子Ｉ
Ｎに入力された音声信号を電力増幅して端子ＯＵＴから
スピーカ負荷（図示せず）に出力するアンプ回路であ
り、図１には入力段と出力段が示してある。出力段はト
ランジスタＱ３、エミッタ抵抗Ｒ４，Ｒ５、トランジス
タＱ４が＋Ｖccと−Ｖccの間に直列接続されたＳＥＰＰ
回路となっている。なお、電源回路９Ａの抵抗Ｒ３とア
ナログスイッチ１５Ａとで電源電圧切替手段が構成され
ている。1 is a circuit diagram of a vehicle-mounted power amplifier according to an embodiment of the present invention. The same components as those in FIG. 5 are designated by the same reference numerals. In this embodiment, the amplifier of FIG. 1 is for a standard 4Ω speaker, but it is assumed that a 4Ω speaker or a 2Ω speaker smaller than the standard is connected. In addition, it is assumed that a class B operation is performed. Reference numeral 19 is a power switch, 9A is a power supply circuit that generates a power supply voltage ± Vcc by the PWM feedback control method, and is the same as the power supply circuit 9 shown in FIG. 5 except that the switch 15 is replaced with an analog switch 15A that can be externally controlled. ± Vcc = ± V depending on whether the analog switch 15A is open or closed.
cc (1) 'and ± Vcc = ± Vcc (2)' are generated (however, Vcc (1) '> Vcc (2)'). 20 is a power supply circuit 9
It operates based on the power supply voltage ± Vcc supplied from
This is an amplifier circuit for power-amplifying the audio signal input to N and outputting the amplified audio signal from a terminal OUT to a speaker load (not shown). FIG. 1 shows an input stage and an output stage. The output stage is a SEPP in which a transistor Q3, emitter resistors R4 and R5, and a transistor Q4 are connected in series between + Vcc and -Vcc.
It is a circuit. The resistance R3 of the power supply circuit 9A and the analog switch 15A constitute a power supply voltage switching means.
【００１０】２１は端子ＩＮへの入力電圧レベル（入力
音声信号電圧の実効値）を検出するための第１の検出回
路であり、増幅回路２２と直流検波回路２３から構成さ
れている。この内、増幅回路２２は入力音声信号の増幅
を行うもので、オペアンプＯＰ１、抵抗Ｒ６〜８から構
成されており、直流検波回路２３は増幅回路２２で増幅
された信号の整流と平滑化を行って直流検波を行うもの
で、ダイオードＤ１、抵抗Ｒ９、コンデンサＣ５から構
成されている。２４は端子ＯＵＴからの出力電流レベル
（スピーカ駆動電流の実効値）を検出する第２の検出回
路であり、増幅回路２５と直流検波回路２６から構成さ
れており、ここではエミッタ抵抗Ｒ４に流れる電流のレ
ベルを検出するようにしてある。増幅回路２５はエミッ
タ抵抗Ｒ４の両端電圧を増幅するもので、オペアンプＯ
Ｐ２、抵抗Ｒ１０〜１４から構成されており、直流検波
回路２６は増幅回路２５で増幅された信号の整流と平滑
化を行って直流検波を行うもので、ダイオードＤ２、抵
抗Ｒ１５、コンデンサＣ６から構成されている。直流検
波回路２３と２６の出力で見た入力電圧レベルと出力電
流レベルの間には比例関係があり、２Ωスピーカ接続時
の方が４Ωスピーカ接続時より比例係数αが大きいが、
増幅回路２２と２５のゲインは２Ωスピーカ接続時はα
＞１、４Ωスピーカ接続時はα＜１となるように設定さ
れている（図２参照）。Reference numeral 21 is a first detection circuit for detecting the input voltage level (effective value of the input audio signal voltage) to the terminal IN, which is composed of an amplification circuit 22 and a DC detection circuit 23. Of these, the amplifier circuit 22 amplifies the input audio signal and is composed of an operational amplifier OP1 and resistors R6 to R8. The DC detection circuit 23 rectifies and smoothes the signal amplified by the amplifier circuit 22. DC detection is performed by using a diode D1, a resistor R9, and a capacitor C5. Reference numeral 24 denotes a second detection circuit for detecting the output current level (effective value of the speaker drive current) from the terminal OUT, which is composed of an amplification circuit 25 and a DC detection circuit 26, and here, a current flowing through the emitter resistor R4. The level of is detected. The amplifier circuit 25 amplifies the voltage across the emitter resistor R4.
