HK1115476A - Bidirectional battery charge controller - Google Patents

Description

Bidirectional battery charging controller

Technical Field

The present invention relates to the field of battery-equipped power supply systems for portable electronic devices, in particular controllers for the bidirectional regulation of the charging and discharging of auxiliary batteries.

Background

In recent years, the development of portable battery-powered devices such as mobile phones, video cameras, portable laptops, etc. has been remarkable, and this trend is expected to continue. These devices typically provide the required power using rechargeable batteries disposed within the devices. The length of time that a battery powers a device is primarily related to the size of the battery and the number of energy consuming components configured within the device. For example, mobile phone manufacturers often incorporate into the phone components, for example, the ability to transmit and receive digital pictures and/or text messages, even real-time video transmissions, depending on the needs of the consumer. Unfortunately, the inclusion of these features often places additional requirements on the rechargeable battery that powers the mobile phone. The net result is a reduction in the run time of the mobile phone due to the increased power requirements. At the same time, the electrical demand of the battery increases, while the size and weight of the mobile phone decreases. As the size of mobile phones decreases, the size of battery packs that are typically disposed within the mobile phones also decreases. The combination of these two trends, increased electrical demand and reduced battery size, often results in mobile phone users experiencing missed phone calls or data transmissions due to phone battery depletion at an inopportune moment. An additional trend that complicates solving this problem is that most mobile phones require batteries with special size and shape characteristics. To encourage consumers to purchase replacement batteries from mobile phone manufacturers, mobile phones are manufactured with batteries having unique shapes, locking mechanisms, voltage requirements, and the like. Further, a charging port configured within the mobile phone limits the types of chargers that may be connected to the mobile phone. Collectively, these factors limit the consumer's ability to easily replace a discarded battery with another power source.

Many attempts have been made to develop a universal auxiliary portable power supply for mobile phones. For example, US6,127,801, "battery pack assembly" by d.manor discloses a power supply including a battery pack and a base unit having a bidirectional circuit. In US6,479,963, "rechargeable battery pack", by d.manor and g.weinstein, rechargeable battery packs for mobile phones or other portable devices are described, comprising a conventional rechargeable battery for powering the device and a user-replaceable primary cell battery as a built-in charger for the device for charging the rechargeable battery when required by the user. The battery pack uses a replaceable cell or cells as its additional energy source, which needs to be replaced with new cells when the replaceable cell or cells are depleted. In another example, US6,709,784, "battery backup for mobile phones" by o.resech discloses a battery pack that can be plugged into a contact of a mobile phone to charge a built-in rechargeable battery and/or directly power the mobile phone. The invention does not provide any voltage conversion circuitry to match the battery pack output voltage to the voltage required to charge the phone's rechargeable battery, but relies on the phone's internal charge control circuitry to ensure proper voltage compatibility. Furthermore, the battery is preferably packaged with a plug that allows the battery pack to be connected to a mobile phone. Therefore, when the battery is depleted, the entire battery pack, including the plug, must be discarded, which increases consumer expense.

Therefore, there is a need for an auxiliary dc power supply that uses a commonly used battery that a consumer can easily insert into and remove from a reusable housing, and that can be a readily available primary cell or cells, or a secondary cell or cell that has the additional option of charging the secondary cell or cell inside the device housing using the device's conventional charging methods. The power supply needs to be lightweight, volume efficient, and easily adaptable to a wide array of mobile phones using batteries of various shapes and sizes.

Furthermore, rechargeable batteries configured within portable electronic devices are generally expensive and not widely available. Since the built-in batteries supplied by device manufacturers are generally selected for optimal performance and operational life, replacing such originally configured batteries with lower cost or more readily available types of batteries generally results in a reduction in the available power of the device or a reduction in the useful time of the device. This is particularly true for notebook and other portable computers where the critical nature of the task being performed generally renders the coordination between the selection and use of the internal battery ineffective. Accordingly, there have been few previous attempts to provide a less expensive or more versatile battery power solution for such portable electronic devices.

Therefore, there is also a need to provide an auxiliary battery pack to provide additional power for adding an internal rechargeable battery to the device, so that the additional power is provided by a lower cost, more readily available power source than the typically expensive rechargeable battery, but not at the expense of the performance of the device.

The disclosure of each publication mentioned in this section and in the remainder of the specification is hereby incorporated by reference in its entirety into the present invention.

Disclosure of Invention

The present invention is directed to a novel bidirectional battery charging control system for portable electronic devices using a main rechargeable battery according to a first preferred embodiment of the present invention. The system enables an auxiliary or accessory battery or cell to be connected to the device for inputting additional current to the device. The combination of the main battery and the auxiliary battery is called a hybrid battery. Control of the current flowing into and out of the auxiliary battery is performed by a bidirectional charge controller. The auxiliary battery may comprise one or more primary or secondary cells, and the bidirectional charge controller is such that if the auxiliary battery is a secondary battery, an external charger, such as a mains wall plug charger (mains wall plug charger), connected to the device and typically used to charge the rechargeable battery of the device, may also recharge the secondary battery within the auxiliary battery.

In accordance with another preferred embodiment of the present invention the bi-directional charge controller also acts as a voltage converter to convert the voltage of the auxiliary battery to the voltage normally required to power the device and for charging the main rechargeable battery of the device. The voltage of the main battery is typically (but not necessarily) higher than the voltage of the auxiliary battery. The ability of the auxiliary battery to charge the main battery of the device is particularly useful because readily available primary cells can be used as auxiliary batteries in situations where the main battery is depleted without being able to communicate with a conventional mains power supply for recharging. Furthermore, the bidirectional charge controller is preferably microprocessor controlled and programmed to detect the battery chemistry of the auxiliary battery and to disable the charging current flowing into the auxiliary battery if the primary cell chemistry is detected. Also, in the opposite direction, the algorithm of the microprocessor is preferably able to regulate the charging current from the auxiliary battery to the main rechargeable battery of the device, so that an optimal energy transfer is obtained for each stage of the main battery state of charge.

Furthermore, the bidirectional charge controller preferably includes intelligent control features that ensure that the current drawn from the auxiliary battery matches the requirements of the device load, matches the depletion level of the main battery, and matches the most efficient way of utilizing the charge capacity of the auxiliary battery, particularly when the auxiliary battery is a primary battery. These charging characteristics are changed in real time based on the detection of the load current and the output terminal voltages of the main and auxiliary batteries at any given time.

