Method and apparatus for controlling the charging phase of an implantable cardioverter-defribrillator
First Claim
1. An implantable cardioverter-defibrillator having a shocking capacitor chargeable during a conversion phase, comprising:
- a battery having an internal battery resistance and a battery voltage that decreases as a function of current drain from the battery due to the internal battery resistance;
flyback transformer means for charging the shocking capacitor during the conversion phase, said conversion phase comprising a series of charging cycles, the flyback transformer means including a primary coil;
charging control means including comparator means for outputting a first reset signal when the battery voltage VB falls below a predetermined reference voltage VR, wherein VR =VB1 -Δ
VB, where VB1 represents the battery voltage before the conversion phase, and Δ
VB represents a maximum drop in battery voltage from VB1 when the battery current drain exceeds a predetermined maximum current, the charging control means comprising;
voltage measuring means for measuring VB1 before the conversion phase; and
processing logic means for computing VR =VB1 -Δ
VB and for providing VR to the comparator means;
primary switching means for coupling the primary coil of the flyback transformer to the battery during an on time of a charging cycle and uncoupling the primary coil from the battery during an off time of a charging cycle; and
whereinthe primary switching means includes a reset input for receiving the first reset signal, wherein the primary switching means terminates the on time in response to the received first reset signal.
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Abstract
The on time of a flyback converter is controlled without the need for a current-sensing resistor. Under one approach, an internal battery resistance RB is used as a substitute for the current-sensing resistor. The battery voltage VB decreases as a function of current drain from the battery due to the internal impedance. Charging control circuitry causes the on time to be terminated when the battery voltage VB falls below a predetermined reference voltage VR, where VR =VB1 -ΔΔVB. VB1 represents the battery voltage before charging is commenced, and ΔVB represents the drop in battery voltage from VB1 when the battery current drain exceeds a predetermined maximum current. Under another approach, the charging control circuitry regulates the time out period ton1 =K/VB, where K is a predetermined constant, such that it is 10-15 percent longer than the on time ton.
40 Citations
13 Claims
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1. An implantable cardioverter-defibrillator having a shocking capacitor chargeable during a conversion phase, comprising:
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a battery having an internal battery resistance and a battery voltage that decreases as a function of current drain from the battery due to the internal battery resistance; flyback transformer means for charging the shocking capacitor during the conversion phase, said conversion phase comprising a series of charging cycles, the flyback transformer means including a primary coil; charging control means including comparator means for outputting a first reset signal when the battery voltage VB falls below a predetermined reference voltage VR, wherein VR =VB1 -Δ
VB, where VB1 represents the battery voltage before the conversion phase, and Δ
VB represents a maximum drop in battery voltage from VB1 when the battery current drain exceeds a predetermined maximum current, the charging control means comprising;voltage measuring means for measuring VB1 before the conversion phase; and processing logic means for computing VR =VB1 -Δ
VB and for providing VR to the comparator means;primary switching means for coupling the primary coil of the flyback transformer to the battery during an on time of a charging cycle and uncoupling the primary coil from the battery during an off time of a charging cycle; and
whereinthe primary switching means includes a reset input for receiving the first reset signal, wherein the primary switching means terminates the on time in response to the received first reset signal. - View Dependent Claims (2, 3, 4, 5)
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6. An implantable cardioverter-defibrillator having a shocking capacitor chargeable during a conversion phase, comprising:
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a battery having an internal battery resistance and a battery voltage that decreases as a function of current drain from the battery due to the internal battery resistance; flyback transformer means for charging the shocking capacitor during the conversion phase, said conversion phase comprising a series of charging cycles, the flyback transformer means including a primary coil; primary switching means for coupling the primary coil of the flyback transformer to the battery during an on time of a charging cycle and uncoupling the primary coil from the battery during an off time of a charging cycle; a reset input, coupled to the primary switching means, for receiving a first reset signal, wherein the primary switching means terminates the on time in response to the received first reset signal; and charging control means including voltage measuring means for measuring the battery voltage VB1 before the conversion phase, and timing control means for outputting the first reset signal to the reset input of the primary switching means to limit the on time to a time ton =K/VB1, where K is a predetermined constant, said charging control means further comprising comparator means for outputting a second reset signal to the reset input of the primary switching means when the battery voltage VB falls below a predetermined reference voltage VR. wherein VR =VB1 -Δ
VB, where VB1 represents the battery voltage before the conversion phase, and Δ
VB represents the drop in battery voltage from VB1 when the battery current drain exceeds a predetermined maximum current;voltage measuring means for measuring VB1 before the conversion phase; and processing logic means for computing VR =VB1 -Δ
VB and for providing VR to the comparator means; and
wherein the primary switching means terminates the on time in response to the received second reset signal and wherein the primary switching means terminates the on time in response to the received second reset signal. - View Dependent Claims (7, 8, 9)
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10. A method of operating an implantable cardioverter-defibrillator including a shocking capacitor and a battery having an internal battery resistance and a battery voltage that decreases as a function of current drain from the battery due to the internal battery resistance, the method comprising the steps of;
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using a flyback transformer to charge the shocking capacitor during a conversion phase, said conversion phase a series of charging cycles, the flyback transformer including a primary coil; generating a first reset signal when the battery voltage VB falls below a predetermined reference voltage VR, wherein VR =VB1 -Δ
VB, VB1 representing the battery voltage before the conversion phase, and Δ
VB representing a maximum drop in battery voltage from VB1 when the battery current drain exceeds a predetermined maximum current;coupling the primary coil of the flyback transformer to the battery during an on time of a charging cycle and uncoupling the primary coil from the battery during an off time of a charging cycle; coupling a first sample-and-hold circuit to the battery before the conversion phase so as to hold VB1 ; coupling a second sample-and-hold circuit to Δ
VB before the conversion phase so as to hold Δ
VB ; andcoupling the first sample-and-hold circuit to the second sample-and-hold circuit in series during the conversion phase so as to provide a representation of the reference voltage VR =VB1 -Δ
VB ; andterminating the on time of a charging cycle in response to the first reset signal. - View Dependent Claims (11)
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12. A method of operating an implantable cardioverter-defibrillator including a shocking capacitor and a battery having an internal battery resistance and a battery voltage that decreases as a function of current drain from the battery due to the internal battery resistance, the method comprising the steps of:
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using a flyback transformer to charge the shocking capacitor during a conversion phase, said conversion phase comprising a series of charging cycles, the flyback transformer including a primary coil; coupling the primary coil of the flyback transformer to the battery during an on time of a charging cycle and uncoupling the primary coil from the battery during an off time of a charging cycle; terminating the on time in response to a first reset signal; measuring the battery voltage VB1 before the conversion phase; generating the first reset signal to limit the on time to a time ton =K/VB1, where K is a predetermined constant; generating a second reset signal when the battery voltage VB falls below a predetermined reference voltage VR, wherein VR =VB1 -Δ
VB, wherein VB1 represents the battery voltage before the conversion phase, and Δ
VB represents the drop in battery voltage from VB1 when the battery current drain exceeds a predetermined maximum current, andterminates the on time in response to the second reset signal; and using a second sample-and-hold means before the conversion phase so as to sample-and-hold Δ
VB, using a first sample-and-hold means in series with the second sample-and-hold means during the conversion phase so as to provide a representation of the reference voltage VR =VB1 -Δ
VB,wherein the comparator means receives the representation of the reference voltage from the secondary switching means. - View Dependent Claims (13)
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Specification