P2 and resistors R10 to 14 are provided. The DC detection circuit 26 performs DC detection by rectifying and smoothing the signal amplified by the amplifier circuit 25, and includes a diode D2, a resistor R15, and a capacitor C6. Has been done. Although there is a proportional relationship between the input voltage level and the output current level seen at the outputs of the DC detection circuits 23 and 26, the proportional coefficient α is larger when the 2Ω speaker is connected than when the 4Ω speaker is connected.
The gain of the amplifier circuits 22 and 25 is α when a 2Ω speaker is connected.
It is set so that α <1 when> 1,4Ω speaker is connected (see FIG. 2).
【００１１】２７は判別回路であり、入力電圧レベルに
対する出力電流レベルの大きさから端子ＯＵＴに接続さ
れたスピーカのインピーダンスが４Ωか２Ωか判別し、
４ΩのときＬレベル、２ΩのときＨレベルをアナログス
イッチ１５Ａに出力し、４Ωのときはスイッチを開か
せ、２Ωのときは閉じさせる。２８は直流検波回路２３
と２６の出力で見た入力電圧レベルに対する出力電流レ
ベルの大きさを比較するコンパレータであり、直流検波
回路２３の出力電圧＞直流検波回路２６の出力電圧（α
＜１）のときＬレベル、直流検波回路２３の出力電圧＜
直流検波回路２６の出力電圧（α＞１）のときＨレベル
を出力する。２９は入力の立ち上がりを検出するコンパ
レータであり、直流検波回路２３から入力した入力電圧
レベルが所定の小さな正の基準電圧＋Ｖref より低いと
きＬレベル、高いときＨレベルを出力する。＋Ｖref は
端子ＩＮの入力が無入力でなく、かつ、音量が非常に小
さく絞られているときを除いて、コンパレータ２９がＨ
レベルを出力できる値に設定されている。３０は電源ス
イッチ１９が閉じたあと一定時間経過するまでＬレベル
を出力し、一定時間経過後Ｈレベルを出力するパワーオ
ンリセット回路、３１はパワーオンリセット回路３０の
出力を一定時間遅延させる遅延回路、３２は遅延回路３
１の出力とコンパレータ２８と２９の出力の論理積を取
るＡＮＤ回路、３３は遅延回路３１の出力を更に一定時
間遅延させる遅延回路、３４は遅延回路３１，コンパレ
ータ２８，２９の出力の論理積を取るＡＮＤ回路、３５
はＲＳフリップフロップ（以下、Ｒ−ＳＦＦと略す）で
あり、ＡＮＤ回路３２の出力がＨレベルになるとリセッ
トし、Ｑ端子からＬレベルの判別信号を出力し、ＡＮＤ
回路３４の出力がＨレベルになるとセットしＨレベルの
判別信号を出力する。Reference numeral 27 denotes a discrimination circuit which discriminates whether the impedance of the speaker connected to the terminal OUT is 4Ω or 2Ω from the magnitude of the output current level with respect to the input voltage level.
When it is 4Ω, the L level is output to the analog switch 15A when it is 2Ω, and when it is 4Ω, the switch is opened, and when it is 2Ω, it is closed. 28 is a DC detection circuit 23
And the output voltage of the DC detection circuit 26> the output voltage of the DC detection circuit 26 (α
When <1), L level, output voltage of DC detection circuit 23 <
When the output voltage of the DC detection circuit 26 (α> 1), the H level is output. Reference numeral 29 is a comparator that detects the rising edge of the input, and outputs an L level when the input voltage level input from the DC detection circuit 23 is lower than a predetermined small positive reference voltage + V ref , and an H level when the input voltage level is high. + V ref is set to H level by the comparator 29 except when the input at the terminal IN is not non-input and the volume is very low.
It is set to a value that can output the level. Reference numeral 30 denotes a power-on reset circuit that outputs an L level until a certain time elapses after the power switch 19 is closed, and outputs an H level after the certain time elapses. , 32 are delay circuits 3
An AND circuit that takes the logical product of the output of 1 and the outputs of the comparators 28 and 29, 33 is a delay circuit that delays the output of the delay circuit 31 for a further fixed time, and 34 is the logical product of the outputs of the delay circuit 31 and the comparators 28 and 29. AND circuit, 35
Is an RS flip-flop (hereinafter abbreviated as R-SFF), which resets when the output of the AND circuit 32 becomes H level, outputs a discrimination signal of L level from the Q terminal, and
When the output of the circuit 34 becomes H level, it is set and the discrimination signal of H level is output.
