JP3805807B2

JP3805807B2 - Secondary battery charging circuit

Info

Publication number: JP3805807B2
Application number: JP01521795A
Authority: JP
Inventors: 信雄塩島
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1995-02-01
Filing date: 1995-02-01
Publication date: 2006-08-09
Anticipated expiration: 2021-08-09
Also published as: JPH08214466A

Description

【０００１】
【産業上の利用分野】
本発明は、二次電池の充電回路に係り、特に電池の種類に応じて定電圧充電と定電流充電とを切り替えて充電する充電回路に関する。
【０００２】
【従来の技術】
二次電池の充電方式は種々提案されているが、リチウムイオン電池などの非水溶媒系二次電池あるいは鉛蓄電池については、定電圧充電方式を用いることが多い。この充電方式は、電池電圧が設定値に達するまでは大電流で充電し、設定値に達すると電池電圧を一定にするように電流を下げる方式である。一方、ニッケル水素蓄電池やニッケルカドニウム蓄電池などのアルカリ蓄電池については、一定の電流で充電し、電池温度、電池電圧、充電時間等の検出により、電池が満充電になったことを検出すると、充電電流を遮断したり、あるいは減少させて充電制御を行う定電流充電方式を用いることが多い。
【０００３】
ところで、このように最適な充電方式の異なる非水溶媒系二次電池とアルカリ蓄電池を同一の充電器で充電する方法として、例えば特開平６−１３３４６６に記載されている方法がある。この方法は、電池をその種類によらず定電圧充電する方法であり、定電圧充電方式で充電を行った場合、非水溶媒系二次電池は満充電になると充電電流は減少するが電池電圧は変化しないのに対して、アルカリ蓄電池は満充電になると電池電圧が所定値低下するか、あるいは充電電流が減少から増加に転じることを利用している。
【０００４】
具体的には、電池パックに電池の種類に応じて異なる値の抵抗を接続した電池判別端子を設け、この端子からの出力電圧を充電器側で検出し、その値に応じて充電電圧の上限を選定すると共に、充電時の電池電圧がピーク値から電池電圧がΔＶ低下したことを検出する電圧検出手段と、充電電流が最小値から所定値ΔＩだけ上昇したことを検出する電流検出手段とを設け、これら電圧検出手段または電流検出手段のいずれかの検出出力が発生したことをもって電池が満充電に達したとみなして充電制御（充電電流を遮断または減少させる制御）を行う方法をとっている。
【０００５】
さらに、この方法では二次電池をその種類によらず定電圧充電するために、充電電圧を二次電池の種類に応じて切り替えている。例えば、非水溶媒系二次電池がリチウム二次電池の場合に定電圧充電方式で充電するのに必要な充電電圧は、４．２Ｖ／セルで２個直列接続した場合は８．４Ｖである。一方、アルカリ蓄電池の場合は最高１．８Ｖ／セルで５個直列接続した場合、定電圧充電方式で充電するのに必要な充電電圧は最高９Ｖである。
【０００６】
【発明が解決しようとする課題】
しかしながら上述した従来技術では、特にアルカリ蓄電池を定電圧充電した場合には、電池が満充電に達しても電池電圧が低下しなかったり充電電流が減少から増加に転じないことがあるため、電池を過充電してしまうことがあり、また電池の種類に応じて充電電圧を変えなければならないという問題があった。
【０００７】
本発明は、最適な充電方式の異なる非水溶媒系二次電池とアルカリ蓄電池を同一の充電器で、しかも充電電圧を変えることなく充電でき、かつ非水溶媒系二次電池のみならずアルカリ蓄電池に対しても過充電することなく確実に満充電まで充電できる二次電池の充電回路を提供することを目的とする。
【０００８】
【課題を解決するための手段】
上記の課題を解決するため、本発明による二次電池の充電回路は、二次電池を充電するための充電用電源と、前記二次電池の両端子にそれぞれ接続された入力端子および基準電位端子と出力端子を有する分圧手段と、この分圧手段の出力端子と基準電位端子との間に接続され、前記二次電池が定電圧充電されるべき電池の場合は非導通状態とされることにより前記分圧手段の出力端子から前記二次電池の端子電圧を分圧した電圧を出力させ、前記二次電池が定電流充電されるべき電池の場合は導通状態とされることにより前記分圧手段の出力端子の電圧を前記基準電位端子の電圧と等しくさせるスイッチ手段と、前記充電用電源から前記二次電池に供給される充電電流を検出し該充電電流に対応した電圧を出力する電流検出手段と、前記分圧手段の出力端子の電圧と前記電流検出手段の出力電圧のうち電圧値の大きい方を選択する選択手段と、この選択手段の出力電圧が基準電圧と等しくなるように該選択回路の出力電圧に応じて前記充電電流を制御する電流制御手段とを具備することを特徴とする。
【００１０】
【作用】
上記のように構成された本発明の二次電池の充電回路では、二次電池がリチウムイオン電池などの非水溶媒系二次電池のように定電圧充電されるべき電池の場合は、分圧手段の出力端子と基準電位端子との間に接続されたスイッチ手段が非導通状態とされるため、分圧手段の出力に電池電圧を分圧した電圧が現れる。充電が進み電池電圧が上昇すると、分圧手段の出力電圧が電流検出手段の出力電圧より大きくなって最大電圧選択手段により選択され、これに基づいて充電電流が制御されることにより、定電圧充電が行われる。
【００１１】
一方、二次電池がニッケル水素蓄電池などのアルカリ蓄電池のように定電流充電されるべき電池の場合は、分圧手段の出力端子と基準電位端子との間がスイッチ手段で短絡されるため、分圧手段の出力電圧はほぼ零となる。従って、今度は電流検出手段の出力電圧が分圧手段の出力電圧より大きくなって最大電圧選択手段により選択され、これに基づいて充電電流が制御されることにより、定電流充電が行われる。
