JP3705432B2

JP3705432B2 - Current measuring device

Info

Publication number: JP3705432B2
Application number: JP2002152548A
Authority: JP
Inventors: 直司鈴木
Original assignee: Advantest Corp
Current assignee: Advantest Corp
Priority date: 2002-05-27
Filing date: 2002-05-27
Publication date: 2005-10-12
Anticipated expiration: 2022-05-27
Also published as: JP2003344461A

Description

【０００１】
【発明の属する技術分野】
この発明は電流測定装置に関し、特に電流検出用抵抗器に過電流が流れることを阻止する機能を付加した保護回路付電流測定装置の改良に関するものである。
【０００２】
【従来の技術】
図８に従来の保護回路付電流測定装置の回路構成を示す。図中１は被測定電流ｉの入力端子、２はヒューズ、３は電流検出用抵抗器、４はこの電流検出用抵抗器３に発生する電圧を測定する電圧測定器、５は電流検出用抵抗器３に過電流及び過電圧が印加されることを阻止するためのダイオード対を示す。
被測定電流ｉの測定は以下の如くして行なわれる。入力端子１に被測定電流ｉが印加され、この被測定電流ｉが電流検出用抵抗器３に流れることにより、電流検出用抵抗器３の両端に電圧Ｖ₁が発生する。電流検出用抵抗器３の抵抗値は予め既知ＲＳであるものとするから、この電圧Ｖ₁を電圧測定器４で測定することで被測定電流ｉは、
ｉ＝Ｖ₁／Ｒｓ
により求められる。
【０００３】
入力端子１に被測定電流ｉを印加する際に、電流検出用抵抗器３の両端の電圧Ｖ_１がダイオード対を構成するダイオードＤ１、Ｄ２の導通電圧＋ＶＥ又は‐ＶＥより大きい値になったとき、ダイオードＤ１又はＤ２が導通し、電流検出用抵抗器３に流れる電流を制限し、電流検出用抵抗器３を保護する。被測定電流ｉが更に大きくなると、ヒューズ２が溶断し、電流検出用抵抗器３およびダイオードＤ１，Ｄ２を保護する。
図８に示した保護回路の欠点はヒューズ２が溶断した場合にヒューズ２を交換しなければならない。つまり、復旧させるために手間が掛る欠点が生じる。
【０００４】
この欠点を解消することができる保護回路の例を図９に示す。図９に示す回路では平素は電流検出用抵抗器３に発生する電圧Ｖ₁は基準電圧源８に設定した基準電圧ｅより低い範囲ｅ＞Ｖ₁で電流の測定が行なわれる。つまり、電流検出用抵抗器３に発生する電圧Ｖ₁が基準電圧ｅより低いｅ＞Ｖ₁の状態では電圧比較器７は電圧比較出力として正電圧を出力し、この正電圧によって能動素子６が充分オンの状態に維持されて電流ｉの測定が支障なく行われる。
電流検出用抵抗器３に発生する電圧Ｖ₁が基準電圧ｅと同じ電圧ｅ≒Ｖ₁になると、電圧比較器７は電流ｉが
ｉ＝ｅ／Ｒｓ
となる様に能動素子６を制御し、定電流回路として動作する。この定電流動作により電流検出用抵抗器３に過電流が流れることを阻止する。但し、ｅ＞Ｖ₁の状態に戻れば能動素子６はオンの状態に復帰し、通常の電流測定モードに戻ることができる。
【０００５】
図９に示した保護回路付電流測定装置によればヒューズの存在がなくとも電流検出用抵抗器３を安全に保護することができることと、無操作でも元の測定モードに復帰できる利点がある。
然し乍ら、この回路では電流制限状態で能動素子６で消費される電力Ｐは、
Ｐ＝（Ｖ₀−Ｖ₁）ｉ
となり、Ｖ₀が高くなるほど能動素子６は大きな消費電力を消費し、それだけ電力容量の大きい能動素子を用いる必要がある。更に、発熱も大きくなることから放熱手段も装備しなくてはならないため、コストが高くなる欠点がある。
【０００６】
この発明の目的は能動素子における電力消費量を抑制し、電力量の小さい能動素子を用いて安全に保護動作を行なわせることができる電流測定装置を提供しようとするものである。
【０００７】
【発明が解決しようとする課題】
