Abstract:
A plurality of batteries is printed on a flexible substrate, where each battery may output the same voltage, such as about 1.5 volts. Batteries in a first subset are connectable in parallel by controllable switches to control the maximum current that can be delivered to a load. Batteries in a second subset are also connectable in parallel by additional controllable switches to control the maximum current that can be delivered to the load. Another group of switches can either connect the two subsets of batteries in series, to generate 3 volts, or connect the subsets in parallel to increase the maximum current. Additional subsets of batteries and their associated switches may be further connected to increase the voltage and current. The power supply may be standardized and configured by the user for a particular load, such as a sensor for a medical skin patch.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on U.S. provisional application Ser. No. 62/108,888, filed Jan. 28, 2015, by Richard Austin Blanchard et al., assigned to the present assignee and incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to printed batteries and, in particular, to an array of printed batteries that can be interconnected by switches to provide a variable voltage and current to a load. 
     BACKGROUND 
     Printed batteries are well-known for use in low power applications. A typical voltage of a single printed battery is about 1-2 volts. To generate a higher voltage for a load, multiple batteries are printed, and traces permanently connect the batteries in series. DC/DC converters are also used to convert the voltage. To increase the maximum current supplied by a single printed battery, the battery is made larger. 
     When a battery is connected to the load, its useful lifetime is shortened. 
     In some cases, it may be desirable to power a load where the voltage or current requirements of the load may vary or where different loads may be connected to the same battery. Therefore, it is inefficient to use the conventional printed battery arrays with their fixed connections for such loads. 
     SUMMARY 
     In one embodiment, a plurality of battery cells is printed on a substrate, where each battery may output the same voltage, such as about 1.5 volts. Batteries in a first subset are connectable in parallel by controllable switches to control the maximum current that can be delivered to a load. Batteries in a second subset are also connectable in parallel by additional controllable switches to control the maximum current that can be delivered to the load. Another group of switches can either connect the two subsets of batteries in series, to generate 3 volts, or connect the subsets in parallel to increase the maximum current. 
     Additional subsets of batteries and their associated switches may be further connected to increase the voltage and current. 
     The switches may be printed field effect transistors (enhancement mode, or depletion mode, or a combination) or other suitable controllable switches. 
     A controller, also on the substrate, controls the switches (e.g., supplies a gate voltage to MOSFETs) to cause the array of batteries to supply the desired voltage and current to the load. A visual voltage indicator on the substrate may also be provided, such as an LED indicator, to give feedback to the user. 
     The load may also be printed on the substrate, or the load may be a pre-formed device (e.g., a medical sensor) that is attached to the power supply leads on the substrate. The load may have variable requirements for voltage and current, and the controller may dynamically control the switches based on such load requirements to most efficiently use the batteries. For example, it may be more efficient to electrically isolate batteries, when not needed, to maximize the overall lifetime of the power supply. Further, dead batteries may be electrically isolated from the load, and fresh batteries may be automatically connected to the load. The switches may be controlled to periodically vary which batteries supply power to the load to maximize the overall life of the power supply. 
     In another embodiment, to preserve battery life, the individual batteries may be selectively activated at any time for initiating the batteries&#39; internal chemical reactions. 
     In one embodiment, the battery array, switches, and controller on a single substrate are standardized to form a variable power source, and the load is separately provided. A wide variety of loads may be powered by the power source, since the voltage and current provided can be customized by the user for the particular load. The load may or may not be mounted on the substrate. 
     The invention is particularly useful for applications where the substrate must be flexible and the battery life must be prolonged, such as for disposable skin patches for medical tests, product packaging, etc. 
     Other embodiments are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a flexible substrate having printed on it an array of interconnectable batteries for powering any type of load mounted on the substrate. 
         FIG. 2  is a cross-section of a printed battery from publication US 2015/0024247. 
         FIG. 3  is a flowchart identifying steps performed by the battery power supply of  FIG. 1 . 
         FIG. 4  illustrates a roll-to-roll process for inexpensively printing components on a flexible substrate. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a flexible substrate  10 , such as a PMMA film, a PET film, any plastic film, cloth, paper, a metal film, or other suitable material. 
     Small batteries B 11 -B 1 X and B 2 -B 2 X are printed on the substrate  10 . Such printed batteries may be silver-oxide batteries disclosed in US 2015/0024247, assigned to the present assignee and incorporated herein by reference, which generate electricity by chemical reactions within the battery. There are many well-known types of printed batteries that may be used instead. Any number of batteries may be located between batteries B 11  and B 1 X and between B 21  and B 2 X. 
       FIG. 2  is a cross-section of a battery taken from US 2015/0024247 and illustrates a substrate  12  (which may be the substrate  10  in  FIG. 1 ), a first metal current collector layer  14  (a metal foil), a first active electrode layer  16 , a separator layer  18 , a second active electrode layer  20 , and a second metal current collector layer  22  (a metal foil). The metal layers  14  and  22  are the anode and cathode conductors for the battery that are contacted by the printed metal traces  24  in  FIG. 1 . Electrical contact to the second metal current collector  22  by a trace  24  may be made by forming the second metal current collector  22  so that an end resides on the surface of the substrate  10  ( FIG. 1 ) planar with the first metal current collector  14 . This configuration makes it easier for the traces  24  to electrically contact the current collectors  14 / 22 . 