【００１２】
このように最適な充電方式の異なる非水溶媒系二次電池とアルカリ蓄電池を同一の充電器で、しかも同じ充電電圧で充電でき、さらに電池の種類に応じて電池電圧を分圧する分圧手段の出力端子と基準電位端子との間をスイッチ手段により導通または非導通状態として、分圧手段の出力電圧と充電電流を検出する電流検出手段の出力電圧のうち電圧値の大きい方を充電制御に用いる方式であるため、いずれの電池に対しても過充電を行うことなく確実に満充電まで充電することが可能となる。
【００１３】
すなわち、本発明では非水溶媒系二次電池に対しては定電圧充電方式で充電を行い、アルカリ蓄電池に対しては定電流充電方式で充電を行うため、両者を共に定電圧充電方式で充電する従来技術のように充電電圧を切り替える必要がないばかりでなく、アルカリ蓄電池に対しては定電流充電方式で充電を行うことによって満充電を公知の満充電検知手段により確実に検知することができるので、従来技術のように過充電を行うおそれがない。
【００１４】
【実施例】
以下、本発明の実施例を図面を参照して説明する。
図１は本発明の一実施例に係る二次電池の充電回路を示す回路図である。この充電回路は大きく分けて充電器と電池パックからなる。電池パック１０は、二次電池１１（以下、単に電池という）とサーミスタ１２を有する。電池１１は、例えばリチウム二次電池等の非水溶媒系二次電池や鉛電池などの定電圧充電されるべき電池、あるいはニッケル水素蓄電池のような定電流充電されるべきアルカリ蓄電池である。以下、定電圧充電されるべき電池がリチウムイオン電池で、定電流充電されるべき電池がニッケル水素蓄電池の場合を例にとり説明する。
【００１５】
電池パック１０の端子＋，−およびＴ，Ｓは外部接続端子であり、端子＋は電池１１の正極端子に接続され、端子−は電池１１の負極端子に接続され、端子Ｔはサーミスタ１２の一端に接続される。サーミスタ１２は電池１１に密着して設置されている。端子Ｓは、電池１１がリチウムイオン電池の場合、端子−に接続され、電池１１がニッケル水素蓄電池の場合、オープンつまり電位的に浮いた状態とされる。
【００１６】
一方、充電器２０は、充電用電源２１、電流制御回路２２、分圧回路２３、スイッチ回路２４、電流検出回路２５、最大電圧検出回路２６および温度制御回路２７からなる。端子＋，−およびＴ，Ｓは、充電器２０の外部接続端子であり、充電時は電池パック１０の対応する端子とそれぞれ接続される。
【００１７】
充電用電源２１は、例えば交流電源の出力を整流して直流を得る電源や他の比較的大容量の電池が用いられ、その一端は電流制御回路２２を介して電池パック１０の端子＋に接続され、電池パック１０の端子−は電流検出回路２５を介して充電用電源２１の他端に接続されている。
【００１８】
電池１１の正極端子および負極端子には、端子＋，−を介して二つの抵抗Ｒ１，Ｒ２の直列回路からなる分圧回路２３の入力端子（抵抗Ｒ１の一端）および基準電位端子（抵抗Ｒ２の一端）がそれぞれ接続されている。基準電位端子は、この例では接地電位となっている。抵抗Ｒ１とＲ２の他端は、分圧回路２３の出力端子となっている。
【００１９】
分圧回路２３の出力端子と基準電位端子との間には、スイッチ回路２４が接続されている。このスイッチ回路２４はＮＰＮトランジスタＱ３と抵抗Ｒｂ，Ｒｃからなり、トランジスタＱ３のコレクタは分圧回路２３の出力端子に接続され、エミッタは分圧回路２３の基準電位端子に接続され、ベースは抵抗Ｒｂの一端に接続されている。抵抗Ｒｂの他端は抵抗Ｒｃを介して正電源Ｖ＋に接続されると共に、電池パック１０の端子Ｓに接続されている。
【００２０】
ここで、電池１１が非水溶媒系電池の場合は、電池パック１０の端子Ｓは端子−に接続されているので、トランジスタＱ３は非導通状態である。従って、分圧回路２３の抵抗Ｒ１，Ｒ２の抵抗値を同じ記号Ｒ１，Ｒ２で表わすと、電池１１の端子電圧（以下、電池電圧という）ＶB は分圧回路２３により次式（１）に示すようにＶ２なる電圧に分圧される。
【００２１】
Ｖ２＝｛Ｒ２／（Ｒ１＋Ｒ２）｝×ＶB …（１）
一方、電池１１がアルカリ蓄電池の場合は、電池パック１０の端子Ｓはオープンであるため、トランジスタＱ３は導通状態である。従って、分圧回路２３の出力電圧Ｖ２は約０ボルトとなる。
【００２２】
電流検出回路２５は、電池パック１０内の電池１１と直列に接続された比較的低い抵抗値（例えば数ｍΩ〜数百ｍΩ）の抵抗Ｒ３と、この抵抗Ｒ３の両端に発生する電圧を増幅する増幅器Ａ２とからなる。抵抗Ｒ３の抵抗値を同じ記号Ｒ３で表わし、増幅器Ａ２の増幅度をＧ、充電電流をＩB とすると、電流検出回路２５の出力電圧Ｖ３は次式（２）に示すようになる。
【００２３】
Ｖ３＝ＩB ×Ｒ３×Ｇ …（２）
分圧回路２３の出力電圧Ｖ２および電流検出回路２５の出力電圧Ｖ３は、最大電圧選択回路２６に入力される。最大電圧選択回路２６は、分圧回路２３の出力電圧Ｖ２と電流検出回路２５の出力電圧Ｖ３のうち電圧値の高い方を選択して出力する回路であり、電圧比較器Ａ３と二つのアナログスイッチＳＷ１，ＳＷ２およびインバータＩＣ１からなる。すなわち、分圧回路２３の出力電圧Ｖ２および電流検出回路２５の出力電圧Ｖ３は、電圧比較器Ａ３の非反転入力端子および反転入力端子にそれぞれ入力される。電圧比較器Ａ３の出力は、分圧回路２３の出力電圧Ｖ２と電流検出回路２５の出力電圧Ｖ３の大小関係がＶ２＞Ｖ３のとき高レベル、Ｖ２＜Ｖ３のとき低レベルとなる。アナログスイッチＳＷ１，ＳＷ２の各一端には分圧回路２３の出力電圧Ｖ２および電流検出回路２５の出力電圧Ｖ３がそれぞれ与えられる。アナログスイッチＳＷ１，ＳＷ２の各他端は最大電圧選択回路２６の内部で共通接続され、この共通接続点から最大電圧選択回路２６の出力が取り出される。アナログスイッチＳＷ１，ＳＷ２は制御信号により導通・非導通が制御されるスイッチであり、制御信号として電圧比較器Ａ３の出力信号およびこれをインバータＩＣ１で反転した信号がそれぞれ与えられ、制御信号が高レベルのとき導通状態、低レベルのとき非導通状態となる。
【００２４】