この発明では電流検出用抵抗器に被測定電流を印加し、電流検出用抵抗器に発生する電圧を測定して被測定電流の値を測定する電流測定装置において、電流検用抵抗器に発生する電圧と、予め設定した基準電圧とを比較し、電流検出用抵抗器に流れる電流が設定値に一致したことを検出する電圧比較器と、電流検出用抵抗器と直列接続され、電圧比較器の比較出力により抵抗値が制御されて電流検出用抵抗器に流れる電流が設定値に一致した状態で電流検出用抵抗器に流れる電流を制限する能電素子と、能電素子と電流検出用抵抗器によって構成される直列回路に印加される電圧が設定値を超えたことを検出する過電圧検出手段と、この過電圧検出手段が過電圧を検出し、直列回路に印加される電圧が更に上昇すると基準電圧の電圧値を漸次低下させる基準電圧制御手段とを付加した構成とした電流測定装置を提案する。
【０００８】
この発明では更に請求項１記載の電流測定装置において、直列回路に正極性の電圧を印加し、電流検出用抵抗器に流れる正極性の電流を測定する電流測定装置にあっては、能電素子はＮチャンネル型電界効果トランジスタ又はＮＰＮ型トランジスタが用いられ、電圧比較器に与える基準電圧は正極性の基準電圧とされ、基準電圧制御手段は電圧比較器に与える正極性の基準電圧を過電流検出時は共通電位に近ずける制御を行なう構成とした電流測定装置を提案する。
【０００９】
この発明では更に請求項１記載の電流測定装置において、直列回路に負極性の電圧を印加し、電流検出用抵抗器を流れる負極性の電流を測定する電流測定装置にあっては、能電素子はＰチャンネル型電界効果トランジスタ或はＰＮＰ型トランジスタが用いられ、電圧比較器に与える基準電圧は負極性の基準電圧とされ、基準電圧制御手段は電圧比較器に与える負極性の基準電圧を共通電位に近づける制御を行なう構成としたことを特徴とした電流測定装置を提案する。
【００１０】
この発明では更に請求項１記載の電流測定装置において、電流検出用抵抗器にＮチャンネル型電界効果トランジスタとＰチャンネル型電界効果トランジスタを直列接続し、Ｎチャンネル型電界効果トランジスタは電流検出用抵抗器に発生する電圧と正極性の基準電圧との比較結果により抵抗値を制御し、Ｐチャンネル型電界効果トランジスタは電流検出用抵抗器に発生する電圧と負極性の基準電圧との比較結果により抵抗値を制御する構成とした電流測定装置を提案する。
【００１１】
作用
この発明による電流測定装置によれば電流検出用抵抗器に発生する電圧が電圧比較器に印加する基準電圧と同じ電圧に至ると、能動素子と電圧比較器とにより定電流動作が実行される。これと共に、入力端子に印加される電圧Ｖ₀が設定値より高くなると過電検出手段が過電圧を検出し、この過電圧の検出により基準電圧制御手段は電圧比較器に印加している基準電圧を共通電位に近ずける方向に制御する。
【００１２】
この結果、能動素子は定電流動作から漸次電流制限動作に入り、定電流状態から電流値を低下させる方向に動作する。入力端子に印加される電圧Ｖ₀が過電圧検出時点より更に上昇すると能動素子の抵抗値が増大し、電流を制限し、最終的にはオフの状態に至る。
従って、この発明によれば入力端子に印加される電圧Ｖ₀が設定値を超えた時点から、能動素子を流れる電流が制限され電流値を漸次減少させるから、能動素子で消費される電力は抑制され、電力容量の小さい能動素子でも充分耐えることができる。また、発熱量も少なくできるため放熱手段を設ける必要がなく、全体として安価なコストで作ることができる利点が得られる。
【００１３】
【発明の実施の形態】
図１にこの発明による電力測定装置の一実施例を示す。図中１０は図９を用いて説明した従来の電流測定回路を示す。つまり、入力端子１に印加された被測定電流ｉは能動素子６を通じて電流検出用抵抗器３に入力され、この電流検出用抵抗器３に発生する電圧Ｖ₁を電圧測定器４で測定し、電流ｉを、
ｉ＝Ｖ₁・ＲＳ：ＲＳは電流検出用抵抗器の抵抗値、
で求める。
【００１４】
平素の電流測定状態では電圧比較器７に印加される基準電圧Ｖ₂は電圧検出用抵抗器３に発生する電圧Ｖ₁より充分大きい正側の電位に設定される。従って、電圧比較器７は正電位の比較出力電圧Ｖ₃を出力し、この正電位の比較出力電圧Ｖ₃によりこの例ではＮチャンネル型電界効果トランジスタで構成された能動素子６がオンの状態に維持される。
【００１５】
この発明では電圧比較器７の基準電圧印加端子９と基準電圧源８との間に基準電圧制御手段２０を接続すると共に入力端子１に印加される電圧Ｖ₀が予め定めた設定値以上の過電圧に上昇したことを、この基準電圧制御手段２０に通知するための過電圧検出手段３０を入力端子１と基準電圧制御手段２０との間に接続した構成を特徴とするものである。
【００１６】
電圧比較器７は一般に知られている演算増幅器が用いられ、その反転入力端子に電流検出用抵抗器３に発生する電圧Ｖ₁を入力する。非反転入力端子は基準電圧印加端子９に接続する。