     The electrodes  16 / 20  comprise gel or paste electrolytes that can be decomposed to supply ions for generating a voltage and providing current, as described in US 2015/0024247. The cathode electrode additionally contains silver-oxide. The battery is referred to as a silver-oxide battery. The separator  18  is permeable to the ions produced and may be a polymer film, cellulose, or other suitable material. Such batteries generate between 1.1-1.8 volts, and the voltage drops as the battery become depleted. For example, the voltage may drop by half over a 24 hour period, depending on the current supplied by the battery, such as 100 uA. Many other well-known battery types can be printed such as lithium-ion batteries and NiCad batteries. The batteries may be rechargeable or non-rechargeable. The thickness of a printed battery is typically less than 1 mm. 
     In  FIG. 1 , each battery has a size that is suitable for the particular application. If the device is only for use for a short period (e.g., a few days), the batteries may be small, such as about 1 cm per side. For higher current needs or for more prolonged use needs, the batteries are made larger, such as 2 cm per side. The shapes of the batteries do not need to be squares, and different shapes, such as serpentine shapes, may provide known benefits. 
     The batteries described herein may be “single layer” types, as shown in  FIG. 2 , where there is only a single interface between two active electrodes, or multiple battery layers may be stacked over each other and interconnected in parallel or series to increase current or voltage. Stacked battery layers make more efficient use of the substrate surface area and may reduce resistive losses. 
     Controllable switches  26 A- 26 G may also be printed on the substrate  10 . Such switches may be FETs of the types used in active displays, such as described in US 2015/0280006, incorporated herein by reference. Such printed transistors are well-known. Many other types of printed switches can also be used. The switches are controlled by supplying a threshold signal to their gates or other control terminals. 
     The switches  26 A and  26 B connect the batteries B 11  and B 1 X to the Vout+ terminal of the power supply. Identical switches are connected to other batteries located between the batteries B 11  and B 1 X. The switches  26 A and  26 B are controlled by the controller  30  to connect any of the batteries B 11 -B 1 X to the load  32 . In other words, such switches selectively connect the batteries B 11 -B 1 X in parallel. The batteries B 11 -B 1 X are in a first subset of the batteries. The load  32 , such as medical diagnosis sensor adjacent a patient&#39;s skin, may also be printed on the substrate  10 , or the load  32  may be pre-formed and mounted on the substrate  10  to electrically connect it to the power supply output terminals. If the device is a sensor for being attached to a patient&#39;s skin, the flexible substrate  10  is provided with an adhesive layer on its back surface. The load  32  may include memory for retaining sensor data for later downloading via an external computer. In one embodiment, the load is removable from the substrate  10  and reusable on another power supply substrate  10 . 
     Similarly, the switches  26 C and  26 D, connecting the batteries B 21  and B 2 X to the Vout− terminal of the power supply, and any switches connected to other batteries located between batteries B 21  and B 2 X, are controlled by the controller  30  to connect any of the batteries B 21 -B 1 X to the load  32 . In other words, such switches selectively connect the batteries B 21 -B 2 X in parallel. The batteries B 21 -B 2 X are in a second subset of the batteries. 
     The switches  26 E- 26 G, also controlled by the controller  30 , are used to connect the two subsets of batteries in series or in parallel. For a series connection, switches  26 F and  26 G are open and switch  26 E is closed. The series connection sums the voltages from the first and second subsets of batteries. For a parallel connection, switches  26 F and  26 G are closed and switch  26 E is open. The parallel connection sums the currents from the first and second subsets of batteries. 
     The power supply  34  may be replicated any number of times on the substrate to add more groups of batteries for selective connection in series or parallel with the power supply  34 . All the switches are controlled by the controller  30 . 
     The resulting battery voltage is applied across the load as the input voltage Vin. 
     The controller  30  may be a state machine or other inexpensive logic circuit that detects a power supply requirement of the load  32  and controls the switches  26 A- 26 G to meet the power supply requirements of the load  32 . For example, the load  32  may have an active mode and a sleep mode. During the active mode of the load  32 , the controller  30  senses a signal from the load  32  and determines, based on a stored program or look-up table in the controller  30 , which switches should be turned on or off to meet the higher current demand of the load  32 . During a sleep mode (or off state) of the load  32 , the controller  30  senses a signal from the load  32  and turns off some or all of the switches  26 A- 26 G to disconnect batteries from the load to reduce drain on the batteries. Although an ideal battery has infinite resistance, actual batteries have a resistance, and removing unneeded batteries from the load  32  improves efficiency and increases the lifetime of the power supply. 