In the case where the auxiliary battery is rechargeable, the bidirectional charge controller enables the auxiliary battery and the main rechargeable battery of the device to operate substantially in communication with each other, so that they can be considered to correspond to one large rechargeable battery. Therefore, the auxiliary battery in this case effectively adds capacity to the main rechargeable battery. This enables the auxiliary battery pack to be considered the only chargeable part of the total battery capacity of the device, and also enables the main battery pack to be permanently wired into the device if required, saving costs and potentially reduced reliability of the battery contacts. Furthermore, when using a rechargeable auxiliary battery, the power management system of the device may be configured to use the capacity of that battery first, and only when it is depleted, use the device's main battery. The total usage of the rechargeable main battery is reduced, so that the service life of the rechargeable main battery is prolonged. According to this configuration, the device can advantageously be constructed so that the only battery within the device that should be easily replaceable by the user is the auxiliary battery, which can preferably be housed within its dedicated case, separate from the main battery that the user does not normally need to consider.

According to another preferred embodiment of the invention, the auxiliary battery may be mounted and used outside the portable device, in a separate housing, and is preferably connected to the portable device by means of a flexible lead, so that the auxiliary battery is inserted into the external charging input of the portable device. In such an embodiment, a bidirectional charge controller is preferably disposed within the housing (typically on a printed circuit board) that includes the auxiliary battery, and enables the auxiliary battery to provide current to a device such as an external charger, or, if it is a secondary battery, allows the auxiliary battery to be charged by connecting to an externally powered charger. Thus, the auxiliary battery can be considered to correspond to a small portable external charger for the device, for example, in the event that the main battery of the device is depleted without connection to a mains recharging power supply.

There is thus provided in accordance with a preferred embodiment of the present invention a battery power supply system for powering an electronic device, including:

(i) a main battery can be charged by the electric power,

(ii) an additional battery comprising one of at least one primary cell and at least one rechargeable cell, an

(iii) A bidirectional charge controller that controls current flowing between the additional battery and the rechargeable battery.

In the above system, the bidirectional charge controller controls the current flowing from the additional battery to the rechargeable battery or the chemical property current flowing from the rechargeable battery to the additional battery.

There is further provided in accordance with another preferred embodiment of the present invention a battery power supply system as described above, wherein the additional battery has a first nominal terminal voltage, the rechargeable battery has a second nominal terminal voltage, and the bidirectional charge controller converts a current output by the additional battery equal to the first nominal terminal voltage to a second voltage for powering the device. Alternatively and preferably, in such an embodiment, the bidirectional charge controller may convert a current output by the additional battery equal to the first nominal terminal voltage to a second voltage for charging the rechargeable battery. In either case, the first nominal terminal voltage may preferably be lower than the second nominal terminal voltage, or the first nominal terminal voltage may preferably be higher than the second nominal terminal voltage.

According to another preferred embodiment of the present invention, there is further provided any one of the above-mentioned battery power supply systems, which determines battery chemistry of the cells in the additional battery, and which allows current to flow into the additional battery only when the additional battery comprises at least one cell rechargeable battery.

According to a further preferred embodiment of the present invention, in the above-described battery power supply system, the additional battery may include at least one primary battery cell, and the bidirectional charge controller preferably adjusts the current supplied from the additional battery so as to charge the rechargeable battery at a rate dependent on the state of charge thereof.

Alternatively and preferably, the additional battery of the battery power supply system may comprise at least one primary cell, and the power supply system preferably starts drawing current from the additional battery only when the main battery has been depleted to a predetermined level. The predetermined criterion may preferably be at least 90% of the main battery consumption.

In any of the above battery power supply systems, the at least one unit rechargeable battery in the additional battery may be any one of a NiMH battery and a NiCd battery. In addition, at least one of the elementary cells in the additional cell may preferably be an alkaline cell or a fuel cell.

According to another further preferred embodiment of the present invention there is also provided a battery power supply system according to any one of the preceding embodiments, wherein the rechargeable battery is socketless (sockettlessly) mounted within the device. According to this embodiment, it is then preferred that only the additional battery is easily replaceable by the user.

There is still further provided in accordance with a preferred embodiment of the present invention a battery power supply system as described above, wherein the additional battery includes at least one cell rechargeable battery, and the bidirectional charge controller draws current from the additional battery preferentially over current drawn from the rechargeable battery. In such an embodiment, it is effective to preferentially draw current from the additional battery before drawing current from the rechargeable battery to extend the life of the rechargeable battery. Furthermore, it is preferable to use the main rechargeable battery only after the additional battery is substantially exhausted, thereby extending the life of the main rechargeable battery.

In any of the foregoing embodiments, the rechargeable battery may preferably be a lithium ion battery, and the portable electronic device may preferably be a mobile phone, a video camera, or a notebook computer.

In any of the foregoing embodiments, it is preferred that the additional battery is mounted within the device. However, according to another preferred embodiment of the present invention, there is provided a battery power supply system according to any one of the preceding embodiments, wherein the additional battery and the bidirectional charge controller are mounted within a housing outside the device. The housing preferably includes a single connector that outputs current from the additional battery to the portable device and inputs charging current from an external charger to the additional battery.

Drawings

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the accompanying drawings in which:

fig. 1 is a block circuit schematic diagram of the overall layout of a bi-directional battery system constructed and operative in accordance with a preferred embodiment of the present invention;

FIG. 2 illustrates operation of the bi-directional battery system shown in FIG. 1 when current is supplied from the auxiliary battery to the main rechargeable battery of the device to provide energy boost to the rechargeable battery when needed;

FIG. 3 illustrates operation of the bi-directional battery system shown in FIG. 1 when current is provided to the rechargeable auxiliary battery from an AC adapter charger of the device via a bi-directional charge controller;

4A-4C are schematic diagrams of the bottom of a notebook computer illustrating different methods of incorporating a hybrid battery system constructed and operable in accordance with another preferred embodiment of the present invention; fig. 4A shows the combined use of standard cells of the prior art, and fig. 4B and 4C show different preferred methods of combined use of the hybrid cell of the present invention;

FIG. 5 is a graph illustrating volt-ampere control characteristics of a charge control algorithm in accordance with a further preferred embodiment of the present invention;

FIG. 6 is a graph illustrating the increased cycle life obtained from the main rechargeable battery of a notebook computer powered using a 30Wh capacity hybrid battery according to the present invention compared to the cycle life of a 30Wh non-hybrid rechargeable battery;

FIG. 7 is a block circuit diagram of the power control system of the bi-directional battery charge controller of the present invention showing a preferred configuration for operating the various components described herein;

fig. 8 schematically illustrates a further preferred embodiment of the invention, whereby the auxiliary battery as an external bidirectional charger unit is mounted and used outside the portable device;

fig. 9 is a block circuit schematic diagram similar to that shown in fig. 1-3 illustrating the operation of the bi-directional battery system of the present invention in accordance with the preferred embodiment shown in fig. 8; and is

Fig. 10 shows a case where a current is input using a portable external charger to charge a battery of a portable electronic device.

