WO2007079355A1 - Method of maintaining wet-tantalum electrolytic capacitors - Google Patents

Method of maintaining wet-tantalum electrolytic capacitors Download PDF

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Publication number
WO2007079355A1
WO2007079355A1 PCT/US2006/062212 US2006062212W WO2007079355A1 WO 2007079355 A1 WO2007079355 A1 WO 2007079355A1 US 2006062212 W US2006062212 W US 2006062212W WO 2007079355 A1 WO2007079355 A1 WO 2007079355A1
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Prior art keywords
capacitor
voltage range
maintenance voltage
maintenance
maintaining
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PCT/US2006/062212
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French (fr)
Inventor
John D. Norton
Ann M. Crespi
Daniel F. Untereker
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Medtronic, Inc.
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Publication of WO2007079355A1 publication Critical patent/WO2007079355A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
    • A61N1/39—Heart defibrillators
    • A61N1/3975—Power supply
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
    • H01G9/004—Details
    • H01G9/04—Electrodes or formation of dielectric layers thereon
    • H01G9/042—Electrodes or formation of dielectric layers thereon characterised by the material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
    • H01G9/004—Details
    • H01G9/14—Structural combinations or circuits for modifying, or compensating for, electric characteristics of electrolytic capacitors

Definitions

  • the present invention relates generally to electrolytic capacitors.
  • the present invention relates to maintaining wet-tantakmi capacitors used in roedicai devices to deliver high energy electrical therapy to a patient.
  • Implantable cardioverter defibrillators ICD' s
  • automatic external defibrillators AED' s
  • ICD' s Implantable cardioverter defibrillators
  • AED' s automatic external defibrillators
  • ICD's implantable cardioverter defibrillators
  • AED' s automatic external defibrillators
  • Wet electrolytic capacitors are typically used in ICD's &n ⁇ AED * s.
  • a wet electrolytic capacitor includes a metallic anode, a metal oxide layer formed on the anode, a liquid electrolyte, and a cathode.
  • wet-tantalum capacitors having a tantalum anode, a tantalum oxide dielectric layer, a liquid electrolyte, and a cathode have been developed for use in ICDs and AEDs.
  • wet-tantalum capacitors exhibit less severe deformation than aluminum electrolytic capacitors, but degradation of vvet-tatitaltun capacitors and techniques for reforming the tantalum/tantalum oxide anode have also been addressed. Methods of reforming wet-tantalum capacitors are described in Harguth et al. US. Patent. Nos. 6,283,985 and 6,706,059, Liu et at Publication No, U.S. 2003/0088273; and Norton et al. Publication No. U.S. 2004/0225327.
  • the present invention maintains a wet-tantalum capacitor used in a medical device so that deformation Is substantially inhibited. Tantalum electrolytic capacitor deformation is controlled by maintaining the capacitor at a maintenance voltage between full energy charges. The maintenance voltage inhibits processes which cause deformation to occur, without causing significant power loss due to capacitor leakage.
  • FlO Hs a flow diagram illustrating a method of maintaining a wet-tantalum capacitor to inhibit deformation.
  • FlO. 2 is a block diagram of an example of an ICD in which the maintenance method of F ⁇ Gv 1 can be used,
  • the deformation of wet-tantalum capacitors is attributed to two related causes.
  • the first contributor is incomplete or poor formation of the anodic oxide (i.e. the TasOj dielectric layer) associated with the deposition of a sparingly soluble phosphate species in the interstices of the anode during formation of the anodic oxide.
  • the second contributor is the operation of the capacitor at voltages above the onset of significant parasitic reactions (those not associated with oxide formation or eapacitive charging), which result in similar deposits of phosphates within, the anode.
  • the deformation mechanism is the result of hydration of either the TasOs dielectric or, more likely, of the phosphate deposit within the interstices of the anode.
  • the phosphate deposit exisis ia a dehydrated state.