基準電圧制御手段２０は非反転入力端子が共通電位に接続された演算増幅器２１と、この演算増幅器２１の反転入力端子と基準電圧源８との間に接続した入力用抵抗器２２と、演算増幅器２１の反転入力端子と出力端子との間に接続した帰還用抵抗器２３とによって構成され、演算増幅器２１の出力端子と帰還用抵抗器２３との接続点を基準電圧印加端子９に接続する。基準電圧源８はここでは負の基準電圧−ｅを発生し、この負の基準電圧−ｅが演算増幅器２１で極性反転され、基準電圧印加端子９には正極性の基準電圧Ｖ₂が印加される。
【００１７】
過電圧検出手段３０は定電圧ダイオード３１と、この定電圧ダイオード３１と直列接続した電流制限用抵抗器３２とによって構成される。電流制限用抵抗器３２と定電圧ダイオード３１とによって構成される直列回路を入力端子１と基準電圧制御手段２０を構成する演算増幅器２１の反転入力端子との間に接続し、入力端子１に印加される電圧Ｖ₀が定電圧ダイオード３１の導通電圧Ｖｚを超えると定電圧ダイオード３１が導通し、その導通電流を基準電圧制御手段２０に印加し、過電圧が入力されたことを基準電圧制御手段２０に伝達する。
【００１８】
ここで、電流検出用抵抗器３の抵抗値をＲｓ、これに発生する電圧をＶ₁、基準電圧印加端子９に印加される基準電圧をＶ₂、電圧比較器７の比較出力電圧をＶ₃、基準電圧制御手段２０を構成する入力用抵抗器２２と、帰還用抵抗器２３の各抵抗値をＲ₁、Ｒ₂、過電圧検出手段３０を構成する定電圧ダイオード３１の導通電圧をＶｚ、電流制限用抵抗器３２の抵抗値をＲ₃として基準電圧制御手段２０と過電圧検出手段３０の動作を説明する。
【００１９】
▲１▼入力電圧Ｖ₀と定電圧ダイオード３１の導通電圧Ｖ₂との間の関係がＶ₀＜Ｖｚの場合、基準電圧印加端子９に印加される基準電圧Ｖ₂は、
Ｖ₂＝（−Ｒ₂／Ｒ₁）（−ｅ）＝（Ｒ₂／Ｒ₁）ｅ
ｉ＜（Ｒ₂／Ｒ₁・Ｒｓ）ｅの間（図２に示す▲１▼）この状態ではＶ₂＞Ｖ₁なので電圧比較器７の比較出力電圧Ｖ₃は正電位方向に充分飽和しているため能動端子６は完全に導通状態にある。入力端子１の電圧Ｖ₀は、
Ｖ₀＝Ｒｓ・ｉ
で定められる。
▲２▼ｉ＝（Ｒ₂／Ｒ₁・Ｒｓ）ｅになると、電圧比較器７と能動素子６は定電流動作に入る。この状態では電流検出用抵抗器３に流れる電流は一定となる（図２▲２▼）。入力端子1の電圧は外部から印加される電圧と一致する。
▲３▼Ｖ₀≧Ｖｚになると、過電圧検出手段３０に電流が流れ、基準電圧Ｖ₂を低下させる。過電流検出手段３０に流れる電流を無視すると、
ｉ＝（−（Ｒ₂／Ｒ₃）Ｖ₀＋Ｒ₂（ｅ／Ｒ₁＋Ｖｚ／Ｒ₃））／Ｒｓ
となり、電流ｉは電圧Ｖ₀の上昇と共に低下する（図2▲３▼）
▲４▼Ｖ₀がＶ_A＝（（Ｒ₃／Ｒ₁）ｅ＋Ｖｚ）になると、基準電圧Ｖ₂はＶ₂＝0となり、この結果能動素子6はオフ、ｉ＝０となる（図２▲４▼）。
【００２０】
以上説明した各状態は図2に示す▲１▼、▲２▼、▲３▼、▲４▼に対応し、電流ｉが設定値（Ｒ₂／Ｒ₁・Ｒｓ）ｅに達すると、定電流特性を呈し、電圧Ｖ₀が定電圧ダイオード３１の導通電圧Ｖｚを超えると電流ｉは減少を始める。
図３に電圧Ｖ₀対電力Ｐの関係を示す。図３に示す電力Ｐは能動素子６に掛る電力と等価である。能動素子６に掛る電力は図３でも明らかなように、Ｖ_A／２の時最大値となり、Ｖ₀≧Ｖ_Aで能動素子６はオフとなり、Ｖ₀がＶ_A以上に上昇しても電力ほぼ０を維持する。Ｖ₀がＶ₀＜Ｖｚの状態に戻れば能動素子６はオンの状態に復帰する。
【００２１】
従って、この発明によれば過電圧保護状態からの復帰は自動復帰であり電流検出用抵抗器３は過電流及び過電圧から保護され、また電力消費量も一定以上にならない。これにより能動素子６としては従来より電力容量が小さい素子を用いることができる。また、発熱量も小さくできるから放熱器を付設する必要がない、よってこの種の電流測定装置を安価に製造することができる利点が得られる。
図４は能動素子６としてＮＰＮ型のトランジスタを用いた実施例を示す。この場合には能動素子６として動作するトランジスタのベースにベース電流制限用抵抗器１１を接続した点が図１と異なるだけである。
【００２２】
図５はこの説明の更に他の実施例を示す。この実施例では基準電圧源８を基準電圧制御手段２０を構成する演算増幅器２１の非反転入力端子と共通電位との間に接続した場合を示す。この場合には演算増幅器２１の非反転入力端子には正極性の基準電圧ｅを印加すると、基準電圧印加端子９に正電圧の基準電圧Ｖ₂が出力される。
図５に示す構成によっても電圧検出手段３０が過電圧を検出すると、基準電圧印加端子９に与えられる基準電圧Ｖ₂は共通電位側に低下し、能動素子６を流れる電流ｉを抑制することができる。
