Circuit and method for detecting battery source end of life
First Claim
1. A self monitoring power source, having a battery source having a resistance-use characteristic with a linear component which increases substantially linearly with battery usage and a non-linear component which increases sharply after a certain usage, said characteristic having a knee caused by said non-linear component, in combination with detecting means connected to said battery source for detecting the occurrence of said knee and providing a signal indicating that said knee has occurred.
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Accused Products
Abstract
A circuit is disclosed for providing automatic detection of end of life of a battery source, particularly a lithium iodine type battery source characterized by a sharply increased internal resistance characteristic near end of life. The circuit periodically samples the short circuit output current of the source, the sampling being done at a high switching speed and for an extremely short time duration so that power consumption is minimized and only the resistive component which causes the knee in the resistance characteristic is measured. In the embodiment as incorporated in a cardiac pacer device, detection of the internal resistance knee is utilized to cause a step change in an operating characteristic of the pacer, such as stimulus rate, whereby end of life can be accurately monitored.
74 Citations
40 Claims
- 1. A self monitoring power source, having a battery source having a resistance-use characteristic with a linear component which increases substantially linearly with battery usage and a non-linear component which increases sharply after a certain usage, said characteristic having a knee caused by said non-linear component, in combination with detecting means connected to said battery source for detecting the occurrence of said knee and providing a signal indicating that said knee has occurred.
- 16. An end-of-life circuit in combination with a lithium type source having a resistance-use characteristic comprising a first portion which increases linearly with source usage followed by a knee portion after which the resistance increases sharply with usage, said circuit having means for determining when said source has reached said knee portion and for providing an end-of-life signal indicating that said source has reached said knee.
- 20. An electrical device in combination with and powered by a lithium-type source having an internal resistance which varies with source usage, said internal resistance comprising a first portion which increases substantially linearly with usage and a second portion which is substantially negligible until a certain usage after which it increases sharply, said device comprising circuit means for determining when said second internal resistance portion has increased following said certain usage.
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23. A detection circuit for detecting end of life of a lithium type source, said source having an effective electrolyte capacitor and resistance in parallel, and an effective depletion resistance, comprising
sampling means for placing a substantial short circuit across said source for a sampling period smaller than the time constant of said electrolyte capacitor and resistance in parallel so that the electrolyte capacitor within said source is effectively shunted and said source provides a short circuit current; -
signal means for generating a current signal representative of said short circuit current and thus of source depletion resistance; and comparing means for comparing said current signal with a predetermined reference and generating an end-of-life signal when the comparison indicates that the depletion resistance has reached a predetermined level. - View Dependent Claims (24, 25, 26, 27)
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28. A cardiac pacer with a battery life detection circuit, comprising:
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a. a battery source having an electrical characteristic represented by an open circuit voltage source and an impedance, said impedance having at least first and second resistance components, said first component having a linearly increasing value with source usage and being in combination with an effective electrolyte capacitance, said second component having a value which is negligible until it increases sharply after a certain source usage; b. a stimulus generating circuit powered by said source for generating stimulus signals; c. battery life circuit means in interfacing connection with said source for determining when said second component has increased from said negligible value to at least a predetermined higher value. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37)
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- 38. Apparatus for automatically monitoring the life of a lithium type battery source having an electrical characteristic represented by an open circuit voltage source and an impedance, said impedance having at least first and second resistance components, said first component having a linearly increasing value with source usage and being in combination with an effective electrolyte capacitance, said second component having a value which is negligible until it increases sharply after a certain source usage, comprising detector circuit means adapted to be connected across the output of said source and having sampling means for placing said detector circuit means into electrical contact with said source for a sampling period of 10-5 seconds or less and for generating a signal indicative of current flow from said source during said sampling period, and means for determining when said signal reaches a predetermined level.
Specification