  • hydration of the phosphate makes it more conductive, allowing electrical access to more Ta ⁇ G* surface area. This increases the amount of energy that is required to charge the capacitor relative to that, required for a fully formed capacitor. Because of the relatively high resistance of fhe hydrated phosphate, the additional capacitance is realized only during the relatively slow capacitor charging process, and not during the much more rapid discharge,
  • Reformation of the capacitor requires dehydration of the phosphate deposit.
  • the dehydration process is assisted by the application of an electric field, ⁇ t has been discovered that the electric field required is relatively low compared to that applied when the capacitor is charged to a high voltage relative to its voltage or maximum energy voltage.
  • capacitor reformation has been achieved at relatively low voltages, as described in Application No. U.S. 2004/0225327.
  • the present invention addresses the issue of deformation by preventing the deformation process from taking place, rather than by performing periodic reformation charging and discharging of the capacitor.
  • the process of deformation may be prevented by maintaining the capacitor at a maintenance voltage between full energy charges. Because the power lost to capacitor leakage current can be very low at these voltages, it does not significantly impact battery life, and therefore ⁇ CD device longevity is not impacted.
  • the maintenance voltage can range from a voltage that at least partially inhibits deformation up to a voltage of about 90% of rated voltage. Generally, the lower the maintenance voltage, the lower the capacitor leakage current. Therefore, maintenance voltages less than about 50%, and particularly about 25% or less of rated voltage will result in lower losses of charge through capacitor leakage current Selection of a maintenance voltage may involve striking a balance between the amount of energy- consumed by leakage and the extent of deformation (if any) that is acceptable.
  • FIG. I illustrates method IO of operating a medical device in a way that inhibits deformation effects in its high voltage wet-tantalum capacitors.
  • a maintenance voltage which is a voltage at which phosphate deposits the anode to the capacitor will be maintained in a substantially dehydrated stale (step 12), This voltage, therefore, will substantially inhibit, deformation from taking place,
  • the charge on the capacitors is maintained within a maintenance voltage range (step 14 ⁇ until there is a need to deliver therapy.
  • the voltage on the capacitors may be sensed, and an additional charge may be delivered to the capacitors from time-to- time in ordcrto maintain the voltage on the capacitors within the desired, maintenance voltage range.
  • the medical device has detected a condition, requiring therapy.
  • a malignant tachycardia may ha ⁇ e been detected, based upon electrogram (EOSVI) or electrocardiogram (KCG) signals sensed by the device
  • the device upon deteimtmng that theiapy will be required, the device causes the wet-tantalum capacitors to be charged to full energy (i e the energy level programmed in the device for the cardioversion or defibrillation shock). Because the capacitors are already partially charged to the maintenance voltage range, and deformation has been substantially inhibited, the charges time to reach full energy is reduced compared to a similar capacitor beginning at an uncharged state
  • the device When the device senses that the capacitors are charged to the desired (full energy) voltage level, the device makes a final determination of whether to deliver the therapy If a condition requiring therapy is still present the capacitors are discharged to deliver therapy to the patient (step 20)
  • the capacitors Once the capacitors have been discharged, they will again be charged to at I east the maintenance voltage (step 12) m ⁇ maintained at that voltage (step 14) until therapy is again needed. This may be a very shoit time period, depending upon whether an additional defibrillation shock is needed Alternatively, if multiple shocks are required, charging again to full energy r ⁇ ay occur without any significant period at which the capacitor remains at the maintenance voltage level. In some cases, ih& full energy level may be increased with successive shocks.
  • FIG. 2 shows iCl> 30.
  • ICD 30 includes balterj' 32, low voltage power supply 34, high voltage charging circuit 36, transformer 38. diodes 40 and 42, wet-tantalum capacitors CI and C2, high voltage output circuit 44, control 46, microcomputer 48, pace/sense circuitry 50, pace/sense terminals S2 and 54. and cardioversion/defibrillation terminals 56, 58, and o0.
