Portable rechargeable battery pack and external adapter for same

Embodiments include a portable rechargeable battery pack, system, and external adapter that allow the portable rechargeable battery pack to both power a host device though a set of host contacts and provide power through a set of charging contacts. The portable rechargeable battery pack includes a charge protection circuit that prevents an excessive discharge current through the charging contacts and allows high charge current when charging the portable rechargeable battery pack. A discharge circuit allows a low level discharge current through the charging contacts to provide power to other devices.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to portable rechargeable battery packs, and more particularly to portable rechargeable battery packs that have both charging contacts and host contacts where the charging contacts have a charge protection means to prevent discharge current being drawn from the charging contacts but through which a charge current can flow, and further to providing power from the portable rechargeable battery pack through the charging contacts via an external adapter.

BACKGROUND

Portable rechargeable battery packs are used to power portable devices, particularly portable devices that are in frequent use and use a significant amount of power. For example, portable communication devices, such as cellular phones and portable two-way radios are typically left on so as to be able to receive communications at any time while in use. Such constant power consumption makes the use of primary battery cells (e.g. non-rechargeable) uneconomical, and in such cases the use of rechargeable battery cells is much more cost efficient.

Many portable rechargeable battery packs are designed to be charged while attached to a device powered by the portable rechargeable battery pack, as well as alone (not attached to a device). Accordingly, it is conventional for a portable rechargeable battery pack to have two sets of contacts: a set for providing power to the host device, and a set for charging the portable rechargeable battery pack while the portable rechargeable battery pack is attached to the host device. The set of contacts used to charge the portable rechargeable battery pack can be referred to as the charging contact set, or simply referred to as charging contacts. Charging contacts can be exposed while the portable rechargeable battery pack is attached to a host device, which can expose them to undesirable conditions, such as short circuiting across the positive and negative charging contacts.

To address the issue of exposed charging contacts, portable rechargeable battery packs are typically provided with a charge protection means in the portable rechargeable battery pack that prevents electric current from discharging through the charging contacts, while also being operable to allow a charging current when the portable rechargeable battery pack is being recharged. For example, it is common to place a diode in series between the positive charging contact and the rechargeable battery cell(s) inside the portable rechargeable battery pack to allow charging current into the portable rechargeable battery pack and block current from discharging through the charging contacts.

There has been a continuing demand for portable devices, and hence the need for portable power. Accessories and other devices are presently available which do not need a conventional AC to DC adapter, but do not have their own power source. For example, there are a number of devices that can be powered from a computer, such as a laptop computer, via a universal serial bus (USB) of the computer. Unfortunately, because of the charge protection circuit typically used in such battery packs, the battery packs cannot be used to power accessory devices from the charging contacts.

Accordingly, there is a need for portable rechargeable battery pack, system, and external adapter that allows powering of devices through the charging contacts but without significantly compromising the safety of charge protection at the charging contacts of a portable rechargeable battery pack.

DETAILED DESCRIPTION

Embodiments include a portable rechargeable battery pack that includes least one rechargeable cell disposed in the portable rechargeable battery pack and a set of host contacts disposed on the battery pack that are configured to provide power from rechargeable cell(s) to a host device coupled to the battery pack. The portable rechargeable battery pack also comprises a set of charging contacts, including a power contact, disposed on the battery pack via which a charging current can be applied to the rechargeable cell(s). The portable rechargeable battery pack can further include a charge protection circuit element coupled between the at least one rechargeable cell and the power contact that is operable to prevent discharge of the rechargeable cell(s) through the set of charging contacts while also able to allow charging currents to flow into the cells through the charging contacts. The portable rechargeable battery pack can further include a discharge circuit having at least one circuit element coupled in parallel with the charge protection circuit element that is operable to allow a discharge current through the power contact.