【００１２】図３は判別回路２７の動作を示すタイムチ
ャートであり、以下、この図を参照して上記した実施例
の動作を説明する。電源スイッチ１９を閉じると、パワ
ーオンリセット回路３０が一定時間Ｌレベルを出力した
のちＨレベルに変わり、ＡＮＤ回路３２の出力が短時
間、ＨレベルとなるのでＲ−ＳＦＦ３５がリセットしＬ
レベルを出力する。よって、アナログスイッチ１５Ａが
開き、電源回路９Ａは±Ｖcc（１）´を発生する。無入
力状態のとき、第１の検出回路２１と第２の検出回路２
４の出力は共に零であり、コンパレータ２８は出力が安
定しない。けれども、入力が立ち上がるまではコンパレ
ータ２９の出力がＬレベルのまであり、パワーオンリセ
ット回路３０の出力がＬレベルからＨレベルに変わり、
更に、遅延回路３１、３３の遅延時間経過したあとも、
無入力状態のままであればＲＳ−ＦＦ回路３５はＬレベ
ルの出力を続ける。FIG. 3 is a time chart showing the operation of the discriminating circuit 27. The operation of the above embodiment will be described below with reference to this figure. When the power switch 19 is closed, the power-on reset circuit 30 outputs the L level for a certain period of time and then changes to the H level, and the output of the AND circuit 32 becomes the H level for a short time. Therefore, the R-SFF 35 resets the L level.
Output level. Therefore, the analog switch 15A is opened, and the power supply circuit 9A generates ± V cc (1) '. When there is no input, the first detection circuit 21 and the second detection circuit 2
The outputs of 4 are both zero, and the output of the comparator 28 is not stable. However, the output of the comparator 29 remains at the L level until the input rises, and the output of the power-on reset circuit 30 changes from the L level to the H level.
Furthermore, even after the delay time of the delay circuits 31 and 33 has passed,
If there is no input, the RS-FF circuit 35 continues to output L level.
【００１３】この状態で端子ＩＮに音声信号が入力され
ると、アンプ回路２０で電力増幅がなされ、端子ＯＵＴ
に接続されたスピーカを駆動する。入力音声信号の電圧
レベルは第１の検出回路２１で検出され、また、スピー
カ駆動電流のレベルは出力段のエミッタ抵抗Ｒ５に流れ
る電流レベルとして、第２の検出回路２４で検出され
る。４Ωスピーカが接続されている場合、第１の検出回
路２１と第２の検出回路２４の出力電圧で見たとき、入
力電圧レベル＞出力電流レベル（α＜１）となり、判別
回路２７のコンパレータ２８はＬレベルを出力し、逆
に、２Ωスピーカが接続されている場合、第１の検出回
路２１と第２の検出回路２４の出力電圧で見たとき、入
力電圧レベル＜出力電流レベル（α＞１）となり、判別
回路２７のコンパレータ２８はＨレベルを出力する。In this state, when an audio signal is input to the terminal IN, the amplifier circuit 20 amplifies the power and outputs the signal to the terminal OUT.
Drive the speaker connected to. The voltage level of the input audio signal is detected by the first detection circuit 21, and the level of the speaker drive current is detected by the second detection circuit 24 as the current level flowing through the emitter resistor R5 of the output stage. When a 4Ω speaker is connected, when viewed from the output voltages of the first detection circuit 21 and the second detection circuit 24, the input voltage level> the output current level (α <1), and the comparator 28 of the determination circuit 27 Outputs an L level, and conversely, when a 2Ω speaker is connected, the input voltage level <output current level (α>) when viewed from the output voltages of the first detection circuit 21 and the second detection circuit 24. 1), and the comparator 28 of the discrimination circuit 27 outputs the H level.