  • Battery 32 provides power through low voltage power supply 34 with the electrical circuitry of ICD 30
  • battery 32 supplies ptmer to high ⁇ r oltage charging circuit 56 thai iv used to cbaigc capacitors Cl and C2
  • High voliage charging circuit 36 and transformer 38 step up the relatively low voltage of battery 32 to the voltage levels needed to charge capacitors Cl and C2 Io full energy, as well as to the maintenance voltage,
  • Pace/sease terminals 52 and 54 are connected to pace/sense electrodes (not shown) used to sense electrical activity of the heart, and to deliver pacing pulses mider the control of pace/sense circuitry 50.
  • the pace/sense electrodes are carried by leads connected to terminals 52 and 54, or may be carried, on the housing or can of ICD 30,
  • Pace/sense circuitry 50 receives EGM signals from terminals 52 and 54 and senses R.-wave activity. In conjunction with microcomputer 48 and control 46, pace/sense circuitry 50 delivers pacing pulses to terminals 52 and 54.
  • the sensed R-vvave activity is also used by microcomputer 4S and control 46 to determine presence of a malignant tachycardia that requires cardioversion/defibrillation shocks.
  • control 46 Upon determining the need for cardioversion/defibrillation, control 46 causes high voltage charging circuit 36 to charge capacitors Cl and C2 to full energy.
  • High voltage output circuit 44 senses the voltage on capacitors C J. and C2 > and provides a feedback signal VCAP io control 46.
  • control 46 detects that VCAP signal matches the programmed energy levels for the cardioversion/defibrillation shock control 46 provides control signals (ENAB and ENBA) to the output circuit 44.
  • Capacitors Cl and 02 are discharged between defibrillation electrodes connected to terroi.na.ts; 58 and 60 and a common or can electrode on the housing of XCD 30 (which is connected to terminal 56).
  • the high voltage therapeutic discharges may be delivered simultaneously or sequentially, or discharge, .may be provided between only one of the terminals 58 and 60 and common terminal 56, If the therapeutic discharge is terminated at a voltage that is greater titan the maintenance voltage, capacitors CI and C2 may be discharged or allowed to bleed down to the maintenance voltage prior to initiation of any maintenance charging.
  • Charging of capacitors Cl and C2 may begin before a final decision is made to deliver cardioversion/defibrillation therapy. If normal rhythm returns and a therapeutic shock is not required, control 46 provides a DUMP control signal to high voltage output circuit 44, which causes the energy on capacitors Cl and C2 to be discharged through a non-therapeutic load within ICD 30, until they reach the maintenance voltage (or alternatively are fully discharged).
  • control 46 causes capacitors Cl and €2 to be charged to the maintenance voltage.
  • Control 46 monitors the voltage on Cl and C2 with the VCAP feedback signal. Tf the voltage on Cl and C2 decreases to a poi ⁇ t at. which deformation can occur, control 46 causes high voltage charging circuit 36 to increase charge on. CI and C2 so that, they are maintained in a voltage range at which deformation is inhibited.
  • This maintenance method addresses deformation by creating conditions that reduce the extent to which deformation of the capacitor anode can occur. As a result, periodic reformation charging and discharging is unnecessary.
  • the maintenance method results in decreased device charging times because the effects of deformation are reduced or eliminated.
  • the capacitors are maintained in a partially charged condition, which also decreases charging time when therapy is needed.
  • the maintenance method also increases device longevity. Less energy is used to charge and maintain the capacitor to a low level than JS used, in periodically reforming the capacitor by charging and then discharging it
  • the method has been described in a specific implementation, of an !.CD shown in FIG.2, the invention can be implemented with other ICD's with different numbers of capacitors, different numbers of electrodes, and different circuitry than that shown in FIG. 2.
  • the method is applicable to other medical, devices (including ABDs) where charging and discharging of wet-tantalum electrolytic capacitors, with intervening periods of inactivity, occur.
