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Battery charging and discharging by using a bi-directional transistor

  • US 7,528,582 B1
  • Filed: 01/16/2004
  • Issued: 05/05/2009
  • Est. Priority Date: 01/21/2003
  • Status: Active Grant
First Claim
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1. A method for controlling battery power comprising the acts of:

  • coupling a first input terminal to a system power terminal, wherein the first input terminal is configured to receive power from an AC adapter;

    coupling a second input terminal in series with a current sensing circuit to the system power terminal, wherein the second input terminal is configured to receive power from a USB interface;

    coupling a portable electronic device to the system power terminal, wherein the portable electronic device is powered by the AC adapter when the AC adapter is connected to the first input terminal, by the USB interface when the USB interface is connected to the second input terminal and the AC adapter is not connected to the first input terminal, and by an internal battery when the AC adapter is not connected to the first input terminal and the USB interface is not connected to the second input terminal;

    coupling the internal battery to the system power terminal via a series-connected bi-directional transistor, wherein the bi-directional transistor comprises a first terminal connected to the system power terminal, a second terminal connected to a positive terminal of the internal battery, a configurable body terminal and a control terminal;

    comparing a voltage at the system power terminal with a voltage at the positive terminal of the internal battery to control connection of the configurable body terminal, wherein the configurable body terminal is connected to the first terminal when the system power terminal has a higher voltage than the positive terminal of the internal battery and connected to the second terminal when the positive terminal of the internal battery has a higher voltage than the system power terminal;

    sensing a voltage difference between the system power terminal and the positive terminal of the internal battery;

    generating a feedback control signal based on the voltage difference and a voltage level at the control terminal of the bi-directional transistor;

    generating a linearly adjustable voltage for driving the bi-directional transistor based on the feedback control signal;

    determining a charging mode of operation when the voltage difference indicates that the system power terminal has a higher voltage than the positive terminal of the internal battery by a first predefined amount;

    charging the internal battery by linearly regulating the bi-directional transistor with the linearly adjustable voltage at the control terminal of the bi-directional transistor to conduct a charging current in a first direction from the system power terminal to the positive terminal of the internal battery during the charging mode;

    using the current sensing circuit to measure current provided by the USB interface and to generate an overriding signal to reduce the charging current in response to an increase in a load current provided to the portable electronic device such that the measured current from the USB interface does not exceed a predetermined current threshold, wherein the overriding signal replaces the feedback control signal to generate the linearly adjustable voltage for driving the bi-directional transistor when the measured current from the USB interface exceeds the predetermine current threshold, and the current sensing circuit does not measure current provided by the AC adapter to generate the overriding signal when the AC adapter is connected to the first input terminal;

    determining a discharging mode of operation when the voltage difference indicates that the system power terminal has a lower voltage than the positive terminal of the internal battery by a second predefined amount; and

    discharging the internal battery by linearly regulating the bi-directional transistor with the linearly adjustable voltage at the control terminal of the bi-directional transistor to conduct a discharging current in a second direction from the positive terminal of the internal battery to the system power terminal during the discharging mode, wherein the level of current provided to the internal battery during the charging mode or current supplied by the internal battery during the discharging mode varies with the level of the linearly adjustable voltage at the control terminal of the bi-directional transistor.

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