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Dokumentenidentifikation EP0862261 04.03.2004
EP-Veröffentlichungsnummer 0000862261
Titel Überstromschutzschaltung und -verfahren
Anmelder Kabushiki Kaisha Toshiba, Kawasaki, Kanagawa, JP
Erfinder Noguchi, Minoru, 1-1 Shibaura 1-chome, Tokyo 105, JP;
Katsumi, Takahiro, 1-1 Shibaura 1-chome, Tokyo 105, JP;
Suzuki, Toshiyuki, 1-1 Shibaura 1-chome, Tokyo 105, JP;
Kawagishi, Toshiyuki, 1-1 Shibaura 1-chome, Tokyo 105, JP
Vertreter Blumbach, Kramer & Partner GbR, 81245 München
DE-Aktenzeichen 69821270
Vertragsstaaten DE, FR, GB
Sprache des Dokument EN
EP-Anmeldetag 19.02.1998
EP-Aktenzeichen 981029333
EP-Offenlegungsdatum 02.09.1998
EP date of grant 28.01.2004
Veröffentlichungstag im Patentblatt 04.03.2004
IPC-Hauptklasse H02H 3/087

Beschreibung[en]

The present invention relates to an overcurrent protection circuit and an overcurrent protection method for protecting an electric or electronic device, such as an IC (Integrated Circuit) incorporated in an IC card, from an overcurrent due to abnormality in the circuits of the device.

An electric or electronic device, such as an IC card, incorporates an overcurrent protection circuit for protecting the device from overcurrent due to abnormality in the circuits of the device.

Conventionally, a type of overcurrent protection circuit in an electric or electronic device is formed of a combination of a microcomputer and a logical circuit for controlling operations of the circuits in the device. Such an overcurrent protection circuit having a microcomputer and a logical circuit may malfunction when the microcomputer goes out of control or malfunctions or power is supplied thereto.

DE 38 42 921 A1 discloses a circuit according to the preamble of claim 1, wherein the predetermined detection level is raised at the initial power supply of the load. US 4,819,117 and DE 43 16 185 A1 each disclose an overcurrent protection circuit, wherein a predetermined overcurrent detection level is adapted at the initial power supply of the load.

It is an object of the present invention to provide an overcurrent protection circuit and method preventing the circuit from malfunctioning when the microcomputer gets out of control or power is first supplied to the circuit.

This object is achieved by a circuit according to claim 1 and a method according to claim 4.

Further developments of the invention are given in the dependent claims.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

  • FIG. 1 is a block diagram showing a schematic structure of an overcurrent protection circuit according to the present invention;
  • FIG. 2 is a circuit diagram of the overcurrent protection circuit of the present invention; and
  • FIG. 3 is a diagram for explaining true values of the flip-flop circuit shown in FIG. 2.

An embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a schematic structure of an overcurrent protection circuit according to the present invention. The overcurrent protection circuit comprises a power source 1 serving as power supplying means, a current detecting section 2 serving as current detecting means, a switch 3 serving as switching means, a load 4 such as an electric or electronic device, a microcomputer 5, a signal controlling section 6 and a control section 7.

The load 4 is, for example, an IC incorporated in an IC card. Power is supplied to the IC card connected to the circuit of the present invention provided in an IC card reader/writer. In the following description, the load is referred to as the IC card 4.

The control section 7 turns on the switch 3 in response to a signal supplied from the microcomputer 5, so that power can be supplied to the IC card 4. After the power is supplied, the current detecting section 2 detects a current flowing through the IC card 4. The control section 7 determines whether the amount of the current is greater or smaller than a preset current, and controls ON/OFF of the switch 3.

The signal controlling section 6 operates so that the control section 7 may not be influenced, even if the microcomputer outputs an abnormal signal, when it goes out of control or malfunctions.