  • ABDs a specific implementation, of an !.CD shown in FIG.2
  • deformation of wet-tan tai urn capacitors can cause delays in charging other devices as well, including external medical devices as well as devices and systems having non-medical uses.

Abstract

Wet-tantalum capacitors used in a medical device are charged to and maintained at a maintenance voltage between full energy charges so that deformation in the wet-tantalum capacitor is substantially inhibited.

Description

METHOD OF MAINTAINING WET-TANTALUM ELECTROLYTIC CAPACITORS
BACKGRQUKD OF THE INVENTION
The present invention relates generally to electrolytic capacitors. In particular, the present invention relates to maintaining wet-tantakmi capacitors used in roedicai devices to deliver high energy electrical therapy to a patient.
Implantable cardioverter defibrillators (ICD' s) and automatic external defibrillators (AED' s) apply a therapeutic electric shock to a patient's heart to restore the heart to a normal rhythm. These devices use high voltage, capacitors that are charged just before the cardioversion, or defibrillation therapy is delivered, and then discharged through electrodes to deliver the therapeutic electrical shock. Wet electrolytic capacitors are typically used in ICD's &nά AED* s. A wet electrolytic capacitor includes a metallic anode, a metal oxide layer formed on the anode, a liquid electrolyte, and a cathode.
Originally, aluminum electrolytic capacitors having an aluminum anode with an aluminum oxide coating were used. More recently, wet-tantalum capacitors having a tantalum anode, a tantalum oxide dielectric layer, a liquid electrolyte, and a cathode (e.g., a tantalum or ruthenium oxide) have been developed for use in ICDs and AEDs.
When wet electrolytic capacitors rest on open circuit for days or longer, a process commonly referred to as "deformation" occurs, As a result, when the capacitor is next charged, an appreciable amount of energy is used to "reform" the oxide dielectric layer. This results in longer than desired charging times for the ICD or /VED. Tt also affects the longevity of the device, because a greater amount of energy from the battery is required during the charging process.
Techniques for reforming electrolytic capacitors in ICD's are discussed in. KmH U.S. Patent No. 5,741,307; Startweather et at. U.S. Patent No. 5,792,188; Kroll U.S. Patent No. 5,861,006; and Silvϊan U.S. Patent No. 6,096,602, These patents describe reform techniques which were originally used with aluminum electrolytic capacitors.
Wet-tantalum capacitors exhibit less severe deformation than aluminum electrolytic capacitors, but degradation of vvet-tatitaltun capacitors and techniques for reforming the tantalum/tantalum oxide anode have also been addressed. Methods of reforming wet-tantalum capacitors are described in Harguth et al. US. Patent. Nos. 6,283,985 and 6,706,059, Liu et at Publication No, U.S. 2003/0088273; and Norton et al. Publication No. U.S. 2004/0225327.
The present invention maintains a wet-tantalum capacitor used in a medical device so that deformation Is substantially inhibited. Tantalum electrolytic capacitor deformation is controlled by maintaining the capacitor at a maintenance voltage between full energy charges. The maintenance voltage inhibits processes which cause deformation to occur, without causing significant power loss due to capacitor leakage.
BR!;SlDBSCJlH>:rϊ0H.OFjϊ;ϊ:!:!:LΪΪRAWϊNGS
FlO, Hs a flow diagram illustrating a method of maintaining a wet-tantalum capacitor to inhibit deformation.
FlO. 2 is a block diagram of an example of an ICD in which the maintenance method of F ϊGv 1 can be used,
DETAILED DESCRIPTION
The deformation of wet-tantalum capacitors is attributed to two related causes. The first contributor is incomplete or poor formation of the anodic oxide (i.e. the TasOj dielectric layer) associated with the deposition of a sparingly soluble phosphate species in the interstices of the anode during formation of the anodic oxide. The second contributor is the operation of the capacitor at voltages above the onset of significant parasitic reactions (those not associated with oxide formation or eapacitive charging), which result in similar deposits of phosphates within, the anode.
