Battery charging system having logarithmic analog-to-digital converter with automatic scaling of analog signal

A method of charging a battery selected from a group of batteries having rated voltages between a first rated voltage and a second substantially greater rated voltage, comprising:

• applying a charging current to the battery;
• monitoring the voltage of the battery at discrete time intervals to obtain a plurality of instantaneous battery voltage samples within a range of voltage values related to the rated voltage of the battery such that a battery having said first rated voltage produces battery voltage samples while charging within a first range of voltage values and a battery having said second rated voltage produces battery voltage samples while charging within a second substantially greater range of voltage values;
• converting said instantaneous battery voltage samples to corresponding digital values so that a given percentage difference in voltage values within either said first or said second ranges of values is represented by substantially the same difference in said corresponding digital values;
• and
• terminating the application of charging current to a battery having said first rated voltage by detecting predetermined incremental changes in the voltage of the battery of a magnitude that are too small to be detectible when charging a battery having said second rated voltage.

A method of charging a battery selected from a group of batteries having a range of different battery voltage ratings, comprising:

• applying a charging current to said battery:
• monitoring the voltage of said battery by sampling at discrete time intervals to obtain a plurality of instantaneous voltage readings:
• converting said instantaneous voltage readings into digital values;
• applying a nonlinear factor to the digital values such that a given percentage change in voltage within said range of different battery voltage ratings is represented by substantially the same change in digital values;
• using a plurality of said scaled digital values to determine a rate of change in battery voltage as charging current is applied;
• terminating charging current when the rate of change in battery voltage changes sign.

A battery charger for charging a battery selected from a group of batteries having a range of different battery voltage ratings including a first range and a second range, comprising:

• a current source for supplying charging current to said battery;
• a battery voltage sensor for sampling the voltage of the battery being charged and for supplying a corresponding digital signal indicative of the sampled battery voltage;
• a controller circuit coupled to said current source and to said battery voltage sensor for terminating the supplying of charging current in response to a predetermined battery voltage condition and based on said digital signal;
• said battery voltage sensor having apparatus for automatically converting battery voltages within said first range into digital signals at a first resolution and for automatically converting battery voltages within said second range into digital signals at a second resolution;
• whereby termination of the supplying of charging current is effected based on voltage readings taken at a resolution automatically determined by the voltage range of the particular battery being charged.