Battery protector

• US 6,433,514 B1
• Filed: 10/04/2000
• Issued: 08/13/2002
• Est. Priority Date: 10/04/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Korsunsky, Roman, Wofford, Larry, McClure, Winthrop H.
• Primary Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US09/678,545
• Time in Patent Office: 678 Days
• Field of Search: 320/135, 320/150, 320/136, 340/602, 340/870.17
• US Class Current: 320/136
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/4257 Smart batteries, e.g. electronic circuits inside the housing of the cells or batteries
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery protection circuit includes a moisture detection circuit, a temperature sensing circuit, and a high-temperature battery discharge circuit. The moisture detection circuit includes a pair of conductive traces closely spaced on a substrate such that a resistive path is formed between the traces when moisture forms on the substrate. The traces are connected between the positive battery terminal and a pull-down current source. When moisture forms on the substrate, pull-up current flows between the traces, and a resulting voltage change on one of the traces is detected by circuit element such as a logic inverter. The temperature sensing circuit includes a voltage reference circuit that generates a proportional-to-temperature voltage and temperature-independent voltage reference signals corresponding to various predetermined temperatures. A measuring circuit operates during a sampling interval to compare each temperature-dependent voltage to the proportional-to-temperature voltage and to store the result of each comparison until a subsequent temperature sampling interval. The measuring circuit includes multiplexing circuitry used to sequentially select each temperature-dependent voltage during a sampling interval. The high-temperature discharge circuit connects a discharge load across the battery when the voltage of the battery is above a high voltage threshold and the temperature of the battery is above the high temperature threshold. When no external charger is active, the discharge current flowing through this load works to reduce battery voltage. helping to prolong battery life.

Claims

1. A moisture detection circuit, comprising:

a substrate having a reference conductor and a sense conductor formed thereon, the conductors being closely spaced apart such that exposure of the substrate to moisture causes formation of a conductive path carrying a sense current between the conductors when the voltage between the conductors is on the order of a circuit operating voltage;

a voltage source coupled between the reference conductor and a reference circuit node to provide substantially the circuit operating voltage therebetween;

a current source coupled between the sense conductor and the reference circuit node, the current source generating a bias current sufficient to maintain a first voltage on the sense conductor in the absence of the sense current and to permit the sense conductor to be driven to a second voltage in the presence of the sense current; and

a voltage detection component coupled to the sense conductor, the voltage detection component being operative to discriminate between the first and second voltages so as to generate a binary output signal indicating whether the substrate is exposed to moisture.

2. A circuit according to claim 1, wherein the reference conductor and the sense conductor are interdigitated.

3. A circuit according to claim 1, wherein the voltage source is a battery.

4. A circuit according to claim 3, wherein the battery provides power for the current source and the voltage detection component.

5. A circuit according to claim 1, wherein the voltage detection component comprises a logic element having an input threshold voltage between the first and second voltages.

6. A circuit according to claim 5, wherein the logic element is an inverter.

7. A high temperature discharge circuit for a battery, comprising:

voltage detection circuitry operative to detect when the voltage of the battery is above a predetermined high voltage threshold;

temperature detection circuitry operative to detect when the temperature of the battery is above a predetermined high temperature threshold;

a latch circuit coupled to the voltage and temperature detection circuitry, the latch circuit being operative to enter a first state when the voltage of the battery is above the high voltage threshold and the temperature of the battery is above the high temperature threshold, and the latch circuit being operative to enter a second state when the voltage of the battery is below the high voltage threshold; and

a switched load coupled across the battery, the switched load having a control input coupled to an output of the latch circuit and being operative to (i) conduct a predetermined discharge current when the latch is in the first state, and (ii) conduct substantially zero current when the latch is in the second state.

8. A circuit according to claim 7, wherein the switched load comprises a resistive element in series with a transistor, and wherein the conduction of the transistor is controlled by the output of the latch circuit.

9. A low-power temperature sensing circuit, comprising:

timing circuitry operative to establish a low-duty-cycle periodic temperature sampling interval;

a voltage reference circuit operative during each temperature sampling interval to generate a proportional-to-temperature (PT) voltage and a plurality of temperature-independent voltages, each temperature-independent voltage representing a corresponding predetermined temperature; and

a measuring circuit operative during each temperature sampling interval to compare each temperature-dependent voltage to the PT voltage and to store the result of each comparison until the subsequent temperature sampling interval.