It is believed the deformation mechanism is the result of hydration of either the TasOs dielectric or, more likely, of the phosphate deposit within the interstices of the anode. When the capacitor is "fully formed", the phosphate deposit, exisis ia a dehydrated state. As the capacitor rests at open circuit with no voltage applied, hydration of the phosphate makes it more conductive, allowing electrical access to more Ta^G* surface area. This increases the amount of energy that is required to charge the capacitor relative to that, required for a fully formed capacitor. Because of the relatively high resistance of fhe hydrated phosphate, the additional capacitance is realized only during the relatively slow capacitor charging process, and not during the much more rapid discharge,
Reformation of the capacitor requires dehydration of the phosphate deposit. The dehydration process is assisted by the application of an electric field, ϊt has been discovered that the electric field required is relatively low compared to that applied when the capacitor is charged to a high voltage relative to its voltage or maximum energy voltage. As such, capacitor reformation has been achieved at relatively low voltages, as described in Application No. U.S. 2004/0225327.
The present invention addresses the issue of deformation by preventing the deformation process from taking place, rather than by performing periodic reformation charging and discharging of the capacitor. The process of deformation may be prevented by maintaining the capacitor at a maintenance voltage between full energy charges. Because the power lost to capacitor leakage current can be very low at these voltages, it does not significantly impact battery life, and therefore ΪCD device longevity is not impacted.
The maintenance voltage can range from a voltage that at least partially inhibits deformation up to a voltage of about 90% of rated voltage. Generally, the lower the maintenance voltage, the lower the capacitor leakage current. Therefore, maintenance voltages less than about 50%, and particularly about 25% or less of rated voltage will result in lower losses of charge through capacitor leakage current Selection of a maintenance voltage may involve striking a balance between the amount of energy- consumed by leakage and the extent of deformation (if any) that is acceptable.
FIG. I illustrates method IO of operating a medical device in a way that inhibits deformation effects in its high voltage wet-tantalum capacitors. When the medical device is initialised, the wet-tantaiurn capacitors are charged to a maintenance voltage, which is a voltage at which phosphate deposits the anode to the capacitor will be maintained in a substantially dehydrated stale (step 12), This voltage, therefore, will substantially inhibit, deformation from taking place,
The charge on the capacitors is maintained within a maintenance voltage range (step 14} until there is a need to deliver therapy. The voltage on the capacitors may be sensed, and an additional charge may be delivered to the capacitors from time-to- time in ordcrto maintain the voltage on the capacitors within the desired, maintenance voltage range.
At step 16, the medical device has detected a condition, requiring therapy. For example, a malignant tachycardia may ha\ e been detected, based upon electrogram (EOSVI) or electrocardiogram (KCG) signals sensed by the device
At step IS. upon deteimtmng that theiapy will be required, the device causes the wet-tantalum capacitors to be charged to full energy (i e the energy level programmed in the device for the cardioversion or defibrillation shock). Because the capacitors are already partially charged to the maintenance voltage range, and deformation has been substantially inhibited, the charges time to reach full energy is reduced compared to a similar capacitor beginning at an uncharged state
When the device senses that the capacitors are charged to the desired (full energy) voltage level, the device makes a final determination of whether to deliver the therapy If a condition requiring therapy is still present the capacitors are discharged to deliver therapy to the patient (step 20)
Once the capacitors have been discharged, they will again be charged to at I east the maintenance voltage (step 12) mά maintained at that voltage (step 14) until therapy is again needed. This may be a very shoit time period, depending upon whether an additional defibrillation shock is needed Alternatively, if multiple shocks are required, charging again to full energy røay occur without any significant period at which the capacitor remains at the maintenance voltage level. In some cases, ih& full energy level may be increased with successive shocks.