     A voltage/current indicator  38  may also be printed on the substrate  10  or mounted on the substrate  10 . The voltage/current indicator  38  may detect the voltage of each battery and also detect the overall voltage Vin into the load  32 . This may provide a feedback signal to the controller  30  to remove dead or unnecessary batteries from the load or to add more batteries in parallel or series to suitable change the voltage Vin or available current. 
     In another embodiment, the voltage/current indicator  38  includes printed light emitting diodes (LEDs) so that a user can readily determine the input voltage Vin into the load  32  to determine if it is the proper voltage. The LED display may also indicate which batteries are dead. 
     Instead of the controller  30  being totally automatically controlled, or in addition to the controller  30  being automatically controlled, the controller  30  may be manually controlled by the user via an external signal, small slide switches on the substrate  10 , or push-button switches on the substrate  10  to cause the power supply to generate a desired voltage or current. The external signals may be digital or an analog voltage level to cause the controller  30  to supply the necessary control signals to the switches  26 A- 26 G to generate the desired voltage or current. In one embodiment, each switch  26 A- 26 G is directly user-controlled, such as by applying digital input signals to the controller  30 , to allow the user to set the voltage Vin and current into the load  32 . 
     If the voltage goes down over time, the controller  30  can be manually controlled or controlled automatically to increase the voltage to within a desired range. 
     Any integrated circuits or other electronic components may be mounted on the substrate  10  to perform a required function, such as to provide DC/DC voltage regulation, provide analog-to-digital conversion, measuring voltages and currents, or provide the load  32  function. 
     In one embodiment, in order to maximize the life of the power supply  34 , different combinations of the batteries may be intermittently connected to the load  32  via the switches  26 A- 26 G so that all the batteries become drained at about the same rate. 
     In one embodiment, all batteries are isolated from one another in a storage mode by all the switches  26 A- 26 G being normally open. The user may then cause the device to be active just prior to use by, for example, manually turning on the controller  30  with a slide switch or push button switch. The batteries may power the controller  30 , or the controller  30  may use a separate power source such as a coin-type battery. 
     In one embodiment, the controller  30  may temporarily increase the output voltage of the power supply  34  beyond a threshold to temporarily turn on a device, such as LEDs printed on the substrate  10 , as an indicator or for another function, and then reduce the output voltage to an operating level. 
     In one embodiment, each battery may be inactive until the user activates the battery by starting the chemical reaction in the batteries. This is particularly useful when the device is to be stored for long periods of time. In one such embodiment, an insulating plastic tape may be initially inserted between the active layers of the battery so no chemical reactions occur. When the device is to be used, the tape is pulled out of the batteries to start the chemical reactions. Other techniques for activating a battery may entail pressing on a battery to break a seal, puncturing a seal in the battery, or tearing a seal. A seal to be broken is represented by a circle  35  within each battery. Prior to the battery being activated, it has a very high resistance so does not load down the circuit. 
     After the device is used for its intended purpose, the device may be disposed of, assuming the batteries are not rechargeable. The device may be inexpensive since most or all of the circuitry can be printed and any ICs or sensors should be inexpensive. 
     In one embodiment, the power supply  34  and circuitry on the substrate  10 , other than the load  32 , form a standardized variable power supply for a load. Various types of loads, such as medical sensors, etc., may be mounted to the standardized substrate  10  and connected to the power supply  34  terminals and to the controller  30  via traces  24 . The load does not have to be mounted to the substrate  10 . The loads may have different power requirements, and the controller  30  controls the switches to supply the required voltage and current to the particular load. For example, a load may provide a signature resistance or other characteristic to the controller  30  signifying its power requirements, and the controller then determines the most efficient interconnections of the batteries needed to meet the load&#39;s power requirements. Alternatively, the user controls the controller  30  to switch any combination of the switches, and the controller  30  supplies the required signals to the switches (e.g., gate voltages) to close them. 
       FIG. 3  is a flowchart identifying various steps employed by the device of  FIG. 1 . In step  50 , the printed batteries, traces, switches, and other circuitry are provided on the substrate  10 . In step  52 , the load requirements are sensed and the controller closes or opens the switches  26 A- 26 G to most efficiently supply the required voltage and current to the load. 
     Alternatively, the user controls the switches to supply the required voltage and current to the load. 
       FIG. 4  illustrates a roll-to-roll process for fabricating the device. The flexible substrate  10  is provided on a first roll  70 . The substrate  10  processing may be standardized and any customized loads or other circuits are mounted later on the standardized power supply substrate  10 . This greatly reduces the overall cost of the device. The substrate  10  acts as a flexible circuit. At station  72 , the conductive traces or other conductor layers are printed by depositing a metal ink and curing the ink. In step  74 , the batteries, switches, and any other suitable components are printed on the substrate  10 . In step  76 , the various inks are cured. The resulting substrate  10  is taken up by a take up roll  78  or singulated as sheets. 
     Other devices may be printed on the substrate  10 , such as photovoltaic devices, etc. 
     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.