Detailed Description

The bi-directional battery system of the present invention is directed to provide an auxiliary battery for a portable electronic device such as a mobile phone, a camcorder, a notebook computer, etc., which provides power that is convenient and versatile to use to expand a main rechargeable battery within the device, and which may include different types of cells for a backup power function.

Reference is now made to fig. 1, which illustrates the overall layout of a bi-directional battery system constructed and operative in accordance with a preferred embodiment of the present invention. The operating circuitry of the portable device is powered in the usual manner by its own built-in rechargeable battery 12, which built-in rechargeable battery 12 may preferably be a Li-ion type battery. The internal protection circuit 14 protects the built-in rechargeable battery from harmful conditions including overcharge, overdischarge, and excessive temperature. Furthermore, an auxiliary or additional battery 20 is provided, which can be incorporated into the device, the battery being easily replaced when and if necessary. It should be noted that the terms battery (battery) and battery cell (cell) may sometimes be used interchangeably in this application with respect to the auxiliary battery, although they differ in form, since the auxiliary "battery (battery)" may comprise a single battery cell or several battery cells. However, whether a cell or battery is used as an auxiliary "battery," it is understood that the present invention is applicable, and when the term battery is used broadly, it is understood that its meanings are sometimes interchangeable, and in fact, only a single cell is intended to be expressed.

The auxiliary battery 20 preferably comprises replaceable, readily available standard size cells or batteries (cells) for inputting auxiliary power to the power system of the device. However, the auxiliary battery differs from those described in the prior art mentioned in the background section in two main respects.

(i) First, the auxiliary battery may comprise a single primary battery or a plurality of single primary batteries, or a single rechargeable battery or a rechargeable battery.

(ii) Second, the auxiliary battery 20 is connected to the device through a bi-directional charger 22, wherein the bi-directional charger 22 monitors and controls the flow of current from the battery into the power system of the device and from the power system of the device into the battery. Furthermore, the bi-directional charger 22 acts as a voltage converter to convert the generally lower battery voltage to a higher voltage required by the device's power system, and conversely converts a higher charging voltage present within the device, such as when connected to an external wall outlet 18, to a lower voltage for charging the auxiliary battery. If the auxiliary battery has a higher terminal voltage than the main battery of the device, the converter operates accordingly. In summary, to control the rate of charging from an external wall outlet, the charging controller 16 is included as part of the device circuitry or within the wall outlet 18.

The second aspect (ii) provides a bi-directional charger with dual functionality. In addition to using energy from the auxiliary battery to charge the main rechargeable battery, the charger may also recharge the auxiliary battery through the device's internal charging circuitry. This means that the energy transferred through the bi-directional charger 22 can flow in both directions-hence the term "bi-directional charger". These two different flow directions are shown in the block circuit diagrams of fig. 2 and 3, where the current direction is indicated by arrows, as follows:

(a) current flows from the auxiliary battery 20 to the main rechargeable battery 12 of the device, boosting the rechargeable battery power when needed. This situation is schematically shown in the block circuit diagram shown in fig. 2.

(b) Current flows from the ac wall outlet chargers 18, 16 connected to the device 10 and thus to its rechargeable battery 12 to the auxiliary battery 20 through the bi-directional charger 22. This option is useful because the auxiliary battery is a rechargeable battery, which is a feature of the present invention. This is shown in the block circuit diagram shown in fig. 3.

The bi-directional charger must be able to provide and control the two possible operational applications of the auxiliary battery accordingly. To effectively satisfy these functions, the bi-directional charger 22 is preferably microprocessor based. A current interface is provided between a single or multi-cell auxiliary battery 20, preferably comprising a secondary battery, such as a nickel metal hydride (NiMH) battery or a nickel cadmium (NiCd) battery, and a primary or unit primary battery, such as an alkaline battery or a fuel cell, and a single or multi-cell main battery of a device, preferably comprising a Li-ion battery. Since the rated operating voltage of the main battery is generally higher than that of the auxiliary battery, for convenience, the auxiliary battery side is referred to as the "low voltage side" and the chargeable main battery side of the device is referred to as the "high voltage side". The bi-directional charger can pass current from the low voltage side to the high voltage side when current is drawn from the auxiliary battery 20, or from the high voltage side to the low voltage side when the external wall outlet charger 18 is connected to the high voltage side, and it can control the battery to charge in the above-mentioned direction.