FIG. 2 shows a structure of the overcurrent protection circuit. The overcurrent protection circuit has the elements described above with reference to FIG. 1. The current detecting section 2 comprises a current detecting resistor R1, reference voltage resistors R2 and R3, and a voltage comparator IC1. The switch 3 comprises a power cutoff transistor Q1. The computer 5 outputs an output 1 through a terminal 9 and an output 2 through a terminal 10.

The signal controlling section 6 comprises a transistor Q3, a power limiting resistor R4, a differential circuit 8 having a resistor R5 and a capacitor C1, an overvoltage protecting diode D1, and a buffer IC4. The control section 7 comprises a transistor Q2, a flip-flop circuit IC2, an inverter IC3 and an adjusting resistor R6. The power limiting resistor R4 limits a charge current supplied to the capacitor C1, when a low pulse of the output 1 from the terminal 9 rises in the microcomputer 5. The overvoltage protecting diode D1 prevents an overvoltage of a terminal R of the flip-flop circuit IC2, when the capacitor C1 is charged.

An operation of the overcurrent protection circuit shown in FIG. 2 will now be described.

First, the microcomputer 5 causes the output 2 from the terminal 10 to be high (Hi). As a result, the base terminal of the transistor Q3 becomes high in level, so that the transistor Q3 is turned on. In the voltage comparator IC1, the negative terminal becomes low (Lo) in level, since the transistor Q3 is on, and the level of the output voltage is high. Since the output voltage of the voltage comparator IC1 is high, a terminal PR of the flip-flop circuit IC2 is high in level. Further, the microcomputer 5 causes the output 1 from the terminal 9 to be low, causing a terminal R of the flip-flop IC2 to be low via the buffer IC4.

In the flip-flop circuit IC2, since the terminal PR is high in level and the terminal R is low in level, the terminal Q is low. The inverter IC3 inverts a low signal output from the terminal Q to a high signal, which is input to the base terminal of the transistor Q2. As a result, the transistor Q2 is turned on.

When the transistor Q2 is on, the transistor Q1 is also on, so that power is supplied from the power source 1 to the IC card 4.

In this embodiment, the microcomputer 5 causes the negative terminal of the voltage comparator IC1 to be low in level, while it is keeping the output 2 from the terminal 10 at the high level. Therefore, the current detecting section 2 does not work until the capacitor (not shown) of the IC card 4 is charged. Thus, the overcurrent protection circuit is prevented from malfunctioning.

After the voltage of the IC card 4 is stabilized, the microcomputer 5 causes the output 2 from the terminal 10 to be low in level, so that a voltage is applied to the negative terminal of the voltage comparator IC1 through the reference voltage resistors R2 and R3. In the voltage comparator IC1 for comparing voltages, the voltage at the positive terminal is varied by a voltage drop due to a current flowing through the current detecting resistor R1.

If the IC card 4 disorders, when the current flowing through the current detecting resistor R1 is increased and the voltage of the positive terminal of the voltage comparator IC1 becomes smaller than that of the negative terminal thereof, the voltage comparator IC1 outputs a voltage of low level, which causes the PR terminal of the flip-flop circuit IC2 to be low in level. As a result, since the terminal PR and the terminal R of the flip-flop circuit IC2 are low in level, the terminal Q thereof is high in level. The inverter IC3 inverts a high signal output from the terminal Q to a low signal, which is input to the base terminal of the transistor Q2, thereby turning off the transistor Q2. When the transistor Q2 is off, the transistor Q1 is also off, with the result that power supply from the power source 1 to the IC card 4 is stopped. Thus, if the IC card 4 disorders, the power supply from the power source 1 to the IC card 4 is stopped by the transistor Q1.

FIG. 3 shows true values of the flip-flop circuit IC2 described above.

For example, in the flip-flop circuit IC2, when the terminal R (Reset) is high and the terminal PR (Preset) is low, the terminal Q is high. The inverter IC3 inverts a high signal output from the terminal Q to a low signal, which is input to the base terminal of the transistor Q2, thereby turning off the transistor Q2. When the transistor Q2 is off, the transistor Q1 is also off, with the result that power supply from the power source 1 to the IC card 4 is stopped.

