Protective circuit for battery

• US 6,377,429 B1
• Filed: 04/19/2000
• Issued: 04/23/2002
• Est. Priority Date: 04/21/1999
• Status: Expired due to Term

• Current Assignee: EM Microelectronic - Marin SA (The Swatch Group AG)
• Original Assignee: EM Microelectronic - Marin SA (The Swatch Group AG)
• Inventors: Descombes, Arthur
• Primary Examiner(s): HUYNH, KIM NGOC
• Application Number:
  US09/552,719
• Time in Patent Office: 734 Days
• Field of Search: 361/18, 361/88, 361/79, 361/90, 361/93.1, 361/93.7, 361/93.9, 361/103, 361/91.4, 361/91.5, 320/137, 320/150, 320/136, 320/152, 320/134, 320/135
• US Class Current: 361/93.8
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

The invention concerns a protective circuit (10) for protecting a rechargeable battery (1) against currents of too high intensity. The protective circuit (10) includes detection and comparison means (30, 31, 32) for generating a control signal (OVRC) in response to the comparison of a reference voltage (V_REF) and a measuring voltage (V_M) representative of the charge or discharge current (I_CH, I_DCH) passing through the battery (1). According to the invention, the detection and comparison means (30, 31, 32) include adjustment means (32) for compensating a temperature dependence of the measuring voltage (V_M) and/or the reference voltage (V_REF), these adjustment means (32) including means for generating diode voltages (V_BE1 to V_BE5).

Claims

1. A protective circuit for protecting a rechargeable battery through which a charge or discharge current can flow, this protective circuit including:

measuring means adapted to be connected in series with said battery and to provide a measuring voltage representative of said current, said measuring voltage being able to have a first temperature dependence;

detection and comparison means adapted to receive said measuring voltage and a reference voltage and to generate a control signal in response to a comparison of said reference and measuring voltages, said reference voltage being able to have a second temperature dependence; and

interruption means adapted to control the flow of said current through said battery in response to said control signal,

wherein said detection and comparison means include adjustment means for compensating said first temperature dependence of the measuring voltage and/or said second temperature dependence of the reference voltage,

said detection and comparison means including;

means for generating first, second, third, fourth and fifth diode voltages, and

calculating means including capacitive elements and switching elements to connect selectively and sequentially, during a first and a second phase, said capacitive elements to said means for generating said diode voltages and to terminals to which are applied said measuring voltage and said reference voltage, so that said calculating means generate said control signal during said second phase,

said adjustment means generating a compensation value defined from the sum;

of the product of the difference between said first and second diode voltages by a first determined coefficient, and

of the product, by a second determined coefficient, of the sum of said third diode voltage and the product of the difference between said fourth and fifth diode voltages by a third determined coefficient,

said control signal being representative of the sum of the difference between said reference voltage and said measuring voltage, and of said compensation value.

2. The protective circuit according to claim 1, wherein said adjustment means are arranged so that said generated control signal is substantially temperature independent.

3. The protective circuit according to claim 1, wherein said adjustment means are arranged so that said generated control signal has a negative temperature coefficient.

4. The protective circuit according to claim 1, wherein said interruption means also form said measuring means, said measuring voltage being thus representative of the current passing through said interruption means.

5. The protective circuit according to claim 1, wherein said calculating means include first, second, third, fourth and fifth capacitive elements each having a first terminal connected to a summing node,

said first and second capacitive elements having substantially equal capacitances,

said third capacitive element having a capacitance which is substantially equal to the product of the capacitance of said first capacitive element by said first determined coefficient,

said fourth capacitive element having a capacitance which is substantially equal to the product of the capacitance of said first capacitive element by said second determined coefficient,

said fifth capacitive element having a capacitance which is substantially equal to the product of the capacitance of said first capacitive element by said second and third determined coefficients, and

wherein said calculating means further include first, second, third, fourth and fifth switching elements respectively connected to said first, second, third, fourth and fifth capacitive elements,

said first switching element being adapted to selectively connect a second terminal of said first capacitive element to said measuring voltage during said first phase and to a determined potential during said second phase,

said second switching element being adapted to selectively connect a second terminal of said second capacitive element to said determined potential during said first phase and to said reference voltage during said second phase,

said third switching element being adapted to selectively connect a second terminal of said third capacitive element to said first diode voltage during said first phase and to said second diode voltage during said second phase,

said fourth switching element being adapted to selectively connect a second terminal of said fourth capacitive element to said determined potential during said first phase and to said third diode voltage during said second phase, and

said fifth switching element being adapted to selectively connect a second terminal of said fifth capacitive element to said fourth diode voltage during said first phase and to said fifth diode voltage during said second phase.

6. The protective circuit according to claim 5, wherein said means for generating said diode voltages include three bipolar transistors whose base is connected to the collector,

a first of said transistors being connected successively in series with first and second current sources, the emitter of said first bipolar transistor being connected to the second terminal of said third capacitive element,

a second of said transistors being connected in series with a third current source, the emitter of said second bipolar transistor being connected to the second terminal of said fourth capacitive element, and

a third of said transistors being connected successively in series with fourth and fifth current sources, the emitter of said third bipolar transistor being connected to the second terminal of said fifth capacitive element.

7. The protective circuit according to claim 5, wherein said third and fifth diode voltages are equal and wherein said means for generating said diode voltages include two bipolar transistors whose base is connected to the collector,

a first of said transistors being connected successively in series with first and second current sources, the emitter of said first bipolar transistor being connected to the second terminal of said third capacitive element, and

a second of said transistors being connected successively in series with third and fourth current sources, the emitter of said second bipolar transistor being connected to the second terminal of said fifth capacitive element,

the second terminal of said fourth capacitive element being connected to the emitter of said second bipolar transistor during said second phase.

8. The protective circuit according to claim 5, wherein said calculating means further include an amplifier having an input connected to said summing node and a sixth switching element for selectively connecting an output of said amplifier to said summing node during said first phase and for disconnecting said output from said summing node during said second phase.

9. The protective circuit according to claim 1, wherein said interruption means are formed of a pair of MOFSET power transistors connected in anti-series source to source, one or the other of the transistors being cut off to interrupt the flow of said current.

10. The protective circuit according to claim 1, wherein said interruption means are formed of a pair of MOFSET power transistors connected in anti-series drain to drain, one or the other of the transistors being cut off to interrupt the flow of said current.

11. The protective circuit according to claim 1, wherein said means for generating said diode voltages include bipolar transistors which are connected in series with current sources and whose base is connected to the collector.

12. A method for generating a control signal for interrupting the flow of a charge or discharge current through a rechargeable battery, said method comprising the steps of:

providing a measuring voltage which is representative of said charge or discharge current flowing through said rechargeable battery;

comparing said measuring voltage with a reference voltage; and

producing said control signal in response to the comparison of said measuring voltage and said reference voltage,

wherein said step of comparing the measuring voltage with the reference voltage further comprises the step of adding a compensation value for compensating a temperature dependence of said measuring voltage and/or a temperature dependence of said reference voltage,

said compensation value being defined from the sum;

of the product of the difference between first and second diode voltages by a first determined coefficient, and

of the product, by a second determined coefficient, of the sum of a third diode voltage and the product of the difference between fourth and fifth diode voltages by a third determined coefficient.

13. The method of claim 12, wherein the generated control signal is substantially temperature independent.

14. The method of claim 12, wherein the generated control signal has a negative temperature coefficient.

15. The method of claim 12, wherein said third diode voltage is selected to be equal to said fourth or fifth diode voltage.