電流制御回路２２は、最大電圧選択回路２６の出力に応じて充電用電源２１から電池１１に供給される充電電流を制御する回路であり、充電用電源２１の一端にエミッタが接続されコレクタが端子＋に接続されたＰＮＰトランジスタである電流制御トランジスタＱ１と、この電流制御トランジスタＱ１のベースにコレクタが接続され、エミッタが電流制御トランジスタＱ１のエミッタに接続されたＰＮＰトランジスタである充電制御トランジスタＱ２、および電流制御トランジスタＱ１のベースに抵抗Ｒａを介して出力端子が接続された誤差増幅器Ａ１からなるドロッパ型構成となっている。誤差増幅器Ａ１は演算増幅器からなり、その非反転入力端子には最大電圧選択回路２６の出力が印加され、反転入力端子には基準電圧発生器Ｖｒｅｆから発生される基準電圧Ｖ１が印加される。
【００２５】
なお、上記構成においては、電池電圧ＶB が設定値Ｖａ（例えば、電池１個当たり４．２Ｖ）に達したときＶ２＝Ｖ１となるように分圧回路２３を構成する抵抗Ｒ１，Ｒ２の値が選定され、また充電電流ＩB が所定の定電流値ＩａのときＶ３＝Ｖ１となるように電流検出回路２５における抵抗Ｒ３の値と増幅器Ａ２の増幅度Ｇが設定されているものとする。言い換えれば、分圧回路２３および電流検出回路２５は、電池電圧ＶB が設定値Ｖａのときの分圧回路２３の出力電圧Ｖ２（＝Ｖ１）と充電電流ＩB が所定の定電流値Ｉａのときの電流検出回路２５の出力電圧Ｖ３（＝Ｖ１）とが等しくなるように構成される。
【００２６】
電池パック１０内のサーミスタ１２には温度制御回路２７の入力端子が端子Ｔを介して接続され、温度制御回路２７の出力端子は電流制御回路２２内の充電制御トランジスタＱ２のベースに接続される。温度制御回路２７はサーミスタ１２からの信号に基づいて電池１１の温度を監視し、温度上昇率が所定値（例えば１℃／分）に達すると低レベルの信号を出力する。
【００２７】
次に、図１の二次電池の充電回路の動作を図２および図３に示すリチウムイオン電池およびニッケル水素蓄電池の充電時の波形図を参照して説明する。図２および図３において（ａ）は充電電流ＩB および電池電圧ＶB の波形、（ｂ）は分圧回路２３の出力電圧Ｖ２と電流検出回路２５の出力電圧Ｖ３の波形、（ｃ）は電圧比較器Ａ３の出力波形、（ｄ）は電池温度の波形、そして（ｅ）は温度制御回路２７の出力波形をそれぞれ示している。
【００２８】
電池１１が非水溶媒系二次電池であるリチウムイオン電池の場合、端子Ｓは端子−に電池パック１０の内部で接続されている。このとき、スイッチ回路２４のトランジスタＱ３は非導通状態であるため、分圧回路２３の出力電圧Ｖ２としては式（１）で示されるように端子電圧ＶB を抵抗Ｒ１とＲ２で分圧した電圧が出力される。
【００２９】
充電が開始されると、充電用電源２１から電流制御回路２２および電流検出回路２５を介して電池１１に充電電流ＩB が供給されはじめる。充電初期は、図２（ａ）に示すように端子電圧ＶB が設定電圧Ｖａより低いため、電池１１は電流Ｉａで充電される。すなわち、充電初期は分圧回路２３の出力電圧Ｖ２と電流検出回路２５の出力Ｖ３の関係が図２（ｂ）に示すようにＶ２＜Ｖ３であるため、電圧比較器Ａ３の出力は図２（ｃ）に示すように低レベルである。これにより、アナログスイッチＳＷ２が導通状態となり、最大電圧選択回路２６で電流検出回路２５の出力電圧Ｖ３が選択され、電流制御回路２２の誤差増幅器Ａ１の非反転入力端子に印加される。この誤差増幅器Ａ１の出力によって、
Ｖ３＝Ｖ１ …（３）
となるように電流制御トランジスタＱ１のベース電流が制御される。つまり、電流検出回路２５によって検出される充電電流ＩB が基準電圧Ｖ１に対応した定電流値Ｉａを保つように充電電流ＩB が制御され、定電流充電動作が行われる。このときの充電電流ＩB の値は、式（２）および（３）から、
ＩB ＝Ｖ１／（Ｒ３×Ｇ）
＝Ｉａ …（４）
となる。
【００３０】
充電が進むと電池電圧ＶB が上昇し、それに伴い分圧回路２３の出力電圧Ｖ２が上昇する。そして、ｔ＝ｔａの時点でＶ２＞Ｖ３となると、図２（ｃ）に示すように最大電圧選択回路２６において電圧比較器Ａ３の出力は高レベルとなる。このため、アナログスイッチＳＷ１が導通状態となり、誤差増幅器Ａ１の非反転入力端子には分圧回路２３の出力電圧Ｖ２が印加される。この誤差増幅器Ａ１の出力によって、
Ｖ２＝Ｖ１ …（５）
となるように、つまり分圧回路２３の出力電圧Ｖ２、つまり電池電圧ＶB に対応した電圧が基準電圧Ｖ１と等しくなるように電流制御トランジスタＱ１のベース電流が制御されるため、電池電圧ＶB は一定に保たれる。すなわち、充電動作は定電流充電動作から定電圧充電動作へと移行する。
【００３１】
なお、一旦スイッチＳＷ１が導通すると、電流制御回路２２が上述のように定電圧充電動作を行うことにより充電電流ＩB が減少し、それに伴って図２（ｂ）に示すように電流検出回路２５の出力電圧Ｖ３が低下するため、Ｖ２＞Ｖ３の関係は維持される。従って、電流制御回路２２が定電流充電動作から定電圧充電動作に移行するときにスイッチＳＷ１とスイッチＳＷ２が交互に導通動作を行ってしまうことはない。
【００３２】
充電がさらに進み、充電電流ＩB が設定値Ｉｂ（例えば１００ｍＡ）まで低下したｔ＝ｔｂの時点で、図示しない公知の電流検出に基づく満充電検出手段により電池３がほぼ満充電まで充電されたと判定される。こうして電池１１が満充電に達したと判定されると、充電が停止するか、またはトリクル充電に移行するか、あるいは充電完了の表示が行われる。
【００３３】
なお、上記のようにリチウムイオン電池を充電しても図２（ｄ）に示すように電池温度はほとんど変化せず、従って温度制御回路２７の出力が低レベルとなることはないので、充電制御トランジスタＱ２は導通しない。このため、電流制御トランジスタＱ１は誤差増幅器Ａ１の出力によってのみ動作する。
【００３４】