【００１４】音量が最小近くに絞られていない限り、音
声信号の入力が開始すれば入力電圧レベルが＋Ｖref を
越えて、コンパレータ２９の出力はＬレベルからＨレベ
ルに変わる。遅延回路３３の出力が既にＨレベルとなっ
ているものとして、４Ωスピーカ接続時はコンパレータ
２８の出力がＬレベルとなっているので、Ｒ−ＳＦＦ回
路３５の出力はＬレベルを保持し、アナログスイッチ１
５Ａが開いたままとなるので電源回路９Ａは、±Ｖcc
（１）´の電源電圧を発生し続ける。電源電圧±Ｖcc
（１）´の状態は電源スイッチ１９が開かれるまで持続
する。アンプ回路２０は４Ωスピーカ用なので最大音量
にしても加熱によるトランジスタの熱破壊が生じること
はない。逆に、音声信号の入力が開始し、入力電圧レベ
ルが＋Ｖref を越えてコンパレータ２９の出力がＬレベ
ルからＨレベルに変わったとき、２Ωスピーカ接続時は
コンパレータ２８の出力がＨレベルとなっているので、
Ｒ−ＳＦＦ回路３５の出力はＨレベルに変わって以降Ｈ
レベルを保持し、アナログスイッチ１５Ａが閉じて電源
回路９Ａは電源電圧を±Ｖcc（２）´に切り替える。電
源電圧±Ｖcc（２）´の状態は電源スイッチ１９が開か
れるまで持続する。Ｖcc（２）´はＶcc（１）´より小
さく、よって、２Ωスピーカ接続時に最大音量にしても
スピーカ駆動電流が過大になることはなく、加熱による
トランジスタの熱破壊が回避される。なお、２Ωスピー
カ接続時でも音量が最小近くに絞られており、入力電圧
レベルが＋Ｖref を越えないときは電源電圧が±Ｖcc
（１）´のままとなるが、スピーカ駆動電流が非常に小
さいので、特に加熱の問題は生じず、音量が少し増大さ
れれば、入力電圧レベルが＋Ｖref を越えるので、電源
電圧が±Ｖcc（２）´に切り替わる。Unless the volume is reduced to the minimum level, the input voltage level exceeds + V ref when the input of the audio signal starts, and the output of the comparator 29 changes from the L level to the H level. Assuming that the output of the delay circuit 33 is already at the H level, the output of the comparator 28 is at the L level when the 4Ω speaker is connected. Therefore, the output of the R-SFF circuit 35 is maintained at the L level and the analog switch 1
Since 5A remains open, the power supply circuit 9A is ± Vcc
The power supply voltage of (1) 'is continuously generated. Power supply voltage ± Vcc
The state of (1) ′ continues until the power switch 19 is opened. Since the amplifier circuit 20 is for a 4Ω speaker, thermal destruction of the transistor due to heating does not occur even at the maximum volume. On the contrary, when the input of the audio signal starts, the input voltage level exceeds + V ref, and the output of the comparator 29 changes from the L level to the H level, the output of the comparator 28 becomes the H level when the 2Ω speaker is connected. Because
The output of the R-SFF circuit 35 changes to the H level and then becomes the H level.
The level is maintained, the analog switch 15A is closed, and the power supply circuit 9A switches the power supply voltage to ± Vcc (2) '. The state of the power supply voltage ± Vcc (2) 'continues until the power switch 19 is opened. Since Vcc (2) 'is smaller than Vcc (1)', the speaker driving current does not become excessive even when the 2Ω speaker is connected even at the maximum volume, and thermal destruction of the transistor due to heating is avoided. Even when the 2Ω speaker is connected, the volume is reduced to the minimum, and if the input voltage level does not exceed + V ref , the power supply voltage is ± Vcc.
(1) 'remains, but since the speaker drive current is very small, there is no particular problem of heating, and if the volume is increased a little, the input voltage level exceeds + V ref , so the power supply voltage is ± Vcc. (2) 'is switched.