【００２３】
図６はこの発明の更に他の実施例を示す。この実施例では能動素子６としてＰチャンネル型電界効果トランジスタを用いた場合を示す。つまり、この実施例では負極性の電流−ｉを測定する電流測定装置を構成するものである。このために、基準電圧源８は正極性の基準電圧ｅを基準電圧制御手段２０を構成する演算増幅器２１の反転入力端子に与え、基準電圧印加端子９には負極性の基準電圧−Ｖ₂を印加する。過電圧検出手段３０を構成する定電圧ダイオード３１は図１、図４、図５に示した実施例とは逆向きに接続される。
【００２４】
電流検出用抵抗器３には負極性の電圧−Ｖ₁が発生し、この電圧−Ｖ₁と基準電圧−Ｖ₂とが電圧比較器７で比較される。平素の電流測定モードでは−Ｖ₁＞−Ｖ₂とされ、電圧比較器７の比較出力電圧は負極性の電圧−Ｖ₃が出力される。この負極性の比較出力電圧−Ｖ₃によりＰチャンネル型電界効果トランジスタ６はオンの状態に維持され電流測定が実行できる。
入力電流ｉが増加し、−Ｖ₁≒−Ｖ₂の状態に達すると、能動素子６と電圧比較器７は定電流回路を構成し、電流検出用抵抗器３に流れる電流を一定電流に制限する。入力端子１の電圧は外部から印加される電圧と一致する。
【００２５】
入力電圧−Ｖ₀が−Ｖ₀≦−Ｖｚに達すると、過電流検出手段３０が過電圧の印加状態を検出し、基準電圧制御手段２０に導通電流を流すから、この時点から入力電圧−Ｖ₀が更に負方向に偏倚する毎に電流ｉは減少し、最終的には能動素子６はオフの状態に至る。
従って、負方向の電流測定装置でも電流検出抵抗器３は保護され、また能動素子６にかかる電力も一定値以上にならず、所定の範囲に制限される。
図７はこの発明の更に他の実施例を示す。この実施例では図１に示した正方向の電流測定と、図６に示した負方向の電流測定の双方を実行できる双方向型の電流測定装置を構成した例を示す。
【００２６】
６ＮはＮチャンネル型電界効果トランジスタ、６ＰはＰチャンネル型電界効果トランジスタを示す。これらの電界効果トランジスタ６Ｎ、６Ｐを入力端子と電流検出用抵抗器３との間に直列接続する。
７Ｎは能動素子６Ｎに電圧比較出力＋Ｖ₃を印加する電圧比較器、７Ｐは能動素子６Ｐに電圧比較出力−Ｖ₃を印加する電圧比較器を示す。８Ｎは基準電圧制御手段２０Ｎを通じて基準電圧印加端子９Ｎに基準電圧＋Ｖ₂を印加するための基準電圧源、８Ｐは基準電圧制御手段２０Ｐを通じて基準電圧印加端子９Ｐに基準電圧−Ｖ₂を印加するための基準電圧源を示す。
【００２７】
３０Ｎは基準電圧制御手段２０Ｎに過電圧検出出力を印加する過電圧検出手段、３０Ｐは基準電圧制御手段２０Ｐに過電圧の検出出力を印加する過電圧検出手段を示す。
これらの構成により、入力端子１には正極性の電圧＋Ｖ₀を印加した状態の電流測定でも、負電圧−Ｖ₀を印加した状態の電流測定でも行なうことができる双方向の電流測定装置が構成される。
【００２８】
【発明の効果】
以上説明したように、この説明によれば電流検出用抵抗器３を保護する動作と、能動素子６に掛る電力を制限する動作の双方を実行することができ、これにより安価なコストで取り扱いが安易な電流測定装置を得ることができる利点が得られる。
【図面の簡単な説明】
【図１】この説明の一実施例を説明するための接続図。
【図２】図１に示した実施例の動作を説明するためのグラフ。
【図３】図２と同様のグラフ。
【図４】この発明の変形実施例を説明するための接続図。
【図５】この発明の更に他の実施例を説明するための接続図。
【図６】この発明の更に他の実施例を説明するための接続図。
【図７】この発明の更に他の実施例を説明するための接続図。
【図８】従来の技術を説明するための接続図。
【図９】従来の技術の他の例を説明するための接続図。
【符号の説明】
１入力端子８基準電圧源
３電流検出用抵抗器９基準電圧印加端子
４電圧測定器１０電流測定回路
６能動素子２０基準電圧制御手段
７電圧比較器３０過電圧検出手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a current measuring device, and more particularly to an improvement in a current measuring device with a protection circuit to which a function for preventing an overcurrent from flowing in a current detecting resistor is added.