次に、電池１１がニッケル水素蓄電池の場合、電池パック１０の端子Ｓはオープンとされる。このとき、スイッチ回路２４のトランジスタＱ３のベースに電源Ｖ＋から抵抗ＲｃとＲｂを介して電流が流れてトランジスタＱ３が導通状態となるため、分圧回路２３の出力電圧Ｖ２は概略０ボルトとなる。従って、分圧回路２３の出力電圧Ｖ２と電流検出回路２５の出力Ｖ３の関係は図３（ｂ）のようにＶ２＜Ｖ３となり、電圧比較器Ａ３の出力は低レベルとなる。これによりアナログスイッチＳＷ２が導通状態となり、最大電圧選択回路２６で電流検出回路２５の出力電圧Ｖ３が選択され、電流制御回路２２の誤差増幅器Ａ１の非反転入力端子に印加される。この誤差増幅器Ａ１の出力によって、式（３）と同様にＶ３＝Ｖ１となるように電流制御トランジスタＱ１のベース電流が制御される結果、図３（ａ）に示すように電池１１がリチウムイオン電池の充電時間が０＜ｔ＜ｔａの場合と同様に、式（４）で示される充電電流ＩB で電池１１は充電される。
【００３５】
ここで、図３（ｄ）に示すように電池１１の温度は充電初期及び中期は緩やかに上昇するが、充電末期になると急激に上昇し、ｔ＝ｔｄの時点で温度制御回路２７は出力は図３（ｅ）に示すように高レベルから低レベルに変化する。すなわち、電池１１が満充電になったと判定される。これにより、電流制御回路２２内の充電制御トランジスタＱ２が導通状態となるため、電流制御トランジスタＱ１は遮断状態となり、充電を停止する。
【００３６】
本発明は、上記実施例に限定されるものでなく、次のように種々変形して実施することができる。
（１）実施例では、分圧回路２３で二次電池の端子電圧ＶB を分圧した電圧Ｖ２を電圧比較器Ａ３の非反転入力端子とアナログスイッチＳＷ１に入力したが、特殊な場合として抵抗Ｒ２の抵抗値を無限大とし、ＶB そのものをＶ２として出力しても良い。
【００３７】
（２）実施例では、スイッチ回路２４を構成するスイッチＳＷ１，ＳＷ２がアナログスイッチの例を示したが、電界効果型トランジスタやバイポーラトランジスタなどの他の半導体スイッチでも良く、機械的リレーであっても良い。
【００３８】
（３）実施例では、最大電圧選択回路２６を電圧比較器Ａ３とアナログスイッチＳＷ１，ＳＷ２およびインバータＩＣＩで構成したが、図４に示すように分圧回路２３の出力電圧Ｖ２および電流検出回路２５の出力電圧Ｖ３を非反転入力端子に入力する２つの演算増幅器Ａ４，Ａ５と、演算増幅器Ａ４，Ａ５の出力端子にアノードが接続されカソードが反転入力端子に接続されると共に最大電圧選択回路２６の出力端子に接続された２つのダイオードＤｉ１，Ｄｉ２、および最大電圧選択回路２６の出力端子と接地間に接続された出力抵抗Ｒｄにより構成しても良い。
【００３９】
（４）実施例では、ニッケル水素蓄電池などのアルカリ蓄電池の充電制御として、温度上昇率検出制御を例にとり説明したが、温度制御、ΔＴ制御（充電初期からの電池温度上昇、または電池温度と周囲温度との差が設定値に達したら充電を制御する）、タイマー制御、電圧制御、−ΔＶ制御、ピーク電圧制御その他の制御法を用いてもよく、またこれらの制御法を適宜組み合わせても良い。これらいずれの制御法を用いても、本発明ではアルカリ蓄電池に対しては定電流充電方式を用いていることから、確実に満充電を検出でき、過充電を起こすことなく電池を満充電まで充電することが可能である。
【００４０】
（５）実施例では、リチウムイオン電池などの非水溶媒系電池の充電制御において、定電圧充電で充電電流が所定値まで低下した場合に満充電と検出して充電を停止するようにしたが、タイマー制御や温度制御（電池温度が所定の範囲を外れた場合に充電停止する制御）、電圧制御等と組み合わせても良い。
【００４１】
（６）実施例では、電池１１が１個の場合について示したが、２個以上の組電池の場合にも本発明を適用することができる。
（７）実施例では、分圧回路２３は２個の抵抗Ｒ１，Ｒ２で説明したが、Ｒ１，Ｒ２のいずれか一方または両方が２個以上の抵抗器（可変抵抗器を含む）の組み合わせであっても良い。
【００４２】
（８）実施例では、電流検出回路２５を電池１１の負極側の充電路に挿入したが、電池１１の正極側の充電路に挿入しても良い。この場合、スイッチ回路２４のトランジスタＱ３を図１の抵抗Ｒ１の両端に接続し、最大電圧選択回路２６は電池１１の正極端子の電位を基準としてＶ２とＶ３のうち絶対値が大きい方を選択して出力するようにすれば良い。
（９）実施例では、電流制御回路をドロップ型で説明したが、スイッチング型でもよく、この方が発熱は少ない。
【００４３】
【発明の効果】
以上説明したように、本発明によれば二次電池がリチウムイオン電池などの非水溶媒系二次電池のように定電圧充電されるべき電池の場合は、分圧手段の出力端子と基準電位端子との間に接続されたスイッチ手段を非導通状態とし、ニッケル水素蓄電池などのアルカリ蓄電池の場合は導通状態として、分圧手段の出力電圧と充電電流の電流検出手段の出力電圧のうち電圧値の大きい方を用いて充電電流を制御することにより、最適な充電方式の異なる複数種類の二次電池を同一の充電器で充電でき、しかもアルカリ蓄電池に対しても過充電を行うことなく確実に満充電まで充電することが可能となる。
【図面の簡単な説明】
【図１】本発明の一実施例に係る二次電池の充電回路の構成を示す回路図
【図２】図１の動作を説明するためのリチウムイオン電池の充電時の各部の波形図
【図３】図１の動作を説明するためのニッケル水素蓄電池の充電時の各部の波形図
【図４】本発明で用いる最大電圧選択回路の他の構成例を示す回路図
【符号の説明】
１０…電池パック
１１…電池
１２…サーミスタ
２０…充電器
２１…充電用電源
２２…電流制御回路
２３…分圧回路
２４…スイッチ回路
２５…電流検出回路
２６…最大電圧選択回路
２７…温度制御回路[0001]
[Industrial application fields]
The present invention relates to a charging circuit for a secondary battery, and more particularly to a charging circuit that switches between constant voltage charging and constant current charging according to the type of battery.