【００１５】この実施例によれば、車載用パワーアンプ
の入力電圧レベルと出力電流レベルを検出し、入力電圧
レベルに対する出力電流レベルの大きさからスピーカイ
ンピーダンスの大小判別をするようにしたので、スピー
カインピーダンスの大小を確実に判別でき、電源電圧の
適正切り替えが可能となる。よって、負荷インピーダン
スの小さいスピーカを接続した場合でも確実に加熱によ
る熱破壊を防止できる。また、音量が最小近くに絞られ
ている場合を除き、電源スイッチ１９を閉じたあと一定
時間経過したときに既に入力が立ち上がっているか、又
は、その後入力が立ち上がれば、直ちに負荷インピーダ
ンスに適した電源電圧に切り替わり、以降、電源スイッ
チ１９が閉じている限り、電源電圧は切り替わらないの
で、不用意に不適正な電源電圧に変わることはない。According to this embodiment, the input voltage level and the output current level of the vehicle-mounted power amplifier are detected, and the speaker impedance is determined from the magnitude of the output current level with respect to the input voltage level. It is possible to reliably determine the magnitude of the impedance and to appropriately switch the power supply voltage. Therefore, even when a speaker with a small load impedance is connected, it is possible to reliably prevent thermal destruction due to heating. In addition, unless the volume is turned down to the minimum level, if the input has already risen when a certain time has passed after the power switch 19 was closed, or if the input rises thereafter, the power supply suitable for the load impedance is immediately obtained. As long as the power switch 19 is closed after switching to the voltage, the power voltage does not switch, so that it does not accidentally change to an improper power voltage.
【００１６】更に、過度の発熱が持続して高温にならな
くても電源電圧が切り替わるので、過度の発熱により部
品の劣化が進んでしまうこともない。また、第２の検出
回路２４の入力をアンプ回路２０の出力段を構成するト
ランジスタＱ３のエミッタ抵抗両端から取り出すように
したので、出力電流レベルの検出の為に特別な検出抵抗
を設ける必要がない。また、電源電圧を切り替えるため
に機械的接点を要しないので信頼性が向上し、図４の符
号７，８の如く大電流用で価格が高いスイッチを設ける
必要もない。更に、負荷インピーダンスに応じて自動的
に電源電圧が切り替わるので、図４の符号７，８、図５
の符号１５の如く設置場所が制約されるマニュアルスイ
ッチを設けなくて済み、設計の自由度が増すとともにパ
ネルを簡略化できる。Further, since the power supply voltage is switched even if excessive heat generation continues and does not reach a high temperature, deterioration of parts does not proceed due to excessive heat generation. Further, since the input of the second detection circuit 24 is taken out from both ends of the emitter resistance of the transistor Q3 forming the output stage of the amplifier circuit 20, it is not necessary to provide a special detection resistance for detecting the output current level. . Further, since no mechanical contact is required to switch the power supply voltage, reliability is improved, and it is not necessary to provide a switch for a large current and a high price as shown by reference numerals 7 and 8 in FIG. Further, since the power supply voltage is automatically switched according to the load impedance, reference numerals 7, 8 and 5 in FIG.
It is not necessary to provide a manual switch whose installation location is restricted as indicated by reference numeral 15, so that the degree of freedom in design is increased and the panel can be simplified.
【００１７】なお、上記した実施例ではアンプ回路２０
の出力段のエミッタ抵抗両端から第２の検出回路２４へ
の入力を取り出すようにしたが、図１のＰ点に電流検出
用の小抵抗を設け、該小抵抗両端から取り出すようにし
ても良く、この場合、アンプ回路がＡ級やＡＢ級動作を
する場合にも適用できる。また、第１の検出手段は端子
ＩＮの入力電圧レベルを検出するようにしたが、アンプ
回路２０の出力電圧レベル（端子ＯＵＴとアース間の電
圧レベル）を検出するようにしても、第１の検出回路と
第２の検出回路の増幅回路のゲインを適切に設定してお
けば、上記した実施例と同様にして、判別回路で出力電
圧レベルに対する出力電流レベルの大きさを比較し、負
荷のインピーダンスの大小を判別することができる。更
に、判別回路２７も、パワーオンリセット回路３０、遅
延回路３１，３３、Ｒ−ＳＦＦ３５などを省略し、コン
パレータ２８の出力をそのままアナログスイッチ１５Ａ
に出力するようにしたり、コンパレータ２８と２９の論
理積を取ったのちアナログスイッチ１５Ａに出力するよ
うにし、回路構成の簡単化を図るようにしても良い。In the above embodiment, the amplifier circuit 20 is used.