The bi-directional charger also allows for optimal and automatic charge control of the chemistry of NiMH, NiCd and Li-ion batteries depending on which current direction is required. On the low voltage side, the bidirectional charger automatically detects the chemical properties of the auxiliary battery and prevents charging if the auxiliary battery comprises a primary cell or a plurality of primary cells. Conversely, when charging from the auxiliary battery to the Li-ion main battery, the bidirectional charger adjusts the charging current in real time to obtain an optimal energy transfer as a function of the voltage of the Li-ion battery. Since the primary cell generally has a high internal resistance, the efficiency of the primary cell decreases as the discharge current increases. Thus, when a primary battery is used within the secondary battery, the charging current from the secondary battery to the Li-ion battery is reduced to improve efficiency when the Li ions are relatively full, and the charging current from the secondary battery to the Li-ion battery is increased to ensure that the device can be operated immediately when the Li ions are relatively empty. As such, if the Li-ion battery is almost or completely depleted, it is possible to use the device immediately using only the auxiliary battery. Under normal conditions, high-consumption devices cannot operate well using galvanic cells because of their low efficiency at high discharge rates. The special charge current algorithm can strike a balance between allowing immediate use of the device and maintaining good efficiency over time, even with depleted or nearly depleted Li-ion batteries. Furthermore, since the auxiliary battery powers the device through the main battery, this allows the main battery, which has a low internal resistance, to deliver any short, high current peaks required by the device, such as a mobile phone. If only a primary or fuel cell is used to power the mobile phone, the functionality of the mobile phone will be significantly impaired in general, since the relatively high internal resistance of the primary or fuel cell will prevent them from handling the high current peaks sometimes obtained by the phone. According to the present invention, even if the main battery is indeed fully depleted, the device is still functional since the main battery can also provide the high currents needed to deliver, when the auxiliary battery provides a low level of continuous current for operating the device, since these currents are very short time peak currents and thus draw very little accumulated energy from the main battery. Furthermore, when charging the Li-ion main battery from a NiMH or NiCd auxiliary battery, the Li-ion powered device sees the two chemical batteries as a single battery source in their entirety. The system of the present invention also preferably incorporates two battery temperature sensors in the auxiliary battery and in the main battery, and the bi-directional charger adjusts the charging current in either direction of current operation based on the measured battery temperature.

The bidirectional charger is flexible to implement because it is microprocessor-based, and preferably includes several I/O interface lines that are programmable according to the particular needs of a particular application.

Some of the above-described operating features of the bi-directional charger are preferably provided by way of a sensing circuit and a voltage conversion circuit configured in the bi-directional charger.

The auxiliary battery as previously mentioned may comprise a single rechargeable battery or a plurality of single batteries, such as NiMH or NiCd batteries, or a single primary battery or a plurality of primary batteries, such as alkaline batteries or fuel cells. The system operates differently for each case.

If the auxiliary battery is rechargeable, the auxiliary battery and the main rechargeable battery of the device may be considered to correspond to a large main rechargeable battery, and thus the auxiliary battery effectively adds capacity to the main rechargeable battery. Therefore, since the auxiliary battery is effectively added to the rechargeable battery of the device itself, it can be considered that the space for the auxiliary battery is effectively used. In this case, according to another preferred embodiment of the present invention, since the auxiliary battery is removable and it effectively provides a portion of the total capacity of the rechargeable battery of the device, the main rechargeable battery can be permanently attached to the device so that it is no longer removable, since there is no need to have two replaceable sets of rechargeable batteries. The use of such a permanently built-in main battery has many advantages, as follows:

(i) the performance of a main rechargeable battery is improved because of not only reduced contact resistance due to the battery being hard-wired into the device, but also the possibility of increasing the battery capacity because of the space savings by eliminating the need for removable components and contacts for the battery by permanently incorporating the battery into the device.

(ii) The rechargeable main battery is built-in, so that the user can not install the non-original battery as the main power supply any more.

(iii) Has lower manufacturing costs because (a) internal battery pack design, internal battery pack materials and manufacturing costs and gold battery pack contacts are not required, (b) assembly is simpler because the rechargeable main battery is assembled in the same process as the entire device rather than in a separate process, and (c) integration of the product is easier, eliminating the need for special considerations in adapting the internal battery pack to the available space within the device.

The above advantages of using a permanently built-in main battery are also applicable when the auxiliary battery is a primary battery, although such embodiments are generally less commercially useful.

It should be understood that the term permanently built-in main battery should not be understood literally, as the main rechargeable battery will still be replaceable, for example, by soldering or re-soldering the battery into the circuit using any other non-plug type component.

If the auxiliary battery is a primary battery or a single primary battery, it may be enhanced as auxiliary energy for the main rechargeable battery of the device, it is possible to provide the main battery completely independent of any electrical outlet or other such source with a recharged charge, and it is possible to take advantage of the wide availability and low price of such primary batteries.

The use of the auxiliary battery of the invention has a number of operational advantages:

(i) such auxiliary batteries provide optional backup energy or energy enhancement for the degraded main battery.

(ii) If the auxiliary battery is rechargeable, then both batteries can be considered to act as one large rechargeable battery, thereby providing the option of efficiently replacing the cells of some "large" batteries, i.e., replacing the cells of the auxiliary battery. Such replacement would enable a "large" battery to have a longer life for two reasons:

(a) when a portion of the "large" battery is replaceable, the replacement provides for the replenishment of a portion of the battery with new capacity; and

(b) the power management of the device may be designed to use the main rechargeable battery only after the auxiliary battery is depleted or nearly depleted, so that the life of the main rechargeable battery itself may be extended because there is less overall use of the main rechargeable battery.

(iii) From a market perspective, because the main rechargeable battery is intrinsic and generally inaccessible, and the consumer only contacts and sees a standard size auxiliary battery, the user believes that the battery is smaller than a battery of a similar device without such an auxiliary battery.

In order to achieve accurate operation of the auxiliary battery, the bi-directional charger according to various preferred embodiments of the present invention should have a number of operating features, as follows:

(i) real-time charging current control is required to control the current from the auxiliary battery to the main rechargeable battery to ensure optimal results for typical portable devices, particularly those with an auxiliary primary battery. The control is performed using a current control algorithm described hereinafter.

(ii) The bi-directional charger should have an associated control algorithm for automatically detecting the chemistry of the auxiliary battery, i.e. whether it is a primary or a rechargeable battery.

(iii) If the chemistry of the rechargeable battery is detected, the bi-directional charger should ensure control of the charging current from the ac outlet charger (when in use) to the auxiliary battery.

(iv) The activation or deactivation of the secondary battery may preferably be made optional or user-selectable via a main user interface of the device, preferably via a menu on the screen. Alternatively and preferably, a mechanical switch on the device/battery may be used.

(v) Options are shown on the main display screen of the device, i.e. the status of the auxiliary battery, e.g. whether the auxiliary battery is idle or supplies current to the main rechargeable battery or the device, or is itself charged.