[0002]
[Prior art]
Various charging methods for secondary batteries have been proposed, but a constant voltage charging method is often used for non-aqueous solvent secondary batteries such as lithium ion batteries or lead-acid batteries. This charging method is a method in which charging is performed with a large current until the battery voltage reaches a set value, and when the battery voltage reaches the set value, the current is decreased so as to keep the battery voltage constant. On the other hand, for alkaline storage batteries such as nickel metal hydride storage batteries and nickel cadmium storage batteries, charging is performed at a constant current, and if the battery temperature, battery voltage, charging time, etc. are detected, the charging current is detected. In many cases, a constant current charging method is used in which charging control is performed by cutting off or reducing charging.
[0003]
By the way, as a method for charging the non-aqueous solvent type secondary battery and the alkaline storage battery having different optimum charging methods with the same charger, there is a method described in, for example, JP-A-6-133466. In this method, the battery is charged at a constant voltage regardless of the type, and when charging is performed by the constant voltage charging method, when the non-aqueous solvent secondary battery is fully charged, the charging current decreases, but the battery voltage is reduced. However, when the alkaline storage battery is fully charged, the battery voltage is decreased by a predetermined value or the charging current is changed from decreasing to increasing.
[0004]
Specifically, the battery pack is provided with a battery discrimination terminal connected with a resistor having a different value depending on the type of battery, the output voltage from this terminal is detected on the charger side, and the upper limit of the charging voltage is determined according to the value. And a voltage detecting means for detecting that the battery voltage has decreased by ΔV from the peak value during charging, and a current detecting means for detecting that the charging current has increased by a predetermined value ΔI from the minimum value. A method of performing charge control (control to cut off or reduce charge current) is performed by assuming that the battery has reached full charge when the detection output of either of these voltage detection means or current detection means is generated. .
[0005]
Furthermore, in this method, the charging voltage is switched according to the type of the secondary battery in order to charge the secondary battery at a constant voltage regardless of the type. For example, when the non-aqueous solvent secondary battery is a lithium secondary battery, the charging voltage required for charging by the constant voltage charging method is 8.4 V when two batteries are connected in series at 4.2 V / cell. . On the other hand, in the case of an alkaline storage battery, when five are connected in series at a maximum of 1.8 V / cell, the charging voltage required for charging by the constant voltage charging method is a maximum of 9 V.
[0006]
[Problems to be solved by the invention]
However, in the above-described prior art, particularly when an alkaline storage battery is charged at a constant voltage, even if the battery reaches full charge, the battery voltage may not decrease or the charging current may not increase from decrease to increase. There is a problem that the battery may be overcharged and the charging voltage must be changed according to the type of the battery.
[0007]
The present invention is capable of charging a non-aqueous solvent type secondary battery and an alkaline storage battery having different optimum charging systems with the same charger and without changing the charging voltage, and is not only a non-aqueous solvent type secondary battery but also an alkaline storage battery. It is another object of the present invention to provide a charging circuit for a secondary battery that can reliably charge up to a full charge without overcharging.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, a charging circuit for a secondary battery according to the present invention includes a charging power source for charging the secondary battery, an input terminal connected to both terminals of the secondary battery, and a reference potential terminal. minutes and pressure means, connected between the output terminal and the reference potential terminal of the voltage divider, Rukoto the secondary battery is a non-conducting state in the case of the battery to be constant voltage charging with the output terminal the partial pressure by the amount of the terminal voltage of the secondary battery from the output terminal of the pressure means to output the divided voltage, the secondary battery if the battery to be constant current charging to be a conductive state by Switch means for making the voltage at the output terminal of the means equal to the voltage at the reference potential terminal; and current detection for detecting a charging current supplied from the charging power source to the secondary battery and outputting a voltage corresponding to the charging current. Means and said partial pressure Selection means for selecting the larger of the voltage value of the output voltage of the voltage and the current detector stage output terminal, depending on the output voltage of the selection circuit so that the output voltage of the selecting means becomes equal to the reference voltage Current control means for controlling the charging current.
[0010]
[Action]
In the secondary battery charging circuit of the present invention configured as described above, when the secondary battery is a battery to be charged at a constant voltage, such as a non-aqueous solvent secondary battery such as a lithium ion battery, Since the switch means connected between the output terminal of the means and the reference potential terminal is rendered non-conductive, a voltage obtained by dividing the battery voltage appears at the output of the voltage dividing means. When charging progresses and the battery voltage rises, the output voltage of the voltage dividing means becomes larger than the output voltage of the current detecting means and is selected by the maximum voltage selecting means, and the charging current is controlled based on this, whereby constant voltage charging is performed. Is done.
[0011]
On the other hand, when the secondary battery is a battery that should be charged with a constant current, such as an alkaline storage battery such as a nickel hydride storage battery, the output terminal of the voltage dividing means and the reference potential terminal are short-circuited by the switch means. The output voltage of the pressure means is almost zero. Therefore, this time, the output voltage of the current detecting means becomes larger than the output voltage of the voltage dividing means and is selected by the maximum voltage selecting means, and the charging current is controlled based on this, whereby constant current charging is performed.
[0012]
In this way, a non-aqueous solvent type secondary battery and an alkaline storage battery with different optimum charging methods can be charged with the same charger and at the same charging voltage, and further, a voltage dividing means for dividing the battery voltage according to the type of battery. Between the output terminal and the reference potential terminal is made conductive or non-conductive by the switch means, and the larger one of the output voltage of the voltage dividing means and the output voltage of the current detecting means for detecting the charging current is used for the charge control. Since it is a system, it becomes possible to charge to any battery reliably to full charge, without performing overcharge.
[0013]
That is, in the present invention, the non-aqueous solvent type secondary battery is charged by the constant voltage charging method, and the alkaline storage battery is charged by the constant current charging method, so both are charged by the constant voltage charging method. In addition to the need to switch the charging voltage as in the prior art, full charge can be reliably detected by known full charge detection means by charging the alkaline storage battery by a constant current charging method. Therefore, there is no risk of overcharging as in the prior art.
