GB2386005A

GB2386005A - Battery charging for portable devices with USB links

Info

Publication number: GB2386005A
Application number: GB0204806A
Authority: GB
Inventors: John Andrew Harley
Original assignee: Matsushita Communication Industrial UK Ltd; Matsushita Electric Industrial Co Ltd
Current assignee: Matsushita Communication Industrial UK Ltd; Panasonic Holdings Corp
Priority date: 2002-03-01
Filing date: 2002-03-01
Publication date: 2003-09-03
Also published as: GB0204806D0

Abstract

A portable terminal (1) such as a mobile phone maintains charge on its internal battery either by means of a dedicated charger (8) or through a USB link (3) to another device. A switching circuit (10) within the portable terminal selects preferentially a dedicated charger as a charging source when a charger is connected to the terminal. A USB connection to a host device is selected automatically as the charging source when a dedicated charger is not connected to the terminal.

Description

Battery charging for portable devices with USB links.

This invention relates to portable electronic devices powered by rechargeable batteries.

The ability to connect various electronic devices together for interactive operation has been supplemented with the availability of the USB (universal serial bus) interface. USB interfaces are likely to be incorporated in many electronic units produced in future. Specifications and other information regarding USB may be accessed at http: \\www. usb. org/.

Alongside the development of the USB interconnection system, the utility of mobile radiotelephones and like devices such as PDA's (personal digital assistant) has been extended to provide convenient internet connection over the wireless interface. The dependency of mobile devices upon the availability of power from their limited life batteries remains, however, a restriction on prolonged use. The limitation on power supply imposed by the batteries is of particular concern when large amounts of data are to be transferred or exchanged via a mobile terminal. A loss of power in the mobile device will cause disruption to the transfer or exchange of data.

A number of peripheral devices may be connected to a host apparatus such as a personal computer via a hub. A mobile terminal may also be connected directly via a USB cable to a USB port of a personal computer (PC) for the purpose of exchanging data between the PC and the mobile terminal. In this arrangement the PC would normally be the host device and the mobile

terminal the client device. Under these circumstances the PC would control any data exchange and would provide a power source to the client mobile terminal over the USB connection.

The portable terminal may be connected separately to a battery charger unit through a dedicated battery charging connector to re-charge or to maintain charge in the battery of the portable terminal. Alternatively the portable terminal may take power from its host device through a USB port. The host device may be powered continuously from an external source such as mains supply or may be reliant for its power upon internal batteries.

In order to avoid overcharging of batteries connected to charging units, timers are set to provide safe limits in the charging cycle. The timers are set in accordance with the parameters of the charging supply and these parameters need to be determined at the outset of charging.

Charging of an external apparatus such as a mobile phone from the USB port of a host whilst exchanging data is known in the prior art from US 6 211 649 Matsuda. The Matsuda patent, however, provides a special cable to connect the USB port of the host with the standard charging and input/ output connectors of the external apparatus.

Provision of an additional specialised cable causes a hindrance and expense for the user of the apparatus that may conveniently be avoided through implementation of the present invention.

According to the present invention there is provided apparatus as set out in the attached claims.

An example of the invention will now be described with reference to the accompanying drawings in which; Figure 1 provides a general view of the connections from host to client apparatus and from client apparatus to battery charger.

Figure 2 is a block diagram showing the disposition of the switching circuit, Figure 3 is a circuit diagram of a switching circuit, Figure 4 is a flow diagram showing the sequence of operations prior to charging.

With reference to figure 1 a radiotelephone 1 is connected through a USB port 2 and cable 3 to a USB port 4 of personal computer PC 5. It may be convenient for the USB port 2 to be located adjacent the charging connector 6. The radiotelephone 1 may also be connected through charging connector 6 and cable 7 to a charging unit 8. Charging unit 8 is fed from mains power 9 and PC 5 may be connected to mains power also as shown in figure 1 or may be powered from an internal source such as batteries.

Data exchange between PC 5 and radiotelephone 1 can proceed through the serial data link from port 2 to port 4. A feature of the universal serial bus

is the ability of a client apparatus to be provided with power from a host apparatus.

The host apparatus in figure 1 is PC 5 and the client apparatus radiotelephone 1. If a constant supply of power from an external source such as mains power 9 is available to the host then the power available from the host to the client will be 500 milliamps at 5 volts. In this condition the host is referred to as"powered". Where the host does not have an external supply and depends for its power upon internal batteries (unpowered host) then the lower current of 100 milliamps at 5 volts is available to the client apparatus.

With charging unit 8 connected via connector 6 to radiotelephone 1 the batteries of radiotelephone 1 can be maintained at full charge by the output from charging unit 8. In this arrangement there is no requirement for radiotelephone 1 to draw current from the host, PC 5.