FIG. 1shows a first side101and an opposing second side102of a portable rechargeable battery pack100in accordance with some embodiments. First side101can be the back of the portable rechargeable battery pack and second side102can be the side of the portable rechargeable battery pack that interfaces with a host device. First side101can interface with a battery charger via a set of charging contacts104that are disposed on the first side101. As used here there term “contact,” unless otherwise indicated, refers to an electrically conductive component that is used to make physical contact with a mating electrically conductive component, and therefore provide an electrical connection. Charging contacts104are designed to mate with corresponding contacts of a battery charger so as to allow charging of the portable rechargeable battery pack. Accordingly, the charging contacts104include power contacts108,110, which can be positive and negative contacts, respectively. While charging, current flows from the charger into the positive power contact108and returns to the charger through the negative power contact110. The charging contacts104can further include one or more information contacts112that each provide information to the charger, such as, for example, battery data and temperature information. The second side102comprises a set of host contacts106which provide power to a host device, such as a portable communication device, such as through a positive host contact114and a negative host contact116. The portable rechargeable battery pack100can include mechanical features for attaching it to, or otherwise retaining it in a host device, such as a latch118and one or more retaining members120. Although the charging contacts104and host contacts106are shown on opposing sides101,102of the portable rechargeable battery pack100, those skilled in the art will appreciate that the contacts and the portable rechargeable battery pack itself can be designed in numerous other arrangements and configurations.

In accordance with some embodiments, the portable rechargeable battery pack100is designed to be mounted or otherwise attached or disposed in a host device to provide power to the host device through host contacts106while, at the same time, the portable rechargeable battery pack and host device together can be placed in a battery charger for charging the portable rechargeable battery pack100through charging contacts104. The portable rechargeable battery pack100contains a charge protection circuit that prevents or limits current from flowing in the opposite direction of a charging current through the charging contacts. However, the portable rechargeable battery pack100, in accordance with embodiments, contains a discharge circuit that allows at least a limited current to be drawn from the portable rechargeable battery pack through the charging contacts104.

FIG. 2is an exploded isometric view of a portable rechargeable battery pack system200in accordance with some embodiments. The portable rechargeable battery pack100is shown, and can be mounted on or otherwise attached to a host device202, and provide power to the host device202through host contacts106(not seen in this view) which mate with corresponding host contacts204on the host device202. An external adapter206is designed to mate with the portable rechargeable battery pack100, and has mating contacts (not seen here) that mate with at least some of the charging contacts104. The external adapter206can receive power (electric current and voltage) from the portable rechargeable battery pack100through the charging contacts104, and provide power through a power connector, such as a female jack208or a USB connector210. Thus, the portable rechargeable battery pack100can power both the host device202via contacts204, and other devices via one or more power connectors208,210, via a discharge circuit in the portable rechargeable battery pack100that allows a safe discharge current through the charging contacts.

FIG. 3is a schematic of a portable rechargeable battery pack system300in accordance with some embodiments. The schematic shows a host device302, portable rechargeable battery pack304, and an external adapter306. The portable rechargeable battery pack304contains at least one rechargeable cell308that is connected between host contacts322,324which mate with mating host contacts348,350, respectively, in the host device302. The portable rechargeable battery pack304also contains a set of charging contacts316,318, and320. Charging contacts316,320comprise power contacts such as a positive and a negative contact. Contact318can be an information contacts that is, for example, connected to a thermistor321which can provide thermal information to a charger. The portable rechargeable battery pack304further contains a charge protection circuit element coupled between a power contact316and the rechargeable cell(s)308, such as a transistor switch310. As used herein, the term “charge protection circuit element” is a circuit element that allows the typically high level charge currents used to charge the rechargeable cell(s)308from the charging contacts, but which can, or is operable to block discharge current. The transistor switch310can be, for example, a P-channel metallic oxide semiconductor field effect transistor (MOSFET). The transistor switch310is controlled by a control switch314, that is, for example, an N-channel MOSFET, that has a control input coupled to the information contact318. In some embodiments the control switch314is connected to the information contact through a resistance326in some embodiments. Signal debounce on the information contact318can be provided by series resistor326and capacitor327. The information contact is further coupled to an information element, such as thermistor321, which can provide temperature information to a charger when the portable rechargeable battery pack304is connected to a charger. When the portable rechargeable battery pack304is coupled to a charger, a voltage on the information contact causes control switch314to close, pulling down the gate voltage of transistor switch310, causing transistor switch310to likewise change to a closed or low impedance state, allowing a high charge current into the portable rechargeable battery pack304to charge the rechargeable cell308. The control switch314is connected to, for example, the gate of transistor switch310. A pull up resistance330can operate to pull up the gate voltage when control switch314is open, resulting in transistor switch310being open. As used herein, the term “open” when used with regard to a switch element refer to an open circuit condition where the impedance of the device is sufficiently high as to be regarded as an open circuit. Likewise, the term “closed” when used in regard to a switch element means a closed or “short” circuit condition where the impedance of the switch element is so low as to be regarded as a closed switch. The portable rechargeable battery pack304further comprises a resistance312coupled in parallel with the transistor switch310. The resistance312is a bias resistance and allows voltage of the rechargeable cell308to reach the power contact316.

