Coulomb Counter for Implantable Devices and External Controller
Publication Date: 2003-Sep-26
The IP.com Prior Art Database
A coulomb counter is used in an implanted medical device that is powered by an energy storage device such as a primary or rechargeable battery. The coulomb counter is used to measure or calculate the quantity of charge flowing into the energy storage device or discharged from the energy storage device to thereby provide rates of charging or discharge and calculate the level of energy remaining in the energy storage device or time remaining left to complete a full recharge. In addition, the coulomb counter may be used in an external controller or device programmer, which is powered by an energy storage device.
Implantable stimulating devices have been used to treat a wide variety of diseases and disorders. Pacemakers and implantable cardiac defibrillators (ICDs) have proven to be highly effective in treating a number of cardiac conditions such as bradycardia and tachycardia. Implantable stimulation systems are also being used successfully to treat chronic, intractable pain. Other forms of stimulation therapy include urinary incontinence and deep brain stimulation to treat various forms of diseases such as Parkinson’s Disease, spastic tremor and epilepsy. Other implantable devices include drug delivery pumps and implantable sensors used to treat various ailments such as diabetes and chronic pain.
Many of these implantable systems utilize energy storage devices such as batteries and super-capacitors. When these storage devices become depleted, the devices either need to be explanted and replaced, e.g., for a primary battery, or need to be recharged. Knowing the level of energy remaining in these energy storage devices is important so that the storage device can be recharged or replaced before it depletes to zero voltage.
Measuring the voltage of the energy storage device may not provide an adequate measure to ascertain the level of energy remaining in the device because the measurement system may be limited by its resolution, e.g., an A/D converter, and by non-linearities exhibited by batteries. The following invention relates to the addition of coulomb counters in implantable devices and, in particular, implantable stimulators for determining the charge status of an energy storage device.
The present invention measures the level of energy remaining in a storage device such as a battery or capacitor by using a coulomb counter to directly measure the quantity of electrical charge that is delivered to the energy storage device or discharged by a device such as an implantable stimulator. Coulomb counters are devices which can measure the quantity of charge that has been delivered by the energy source or, alternatively, the amount of charge delivered to the energy source and use this information to calculate the remaining energy left in an energy storage device.
FIG. 1 shows a block diagram of a system using coulomb counters as provided in the invention. An energy storage device 30 may be a rechargeable battery and connected to a coulomb counter 20 which can be connected, in turn, to a power source 10. The amount of charge delivered to the storage device 30 may be measured by the coulomb counter 20, and this data may be stored in memory 25 that may be part of the coulomb counter 20, or in another location. Separately or, in addition, a coulomb counter 40 may be connected to the energy storage device 30 to detect the quantity of charge that is discharged from the energy storage device 30 and this data may be stored in memory 45 located in the coulomb counter...