Although the input to the second detection circuit 24 is taken out from both ends of the emitter resistance of the output stage, a small resistor for current detection may be provided at point P in FIG. 1 and taken out from both ends of the small resistor. In this case, it can be applied to the case where the amplifier circuit performs class A or class AB operation. Further, although the first detecting means detects the input voltage level of the terminal IN, the first detecting means detects the output voltage level of the amplifier circuit 20 (voltage level between the terminal OUT and the ground). If the gains of the detection circuit and the amplification circuit of the second detection circuit are appropriately set, the size of the output current level with respect to the output voltage level is compared by the determination circuit, and the load load is determined in the same manner as in the above-described embodiment. The magnitude of impedance can be discriminated. Further, the discrimination circuit 27 also omits the power-on reset circuit 30, the delay circuits 31 and 33, the R-SFF 35, and the like, and outputs the output of the comparator 28 as it is to the analog switch 15A.
It is also possible to simplify the circuit configuration by outputting the signal to the analog switch 15A after the logical product of the comparators 28 and 29 is obtained.
【００１８】また、上記した実施例ではＰＷＭ制御方式
の電源回路を例に挙げたが、シリーズレギュレータであ
っても、基準電圧発生用のツェナーダイオードを切り替
えるなどして、電源電圧の切り替えを行うようにした
り、ＡＣ電源を入力する図４の如きパワーアンプの場
合、スイッチ７，８をリレースイッチに置き換え、判別
回路の出力に基づきリレースイッチを切り替えるように
してもよい。Further, in the above embodiment, the PWM control type power supply circuit is taken as an example, but even the series regulator can switch the power supply voltage by switching the Zener diode for generating the reference voltage. Alternatively, in the case of the power amplifier as shown in FIG. 4 which inputs AC power, the switches 7 and 8 may be replaced with relay switches, and the relay switches may be switched based on the output of the determination circuit.
【００１９】[0019]
【発明の効果】本発明によれば、電力増幅器の入力電圧
レベルまたは出力電圧レベルと、出力電流レベルを検出
し、入力電圧レベルまたは出力電圧レベルに対する出力
電流レベルの大きさから負荷のインピーダンスの大小を
判別し、判別結果に基づき電源手段の発生する電源電圧
を切り替えるようにしたので、確実に負荷インピーダン
スの大小を判別することができ、電源電圧の適正切り替
えが可能となる。よって、負荷インピーダンスの小さい
スピーカを接続した場合でも確実に加熱による熱破壊を
防止できる。According to the present invention, the input voltage level or the output voltage level of the power amplifier and the output current level are detected, and the magnitude of the load impedance is determined from the magnitude of the input current level or the output current level with respect to the output voltage level. Since the power source voltage generated by the power source means is switched based on the determination result, the magnitude of the load impedance can be reliably determined, and the power source voltage can be appropriately switched. Therefore, even when a speaker with a small load impedance is connected, it is possible to reliably prevent thermal destruction due to heating.
【００２０】また、他の発明によれば、第２の検出手段
の入力を電力増幅手段の出力段を構成するトランジスタ
のエミッタ抵抗両端から取り出すようにしたので、出力
電流レベルの検出の為に特別な検出抵抗を設ける必要が
ない。また、更に他の発明によれば、判別手段に入力の
立ち上がりを検出する立ち上がり検出手段を設け、判別
手段は負荷のインピーダンスの大小判別を立ち上がり検
出手段が入力の立ち上がりを検出した時点で行うように
したので、無入力時に電源電圧が変動し異音を発するの
を防止できる。According to another aspect of the invention, since the input of the second detecting means is taken out from both ends of the emitter resistance of the transistor forming the output stage of the power amplifying means, it is special for detecting the output current level. It is not necessary to provide a special detection resistor. According to still another aspect of the invention, the discriminating means is provided with a rising edge detecting means for detecting the rising edge of the input, and the discriminating means judges the magnitude of the impedance of the load when the rising edge detecting means detects the rising edge of the input. Therefore, it is possible to prevent the generation of abnormal noise due to the fluctuation of the power supply voltage when there is no input.
【００２１】また、更に他の発明によれば、判別手段は
負荷のインピーダンスの大小を判別したのち、判別結果
を保持して切り替え手段に出力するようにしたので、一
旦、適正な電源電圧に切り替えられたあと、不用意に不
適正な電源電圧に変わってしまうのを防止できる。According to still another aspect of the invention, the determination means determines the magnitude of the impedance of the load and then holds the determination result and outputs it to the switching means. It is possible to prevent the power supply voltage from being inadvertently changed to an improper power supply voltage.