The external adapter306includes mating charging contacts332,334, and336that mate with charging contacts316,318, and320, respectively, of the portable rechargeable battery pack304. The external adapter306further includes a power connector342that provides power to external device via, for example, a positive connector lead344and a negative connector lead346. Power is provided to the power connector342by a circuit coupled between the power connector342and the mating power contact332, that can include, for example, a fuse device338. The fuse device is a current limiting circuit, such as a regulator, or a positive temperature coefficient (PTC) polymer switch, or a simple fuse. The circuit between the power connector342and the mating power contact332can further include a soft start circuit340. When the external adapter306is coupled to the portable rechargeable battery pack304, the voltage provided to the power contact316, and thus to mating power contact332by resistance312is fed to mating information contact334, and thus to information contact318, causing control switch314to close, in turn causing transistor switch310to close. When transistor switch310closes, current flows from the rechargeable cell(s)308to the external adapter306. The soft start circuit340, when present, can have a delayed switch circuit that ensures voltage from the mating power contact332causes control switch314to close before a load coupled to the power connector324can pull the voltage at the mating power contact low, preventing the control switch314from closing.

As used herein, the term “discharge circuit” refers to those circuit elements that facilitate the safe discharge of current through the charging contacts. The discharge circuit and the charge protection circuit can share circuit elements. InFIG. 3the discharge circuit includes resistors312,326,330, control switch314, and transistor switch310. Even though transistor switch310is closed discharging inFIG. 3, it is only able to occur by virtue of the external adapter coupling the voltage at the power contact316to the information contact318. Thus, a short between contacts316and320would not necessarily cause control switch314to close, and transistor switch310would remain open, blocking discharge current.

FIG. 4is a schematic of a soft start circuit400in accordance with some embodiments. The soft start circuit400is used as soft start circuit340ofFIG. 3. The soft start circuit400includes a P-channel MOSFET402that is coupled between the mating power contact332and positive connector lead344(or fuse338). A pull up resistance406is coupled between the gate and source of the MOSFET402. An N-channel MOSFET404is used to control the P-channel MOSFET402, and is itself controlled by a time delay circuit comprised of a voltage divider of resistances408,410, and a capacitor412coupled in parallel with the lower resistor410of the resistor divider. Accordingly, when voltage is first applied to the mating power contact, which is coupled to line414, the capacitor412will begin to charge, as determined by the effective RC time constant of resistors408,410and the capacitance of capacitor412. Eventually the voltage will rise to a level high enough to cause the N-channel MOSFET404to close, in turn causing P-channel MOSFET to close and allow current to flow from the mating power contact coupled to line414to the power connector (e.g.342). The soft start circuit400is one example of a time delayed switch circuit, and other variations and arrangements may occur to those skilled in the art.

FIG. 5is a schematic of a portable rechargeable battery pack system500in accordance with some embodiments. The portable rechargeable battery pack system500shows discharge circuit in accordance with some embodiments. Whereas inFIG. 3, a resistance (312) was coupled in parallel with the charge protection circuit (e.g. transistor switch310), here a PTC polymer switch502is coupled in parallel with the charge protection circuit. The PTC switch502is a polymeric positive temperature coefficient device and generally allows the free flow of electrical current up to a threshold current level, at which point the PTC polymer switch transitions from a very low resistance to a high resistance (e.g. effectively an open circuit). Thus, PTC polymer switch502acts as a current limiter and allows enough current to flow from the rechargeable battery cell(s)308to the power contact316to power a device via the external adapter306, and limits the current in a resettable fuse manner to prevent an unnecessarily high current level to flow out of the charging contacts without interfering with powering the host device. The trip current level of the PTC polymer switch502can be on the order of 100-200 milliamps. Accordingly, external adapter306does not require the functionality of the fuse338or soft start circuit340. In the present exemplary schematic, information contact318does not need to be used, although it is still present for use with a battery charger so as to be able to close transistor switch310as described with reference toFIG. 3. In embodiments according toFIG. 5, the charge protection circuit includes the transistor switch310and the discharge circuit includes the PTC polymer switch502.