10. A circuit according to claim 9, wherein the voltage reference circuit includes fast start circuitry operative to maintain a biased condition during an inactive interval prior to the sampling interval such that the voltage reference signals quickly reach respective quiescent values at the beginning of the sampling interval.

11. A circuit according to claim 9, wherein the voltage reference circuit comprises:

a feedback amplifier operative to generate a main temperature-independent voltage; and

a cascade of series-connected resistors connected between the main temperature-independent voltage and a circuit reference node, such that each temperature-independent voltage generated by the voltage reference circuit appears between a corresponding pair of the resistors.

12. A circuit according to claim 9, wherein the measuring circuit is operative to perform the comparing and storing for each temperature-independent voltage in sequence during the sampling interval.

13. A circuit according to claim 12, wherein the measuring circuit comprises:

a two-input comparator having one input coupled to receive the PT voltage;

multiplexing circuitry operative to selectively provide each temperature-independent voltage to the other input of the comparator;

a set of storage devices having respective inputs coupled to the output of the comparator, each storage device being associated with a corresponding one of the temperature-independent voltages; and

a control circuit operative for each temperature-independent voltage to (i) configure the multiplexing circuitry to provide the temperature-independent voltage to the comparator, and (ii) enable the corresponding storage device to receive the output of the comparator.

14. A protection circuit for a battery, comprising:

a current bias reference circuit operative to be powered by the battery and to generate one or more current bias reference signals;

a moisture transducer operative in conjunction with the current bias reference circuit and in response to one of the current bias reference signals to detect the presence of moisture in the battery and to generate a moisture detection signal indicating whether the presence of moisture in the battery has been detected;

a voltage reference circuit operative to be powered by the battery and to generate a proportional-to-temperature (PT) voltage and a plurality of temperature-independent voltages representing corresponding predetermined temperatures including a predetermined high temperature threshold;

a temperature detection circuit operative to be powered by the battery and to compare, based on one or more of the current bias reference signals, each temperature-dependent voltage to the PT voltage to ascertain the operating temperature of the battery; and

a high-temperature discharge circuit including (1) a voltage detection circuit operative to detect when the voltage of the battery is above a predetermined high voltage threshold, and (2) a switched load coupled across the battery, the switched load being operative to conduct a predetermined discharge current when the voltage of the battery exceeds the high voltage threshold and the operating temperature of the battery exceeds the high temperature threshold, and the switched load being operative to conduct substantially zero discharge current when the voltage of the battery does not exceed the high voltage threshold.

15. A protection circuit according to claim 14, wherein the moisture transducer comprises a substrate having a reference conductor and a sense conductor formed thereon, the conductors being closely spaced apart such that exposure of the substrate to moisture causes formation of a conductive path carrying a sense current between the conductors when the voltage between the conductors is on the order of a circuit operating voltage, and wherein the battery voltage is coupled between the reference conductor and a reference circuit node to provide substantially the circuit operating voltage therebetween, and wherein the one current bias reference signal is operative to maintain a first voltage on the sense conductor in the absence of the sense current and to permit the sense conductor to be driven to a second voltage in the presence of the sense current, and further comprising a voltage detection component coupled to the sense conductor, the voltage detection component being operative to discriminate between the first and second voltages so as to generate the moisture detection signal.

16. A protection circuit according to claim 14, wherein the discharge circuit comprises a latch circuit coupled to the voltage and temperature detection circuits, the latch circuit being operative to enter a first state when the voltage of the battery is above the high voltage threshold and the temperature of the battery is above the high temperature threshold, and the latch circuit being operative to enter a second state when the voltage of the battery is below the high voltage threshold, and wherein the switched load is operative in response to the state of the latch circuit.

17. A protection circuit according to claim 14, wherein the temperature detection circuit comprises timing circuitry operative to establish a low-duty-cycle periodic temperature sampling interval, and wherein the voltage reference circuit is operative during each temperature sampling interval to generate the PT voltage and the temperature-independent voltages for the sampling interval, and wherein the temperature detection circuit further comprises a measuring circuit operative during each temperature sampling interval to compare each temperature-dependent voltage to the PT voltage and to store the result of each comparison until the subsequent temperature sampling interval.