FIG. 2 shows iCl> 30. which is an example of a medical device in \\,hich the capacitor maintenance of the present invention can be implemented ICD 30 includes balterj' 32, low voltage power supply 34, high voltage charging circuit 36, transformer 38. diodes 40 and 42, wet-tantalum capacitors CI and C2, high voltage output circuit 44, control 46, microcomputer 48, pace/sense circuitry 50, pace/sense terminals S2 and 54. and cardioversion/defibrillation terminals 56, 58, and o0.
Battery 32 provides power through low voltage power supply 34 with the electrical circuitry of ICD 30 In addition, battery 32 supplies ptmer to high \roltage charging circuit 56 thai iv used to cbaigc capacitors Cl and C2 High voliage charging circuit 36 and transformer 38 step up the relatively low voltage of battery 32 to the voltage levels needed to charge capacitors Cl and C2 Io full energy, as well as to the maintenance voltage,
Pace/sease terminals 52 and 54 are connected to pace/sense electrodes (not shown) used to sense electrical activity of the heart, and to deliver pacing pulses mider the control of pace/sense circuitry 50. The pace/sense electrodes are carried by leads connected to terminals 52 and 54, or may be carried, on the housing or can of ICD 30,
Pace/sense circuitry 50 receives EGM signals from terminals 52 and 54 and senses R.-wave activity. In conjunction with microcomputer 48 and control 46, pace/sense circuitry 50 delivers pacing pulses to terminals 52 and 54.
The sensed R-vvave activity is also used by microcomputer 4S and control 46 to determine presence of a malignant tachycardia that requires cardioversion/defibrillation shocks. Upon determining the need for cardioversion/defibrillation, control 46 causes high voltage charging circuit 36 to charge capacitors Cl and C2 to full energy. High voltage output circuit 44 senses the voltage on capacitors C J. and C2> and provides a feedback signal VCAP io control 46. When control 46 detects that VCAP signal matches the programmed energy levels for the cardioversion/defibrillation shock control 46 provides control signals (ENAB and ENBA) to the output circuit 44. Capacitors Cl and 02 are discharged between defibrillation electrodes connected to terroi.na.ts; 58 and 60 and a common or can electrode on the housing of XCD 30 (which is connected to terminal 56). The high voltage therapeutic discharges may be delivered simultaneously or sequentially, or discharge, .may be provided between only one of the terminals 58 and 60 and common terminal 56, If the therapeutic discharge is terminated at a voltage that is greater titan the maintenance voltage, capacitors CI and C2 may be discharged or allowed to bleed down to the maintenance voltage prior to initiation of any maintenance charging.
Charging of capacitors Cl and C2 may begin before a final decision is made to deliver cardioversion/defibrillation therapy. If normal rhythm returns and a therapeutic shock is not required, control 46 provides a DUMP control signal to high voltage output circuit 44, which causes the energy on capacitors Cl and C2 to be discharged through a non-therapeutic load within ICD 30, until they reach the maintenance voltage (or alternatively are fully discharged).
During time periods between full energy charging and discharging of capacitors Cl and C2, control 46 causes capacitors Cl and €2 to be charged to the maintenance voltage. Control 46 monitors the voltage on Cl and C2 with the VCAP feedback signal. Tf the voltage on Cl and C2 decreases to a poiαt at. which deformation can occur, control 46 causes high voltage charging circuit 36 to increase charge on. CI and C2 so that, they are maintained in a voltage range at which deformation is inhibited.
This maintenance method addresses deformation by creating conditions that reduce the extent to which deformation of the capacitor anode can occur. As a result, periodic reformation charging and discharging is unnecessary.
The maintenance method, results in decreased device charging times because the effects of deformation are reduced or eliminated. In addition, the capacitors are maintained in a partially charged condition, which also decreases charging time when therapy is needed.