[0014]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit diagram showing a charging circuit for a secondary battery according to an embodiment of the present invention. This charging circuit is roughly divided into a charger and a battery pack. The battery pack 10 includes a secondary battery 11 (hereinafter simply referred to as a battery) and a thermistor 12. The battery 11 is a non-aqueous solvent secondary battery such as a lithium secondary battery, a battery to be charged at a constant voltage such as a lead battery, or an alkaline storage battery to be charged at a constant current such as a nickel hydride storage battery. Hereinafter, the case where the battery to be charged at a constant voltage is a lithium ion battery and the battery to be charged at a constant current is a nickel metal hydride storage battery will be described as an example.
[0015]
Terminals +, − and T, S of the battery pack 10 are external connection terminals, the terminal + is connected to the positive terminal of the battery 11, the terminal − is connected to the negative terminal of the battery 11, and the terminal T is one end of the thermistor 12. Connected to. The thermistor 12 is installed in close contact with the battery 11. The terminal S is connected to the terminal − when the battery 11 is a lithium ion battery, and is open, that is, in a potential floating state, when the battery 11 is a nickel metal hydride storage battery.
[0016]
On the other hand, the charger 20 includes a charging power source 21, a current control circuit 22, a voltage dividing circuit 23, a switch circuit 24, a current detection circuit 25, a maximum voltage detection circuit 26, and a temperature control circuit 27. Terminals +, − and T, S are external connection terminals of the charger 20, and are connected to corresponding terminals of the battery pack 10 during charging.
[0017]
As the charging power source 21, for example, a power source that rectifies the output of the AC power source to obtain a direct current or other relatively large capacity battery is used, and one end thereof is connected to the terminal + of the battery pack 10 via the current control circuit 22. The terminal − of the battery pack 10 is connected to the other end of the charging power source 21 via the current detection circuit 25.
[0018]
The positive terminal and the negative terminal of the battery 11 are connected to the input terminal (one end of the resistor R1) and the reference potential terminal (resistor R2) of the voltage dividing circuit 23 formed of a series circuit of two resistors R1 and R2 via terminals + and −. One end) is connected to each other. The reference potential terminal is a ground potential in this example. The other ends of the resistors R1 and R2 are output terminals of the voltage dividing circuit 23.
[0019]
A switch circuit 24 is connected between the output terminal of the voltage dividing circuit 23 and the reference potential terminal. The switch circuit 24 includes an NPN transistor Q3 and resistors Rb and Rc. The collector of the transistor Q3 is connected to the output terminal of the voltage dividing circuit 23, the emitter is connected to the reference potential terminal of the voltage dividing circuit 23, and the base is the resistor Rb. It is connected to one end. The other end of the resistor Rb is connected to the positive power source V + via the resistor Rc and also connected to the terminal S of the battery pack 10.
[0020]
Here, when the battery 11 is a non-aqueous solvent battery, since the terminal S of the battery pack 10 is connected to the terminal −, the transistor Q3 is non-conductive. Therefore, when the resistance values of the resistors R1 and R2 of the voltage dividing circuit 23 are represented by the same symbols R1 and R2, the terminal voltage (hereinafter referred to as battery voltage) VB of the battery 11 is expressed by the following equation (1) by the voltage dividing circuit 23. Thus, the voltage is divided to a voltage of V2.
[0021]
V2 = {R2 / (R1 + R2)} × VB (1)
On the other hand, when the battery 11 is an alkaline storage battery, since the terminal S of the battery pack 10 is open, the transistor Q3 is in a conductive state. Accordingly, the output voltage V2 of the voltage dividing circuit 23 is about 0 volts.
[0022]
The current detection circuit 25 amplifies a resistor R3 having a relatively low resistance value (for example, several mΩ to several hundred mΩ) connected in series with the battery 11 in the battery pack 10 and a voltage generated at both ends of the resistor R3. It comprises an amplifier A2. When the resistance value of the resistor R3 is represented by the same symbol R3, the amplification degree of the amplifier A2 is G, and the charging current is IB, the output voltage V3 of the current detection circuit 25 is expressed by the following equation (2).
[0023]
V3 = IB * R3 * G (2)
The output voltage V2 of the voltage dividing circuit 23 and the output voltage V3 of the current detection circuit 25 are input to the maximum voltage selection circuit 26. The maximum voltage selection circuit 26 is a circuit that selects and outputs the higher one of the output voltage V2 of the voltage dividing circuit 23 and the output voltage V3 of the current detection circuit 25. The voltage comparator A3 and two analog switches It consists of SW1, SW2 and inverter IC1. That is, the output voltage V2 of the voltage dividing circuit 23 and the output voltage V3 of the current detection circuit 25 are input to the non-inverting input terminal and the inverting input terminal of the voltage comparator A3, respectively. The output of the voltage comparator A3 is high when the magnitude relationship between the output voltage V2 of the voltage dividing circuit 23 and the output voltage V3 of the current detection circuit 25 is V2> V3, and is low when V2 <V3. The output voltage V2 of the voltage dividing circuit 23 and the output voltage V3 of the current detection circuit 25 are applied to one ends of the analog switches SW1 and SW2, respectively. The other ends of the analog switches SW1 and SW2 are commonly connected inside the maximum voltage selection circuit 26, and the output of the maximum voltage selection circuit 26 is taken out from this common connection point. The analog switches SW1 and SW2 are switches whose conduction and non-conduction are controlled by a control signal, and an output signal of the voltage comparator A3 and a signal obtained by inverting the signal by the inverter IC1 are given as control signals, respectively, and the control signal is at a high level. When it is low, it is in a conductive state, and when it is low, it is in a non-conductive state.
[0024]
The current control circuit 22 is a circuit that controls the charging current supplied from the charging power supply 21 to the battery 11 in accordance with the output of the maximum voltage selection circuit 26. The emitter is connected to one end of the charging power supply 21, and the collector is connected to the terminal. A current control transistor Q1 which is a PNP transistor connected to +, a charge control transistor Q2 which is a PNP transistor whose collector is connected to the base of this current control transistor Q1, and whose emitter is connected to the emitter of the current control transistor Q1, and It has a dropper type configuration comprising an error amplifier A1 having an output terminal connected to the base of the current control transistor Q1 via a resistor Ra. The error amplifier A1 is composed of an operational amplifier. The output of the maximum voltage selection circuit 26 is applied to its non-inverting input terminal, and the reference voltage V1 generated from the reference voltage generator Vref is applied to its inverting input terminal.