[0002]
[Prior art]
FIG. 8 shows a circuit configuration of a conventional current measuring device with a protection circuit. In the figure, reference numeral 1 is an input terminal for the current to be measured i, 2 is a fuse, 3 is a resistor for current detection, 4 is a voltage measurement device for measuring a voltage generated in the current detection resistor 3, and 5 is a resistor for current detection. 3 shows a diode pair for preventing overcurrent and overvoltage from being applied to the device 3.
The current to be measured i is measured as follows. When the current to be measured i is applied to the input terminal 1 and the current to be measured i flows through the current detecting resistor 3, a voltage V ₁ is generated at both ends of the current detecting resistor 3. Since the resistance value of the current detecting resistor 3 is assumed to be a known RS in advance, by measuring the voltage V ₁ with the voltage measuring device 4, the current to be measured i is
i = V ₁ / Rs
Is required.
[0003]
When applying the measured current i to the input terminal 1, when in a conducting voltage + VE or -VE greater than the diodes D1, D2 of the voltage V ₁ of the two ends of the current detecting resistor 3 constitute a diode pair The diode D1 or D2 becomes conductive, restricts the current flowing through the current detection resistor 3, and protects the current detection resistor 3. When the current to be measured i further increases, the fuse 2 is blown to protect the current detection resistor 3 and the diodes D1 and D2.
The disadvantage of the protection circuit shown in FIG. 8 is that when the fuse 2 is blown, the fuse 2 must be replaced. That is, there is a drawback that it takes time to recover.
[0004]
FIG. 9 shows an example of a protection circuit that can eliminate this drawback. In the circuit shown in FIG. 9, the current is measured in the range e> V ₁ where the voltage V ₁ generated in the current detection resistor 3 is lower than the reference voltage e set in the reference voltage source 8. That is, the voltage V ₁ generated in the current detection resistor 3 is lower than the reference voltage e. When e> V ₁ , the voltage comparator 7 outputs a positive voltage as a voltage comparison output, and the positive voltage causes the active element 6 to The current i is measured without any trouble while being kept sufficiently on.
When the voltage V ₁ generated in the current detection resistor 3 becomes the same voltage e≈V ₁ as the reference voltage e, the voltage comparator 7 determines that the current i is i = e / Rs.
Thus, the active element 6 is controlled so as to operate as a constant current circuit. This constant current operation prevents overcurrent from flowing through the current detection resistor 3. However, if the state returns to the state of e> V _1, the active element 6 returns to the on state and can return to the normal current measurement mode.
[0005]
The current measuring device with a protection circuit shown in FIG. 9 has an advantage that the current detecting resistor 3 can be safely protected without the presence of a fuse and that the original measuring mode can be restored without any operation.
However, in this circuit, the power P consumed by the active element 6 in the current limited state is
P = (V ₀ −V ₁ ) i
Thus, as V ₀ increases, the active element 6 consumes a large amount of power, and it is necessary to use an active element having a large power capacity. Further, since heat generation is increased, a heat dissipating means must be provided.
[0006]
An object of the present invention is to provide a current measuring device capable of suppressing power consumption in an active element and performing a protective operation safely using an active element having a small amount of power.
[0007]
[Problems to be solved by the invention]
According to the present invention, in a current measuring device that applies a current to be measured to a current detecting resistor, measures a voltage generated in the current detecting resistor, and measures a value of the current to be measured, it is generated in the current detecting resistor. A voltage comparator that compares the voltage with a preset reference voltage and detects that the current flowing through the current detection resistor matches the set value and a current detection resistor are connected in series, and the voltage comparator An active element that limits the current flowing through the current detection resistor in a state where the resistance value is controlled by the comparison output and the current flowing through the current detection resistor matches the set value, and the active element and the current detection resistor Overvoltage detection means for detecting that the voltage applied to the series circuit constituted by the circuit exceeds a set value, and when the overvoltage detection means detects the overvoltage and the voltage applied to the series circuit further increases, the reference voltage Gradually voltage value Proposed configuration obtained by adding the reference voltage control means for Do and the current measuring device.
[0008]
According to the present invention, in the current measuring device according to claim 1, in the current measuring device for applying a positive voltage to the series circuit and measuring the positive current flowing in the current detection resistor, an active element N-channel field effect transistor or NPN transistor is used, the reference voltage supplied to the voltage comparator is a positive reference voltage, and the reference voltage control means detects the positive reference voltage supplied to the voltage comparator overcurrent. We propose a current measurement device that is configured to control close to the common potential.
[0009]
According to the present invention, in the current measuring device according to claim 1, in the current measuring device for applying a negative voltage to the series circuit and measuring the negative current flowing through the current detection resistor, a current-generating element is provided. Is a P-channel field effect transistor or PNP transistor, the reference voltage applied to the voltage comparator is a negative reference voltage, and the reference voltage control means uses the negative reference voltage applied to the voltage comparator as a common potential. Proposed is a current measuring device characterized in that it is configured to perform control close to.
