Linearly regulated battery charger
First Claim
1. A method for controlling battery power comprising the acts of:
- coupling a first input terminal for receiving a first external power source to a system power terminal via a first isolation diode, wherein the first external power source is provided by an AC adapter;
coupling a second input terminal for receiving a second external power source to the system power terminal via a second isolation diode connected in series with a current sensing circuit, wherein the second external power source is provided by a USB interface;
coupling a first bypass transistor across the first isolation diode, wherein the first bypass transistor is turned on when the first external power source is selected to provide power to the system power terminal;
coupling a second bypass transistor across the second isolation diode, wherein the second bypass transistor is turned on when the second external power source is selected to provide power to the system power terminal;
coupling an overriding diode between the first input terminal and a control terminal of the second bypass transistor to force the second bypass transistor off and to effectively isolate the USB interface from the system power terminal when the AC adapter is connected to the first input terminal;
coupling an internal battery to the system power terminal via a series-connected regulating transistor, wherein the regulating transistor comprises a first terminal connected to the system power terminal, a second terminal connected to the internal battery, a control terminal, and a configurable body terminal connected to the system power terminal when the system power terminal has a greater voltage than the internal battery and connected to the internal battery when the internal battery has a greater voltage than the system power terminal;
charging the internal battery by linearly regulating the regulating transistor with an adjustable voltage at the control terminal of the regulating transistor to conduct a charging current in a first direction from the system power terminal to a positive terminal of the internal battery during a charging mode; and
using the current sensing circuit to measure current provided by the USB interface and to reduce the charging current in response to an increase in load current by varying the adjustable voltage at the control terminal of the regulating transistor when the measured current from the USB interface exceeds a predefined current threshold, wherein the current sensing circuit does not measure current provided by the AC adapter to reduce the charging current.
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Accused Products
Abstract
A battery charger for an electronic device receives current limited power from an external power source, such as a Universal Serial Bus power interface. The battery charger can linearly regulate a charging current to an internal battery and limit the charging current so as not to demand current in excess of what the external power source can provide. A bi-directional pass element coupled between a system power terminal and the internal battery controls the charging current and effectively isolates the internal battery from a system load during charging of the battery while providing a low impedance path from the internal battery to the system load during discharging of the battery.
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Citations
17 Claims
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1. A method for controlling battery power comprising the acts of:
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coupling a first input terminal for receiving a first external power source to a system power terminal via a first isolation diode, wherein the first external power source is provided by an AC adapter; coupling a second input terminal for receiving a second external power source to the system power terminal via a second isolation diode connected in series with a current sensing circuit, wherein the second external power source is provided by a USB interface; coupling a first bypass transistor across the first isolation diode, wherein the first bypass transistor is turned on when the first external power source is selected to provide power to the system power terminal; coupling a second bypass transistor across the second isolation diode, wherein the second bypass transistor is turned on when the second external power source is selected to provide power to the system power terminal; coupling an overriding diode between the first input terminal and a control terminal of the second bypass transistor to force the second bypass transistor off and to effectively isolate the USB interface from the system power terminal when the AC adapter is connected to the first input terminal; coupling an internal battery to the system power terminal via a series-connected regulating transistor, wherein the regulating transistor comprises a first terminal connected to the system power terminal, a second terminal connected to the internal battery, a control terminal, and a configurable body terminal connected to the system power terminal when the system power terminal has a greater voltage than the internal battery and connected to the internal battery when the internal battery has a greater voltage than the system power terminal; charging the internal battery by linearly regulating the regulating transistor with an adjustable voltage at the control terminal of the regulating transistor to conduct a charging current in a first direction from the system power terminal to a positive terminal of the internal battery during a charging mode; and using the current sensing circuit to measure current provided by the USB interface and to reduce the charging current in response to an increase in load current by varying the adjustable voltage at the control terminal of the regulating transistor when the measured current from the USB interface exceeds a predefined current threshold, wherein the current sensing circuit does not measure current provided by the AC adapter to reduce the charging current. - View Dependent Claims (2, 3, 4, 5, 12, 13, 14)
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6. A method for controlling power to a battery, the method comprising:
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coupling a first isolation diode between a first input terminal for receiving an external primary power source via an AC adapter and a system power terminal, wherein the first isolation diode has an anode coupled to the first input terminal and a cathode coupled to the system power terminal; coupling a second isolation diode between a second input terminal for receiving an external secondary power source via a USB interface and the system power terminal, wherein the second isolation diode has an anode coupled to the second input terminal and a cathode coupled to the system power terminal; coupling a first bypass transistor across the first isolation diode; coupling a second bypass transistor across the second isolation diode; coupling an electronic device to the system power terminal, wherein the electronic device demands a load current from the system power terminal; coupling an internal battery to the system power terminal through a regulating transistor, wherein the regulating transistor comprises a first terminal connected to the system power terminal, a second terminal connected to the internal battery, a configurable body contact, and a control terminal; sensing respective voltages of the system power terminal and the internal battery to control a connection of the configurable body contact, wherein the configurable body contact is connected to the first terminal when the system power terminal has a greater voltage than the internal battery and connected to the second terminal when the internal battery has a greater voltage than the system power terminal; driving the control terminal of the regulating transistor with a driving signal having linearly adjustable voltage levels to linearly regulate the level of a charging current conducted by the regulating transistor to charge the internal battery, wherein the level of the charging current provided to the internal battery is determined by the voltage level of the driving signal; and sensing current provided by the USB interface to vary the charging current in response to changes in the load current such that a total current provided by the USB interface does not exceed a threshold current value, wherein the current provided by the AC adapter is not sensed and is not used to vary the charging current in the response to changes in the load current. - View Dependent Claims (7, 8, 9, 10, 11, 15, 16, 17)
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Specification