Reference is now made to fig. 4A-4C, which are schematic diagrams of the bottom of a laptop computer 30, illustrating a method of incorporating an auxiliary battery and a bidirectional charge control system in accordance with a more preferred embodiment of the present invention. A typical example of a prior art standard rechargeable battery pack 32 inserted into a recess 34 in the back side of the computer 30 is shown in fig. 4A. An extended hybrid battery pack 36 according to a preferred embodiment of the present invention is shown in fig. 4B, similar in size to extended battery packs supplied by some laptop computer manufacturers, with an auxiliary battery 38 mounted in a separate compartment 40 in the back of the battery pack. The compartment has conventional battery contacts for the auxiliary battery and preferably has a sliding or hinged or removable cover 42 or other member so that it is easy for the user to use the compartment to replace the auxiliary battery 38 if desired. The auxiliary battery may preferably be a set of 4 or 6, readily available, AA-sized primary or rechargeable cells. The bidirectional charge controller circuit is preferably configured within the power management circuit of the computer or within the battery pack itself.

According to one exemplary assembly design, such a hybrid battery pack embodiment may comprise:

(i) a standard Li-ion battery having a rechargeable energy of 28 watt-hours (Wh); and

(ii) if a NiMH battery is used to provide 10Wh of additional rechargeable energy, or if Li/FeS is used₂The primary cell provides an auxiliary battery with a primary energy of up to 14 Wh. The auxiliary battery may preferably be in the form of a set of 4 AA size cells in a compartment located in a 17mm deep, 17mm high additional housing at the back of the battery pack.

In such an embodiment, the compartment at the back of the computer would be readily available for removal of its cover to replace the auxiliary battery if necessary.

Reference is now made to fig. 4C, which is a schematic illustration of a laptop computer 50 in which the hybrid battery is not designed as a plug-in replacement for the standard battery pack as shown in fig. 4B, but rather as an integral part of the computer. In such an embodiment, the Li-ion main battery is preferably configured in the computer as a non-removable component 52, whether hard-wired or plug-in, but not as practical for current applications, preferably not readily accessible to the user. On the other hand, the batteries of the auxiliary battery 54 are arranged to be user removable, for example by mounting them in a cavity 56 designed for this purpose in the computer, preferably with a removable, retractable or hinged lid 58. This type of design provides improved power performance if the main battery 52 is hardwired internally, but unlike the embodiment of fig. 4B, does require the hybrid battery design to be incorporated into the mechanical design process of the entire notebook computer.

According to a further preferred embodiment of the invention, the bidirectional charge control system is provided with a power management algorithm for ensuring optimal utilization of the auxiliary battery and the main battery in various states of exhaustion of the main battery. Several preferred power management algorithms are provided according to various embodiments of the present invention. Although these algorithms are applicable to any mobile device, they are particularly suitable for use in portable computer and mobile phone applications, and as such will be described below.

According to a preferred embodiment of the power management algorithm, the first algorithm ensures that the current drawn is regulated in real time according to the instantaneous current needs of the device when the auxiliary battery is in use, thereby avoiding inefficient high current drain from the auxiliary battery. Thus, under normal operating conditions, when the main battery is not fully depleted, or when the device is not turned on and the main battery is charged by the auxiliary battery, the algorithm ensures that, depending on the type of main battery and auxiliary battery, an intelligent charging mode (profile) is followed to ensure the most efficient use of the available power capacity of the auxiliary battery.

This charge control algorithm is particularly important for use with mobile phones because of the large variation in the current drawn (draw) by the device in the transmit and receive states. During transmission, the peak current requirements may well exceed the current that the auxiliary battery alone can provide, particularly when the auxiliary battery comprises a primary battery. Thus, for example, while the maximum average current required to power a mobile phone is typically on the order of 400mA, current peaks of up to 2A are also used in the transmission. Mobile phones also typically operate at 3-4.1V. This means that the primary cell of the hybrid battery used for this application must provide at least 6W of power in order to supply the peak current to the device. Since a standard alkaline primary cell operates at about 1.2V, this would require a current spike of 5A from the cell. Primary batteries are generally unable to provide such a current load because of their high internal resistance.

Using the hybrid battery of the present invention, this problem is solved by programming the charge controller so that the main rechargeable battery supplies the peak current as a charging capacitor, while the primary auxiliary battery meets the average current requirements as a power supply. Meeting peak current requirements in the case of, for example, the above-mentioned mobile phones, in fact requires only a very small amount of energy from the secondary battery, because the peak lasts only a very short time. Therefore, the charge controller must respond to the average current load, not the instantaneous current.

Reference is now made to fig. 5, which is a graph illustrating the current-voltage control characteristics of the algorithm of the charge controller, in accordance with a further preferred embodiment of the present invention. This characteristic must supply enough current from the complete hybrid battery to operate the device, and on the other hand, it must minimize the losses associated with drawing too high a current from the auxiliary primary battery. Fig. 5 illustrates how the charging current from the auxiliary cells is controlled as a function of the voltage of the main secondary cell voltage. Since a low main battery voltage is indicative of a partially depleted main battery or of a high average current usage of the device, the charging current is maintained at a high level when the main secondary battery voltage is low. Then, as the main battery is further charged, the charging current is decreased until the charging current is stabilized at a constant minimum value, as indicated by the voltage rise of the main battery. Thus, in any case, keeping the charging current at its minimum possible value minimizes the losses from the internal resistance of the primary cell.

Referring again to fig. 5, the load current lines are depicted as high load and low load. When the device has a high average current load, the controller is programmed at start-up to exceed the average current required to ensure that sufficient current is available to operate the device and to fill any losses of the main battery. This characteristic then reduces the supplied current to a balanced level where the charging current is equal to the load current. During the initial overrun period, the energy supplied due to the excess current is not lost, but is stored within the secondary battery. This current is relied upon when the primary cell is close to depletion and may no longer provide the minimum operating current. If the control characteristic is such that the required average current is not exceeded, the device will not respond immediately to operation.

As shown in fig. 5, when the device is off or in standby mode with very low current load, the controller also starts with high charging current and then quickly reduces the current to a minimum current. Because the load current is very low, the primary battery can keep charging the secondary battery stably and slowly at a low current, which is the most efficient method of extracting current from the primary battery.

Thus, the graph of fig. 5 illustrates how the charge control algorithm covers the entire range of usage including voltage controlled charging when the secondary battery is near full capacity, which is a requirement of Li-ion batteries.

