Dual battery power system for an implantable cardioverter defibrillator with voltage booster

Abstract

An improved dual battery power system uses two separate battery power sources for an implantable cardioverter defibrillator, each having optimized characteristics for monitoring functions and for output energy delivery functions, respectively. The monitoring functions are supplied electrical power by a first battery source, such as a conventional pacemaker power source in the form of a lithium iodide battery which is optimized for long life at very low current levels. The output energy delivery functions are supplied by a separate second battery source, such as a pair of lithium vanadium pentoxide batteries, which is optimized for high current drain capability and low self-discharge for long shelf life. The first battery source provides electrical power only to the monitoring functions of the implantable cardioverter defibrillator, and the second battery source provides all of the electrical power for the output energy delivery functions.

Description

RELATED APPLICATIONS

operatea capacitor 146 . The 3.75 V output of the charge pump circuit 136 and the unregulated 6.0 Volt Bus are fed as inputs to a dual input voltage regulator 152. A voltage/current reference circuit 146 provides a reference voltage of 1.28 V and a reference current of 100 nA to the voltage regulator 152. A p-n-p transistor 154 controls whether the 6.0 Volt Bus input will be added to the 3.75 V output of the charge pump circuit 136 if a current overdraw condition exists with respect to the monitoring battery cell 111. The charge pump circuit 136 also provides a negative output of −2.0 to −2.5 V to supply the Main Power System negative voltage requirements of op amps, etc.

Referring now to FIG. 6, a more detailed explanation of the operation of the backup feature of a preferred embodiment of the present invention is shown. A feedback amplifier circuit 156 compares the reference voltage signal from the voltage/current reference circuit 146 to a divided down value of the 3 Volt Bus signal. The divide down is accomplished by resistors 158 and 160 and capacitor 162. A FET transistor circuit 164 responds to an output of the feedback amplifier circuit 156 to keep the voltage on the 3 Volt Bus at 3.0 V. If the current drain through the gate of the FET transistor circuit 164 is more than the maximum current draw for the monitoring battery cell 111, then the transistor circuit 154 is turned on by feedback amplifier circuit 156 to supply the necessary overdraw current from the output battery cells 121, 122 via the 6 Volt Bus. In the preferred embodiment, a local feedback loop is added to transistor circuit 154 to sin-relate a quasi-complementary darlington circuit in order to achieve a low drop voltage across transistor circuit 154.

Referring now to FIG. 7, a more detailed explanation of the operation of the booster feature of a preferred embodiment of the present invention is shown. Voltage supply ripple is caused by changes in the battery impedance due to the high current draw required by the flyback charging operation of inverter circuit 140. If the drop out voltage of the voltage supply is too great, or if the power supply rejection ratio of monitoring circuitry 34 and output circuitry 38 is exceeded. The result may exceeded, the result may be either local or catostrophic circuit failure. To prevent voltage supply ripple from affecting the voltage supply of the preferred embodiment of the present invention, a voltage booster 130 is used.

The voltage booster 130 of the preferred embodiment as shown in FIG. 7 runs the battery output current through an inductor 170 for a period of time, and then switches the current through a zener diode 172 to a capacitor 174 and to ground. Zener diode 172 regulates the voltage on capacitor 174 and also blocks capacitor 174 from creating ripple in the voltage supply (V_DD). Voltage booster 130 senses activity by inverter circuit 140 using a FET transistor 176 and begins cycling inductor 170 in accordance with the delays generated by diodes 178 in response to the value of the voltage supply (V_DD) and the switching of logic gate 180 and FET transistor 182. In this way, voltage booster 130 may efficiently adjust its cycle time to immediately match the various levels of the voltage supply (V_DD) that may be encountered during the charging operation. In the preferred embodiment, voltage booster 130 runs at a fixed frequency with a variable duty cycle dependent upon the output voltage of the battery. When voltage booster 130 is not active, current from the output of the battery is routed through Schottky diode 184 and through a choke inductor 186 to the voltage supply (V_DD).

Claims

1. An improved power system for an implantable cardioverter defibrillator that is a self-contained human implantable device having comprising:

monitoring means for detecting myocardial arrhythmias in a human patient; and

output means for selectively determining an appropriate electrical pulse therapy to be delivered in response to a myocardial arrhythmia detected by the monitoring means and delivering the appropriate electrical pulse therapy to two or more implanted electrodes, the improved power system comprising: ;

first battery means for providing electrical power primarily to the monitoring means;

second battery means for providing substantially all of its electrical power to the output means; and

backup means for allowing the second battery means to provide electrical power to the monitoring means in the event that the first battery means can no longer provide electrical power to the monitoring means.