[0010]
According to the present invention, in the current measuring device according to claim 1, an N-channel field effect transistor and a P-channel field effect transistor are connected in series to the current detection resistor, and the N-channel field effect transistor is a current detection resistor. The resistance value is controlled based on the comparison result between the voltage generated at the positive electrode and the positive reference voltage, and the resistance value of the P-channel field effect transistor is determined according to the comparison result between the voltage generated at the current detection resistor and the negative reference voltage. A current measuring device configured to control the current is proposed.
[0011]
Action According to the current measuring device of the present invention, when the voltage generated in the current detection resistor reaches the same voltage as the reference voltage applied to the voltage comparator, the active element and the voltage comparator operate at a constant current. Is executed. At the same time, when the voltage V ₀ applied to the input terminal becomes higher than the set value, the overpower detection means detects the overvoltage, and the reference voltage control means shares the reference voltage applied to the voltage comparator by detecting this overvoltage. Control in the direction approaching the potential.
[0012]
As a result, the active element gradually enters the current limiting operation from the constant current operation, and operates in the direction of decreasing the current value from the constant current state. When the voltage V ₀ applied to the input terminal further rises from the point of overvoltage detection, the resistance value of the active element increases, limiting the current, and finally turning off.
Therefore, according to the present invention, since the current flowing through the active element is limited and the current value is gradually reduced from when the voltage V ₀ applied to the input terminal exceeds the set value, the power consumed by the active element is suppressed. Therefore, even an active element having a small power capacity can sufficiently withstand. Further, since the amount of heat generated can be reduced, there is no need to provide a heat dissipating means, and there is an advantage that it can be manufactured at a low cost as a whole.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a power measuring apparatus according to the present invention. In the figure, reference numeral 10 denotes a conventional current measuring circuit described with reference to FIG. That is, the current to be measured i applied to the input terminal 1 is input to the current detecting resistor 3 through the active element 6, and the voltage V ₁ generated in the current detecting resistor 3 is measured by the voltage measuring device 4. The current i,
i = V ₁ · RS: RS is the resistance value of the current detection resistor,
Ask for.
[0014]
In the normal current measurement state, the reference voltage V ₂ applied to the voltage comparator 7 is set to a positive potential sufficiently higher than the voltage V ₁ generated in the voltage detection resistor 3. Therefore, the voltage comparator 7 outputs a comparison output voltage V ₃ of the positive potential, this by the positive potential comparison output voltage V ₃ of the active element 6 constituted by N-channel field effect transistor in this example is on state Maintained.
[0015]
In the present invention, the reference voltage control means 20 is connected between the reference voltage application terminal 9 and the reference voltage source 8 of the voltage comparator 7 and the voltage V ₀ applied to the input terminal 1 is an overvoltage equal to or higher than a predetermined set value. The overvoltage detection means 30 for notifying the reference voltage control means 20 that the voltage has risen is connected between the input terminal 1 and the reference voltage control means 20.
[0016]
A generally known operational amplifier is used as the voltage comparator 7, and the voltage V ₁ generated in the current detection resistor 3 is input to its inverting input terminal. The non-inverting input terminal is connected to the reference voltage application terminal 9.
The reference voltage control means 20 includes an operational amplifier 21 having a non-inverting input terminal connected to a common potential, an input resistor 22 connected between the inverting input terminal of the operational amplifier 21 and the reference voltage source 8, and an operational amplifier. The feedback resistor 23 is connected between the inverting input terminal 21 and the output terminal 21, and the connection point between the output terminal of the operational amplifier 21 and the feedback resistor 23 is connected to the reference voltage application terminal 9. Here, the reference voltage source 8 generates a negative reference voltage −e, the polarity of the negative reference voltage −e is inverted by the operational amplifier 21, and a positive reference voltage V ₂ is applied to the reference voltage application terminal 9. The
[0017]
The overvoltage detection means 30 includes a constant voltage diode 31 and a current limiting resistor 32 connected in series with the constant voltage diode 31. A series circuit composed of a current limiting resistor 32 and a constant voltage diode 31 is connected between the input terminal 1 and the inverting input terminal of the operational amplifier 21 constituting the reference voltage control means 20 and applied to the input terminal 1. When the applied voltage V ₀ exceeds the conduction voltage Vz of the constant voltage diode 31, the constant voltage diode 31 becomes conductive, the conduction current is applied to the reference voltage control means 20, and the reference voltage control means 20 indicates that an overvoltage has been input. To communicate.
[0018]
Here, the resistance value of the current detection resistor 3 is Rs, the voltage generated at this is V ₁ , the reference voltage applied to the reference voltage application terminal 9 is V ₂ , and the comparison output voltage of the voltage comparator 7 is V _3. The resistance values of the input resistor 22 and the feedback resistor 23 constituting the reference voltage control means 20 are R ₁ and R ₂ , the conduction voltage of the constant voltage diode 31 constituting the overvoltage detection means 30 is Vz, and the current The operation of the reference voltage control means 20 and the overvoltage detection means 30 will be described with the resistance value of the limiting resistor 32 as R ₃ .