[0025]
In the above configuration, when the battery voltage VB reaches a set value Va (for example, 4.2 V per battery), the values of the resistors R1 and R2 constituting the voltage dividing circuit 23 are set so that V2 = V1. It is assumed that the value of the resistor R3 in the current detection circuit 25 and the amplification degree G of the amplifier A2 are set so that V3 = V1 when the charging current IB is a predetermined constant current value Ia. In other words, the voltage dividing circuit 23 and the current detection circuit 25 are used when the output voltage V2 (= V1) of the voltage dividing circuit 23 when the battery voltage VB is the set value Va and the charging current IB is a predetermined constant current value Ia. The output voltage V3 (= V1) of the current detection circuit 25 is configured to be equal.
[0026]
The input terminal of the temperature control circuit 27 is connected to the thermistor 12 in the battery pack 10 via the terminal T, and the output terminal of the temperature control circuit 27 is connected to the base of the charge control transistor Q2 in the current control circuit 22. The temperature control circuit 27 monitors the temperature of the battery 11 based on the signal from the thermistor 12, and outputs a low level signal when the rate of temperature increase reaches a predetermined value (for example, 1 ° C./min).
[0027]
Next, the operation of the charging circuit for the secondary battery in FIG. 1 will be described with reference to waveform diagrams during charging of the lithium ion battery and the nickel hydride storage battery shown in FIGS. 2 and 3, (a) shows the waveforms of the charging current IB and the battery voltage VB, (b) shows the waveforms of the output voltage V2 of the voltage dividing circuit 23 and the output voltage V3 of the current detecting circuit 25, and (c) shows a voltage comparison. The output waveform of the device A3, (d) shows the waveform of the battery temperature, and (e) shows the output waveform of the temperature control circuit 27, respectively.
[0028]
When the battery 11 is a lithium ion battery that is a nonaqueous solvent secondary battery, the terminal S is connected to the terminal − inside the battery pack 10. At this time, since the transistor Q3 of the switch circuit 24 is in a non-conductive state, the output voltage V2 of the voltage dividing circuit 23 is a voltage obtained by dividing the terminal voltage VB by the resistors R1 and R2 as shown by the equation (1). Is output.
[0029]
When charging is started, the charging current IB starts to be supplied from the charging power source 21 to the battery 11 via the current control circuit 22 and the current detection circuit 25. At the initial stage of charging, as shown in FIG. 2A, since the terminal voltage VB is lower than the set voltage Va, the battery 11 is charged with the current Ia. That is, since the relationship between the output voltage V2 of the voltage dividing circuit 23 and the output V3 of the current detection circuit 25 is V2 <V3 as shown in FIG. 2B at the initial stage of charging, the output of the voltage comparator A3 is as shown in FIG. As shown in c), the level is low. Thus, the analog switch SW2 is turned, the output voltage V3 of the current detection circuit 25 up to the voltage selection circuit 26 is selected and marked addition to the non-inverting input terminal of the error amplifier A1 the current control circuit 22. By the output of this error amplifier A1,
V3 = V1 (3)
Thus, the base current of the current control transistor Q1 is controlled. That is, the charging current IB is controlled so that the charging current IB detected by the current detection circuit 25 maintains the constant current value Ia corresponding to the reference voltage V1, and the constant current charging operation is performed. The value of the charging current IB at this time is obtained from the equations (2) and (3).
IB = V1 / (R3 × G)
= Ia (4)
It becomes.
[0030]
As the charging proceeds, the battery voltage VB increases, and the output voltage V2 of the voltage dividing circuit 23 increases accordingly. When V2> V3 at the time of t = ta, the output of the voltage comparator A3 becomes high in the maximum voltage selection circuit 26 as shown in FIG. 2C. Therefore, the analog switch SW1 is turned on, and the output voltage V2 of the voltage dividing circuit 23 is applied to the non-inverting input terminal of the error amplifier A1. By the output of this error amplifier A1,
V2 = V1 (5)
In other words, the base voltage of the current control transistor Q1 is controlled so that the output voltage V2 of the voltage dividing circuit 23, that is, the voltage corresponding to the battery voltage VB becomes equal to the reference voltage V1, so that the battery voltage VB is constant. To be kept. That is, the charging operation shifts from the constant current charging operation to the constant voltage charging operation.
[0031]
Note that once the switch SW1 is turned on, the current control circuit 22 performs the constant voltage charging operation as described above, whereby the charging current IB is reduced. Accordingly, as shown in FIG. Since the output voltage V3 decreases, the relationship of V2> V3 is maintained. Therefore, when the current control circuit 22 shifts from the constant current charging operation to the constant voltage charging operation, the switch SW1 and the switch SW2 do not alternately conduct.
[0032]
When charging further proceeds and the charging current IB is reduced to a set value Ib (for example, 100 mA) at t = tb, it is determined that the battery 3 is almost fully charged by a full charging detection means based on known current detection (not shown). Is done. When it is determined that the battery 11 has reached full charge in this manner, the charging is stopped, the trickle charging is performed, or the charging completion is displayed.
[0033]
Even if the lithium ion battery is charged as described above, the battery temperature hardly changes as shown in FIG. 2 (d), and therefore the output of the temperature control circuit 27 does not become low. Transistor Q2 does not conduct. For this reason, the current control transistor Q1 operates only by the output of the error amplifier A1.
[0034]
Next, when the battery 11 is a nickel metal hydride storage battery, the terminal S of the battery pack 10 is opened. At this time, a current flows from the power source V + to the base of the transistor Q3 of the switch circuit 24 via the resistors Rc and Rb, and the transistor Q3 becomes conductive, so that the output voltage V2 of the voltage dividing circuit 23 is approximately 0 volts. Therefore, the relationship between the output voltage V2 of the voltage dividing circuit 23 and the output V3 of the current detection circuit 25 is V2 <V3 as shown in FIG. 3B, and the output of the voltage comparator A3 is at a low level. As a result, the analog switch SW2 becomes conductive, and the output voltage V3 of the current detection circuit 25 is selected by the maximum voltage selection circuit 26 and applied to the non-inverting input terminal of the error amplifier A1 of the current control circuit 22. The base current of the current control transistor Q1 is controlled by the output of the error amplifier A1 so that V3 = V1 as in the expression (3). As a result, the battery 11 is a lithium ion battery as shown in FIG. In the same manner as in the case of 0 <t <ta, the battery 11 is charged with the charging current IB represented by the equation (4).