【図１】本発明の一実施例に係る車載用パワーアンプの
回路図である。FIG. 1 is a circuit diagram of a vehicle-mounted power amplifier according to an embodiment of the present invention.
【図２】第１の検出回路の出力で見た入力電圧レベルと
第２の検出回路の出力で見た出力電流レベルの関係を示
す線図である。FIG. 2 is a diagram showing the relationship between the input voltage level seen at the output of the first detection circuit and the output current level seen at the output of the second detection circuit.
【図３】判別回路の動作を示すタイムチャートである。FIG. 3 is a time chart showing the operation of the discrimination circuit.
【図４】従来の電源電圧切り替え可能なパワーアンプの
一例を示す示す回路図である。FIG. 4 is a circuit diagram showing an example of a conventional power amplifier capable of switching a power supply voltage.
【図５】従来の電源電圧切り替え可能なパワーアンプの
他の例を示す示す回路図である。FIG. 5 is a circuit diagram showing another example of a conventional power amplifier capable of switching a power supply voltage.
９Ａ 電源回路 １２ コントロー
ラ １５Ａ アナログスイッチ ２０ アンプ回路 ２１ 第１の検出回路 ２４ 第２の検出
回路 ２７ 判別回路 Ｒ１〜Ｒ４ 抵抗9A power supply circuit 12 controller 15A analog switch 20 amplifier circuit 21 first detection circuit 24 second detection circuit 27 discrimination circuit R1 to R4 resistance
Claims (4)
れたスピーカ負荷を駆動する電力増幅手段と、電力増幅
手段に動作電源を供給する電源手段を備えた電力増幅器
において、 電力増幅器の入力電圧レベルまたは出力電圧レベルを検
出する第１の検出手段と、 電力増幅器の出力電流レベルを検出する第２の検出手段
と、 電力増幅器の入力電圧レベルまたは出力電圧レベルに対
する電力増幅器の出力電流レベルの大きさから負荷のイ
ンピーダンスの大小を判別する判別手段と、 判別手段での判別結果に基づき電源手段の発生する電源
電圧を切り替えさせる切り替え手段と、 を備えたことを特徴とする電力増幅器。1. A power amplifier comprising power amplification means for power-amplifying an audio signal to drive a speaker load connected to an output side, and power supply means for supplying an operating power supply to the power amplification means. A first detecting means for detecting a voltage level or an output voltage level; a second detecting means for detecting an output current level of the power amplifier; and a second detecting means for detecting an output current level of the power amplifier with respect to an input voltage level or an output voltage level of the power amplifier. A power amplifier comprising: a discriminating unit that discriminates the magnitude of the impedance of the load based on the size; and a switching unit that switches the power supply voltage generated by the power supply unit based on the discrimination result by the discriminating unit.
出力段を構成するトランジスタのエミッタ抵抗両端から
取り出すようにしたこと、 を特徴とする請求項１記載の電力増幅器。2. The power amplifier according to claim 1, wherein the input of the second detecting means is taken out from both ends of the emitter resistance of the transistor forming the output stage of the power amplifying means.
立ち上がり検出手段を設け、 判別手段は負荷のインピーダンスの大小判別を立ち上が
り検出手段が入力の立ち上がりを検出した時点で行うよ
うにしたこと、 を特徴とする請求項１記載の電力増幅器。3. The discriminating means is provided with a rising edge detecting means for detecting the rising edge of the input, and the discriminating means judges the magnitude of the impedance of the load when the rising edge detecting means detects the rising edge of the input. The power amplifier according to claim 1.
を判別したのち、判別結果を保持して切り替え手段に出
力するようにしたこと、 を特徴とする請求項１または３記載の電力増幅器。4. The power amplifier according to claim 1, wherein the discriminating means discriminates the magnitude of the impedance of the load and then holds the discrimination result and outputs it to the switching means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6056613A JPH07240636A (en) | 1994-03-01 | 1994-03-01 | Power amplifier |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6056613A JPH07240636A (en) | 1994-03-01 | 1994-03-01 | Power amplifier |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH07240636A true JPH07240636A (en) | 1995-09-12 |
Family
ID=13032114
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP6056613A Pending JPH07240636A (en) | 1994-03-01 | 1994-03-01 | Power amplifier |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH07240636A (en) |
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- 1994-03-01 JP JP6056613A patent/JPH07240636A/en active Pending
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