[0019]
(1) When the relationship between the input voltage V ₀ and the conduction voltage V ₂ of the constant voltage diode 31 is V ₀ <Vz, the reference voltage V ₂ applied to the reference voltage application terminal 9 is
_{_{V 2 = (- R 2 /}} R 1) (- e) = (R 2 / R 1) e
i <(R ₂ / R ₁ · Rs) e ((1) shown in FIG. 2) In this state, since V ₂ > V ₁ , the comparison output voltage V ₃ of the voltage comparator 7 is sufficiently saturated in the positive potential direction. Therefore, the active terminal 6 is completely conductive. The voltage V ₀ of the input terminal 1 is
V ₀ = Rs · i
Determined by
( ₂ ) When i = (R ₂ / R ₁ · Rs) e, the voltage comparator 7 and the active element 6 enter a constant current operation. In this state, the current flowing through the current detection resistor 3 is constant ((2) in FIG. 2). The voltage at the input terminal 1 matches the voltage applied from the outside.
(3) When V ₀ ≧ Vz, a current flows through the overvoltage detecting means 30 and the reference voltage V ₂ is lowered. If the current flowing through the overcurrent detection means 30 is ignored,
i = (− (R ₂ / R ₃ ) V ₀ + R ₂ (e / R ₁ + Vz / R ₃ )) / Rs
The current i decreases as the voltage V ₀ increases ((3) in FIG. 2).
(4) When V ₀ becomes V _A = ((R ₃ / R ₁ ) e + Vz), the reference voltage V ₂ becomes V ₂ = 0. As a result, the active element 6 is turned off and i = 0 (FIG. 2). 4 ▼).
[0020]
Each state described above corresponds to ( ₁ ), ( ₂ ), (3), and (4) shown in FIG. 2, and when the current i reaches the set value (R ₂ / R ₁ · Rs) e, the constant current When the voltage V ₀ exceeds the conduction voltage Vz of the constant voltage diode 31, the current i starts to decrease.
FIG. 3 shows the relationship between the voltage V _{0 and the} power P. The power P shown in FIG. 3 is equivalent to the power applied to the active element 6. As is apparent from FIG. 3, the power applied to the active element 6 becomes a maximum value when V _A / 2, and when V ₀ ≧ V _A , the active element 6 is turned off, and even if V ₀ rises above V _{A, the} power is increased. Maintain almost zero. When V ₀ returns to the state of V ₀ <Vz, the active element 6 returns to the on state.
[0021]
Therefore, according to the present invention, recovery from the overvoltage protection state is automatic recovery, and the current detection resistor 3 is protected from overcurrent and overvoltage, and the power consumption does not exceed a certain level. As a result, an element having a smaller power capacity than the conventional element can be used as the active element 6. In addition, since the amount of heat generated can be reduced, there is no need to add a radiator, and therefore an advantage that this type of current measuring device can be manufactured at low cost is obtained.
FIG. 4 shows an embodiment using an NPN transistor as the active element 6. In this case, the only difference is that the base current limiting resistor 11 is connected to the base of the transistor operating as the active element 6.
[0022]
FIG. 5 shows yet another embodiment of this description. In this embodiment, the reference voltage source 8 is connected between the non-inverting input terminal of the operational amplifier 21 constituting the reference voltage control means 20 and the common potential. In this case, when a positive reference voltage e is applied to the non-inverting input terminal of the operational amplifier 21, a positive reference voltage V ₂ is output to the reference voltage application terminal 9.
Even when the voltage detection means 30 detects an overvoltage in the configuration shown in FIG. 5, the reference voltage V ₂ applied to the reference voltage application terminal 9 decreases to the common potential side, and the current i flowing through the active element 6 can be suppressed. .
[0023]
FIG. 6 shows still another embodiment of the present invention. In this embodiment, a case where a P-channel field effect transistor is used as the active element 6 is shown. That is, in this embodiment, a current measuring device for measuring the negative current -i is configured. For this purpose, the reference voltage source 8 applies a positive reference voltage e to the inverting input terminal of the operational amplifier 21 constituting the reference voltage control means 20, and a negative reference voltage −V ₂ is applied to the reference voltage application terminal 9. Apply. The constant voltage diode 31 constituting the overvoltage detection means 30 is connected in the opposite direction to the embodiment shown in FIGS.
[0024]
The current detecting resistor 3 and the voltage -V ₁ negative polarity is generated, and this voltage -V ₁ and the reference voltage -V ₂ is compared by the voltage comparator 7. In the plain current measurement mode, −V ₁ > −V ₂ is satisfied, and the negative output voltage −V ₃ is output as the comparison output voltage of the voltage comparator 7. The negative channel comparison output voltage −V ₃ maintains the P-channel field effect transistor 6 in the ON state, and current measurement can be performed.
When the input current i increases and reaches the state of −V ₁ ≈−V ₂ , the active element 6 and the voltage comparator 7 constitute a constant current circuit, and the current flowing through the current detection resistor 3 is limited to a constant current. To do. The voltage at the input terminal 1 matches the voltage applied from the outside.