In devices with relatively high electrical loads, such as laptops, the power management algorithm is additionally designed to enable the auxiliary battery to power the device without interruption in the worst case when the main battery is almost exhausted. In summary, auxiliary batteries using primary batteries have a defined power output that may not be sufficient to power the device alone. Thus, if the main battery is allowed to be fully depleted before switching to the auxiliary battery, the user will have to wait slightly for the auxiliary battery to charge the main battery before being able to continue operation. Thus, the algorithm operates by first detecting when the main battery is near depletion. The degree of near depletion is determined by a predetermined criterion, but is generally 10% or more of the total charge capacity, and is preferably determined by the terminal voltage of the main battery. When such a condition is detected, the power management system takes appropriate action by initiating the draw of power from the auxiliary battery in order to prevent the main battery from being fully depleted, if this has not already occurred. The action may be performed by indicating to the user that the action is to be performed, preferably accessing a screen display message or audible alarm of the auxiliary battery, or automatically by the control system. Thus, the power of the auxiliary battery is used together with the remaining power available from the almost depleted main battery to provide sufficient power to continue the immediate operation of the device until both batteries are fully depleted. When both batteries are completely depleted, in order to continue the operation of the computer, a new auxiliary battery pack is installed to continue the operation or charge the main battery, or access to an external power charger must be made available.

According to one exemplary embodiment, a notebook computer requiring 14W of power to operate has a 28Wh Li-ion main battery and a battery consisting of 4 Li/FeS₂The AA-sized single battery of (1) can provide a maximum output current of 2A. This means a maximum output power of about 2.5W, i.e. 10W for all 4 cells. Because these batteries can provide about 10Wh of energy, at this power output, the batteries can last for about 1 hour of service. Because the power consumption of the notebook computer is not significant above the power output of the auxiliary battery, the computer may continue to run on the remainder of the combined hybrid battery's charge life, provided that sufficient power remains in the main battery when the power management algorithm commands access to the auxiliary battery power. In this example, the algorithm should ensure that at least 4Wh remains in the Li-ion battery (4W of power output for 1 hour) before the auxiliary battery is used. Theoretically, from this momentBy the way, the user should still have a full 60 minute usage time, 10W from the auxiliary battery and 4W from the Li-ion battery. For this remaining time, the additional time effectively provided by using the auxiliary battery was 43 minutes.

In summary, it should be noted that, because of Li/FeS₂The cell has a higher energy density than a NiMH cell, and so contains, for example, the Li/FeS described above₂The auxiliary battery of the primary battery of the battery provides a computer with a longer operation than an auxiliary battery using a secondary battery such as a NiMH battery. NiMH batteries, however, have a high current capacity, so they can power computers alone when the main battery is fully depleted.

Since such Li/FeS is used if at its maximum power consumption₂Batteries that not only generate large amounts of heat, but also operate at less than their optimum efficiency, so the use of this Li/FeS in the worst case scenario described above should preferably be avoided₂A battery. According to another preferred method of the invention, the power management system is programmed to provide an audible or on-screen advance notice to the user, i.e. when the main battery is running low, advising the user to start using the auxiliary battery even if the main battery has not reached the above "near depletion" threshold. This timely use of the auxiliary battery ensures optimal efficiency of the power stored therein.

All rechargeable batteries have a limited cycle life-the higher the number of charge-discharge cycles performed, the lower their available capacity. When the auxiliary battery includes a secondary battery such as a NiMH battery, the main battery and the auxiliary battery operate together like one large rechargeable battery. As mentioned above, this in itself extends the life of the expensive main battery, since the inexpensive rechargeable auxiliary battery takes part of the load. However, in addition to this overall effect, according to a further preferred algorithm of the invention, when the auxiliary battery comprises a secondary battery, the device is programmed to manage power consumption primarily from the auxiliary battery, so that the inexpensive replaceable auxiliary battery is subjected to many charge/discharge cycles that would otherwise be provided by replacing the expensive main battery. As long as the discharge cycle is shallow, i.e. only partially discharging the battery between charges, as is typically the case with laptops, for example, the algorithm ensures that almost all current loss comes from the auxiliary battery. With this method, the use of replacement of the expensive main battery is substantially reduced, thus substantially increasing its lifetime.

To illustrate this effect, fig. 6, with reference now to fig. 6, illustrates some experimental results obtained by powering a notebook computer according to the present invention using a 30Wh capacity hybrid battery comprising an auxiliary battery having 4 NiMH cells providing 10Wh of energy, and a Li-ion main battery providing 20Wh of energy. An equivalent battery of 30Wh capacity containing only Li-ion batteries will drop to 75% charge retention after 200 cycles for a 50% deep discharge cycle. On the other hand, when the hybrid battery of the present invention is used, as shown in the upper graph, the Li-ion portion of the hybrid battery still has a 95% retention after 200 cycles, and will still tolerate hundreds of cycles before its retention drops to 75%. Thus, it can be seen that the life of the Li-ion battery is increased several times. For a 33% deep discharge, the life of the Li-ion battery within the hybrid battery of the present invention may be on the order of magnitude higher than a typical main battery having only Li-ion batteries.

Reference is now made to fig. 7, which is a block circuit diagram of a power control system of a bidirectional battery charge controller showing a structure enabling the above-described features of the present invention. The embodiment shown in fig. 7 is a more general case where the voltage of the main battery powering the device is higher than that of the auxiliary battery. However, the opposite situation may also be found in some devices, where the voltage of the main battery powering the device is lower than that of the auxiliary battery, and in such a case some of the circuit functions that require the block circuits of the embodiment of fig. 7 are opposite, but the overall functional structure is similar.

Referring now to fig. 7, the auxiliary battery 81 is preferably constructed such that the voltage of each unit cell can be separately determined. This may be achieved by providing each individual cell with contacts from both ends of the cell to the outside. This enables the implementation of a detection algorithm for battery chemistry, such as the algorithm described in the co-pending application "method for charging a battery-powered device" of the present invention to be filed for each cell of an auxiliary battery. The control system may then provide an alert to the user regarding any particular cell of the battery. The voltage terminals are connected to the remaining control circuit via a switching element 82. In the example shown in fig. 7, an auxiliary battery having two unit batteries is shown, and therefore three wires are required to be output to the switching section to allow the voltage of each of the two unit batteries to be determined. The switching section 82 is organized to output the voltage between one end of the auxiliary battery and one end of only one unit battery to the remaining circuits at a time. This feature is used in a cell balancing algorithm, which is also described in the inventor's co-pending application "method of charging for battery powered devices".