FIG. 6shows schematics of charge protection circuits600,606in accordance with some embodiments. Circuit600shows the use of a diode602to prevent excess discharge current. The diode602can replace transistor switch310in some embodiments. The diode602acts as the charge protection circuit while the PTC polymer switch604, coupled in parallel with the diode602, acts as the discharge circuit. The PTC polymer switch604, while being bi-directional (e.g. allows current in both directions), has a trip current level that is significantly below a desired charge current level. Hence, when charging, charge current can pass through the diode602, and when the portable rechargeable battery pack is used to power external device via the charging contacts (e.g. though external adapter306), the discharge current can flow through PTC polymer switch604. Circuit606is similar but instead of a diode it uses a diode-connected bipolar junction (BJT) transistor608. The BJT608can be a PNP transistor, having its base coupled to its collector terminal via resistor612. When so connected, the BJT608operates substantially like diode602. A benefit of the circuits600,606is that they do not need additional circuitry to switch them on or off, as with MOSFET transistor switch310, and they can be less expensive. Due to the voltage drop of around 0.7 volts, circuits600,606are more suitable for applications using a lower charge current than applications which require a MOSFET.

FIG. 7is a schematic of a portable rechargeable battery pack system700in accordance with some embodiments. In the present schematic, transistor switch310is normally closed (low impedance). When a load is attached to the charging contacts that would draw current through the charging contacts316,320in the discharge direction, the transistor switch310is opened (high impedance) until the load is removed. Thus, the switch transistor310, as inFIG. 3, plays a role in both the charge protection and the discharge circuits. The control is provided by a cell side resistor divider704,706, a load side resistor divider708,710, a bias resistor312coupled in parallel with the switch transistor310, and a comparator712which samples the divided voltages provided by the cell side resistor divider704,706and the load side resistor divider708,710, and provides an output to control switch314. The cell side resistor divider is coupled in parallel with the rechargeable cell(s)308on the host side of the transistor switch310. The load side resistor divider708,710is coupled between the power contacts316,320of the charging contacts. While the switch transistor310can be switched to a low impedance, on the order of tenths of an ohm, or lower, it does have a determinable “on” resistance. The resistor dividers704,706and708,710are selected so that, with no load on the charging contacts (e.g. a discharge current), the comparator712provides a “high” output, causing control switch314to be closed, pulling down the gate voltage of transistor switch310, thereby causing transistor switch310to be closed. Thus, when there is no load, the voltage sampled by the comparator712from the load side resistor divider708,710will be higher than the voltage sampled from the cell side resistor divider704,706. When a charge current is applied through the charging contacts316,320, the voltage on the load side resistor divider will rise slightly due to the on resistance of the transistor switch310. However, when a discharge current is provided through transistor switch310through the charging contacts, the on resistance of the transistor switch310will cause the voltage on the load side resistor divider708,710to drop below the voltage provided by the cell side resistor divider704,706, and when it drops far enough, such as due to an excessive load (or short circuit), the output of the comparator will switch from “high” to “low,” causing the control switch314to open (high impedance), resulting in the gate voltage of the transistor switch310to rise, causing it to open as well. While the excessive load remains, the voltage on the load side resistor divider708,710will remain substantially below the voltage evident at the cell side resistor divider704,706, which will keep the output of the comparator712low and transistor switch310open, thus blocking any significant discharge current out of the portable rechargeable battery pack702through the charging contacts. The output of the comparator712is integrated via a series resistor714and capacitor327to prevent signal “bounce” as the voltages sampled by the comparator change past each other. In embodiments according toFIG. 7, the charge protection circuit includes the transistor switch310and the discharge circuit also includes the transistor switch310and also the cell side resistor divider704,706, the load side resistor divider708,710, the comparator712, and control switch314.

Embodiments as described here allow the use of a portable rechargeable battery pack that has charge protection to provide a useful amount of power through the charging contacts (and the host contacts) while retaining protection against an undesirably high discharge current. Thus, accessory devices and other devices can be powered by a portable rechargeable battery pack even while the battery pack is attached to, and powering, a host device.