[0025]
When the input voltage -V ₀ reaches -V ₀ ≦ -Vz, overcurrent detection means 30 detects the applied state of the overvoltage, since flow conducting current to the reference voltage control unit 20, input from the time the voltage -V ₀ Each time the current i is further deviated in the negative direction, the current i decreases, and the active element 6 is finally turned off.
Therefore, the current detection resistor 3 is protected even in the current measuring device in the negative direction, and the power applied to the active element 6 does not exceed a predetermined value and is limited to a predetermined range.
FIG. 7 shows still another embodiment of the present invention. In this embodiment, an example is shown in which a bidirectional current measuring apparatus capable of performing both the current measurement in the positive direction shown in FIG. 1 and the current measurement in the negative direction shown in FIG. 6 is configured.
[0026]
6N represents an N-channel field effect transistor, and 6P represents a P-channel field effect transistor. These field effect transistors 6N and 6P are connected in series between the input terminal and the current detection resistor 3.
7N denotes a voltage comparator that applies a voltage comparison output + V ₃ to the active element 6N, and 7P denotes a voltage comparator that applies a voltage comparison output −V ₃ to the active element 6P. 8N is a reference voltage source for applying the reference voltage + V ₂ to the reference voltage application terminal 9N through the reference voltage control means 20N, and 8P is for applying the reference voltage −V ₂ to the reference voltage application terminal 9P through the reference voltage control means 20P. The reference voltage source is shown.
[0027]
30N represents an overvoltage detection means for applying an overvoltage detection output to the reference voltage control means 20N, and 30P represents an overvoltage detection means for applying an overvoltage detection output to the reference voltage control means 20P.
With these configurations, a bidirectional current measuring device that can perform both current measurement in a state where a positive voltage + V ₀ is applied to the input terminal 1 and current measurement in a state where a negative voltage −V ₀ is applied to the input terminal 1 is configured. Is done.
[0028]
【The invention's effect】
As described above, according to this description, both the operation for protecting the current detection resistor 3 and the operation for limiting the power applied to the active element 6 can be executed. There is an advantage that an easy current measuring device can be obtained.
[Brief description of the drawings]
FIG. 1 is a connection diagram for explaining one embodiment of this explanation.
FIG. 2 is a graph for explaining the operation of the embodiment shown in FIG. 1;
FIG. 3 is a graph similar to FIG.
FIG. 4 is a connection diagram for explaining a modified embodiment of the present invention.
FIG. 5 is a connection diagram for explaining still another embodiment of the present invention.
FIG. 6 is a connection diagram for explaining still another embodiment of the present invention.
FIG. 7 is a connection diagram for explaining still another embodiment of the present invention.
FIG. 8 is a connection diagram for explaining a conventional technique.
FIG. 9 is a connection diagram for explaining another example of the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Input terminal 8 Reference voltage source 3 Current detection resistor 9 Reference voltage application terminal 4 Voltage measurement device 10 Current measurement circuit 6 Active element 20 Reference voltage control means 7 Voltage comparator 30 Overvoltage detection means

Claims

In a current measuring device that applies a current to be measured to a current detecting resistor, measures a voltage generated in the current detecting resistor, and measures a value of the current to be measured.
A voltage comparator that compares the voltage generated in the current detection resistor with a preset reference voltage and detects that the current flowing in the current detection resistor matches a set value;
The current detection resistor is connected in series with the current detection resistor, the resistance value is controlled by the comparison output of the voltage comparator, and the current flowing through the current detection resistor flows through the current detection resistor in a state where the current matches the set value. An active element that limits the current;
An overvoltage detecting means for detecting that a voltage applied to a series circuit constituted by the active element and the current detecting resistor exceeds a set value;
A reference voltage control means for detecting an overvoltage by the overvoltage detection means and gradually lowering the voltage value of the reference voltage when the voltage applied to the series circuit further increases;
A current measuring device characterized by having a configuration to which is added.

2. The current measuring device according to claim 1, wherein a positive voltage is applied to the series circuit to measure a positive current flowing through the current detection resistor. An N-channel field effect transistor or an NPN transistor is used, the reference voltage supplied to the voltage comparator is a positive reference voltage, and the reference voltage control means exceeds the positive reference voltage supplied to the voltage comparator. A current measuring device having a configuration in which control close to a common potential is performed during current detection.

2. The current measuring device according to claim 1, wherein a negative voltage is applied to the series circuit to measure a negative current flowing through the current detection resistor. A P-channel field effect transistor or a PNP transistor is used, and the reference voltage supplied to the voltage comparator is a negative reference voltage. The reference voltage control means uses a negative reference voltage supplied to the voltage comparator. A current measuring device characterized in that it is configured to perform control close to a common potential.

2. The current measuring device according to claim 1, wherein an N-channel field effect transistor and a P-channel field effect transistor are connected in series to the current detection resistor, and the N-channel field effect transistor is connected to the current detection resistor. The resistance value is controlled by a comparison result between the generated voltage and the positive reference voltage, and the P-channel field effect transistor has a resistance according to a comparison result between the voltage generated in the current detection resistor and the negative reference voltage. A current measuring device characterized in that the value is controlled.