[0035]
Here, as shown in FIG. 3 (d), the temperature of the battery 11 rises gently at the beginning and middle of charging, but rises rapidly at the end of charging, and the output of the temperature control circuit 27 at time t = td As shown in FIG. 3E, the level changes from a high level to a low level. That is, it is determined that the battery 11 is fully charged. As a result, the charge control transistor Q2 in the current control circuit 22 is turned on, and the current control transistor Q1 is turned off to stop charging.
[0036]
The present invention is not limited to the above embodiments, and can be implemented with various modifications as follows.
(1) In the embodiment, the voltage V2 obtained by dividing the terminal voltage VB of the secondary battery by the voltage dividing circuit 23 is input to the non-inverting input terminal of the voltage comparator A3 and the analog switch SW1, but as a special case, the resistor R2 May be output as V2, and VB itself may be output as V2.
[0037]
(2) In the embodiment, the switches SW1 and SW2 constituting the switch circuit 24 are analog switches. However, other semiconductor switches such as field effect transistors and bipolar transistors may be used, and mechanical switches may be used. good.
[0038]
(3) In the embodiment, the maximum voltage selection circuit 26 is constituted by the voltage comparator A3, the analog switches SW1 and SW2 and the inverter ICI. However, as shown in FIG. 4, the output voltage V2 of the voltage dividing circuit 23 and the current detection circuit 25 Of the two operational amplifiers A4 and A5 that input the output voltage V3 to the non-inverting input terminal, the anode is connected to the output terminals of the operational amplifiers A4 and A5, the cathode is connected to the inverting input terminal, and the maximum voltage selection circuit 26 The two diodes Di1 and Di2 connected to the output terminal and the output resistor Rd connected between the output terminal of the maximum voltage selection circuit 26 and the ground may be used.
[0039]
(4) In the embodiment, the temperature increase rate detection control is described as an example of charge control of an alkaline storage battery such as a nickel metal hydride storage battery. However, temperature control, ΔT control (battery temperature increase from the initial charge, or battery temperature and ambient temperature) When the difference from the temperature reaches a set value, charging is controlled), timer control, voltage control, -ΔV control, peak voltage control, and other control methods may be used, or these control methods may be combined as appropriate. . Regardless of which control method is used, the present invention uses a constant current charging method for alkaline storage batteries, so that full charge can be reliably detected and the battery is fully charged without causing overcharge. Is possible.
[0040]
(5) In the embodiment, in charging control of a non-aqueous solvent battery such as a lithium ion battery, when charging current is reduced to a predetermined value by constant voltage charging, charging is detected by detecting full charging. , Timer control, temperature control (control for stopping charging when the battery temperature is out of a predetermined range), voltage control, and the like may be combined.
[0041]
(6) In the embodiment, the case where the number of the batteries 11 is one has been described. However, the present invention can be applied to the case of two or more assembled batteries.
(7) In the embodiment, the voltage dividing circuit 23 has been described with the two resistors R1 and R2, but either one or both of R1 and R2 is a combination of two or more resistors (including variable resistors). There may be.
[0042]
(8) In the embodiment, the current detection circuit 25 is inserted into the charging path on the negative electrode side of the battery 11, but it may be inserted into the charging path on the positive electrode side of the battery 11. In this case, the transistor Q3 of the switch circuit 24 is connected to both ends of the resistor R1 in FIG. 1, and the maximum voltage selection circuit 26 selects the one having the larger absolute value of V2 and V3 with reference to the potential of the positive terminal of the battery 11. Output.
(9) Although the current control circuit has been described as a drop type in the embodiments, a switching type may be used, and this generates less heat.
[0043]
【The invention's effect】
As described above, according to the present invention, when the secondary battery is a battery to be charged at a constant voltage, such as a nonaqueous solvent secondary battery such as a lithium ion battery, the output terminal of the voltage dividing means and the reference potential The switch means connected between the terminals is in a non-conductive state, and in the case of an alkaline storage battery such as a nickel metal hydride storage battery, it is in a conductive state, and the voltage value of the output voltage of the voltage dividing means and the output voltage of the current detection means of the charging current By controlling the charging current using the larger one, it is possible to charge multiple types of secondary batteries with different optimal charging methods with the same charger and reliably without overcharging even alkaline storage batteries It becomes possible to charge to full charge.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a charging circuit for a secondary battery according to an embodiment of the present invention. FIG. 2 is a waveform diagram of each part during charging of a lithium ion battery for explaining the operation of FIG. 3 is a waveform diagram of each part during charging of the nickel metal hydride storage battery for explaining the operation of FIG. 1. FIG. 4 is a circuit diagram showing another configuration example of the maximum voltage selection circuit used in the present invention.
DESCRIPTION OF SYMBOLS 10 ... Battery pack 11 ... Battery 12 ... Thermistor 20 ... Charger 21 ... Charging power supply 22 ... Current control circuit 23 ... Voltage dividing circuit 24 ... Switch circuit 25 ... Current detection circuit 26 ... Maximum voltage selection circuit 27 ... Temperature control circuit

Claims

A charging power source for charging the secondary battery;
A voltage dividing means having an input terminal connected to both terminals of the secondary battery, a reference potential terminal and an output terminal ;
This is connected between the output terminal and a reference potential terminal of the voltage divider, the output terminal of the voltage divider when the secondary battery of the battery to be constant voltage charge by Rukoto is nonconductive A voltage obtained by dividing the terminal voltage of the secondary battery is output, and when the secondary battery is a battery to be charged with a constant current , the voltage at the output terminal of the voltage dividing means is set to the reference potential by being turned on. Switch means for equalizing the terminal voltage ;
Current detection means for detecting a charging current supplied to the secondary battery from the charging power supply and outputting a voltage corresponding to the charging current;
A selection means for selecting the larger voltage value of the voltage at the output terminal of the voltage dividing means and the output voltage of the current detection means;
A charging circuit for a secondary battery, comprising: current control means for controlling the charging current according to the output voltage of the selection circuit so that the output voltage of the selection means becomes equal to a reference voltage.

The secondary battery charging circuit according to claim 1, wherein the battery to be charged at a constant voltage is a non-aqueous solvent secondary battery, and the battery to be charged at a constant current is an alkaline storage battery.