When the power supply to the IC card 4 is stopped, the amount of current flowing through the current detecting resistor R1 is reduced. Accordingly, the voltage at the positive terminal of the voltage compactor IC1 is increased and becomes higher than the voltage at the negative terminal thereof. Therefore, the voltage comparator IC1 outputs a voltage of high level, which is input to the terminal PR of the flip-flop circuit IC2. However, in the flip-flop circuit IC2, even if a signal input to the terminal PR is changed, the state of the terminal Q remains unchanged, unless a low signal is input to the terminal R. Therefore, the power supply of the IC card 4 is kept stopped.

At this time, if the microcomputer 5 goes out of control or malfunctions, the output 1 from the terminal 9 is a low signal. However, since only low pulses of the output 1 from the terminal 9 are input through the differential circuit 8 to the terminal R of the flip-flop circuit IC2, the overcurrent protection circuit is prevented from malfunctioning.

As described above, according to the embodiment of the present invention, the overcurrent protection circuit is prevented from malfunctioning when power is supplied to the IC card (load) and from stopping when the microcomputer goes out of control.


Anspruch[de]
  1. Überstromschutzschaltung mit

       einem Energieversorgungsmittel (1) zur Lieferung von Energie,

       einem Schaltmittel (3) zum Schalten der Energie an eine Last (4), die mit dem Energieversorgungsmittel verbunden ist, und zum Stoppen der Energie;

       einem Stromdetektionsmittel (2) zum Erkennen, ob ein Strom einen vorbestimmten Detektionspegel überschreitet, wenn Energie von dem Energieversorgungsmittel an die Last geliefert wird,

       einem Stoppmittel (7) zum Stoppen der Energielieferung, indem das Schaltmittel geschaltet wird, wenn das Stromdetektionsmittel detektiert, dass der Strom den vorbestimmten Detektionspegel überschreitet, und

       einem Mikrocomputer (5) zum Ausgeben eines Anweisungssignals zum Schalten des Schaltmittels, gekennzeichnet durch

       die Last, die eine IC-Karte (4) ist,

       den Mikrocomputer (5), der ausgelegt ist zum Ausgeben eines ersten und zweiten Anweisungssignals (OUTPUT 2, OUTPUT 1) zum Schalten des Schaltmittels,

       ein erstes Steuermittel (6, Q3) zum Stoppen des Betriebs des Stromdetektionsmittels bis eine Lastspannung der IC-Karte stabil ist, wenn die Energie von dem Energieversorgungsmittel an die IC-Karte geliefert wird, indem das Schaltmittel gemäß dem ersten Anweisungssignal (OUTPUT 2), das von dem Mikrocomputer ausgegeben worden ist, geschaltet wird; und

