Lithium-ion battery charger power limitation method

A battery charger for charging a battery from a power source, comprising:

• a charge circuit in series with the power source and the battery, the charge circuit, controllable in response to a charge control signal, to control charging current flowing between the battery and the power source;
• a current sense circuit in series with the battery, to generate a current sense signal representative of the charging current;
• and
• a control circuit to generate the charge control signal in response to the current sense signal and a first voltage signal representative of voltage across the charge circuit, the control circuit including at least two operating modes;
• during a first mode of the at least two operating modes, controlling the charging current such that the power dissipated in the charge circuit is about a predetermined maximum dissipation in response to the charge control signal computed by using the current sense signal and the first voltage signal;
• and
• during a second mode of the at least two operating modes, limiting the charging current to a predetermined current level.

A battery charger for charging a battery from a power source, comprising:

• a charge circuit in series with the power source and the battery, the charge circuit, controllable in response to a charge control signal, to control charging current flowing between the battery and the power source;
• a current sense resistor in series with the battery, to generate a current sense signal representative of the charging current;
• a control circuit to generate the charge control signal in response to the current sense signal and a first voltage signal representative of voltage across the charge circuit, the control circuit including;
• an A/D to digitize the current sense signal and the first voltage signal;
• a CPU to generate a digital control signal computed form the digitized current sense signal and first voltage signal;
• a D/A to convert the digital control signal to an analog signal;
• and
• a buffer coupled between the D/A and the charge control circuit to generate the charge control signal from the analog signal;
• the control circuit having at least two operating modes;
• during a first mode of the at least two operating modes, controlling the charging current such that the power dissipated in the charge circuit is about a predetermined maximum dissipation;
• and
• during a second mode of the at least two operating modes, limiting the charging current to a predetermined current level.