The current to or from the auxiliary battery 81 flows into a bi-directional DC-DC power stage 84, which power stage 84 is a bi-directional voltage conversion device that allows current to flow from the auxiliary battery 81 to the main battery 85 and vice versa, thereby converting terminal voltage depending on the direction of the current.

The magnitude of the current flowing into or out of the auxiliary battery 81 is measured by a bi-directional current sensor 83, the bi-directional current sensor 83 sensing the current flowing through an inductor within a bi-directional DC-DC converter 84. Because some designs of current sensors require knowledge of the direction of the current, the direction of the sensed current is reversed based on the signal received from control block 88.

The main battery 85, which includes one or more battery cells, used to power the device 89 typically includes a rechargeable Li-ion battery. Typically, the main battery 85 is physically disposed within the portable device. Conventionally, a wall-plug charger 90 is provided within the portable device for charging from an external voltage source, such as a mains supply, when charging is required. The portable device may also receive power from an auxiliary battery 81.

The control block 88 is the main control unit of the bi-directional battery charge controller and it controls the overall operation of the entire circuit. The control block 88 receives inputs relating to the voltage, current and temperature of each cell and controls the overall system using the algorithms described above, including controlling the desired level of current and current direction. The desired level of current is determined by control block 88. The control level or direction of current output from the console 88 may be used to turn off the current. Data communication between portable device 89 and control block 88 may be accomplished through the use of standard data communication lines employed within such devices for communicating user-generated commands from the device and for returning control-generated signals to the user.

A number of additional control elements are used within the structure of fig. 7. The voltage and temperature detection block 86 is connected to the auxiliary battery 81, and preferably detects the terminal voltage and temperature of each unit cell within the auxiliary battery 81, respectively. The current controller 87 controls the current level through the DC-DC converter by delivering PWM pulses of appropriate duty cycle to the drivers within the bi-directional DC-DC power stage 84 using a current mode control loop. The PWM pulses are output according to the desired current level set point received from control block 88.

Current controller 87 also receives inputs from a system clock from control block 88 and the active current level from current sensor 83.

Referring now to fig. 8, fig. 8 illustrates a further preferred embodiment of the present invention, in which the auxiliary battery 100 is mounted and used outside the portable device 104 including the main battery. As shown, the auxiliary battery 100 is enclosed in a separate housing 102, which is preferably connected to the portable device by a single connector 28 and flexible leads 106 for insertion into an external charging inlet 108 of the portable device. In this embodiment, the bi-directional charge controller is also disposed within a housing containing the auxiliary battery, preferably on the printed circuit board 110. Thus, in the event that the main battery of the device is depleted, for example, without mains charging power access, the auxiliary battery may be considered to correspond to a small portable external charger or power supply for the device.

The bidirectional charge controller of the portable external charger preferably incorporates all of the functions of the controller circuit shown in fig. 7 described above. However, two functions are very important. First, because of the exposed nature of the housing, it is important that the unit detect the battery chemistry of the battery inserted into the housing to prevent charging of the primary battery. Furthermore, it is important that the unit efficiently converts the voltage of the current controlled according to whether the auxiliary battery supplies current or is charged. In the previously described embodiments, the auxiliary battery is configured within a known device assuming that the characteristics and requirements of the main battery are known, and unlike those previously described, this embodiment relates to a portable power supply that can be used to power any device having a compatible connector. Thus, since the manufacturer cannot control the type of device that the auxiliary battery of the unit is to power, it may be necessary to incorporate additional functionality into the control circuitry, such as checking the state of the device's main battery to determine that it is suitable for charging, or providing a visual signal to the user, such as by an LED or the like, that the unit includes a battery ready to supply current, or the like.

Furthermore, the auxiliary battery of the portable external charger has many operational differences from the internal auxiliary battery described in the previous embodiments. For example, before the unit is connected to the portable device, it has no electrical contact with the power supply of the device's main battery. Therefore, the bi-directional charge controller has to be fully self-powered by the battery inserted into the housing. The bi-directional charge controller circuit 110 is therefore designed to have a very low standby current load that can be set to only a few tens of microamperes, enabling the unit to be standby for months without draining the battery after it is inserted. Furthermore, even under these conditions, and while not yet connected to a load for charging, a higher voltage suitable for effecting charging must be generated at the flexible lead 106 of the auxiliary battery so that the portable device detects the presence of the charging device as soon as the lead is inserted into the external charging inlet 108 on the device.

Furthermore, because wall outlets and their similar external power chargers are generally designed for simpler features than the bidirectional charge charger of the present invention, the auxiliary battery cell of this embodiment may preferably incorporate a bidirectional charge controller having a simpler charging algorithm than the previous embodiments. Generally, an external wall type charger corresponds to a constant current source that simply pushes a charging current into an external charging input port of the device, and a charging circuit of the portable device itself controls the inflow of the charging current until the main battery is fully charged. Therefore, the charging algorithm of the bidirectional charge controller of the external auxiliary battery cell of this embodiment can also be constructed to supply current to the device with similar characteristics, and thus, it is greatly simplified as compared with the charging algorithm of the foregoing embodiment. Thus, because the internal charge control circuitry of the device is designed to follow the overall charging pattern, it will not be necessary to perform any "stop charging" procedure as with the charging algorithm described previously, for example, when the main battery is nearly full. On the other hand, there is still a need for a charging current algorithm that can properly control the charging mode of the auxiliary battery for charging current flowing from the wall outlet charger to the portable external charging auxiliary battery through the bi-directional charging controller.

Since the bidirectional charging controller of the portable external charger allows it to be used for charging or to be charged through the same connector without any user intervention to select either of these two tasks, it is important that the portable external charger be able to determine whether the device itself is connected to a device as a load or to a wall charger for charging its own battery. Because the wall charger and the converted voltage powering the device may have similar levels, a simple voltage test on the connector is not sufficient. Therefore, according to another preferred embodiment of the invention, the portable external charger is configured with a functional check program to remove the output voltage on the connector at regular intervals of short time, typically every few seconds for a duration on the order of tenths of a second (typically below 0.5sec), and to measure the voltage of the connector. If the measurement results show a substantially stable voltage, it is clear that the portable external charger is connected to a wall charger or another external power source for powering its own auxiliary battery. On the other hand, if the voltage drops to a lower level, typically 0.3 volts or more, during the measurement, it is apparent that a portable external charger is connected to the device for charging the main battery of the device and thus switching the control functions of the bidirectional charge controller.