       ein zweites Steuermittel (6, IC4, 8, Dl) zur Steuerung des Betriebs des Stoppmittels, die Energieversorgung gestoppt zu halten, bis im Falle einer Fehlfunktion oder eines Fehlers des Mikrocomputers, das zweite Anweisungssignal (OUTPUT 1) von dem Mikrocomputer ausgegeben wird, und folglich durch das Schaltmittel gestoppt werden kann, gemäß einem Signal, das von dem Stromdetektionsmittel (2) ausgegeben wird, welches die Detektion eines Stroms anzeigt, der den vorbestimmten Detektionspegel überschreitet, um eine Fehlfunktion aufgrund eines falschen Signals von dem Mikrocomputer zu verhindern.
  2. Überstromschutzschaltung nach Anspruch 1, dadurch gekennzeichnet, dass das erste Steuermittel (6) ausgelegt ist, um den Betrieb der Stromdetektion zu stoppen, wenn die Energie zuerst von dem Energieversorgungsmittel an die IC-Karte geliefert wird, indem das Schaltmittel gemäß einem ersten Anweisungssignal geschaltet wird, welches von dem Mikrocomputer ausgegeben wird, und ausgelegt ist, um das Stromdetektionsmittel zu steuern, um bei dem vorbestimmten Detektionspegel zu arbeiten, gemäß einem zweiten Anweisungssignal, das von dem Mikrocomputer ausgegeben wird, wenn die Lastspannung der IC-Karte, die mit der Energie geliefert wird, stabil ist.
  3. Überstromschutzschaltung nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das zweite Steuermittel (6) eine Differentialschaltung (8) aufweist, um die Energieversorgung von dem Energieversorgungsmittel an die IC-Karte gestoppt zu halten, bis ein bestimmtes Anweisungssignal (low-Impuls) von dem Mikrocomputer ausgegeben wird.
  4. Verfahren zur Steuerung einer Überstromschutzschaltung für einen IC-Kartenleser/-schreiber gemäß einem der Ansprüche 1 bis 3, welches Verfahren aufweist:
    • Stoppen des Betriebs des Stromdetektionsmittels, wenn die Energie zuerst von dem Energieversorgungsmittel an die IC-Karte geliefert wird, indem das Schaltmittel gemäß einem Anweisungssignal geschaltet wird, welches von dem Mikrocomputer ausgegeben wird, und
    • Steuern des Stromdetektionsmittels, um bei dem vorbestimmten Detektionspegel zu arbeiten, gemäß einem Anweisungssignal, das von dem Mikrocomputer ausgegeben wird, wenn die Lastspannung der IC-Karte, die mit der Energie geliefert wird, stabil ist.
Anspruch[en]
  1. An overcurrent protection circuit, comprising

       power supply means (1) for supplying power,

       switch means (3) for switching power supply and stopping the power supply to a load (4) connected to the power supply means;

       current detecting means (2) for detecting whether a current exceeds a predetermined detection level when power is supplied from the power supply means to the load,

       stop means (7) for stopping the power supply by switching the switch means when the current detecting means detects that the current exceeds the predetermined detection level, and

       a microcomputer (5) for outputting an instruction signal for switching the switch means,

    characterized by

       the load being an IC card (4),

       the microcomputer (5) being adapted for outputting first and second instruction signals (OUTPUT 2, OUTPUT 1) for switching the switch means,

       first control means (6, Q3) for controlling the operation of the current detecting means to be stopped until a load voltage of the IC card is stabilized, when the power is supplied from the power supply means to the IC card by switching the switch means in accordance with the first instruction signal (OUTPUT 2) outputted from the microcomputer; and

       second control means (6, IC4, 8, D1) for controlling the operation of the stop means to keep the power supply stopped unless, in use of malfunction of Failure of the microcomputer, the second instruction signal (OUTPUT 1) is output from the microcomputer power supply and therefore can be stopped by the switching means in accordance with a signal outputted form the current detecting means (2) indicating a detection of a current exceeding the predetermined detection level to prevent a malfunction due to a false signal from the microcomputer.
  2. The overcurrent protection circuit according to claim 1,

       characterized in that the first control means (6) is adapted to stop the operation of the current detecting when the power is first supplied from the power supply means to the IC card by switching the switch means in accordance with a first instruction signal outputted from the microcomputer and it is adapted to control the current detecting means to operate at the predetermined detection level in accordance with a second instruction signal outputted from the microcomputer when the load voltage of the IC card supplied with the power is stabilized.
  3. The overcurrent protection circuit according to claim 1 or 2,

       characterized in that the second control means (6) comprises a differential circuit (8) for keeping the power supply from the power supply means to the IC card stopped unless a specific instruction signal (low pulse) is output from the microcomputer.
  4. A method for controlling an overcurrent protection circuit for an IC card reader/writer according to one of claims 1 to 3, the method comprising

       stopping the operation of the current detecting means when the power is first supplied from the power supply means to the IC card by switching the switch means in accordance with an instruction signal outputted from the microcomputer, and

