Ionic conductivity is commonly associated with the flow of ions through a liquid solution of salts. In the vast majority of practical uses of ionic conductors, i.e., as electrolytes for dry cell and sealed lead acid batteries, the liquid solution is immobilized in the form of a paste or gelled matrix or is absorbed in a separator to overcome the difficulties associated with handling and packaging a liquid. However, even after immobilization, the system is still subject to possible leakage, has a limited shelf life due to drying out or crystallization of the salts and is suitable for use only within a limited temperature range corresponding to the liquid range of the electrolyte. In addition, the use of a large volume of immobilizing material has hindered the aims of miniaturization.
Improved microelectronic circuit designs have generally decreased the current requirements for electronic devices. This in turn has enhanced the applicability of solid electrolyte power sources which usually can deliver currents only in the microampere range. These solid electrolyte systems have the inherent advantages of being free of electrolyte leakage and internal gassing problems due to the absence of a liquid phase. In addition, they also have a much longer shelf life than the conventional liquid electrolyte power sources.
In attempting to avoid the shortcomings of liquid systems, investigators have surveyed a large number of solid compounds seeking to find compounds which are solid at room temperature and have specific conductances approaching those exhibited by the commonly used liquid systems. Solid electrolytes must be essentially electronic insulators so as not to internally short the cell while at the same time they must allow for ionic migration if the cell is to operate properly. There are many solid state electrolytes disclosed in the art that can be used for solid state cells but many can only operate efficiently at higher temperatures, have low operating voltages, or have high resistance.
In some applications requiring a portable constant current source, a battery is appropriately arranged with a constant current device so as to provide a constant current. In some applications, the connection between a battery and a current regulating device requires insulated wires and careful attention to the polarity of the connections. The connections are commonly made by welding or soldering the leads together. In humid environments, these types of connections can corrode.
Constant current devices connected to flat aqueous battery have been used but when using such batteries there is always a tendency that the batteries could leak and short out the connections of the constant current devices.
It is an object of the present innovation to provide a constant current source power supply employing a flat solid electrolyte battery which is flexible and not subject to electrolyte leakage.
It is another object of the present invention to provide a constant current source power supply that employs a solid electrolyte battery and a constant current device composed of a transistor and resistor means mounted on a circuit board.
It is another object of the present invention to provide a constant current source power supply that employs a flexible flat solid electrolyte battery having a solid electrolyte separator strip of poly(ethylene oxide) along with a lithium salt, ethylene carbonate and propylene carbonate, and a transistor-resistor assembly electrically secured to said battery to insure a constant current supply.