2. The improved power system implantable cardioverter defibrillator of claim 1 wherein the implantable cardivoerter cardioverter defibrillator includes a capacitor means for storing an electrical charge which is charged from the second battery means and wherein the output means selects the appropriate electrical pulse therapy from a set that includes:

one or more cardioversion/defibrillation pulses, each cardioversion/defibrillation pulse being delivered by the output means as a capacitive discharge pulse from the capacitor means; and

one or more pacing pulses, each pulse being delivered by the output means as an electrical pulse directly powered from the second battery means.

3. The improved power system implantable cardioverter defibrillator of claim 1 wherein the backup means comprises:

transistor means operably connected to outputs of the first battery means and the second battery means to sense a current drain on the output of the first battery means and switch on the output of the second battery means to add to the output of the first battery means in the event that the current drain exceeds a maximum current drain of the first battery means.

4. The improved power system implantable cardioverter defibrillator of claim 1 further comprising:

voltage regulation means operably connected to an output of the first battery means and to a reference voltage value for regulating the output of the first battery means to a predetermined voltage value.

5. The improved power system implantable cardioverter defibrillator of claim 1 wherein the first battery means is a relatively low current source, and wherein the second battery means is a relatively high current source.

6. The improved power system implantable cardioverter defibrillator of claim 5, wherein the relatively low current source is a 1.5 to 3.0 volt battery and the relatively high current source is a 6 to 18 volt battery.

7. The improved power system implantable cardioverter defibrillator of claim 1 wherein the first battery means is one or more lithium iodide battery cells.

8. The improved power system implantable cardioverter defibrillator of claim 1 wherein said second battery means is one or more battery cells selected from the group consisting of:

lithium silver vanadium oxides, thionyl chlorides or rechargeable battery cells.

9. The implantable cardioverter defibrillator of claim 1, further comprising:

a voltage booster connected to said second battery means to insure a minimum boosted voltage to said output means during periods of high current draw.

10. The implantable cardioverter defibrillator of claim 1, further comprising:

a voltage booster connected to said second battery means to prevent voltage ripple to said output means during periods of high current draw.

11. An implantable cardioverter defibrillator that is a self-contained human implantable device comprising:

monitoring means for detecting myocardial arrhythmias in a human patient;

output means for selectively determining an appropriate electrical pulse therapy to be delivered in response to a myocardial arrhythmia detected by the monitoring means and delivering the appropriate electrical pulse therapy to two or more implanted electrodes;

at least one battery means for providing electrical power to the output means; and

a voltage booster connected to at least one of said at least one battery means to insure a minimal booster voltage output of said at least one of said at least one battery means during periods of high current draw.

12. The implantable cardioverter defibrillator of claim 11, further comprising:

a diode connected to said voltage booster to isolate the boosted voltage output from a voltage output of said at least one battery means.

13. The implantable cardioverter defibrillator of claim 11, further comprising:

a charge pump circuit connected to the boosted voltage output to increase the boosted voltage output; and

an inverter circuit including a high voltage transformer connected to said charge pump circuit to produce a high voltage output from the increased boosted voltage output to charge the output means.

14. The implantable cardioverter defibrillator of claim 13, further comprising:

a capacitor connected between said inverter circuit and said at least one battery means to decouple said at least one battery means from said inverter circuit.

15. An implantable cardioverter defibrillator that is a self-contained human implantable device comprising:

monitoring means for detecting myocardial arrhythmias in a human patient;

output means for selectively determining an appropriate electrical pulse therapy to be delivered in response to a myocardial arrhythmia detected by the monitoring means and delivering the appropriate electrical pulse therapy to two or more implanted electrodes;

at least one battery means connected to the output means;

an inverter circuit, including a high-voltage transformer, connected to the output means to provide a high voltage pulse to the output means; and

a voltage booster connected to at least one of said at least one battery, to insure a minimum boosted voltage output of said at least one of said at least one battery during periods of high current draw.

16. The implantable cardioverter defibrillator of claim 15, wherein said at least one battery comprises a first battery and a second battery, said first battery provided for supplying electrical power primarily to the monitoring means and said second battery connected to said voltage booster.

17. The implantable cardioverter defibrillator of claim 16, further comprising a diode connected to said voltage booster to isolate a boosted voltage output of said voltage booster from a voltage output of said second battery during periods of high current draw.

18. The implantable cardioverter defibrillator of claim 15, further comprising a charge pump circuit connected to the minimum boosted voltage output and to said inverter circuit.

19. The implantable cardioverter defibrillator of claim 15, wherein said voltage booster comprises:

at least one capacitor for storing a boosted voltage; and

a diode connected to said at least one capacitor to regulate said boosted voltage on said at least one capacitor, and to prevent said at least one capacitor from creating ripple in the voltage supplied to the output means.

20. The implantable cardioverter defibrillator of claim 19, wherein said voltage booster further comprises:

an activity monitor connected to said inverter circuit to time a charging operation of said at least one capacitor in accordance with activity by said inverter circuit.