If charging unit 8 is not connected to radiotelephone 1, however, then in order to maintain power in the batteries of radiotelephone 1, current is drawn from PC 5 through the cable 3. The disposition of the switching circuit 10 within radiotelephone 1 is shown in figure 2. Switching circuit 10 selects the appropriate source of power automatically to maintain charge on the battery of radiotelephone 1. As shown in figure 2, switching circuit 10 has connections to charging connector 6, digital baseband device 11 and analogue baseband device 12.

A further connection from switching circuit 10 is to the USB pin Vo. The USB connector has four pins, as illustrated in figure 2, Vo the power pin, D+ and D-the data pins and GND the ground pin.

A charger 8 may be connected to charging connector 6 and a USB cable may be connected to USB port 2. When a charger is connected to connector 6, and a USB cable from a host apparatus is connected at USB port 2, the physical presence of the charger 8 is detected by a switch (not shown) in connector 6. Alternatively the availability of the charger 8 can be detected from the open circuit charger voltage in analogue baseband device 12.

The switching circuit 10 is shown in detail in figure 3. When the availability of the charger is detected, FET1 is controlled by the analogue baseband device in order to charge the battery in accordance with its appropriate charging profile. The charging profile will depend upon the chemical composition of the battery cells. The level of current from the charger can be measured by means of the sense resistor Rl or by using the method described in patent application GB 0113306.5. A suitable safety timer is selected dependent on the presently configured mode of operation of radiotelephone 1 and the measured charger current. The safety timer can be adjusted if the mode of operation of radiotelephone 1 changes.

Radiotelephone 1 can be used for over-the-air transmission and reception and/or data exchange with PC5 whilst the charging of its battery proceeds.

When no charger is connected at connector 6 but radiotelephone 1 is connected via USB port 2 and cable 3 to a host device (PC5), then switching circuit 10 connects pin Vo of the USB to the charging circuit.

The type of USB host connected at USB port 2 and whether or not it is a powered device is determined via the standard USB protocol. Using the information on the type of USB host, the current flow into the battery can be set by means of FET1 such that the USB voltage supply remains within specification. The USB supply voltage is monitored by analogue baseband device 12 to ensure that the specified voltage is maintained.

Following the setting of a suitable safety timer to avoid any overcharging potential, TRI is activated by the digital baseband device 11, through a low to high level change, causing closure of FET2 to enable the charging supply. Charging of the battery of radiotelephone 1 from the USB port then proceeds. The purpose of R2 is to turn FET2 off when the digital baseband device 11 disables TRI by raising the voltage on the gate of FET2 to the source level.

The voltage available from the USB pin Vu will normally be insufficient to charge the battery completely but can be expected to maintain sufficient charge for continuous operation of radiotelephone 1. Whilst radiotelephone 1 is charging its battery from a host device through a USB port, dedicated battery charger 8 may be connected to connector 6. The presence of the charger 8 causes the USB charging to be discontinued. Digital baseband device 11 disables TR1 thereby to turn off FET2. Charging of radiotelephone 1 then continues from charger 8.

With radiotelephone 1 connected to charger 8, the capability exists for radiotelephone 1 to act as a host for another device. In these circumstances, radiotelephone 1 may supply power to that other, client device.

The flow chart of figure 4 illustrates the sequence of steps in the portable terminal prior to battery charging. The first step at 401 is to check whether or not a dedicated charger is connected to the terminal. When a charger is connected then charging proceeds in the normal way at 402. If no charger is connected to the terminal then the USB interface is determined at 403 and if no USB connection exists no charging will take place (404). Where a USB connection exists, the configuration of the host as powered or unpowered is established at 405. If the host is powered then charging current is set to 500 milliamperes at 407 otherwise charging current is limited to 100 milliamperes at 406. Charging then proceeds from the USB port (408).

Claims

Claims 1. A portable communications terminal having a rechargeable battery and incorporating a USB port and a dedicated charging connector and in which a switching circuit automatically effects charging of said rechargeable battery from a charger connected to the dedicated charging connector or effects charging from a host apparatus through said USB port when no charger is connected to the dedicated charging connector.
2. A portable communications terminal as in claim lin which exchange of data with a host apparatus proceeds through a USB port whilst charging from a charger connected to the dedicated charging connector continues.
3. A portable communications terminal as in claim lin which exchange of data with a host apparatus proceeds through a USB port whilst charging from the host apparatus through said USB port continues.
4. A portable communications terminal as in any preceding claim in which the host apparatus is a PC.
5. A portable communications terminal substantially as hereinbefore described with relation to or as illustrated in figures 1 to 3.