The auxiliary battery is preferably a secondary battery and the use of the bidirectional charge controller circuit also allows the battery to be charged when needed by connecting the housing of the auxiliary battery to an output outlet of an external charger, such as a wall-mounted charger, or to a dashboard outlet. The portable external charger has a dual and opposite function-it can charge the portable device by connecting to the charging input connector of the portable device and it can charge itself by connecting to the external wall charger output connector. As with the usual configuration, if the polarity of the charging input connector of the device is opposite to that of the external wall charger output connector, a polarity-shifter (male-to-male adapter) would be required, or two separate connecting wires for both operations would be required. If a non-polar connector is used for the charging function, the adapter would not be needed.

Alternatively and preferably, a primary battery may be used as an auxiliary battery, then the unit provides all the advantages of the control functions of the bidirectional charge controller, such as voltage detection, voltage conversion and charge rate control, but because the battery is not rechargeable it must be replaced when it is depleted.

The embodiment shown in fig. 8 is particularly convenient because it allows the use of a single AA size cell that is widely available and inexpensive. The voltage converter circuit ensures that the relatively low voltage of the cell auxiliary battery is amplified to the voltage required by the device circuitry when the unit is supplying current, and it effectively reduces the external charger voltage output, thereby defining the charging current when charging the cells within the unit. However, it is understood that such an external charger auxiliary battery may also preferably include more than one battery cell.

Reference is now made to fig. 9 and 10, which are block circuit schematic diagrams similar to fig. 1-3, illustrating the operation of a bi-directional battery system having an external auxiliary battery within a portable external charger, as shown in the embodiment of fig. 8, i.e., when the auxiliary battery 100 is charged directly by connection to the external wall plug charger 18. This charging mode of operation generally replaces the charging operation shown in fig. 3, because unlike the embodiment shown in fig. 3, when a conventional wall-mounted charger 18 is connected to an external auxiliary battery 20 in order to charge the external auxiliary battery 20, the auxiliary battery cannot be connected to the device at the same time because there is generally only one connector 28. Fig. 9 shows the situation when a portable external charger is used to input current to charge the battery 12 of the portable electronic device 10. Details of the operation and use of a bidirectional charge controller with an external attached battery can be found in the co-pending PCT application entitled "portable battery operated power supply" by the inventor of the present application.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not in the prior art.

Claims (24)

1. A battery power supply system for powering an electronic device, comprising:

a rechargeable main battery;

an additional battery comprising one of at least one primary cell and at least one rechargeable cell; and

a bidirectional charge controller that controls current flow between the additional battery and the rechargeable battery.

2. A battery power supply system according to claim 1 and wherein said bidirectional charge controller controls the flow of current from said additional battery to said rechargeable battery.

3. A battery power supply system according to claim 1 and wherein said bidirectional charge controller controls the flow of current from said rechargeable battery to said additional battery.

4. A battery power supply system according to any of the preceding claims and wherein said additional battery has a first nominal terminal voltage and said rechargeable battery has a second nominal terminal voltage, and said bidirectional charge controller converts current output by said additional battery equal to said first nominal terminal voltage to a second voltage for powering said device.

5. A battery power supply system according to any of the preceding claims and wherein said additional battery has a first nominal terminal voltage and said rechargeable battery has a second nominal terminal voltage, and said bidirectional charge controller converts current output by said additional battery equal to said first nominal terminal voltage to a second voltage for charging said rechargeable battery.

6. A battery power supply system according to claim 4 or 5, wherein said first rated terminal voltage is lower than said second rated terminal voltage.

7. The battery power supply system according to claim 4 or 5, wherein the first rated terminal voltage is higher than the second rated terminal voltage.

8. A battery power supply system according to any of the preceding claims and which determines the battery chemistry of the cells within said additional battery and allows current to flow into said additional battery only if said additional battery comprises at least one cell rechargeable battery.

9. A battery power supply system according to any of the preceding claims and wherein said additional battery comprises at least one primary cell and wherein said bidirectional charge controller regulates the current supplied by said additional battery to charge said rechargeable battery at a rate dependent on its state of charge.

10. A battery power supply system according to any of the preceding claims, wherein said additional battery comprises at least one primary cell, and wherein said power supply system only starts to draw current from said additional battery when the main battery has been depleted to a predetermined level.

11. A battery power supply system according to claim 10, wherein said predetermined criterion is that said main battery consumes at least 90%.

12. A battery power supply system according to any of the preceding claims and wherein said at least one battery cell within said additional battery is any one of a battery cell NiMH and a battery cell NiCd.

13. A battery power supply system according to any of the preceding claims and wherein said at least one primary cell within said additional battery is a single alkaline battery.

14. A battery power supply system according to any of the preceding claims and wherein said at least one primary cell within said additional battery is a fuel cell.

15. A battery power supply system according to any of the preceding claims and wherein said rechargeable battery is socketless mounted within said device.

16. A battery power supply system according to claim 15 and wherein said additional battery is only made readily available for replacement by a user.

17. A battery power supply system according to any of the preceding claims and wherein said additional battery comprises at least one single rechargeable battery and said bidirectional charge controller preferably draws current from said additional battery prior to drawing current from said rechargeable battery.

18. A battery power supply system according to claim 17 and wherein said drawing of current from said additional battery, preferably before said rechargeable battery, serves to extend the life of said rechargeable battery.

19. A battery power supply system according to claim 17 and wherein said main rechargeable battery is only used after said additional battery is substantially depleted, thereby extending the life of said main rechargeable battery.

20. A battery power supply system according to any of the preceding claims and wherein said rechargeable battery is a Li-ion battery.

21. A battery operated system according to any of the preceding claims, wherein the portable electronic device is any of a mobile phone, a video camera and a laptop.

22. A battery power supply system according to any of the preceding claims and wherein said additional battery is mounted within said device.

23. A battery power supply system according to any of claims 1-8 and 12 and wherein said additional battery and said bidirectional charge controller are mounted within an external housing of said device.

24. A battery power supply system according to claim 23 and wherein said housing includes a single connector that both outputs current from said additional battery to said portable device and inputs charging current to said additional battery from an external charger.