The maintenance method also increases device longevity. Less energy is used to charge and maintain the capacitor to a low level than JS used, in periodically reforming the capacitor by charging and then discharging it Although the method has been described in a specific implementation, of an !.CD shown in FIG.2, the invention can be implemented with other ICD's with different numbers of capacitors, different numbers of electrodes, and different circuitry than that shown in FIG. 2. Similarly, the method is applicable to other medical, devices (including ABDs) where charging and discharging of wet-tantalum electrolytic capacitors, with intervening periods of inactivity, occur. Although particularly beneficial for implantable medical devices, where capacitor size and battery life are important, deformation of wet-tan tai urn capacitors can cause delays in charging other devices as well, including external medical devices as well as devices and systems having non-medical uses.
Although the present, invention has been described with reference to preferred embodiments, workers skilled in the art will recognise that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

1 , A method of maintaining a wet-tantalum capacitor in. a medical device, the method comprising: charging the capacitor to a therapeutically useful energy level in response to a detected condition requiring therapy; discharging the capacitor to provide the therapy to a patient; charging the capacitor to a maintenance voltage less than the therapeutically useful energy level; and maintaining charge on the capacitor within the maintenance voltage range until the capacitor is again charged to the therapeutically useful energy level.
2, The method of claim ϊ, wherein at the maintenance voltage range phosphate deposits at an anode of the capacitor are maintained in a substantially dehydrated state.
3 , The method of claim .! , wherein the maintenance voltage range includes voltages at which deformation is at least partially inhibited.
4, The method of claim 3, wherein the maintenance voltage range includes voltages of up to about 90% of a rated voltage of the capacitor.
5, The method of claim 4, wherein the maintenance voltage range includes voltages of up to about 50% of the rated voltage.
6, The method of claim 5, wherein the maintenance voltage range includes voltages of tip to about 25% of the rated voltage.
7, A method of maintaining a wewanialum capacitor in a medical device that is charged to full energy and discharged, to provide a therapy to a patient, the method comprising: charging the capacitor to a maintenance voltage range at which deformation, effects aτe reduced; and maintaining charge on the capacitor within the maintenance voltage range between full energy charging events .
8. Tibe method of claim 7, wherein the maintenance voltage range include voltages at which deformation is at least partially inhibited.
9. The method of claim S, wherein the maintenance voltage range includes voltages of up to about 90% of a rated voltage of the capacitor.
10. The method of claim S, wherein the maintenance voltage range includes voltages of wp to about 50% of the rated voltage.
13. The method of claim 8, wherein the maintenance voltage range includes voltages of up to about 25% of the rated voltage.
12. A method of maintaining a wet-tantalum capacitor, comprising: charging the capacitor to a maintenance voltage range that is less than one of a maximum and rated voltage for the capacitor; and maintaining charge on the capacitor within the maintenance voltage range between full energy charging events .
13. The method of claim 12, wherein the maintenance voltage range include voltages at which deformation is at least partially inhibited,
14. A. medical device comprising: a wet-tantalum capacitor that is charged to full energy and discharged to provide a therapy to a patient; ami means for maintaining charge on the capacitor within a maintenance voltage range at which deformation effects are reduced between full, energy charging events.
\ 5. The medical device of claim 13, wherein the maintenance voltage range includes voltages of tip to about 90% of a rated voltage of the capacitor-
16. The medical device of claim „ 3» wherein the maintenance voltage range includes voltages of up to about 50% of the rated voltage.
.
17. The medical device of claim 13, wherein the maintenance voltage range includes voltages of up to about 25% of the rated, voltage,
18. A method of maintaining a wet-tantalum capacitor, comprising: applying an electric field across the capacitor dielectric to cause dehydration of an anodic oxide phosphate deposit; and maintaining she electric field to prevent hydration of the anodic oxide phosphate deposit during periods of inactivity of the capacitor.
19. The method of claim 18, wherein the anodic oxide comprises Ta2Os.
20. The method of claim 19, wherein the phosphate deposit is located in the interstices of the anodic oxide.
PCT/US2006/062212 2005-12-30 2006-12-18 Method of maintaining wet-tantalum electrolytic capacitors WO2007079355A1 (en)

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