       controlling the current detecting means to operate at the predetermined detection level in accordance with an instruction signal outputted from the microcomputer when the load voltage of the IC card supplied with the power is stabilized.
Anspruch[fr]
  1. Circuit de protection vis-à-vis d'une surintensité, comprenant :
    • un moyen d'alimentation (1) pour appliquer de la puissance ;
    • un moyen de commutation (3) pour commuter l'alimentation et pour arrêter l'alimentation sur une charge (4) qui est connectée au moyen d'alimentation ;
    • un moyen de détection de courant (2) pour détecter si un courant excède un niveau de détection prédéterminé lorsque de la puissance est appliquée depuis le moyen d'alimentation sur la charge ;
    • un moyen d'arrêt (7) pour arrêter l'alimentation en commutant le moyen de commutation lorsque le moyen de détection de courant détecte que le courant excède le niveau de détection prédéterminé ; et
    • un micro-ordinateur (5) pour émettre en sortie un signal d'instruction pour commuter le moyen de commutation,
       caractérisé en ce que :
    • la charge est une carte IC (4) ;
    • le micro-ordinateur (5) étant adapté pour émettre en sortie des premier et second signaux d'instruction (OUTPUT2, OUTPUT1) pour commuter les moyens de commutation ;
    • un premier moyen de commande (6, Q3) pour commander le fonctionnement du moyen de détection de courant de telle sorte qu'il soit arrêté jusqu'à ce qu'une tension de charge de la carte IC soit stabilisée, lorsque la puissance est appliquée depuis le moyen d'alimentation sur la carte IC, en commutant le moyen de commutation conformément au premier signal d'instruction (OUTPUT2) qui est émis en sortie depuis le micro-ordinateur ; et
    • un second moyen de commande (6, IC4, 8, D1) pour commander le fonctionnement du moyen d'arrêt afin de maintenir l'alimentation arrêtée sauf si, dans le cas d'un dysfonctionnement ou d'une défaillance du micro-ordinateur, le second signal d'instruction (OUTPUT1) est émis en sortie depuis le micro-ordinateur et par conséquent, l'alimentation peut être arrêtée par le moyen de commutation conformément à un signal qui est émis en sortie depuis le moyen de détection de courant (2) indiquant une détection d'un courant qui excède le niveau de détection prédéterminée afin d'empêcher un dysfonctionnement dû à un signal faux en provenance du micro-ordinateur.
  2. Circuit de protection vis-à-vis d'une surintensité selon la revendication 1, caractérisé en ce que le premier moyen de commande (6) est adapté pour arrêter l'opération de détection de courant lorsque la puissance est en premier lieu appliquée depuis le moyen d'alimentation sur la carte IC en commutant le moyen de commutation conformément à un premier signal d'instruction qui est émis en sortie depuis le micro-ordinateur et est adapté pour commander le moyen de détection de courant pour un fonctionnement au niveau de détection prédéterminé conformément à un second signal d'instruction qui est émis en sortie depuis le micro-ordinateur lorsque la tension de charge de la carte IC qui reçoit en application de la puissance est stabilisée.
  3. Circuit de protection vis-à-vis d'une surintensité selon la revendication 1 ou 2, caractérisé en ce que le second moyen de commande (6) comprend un circuit différentiel (8) pour maintenir arrêtée l'alimentation en provenance du moyen d'alimentation sur la carte IC sauf si un signal d'instruction spécifique (impulsion de niveau bas) est émis en sortie depuis le micro-ordinateur.
  4. Procédé pour commander un circuit de protection vis-à-vis d'une surintensité pour un dispositif de lecture/écriture de carte IC selon l'une quelconque des revendications 1 à 3, le procédé comprenant :
    • l'arrêt du fonctionnement du moyen de détection de courant lorsque la puissance est appliquée en premier lieu depuis le moyen d'alimentation sur la carte IC en commutant le moyen de commutation conformément à un signal d'instruction qui est émis en sortie depuis le micro-ordinateur ; et
    • la commande du moyen de détection de courant pour qu'il fonctionne au niveau de détection prédéterminée conformément à un signal d'instruction qui est émis en sortie depuis le micro-ordinateur lorsque la tension de charge de la carte IC sur laquelle est appliquée la puissance est stabilisée.






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