Portable battery charger

Automatic battery charging apparatus for charging a battery from a supply voltage generated by a voltage source, said battery including temperature sensing means for generating a first output signal having a magnitude related to the temperature of the battery, said apparatus comprising:

• first source means coupled between the supply voltage and the battery for generating a first charging current;
• second source means coupled between the supply voltage and the battery for generating a second charging current in response to a first state of a control signal and disabling generation of the second charging current in response to a second state of the control signal, said second charging current having a magnitude greater than the first charging current;
• means for generating a reference voltage;
• selecting means responsive to the supply voltage for selecting one of first and second high-temperature thresholds, said selecting means further including first means coupled to said reference voltage for producing the first high-temperature threshold and second means coupled to said reference voltage and the supply voltage for producing the second high-temperature threshold;
• first comparing means for producing a second output signal when the first output signal of the temperature sensing means exceeds said selected one of the first and second high-temperature thresholds;
• second comparing means for producing a third output signal when the first output signal of the temperature sensing means exceeds a low-temperature threshold;
• third comparing means for producing a fourth output signal when the battery voltage is greater than a predetermined maximum voltage;
• fourth comparing means for producing a fifth output signal when the battery voltage is less than a predetermined minimum voltage;
• and
• control means for generating the first state of the control signal initially and the second state of the control signal in response to one or more of the second, third, fourth and fifth output signals of the first, second, third and fourth comparing means, respectively, whereby the battery is protected from damage due to charging current and temperature.

A method for charging a battery from a supply voltage generated by a voltage source, said battery including temperature sensing means for generating an output signal having a magnitude related to the temperature of the battery, said method comprising the steps of:

• coupling to the battery a first charging current produced by a first source means;
• coupling to and decoupling from the battery a second charging current produced by second source means in response to first and second states of a control signal, respectively, said second charging current having a magnitude greater than the first charging current;
• generating a reference voltage;
• producing a first threshold from said reference voltage;
• producing a second threshold from said reference voltage and the supply voltage;
• selecting in response to the second charging current one of the first and second thresholds;
• generating the first state of the control signal initially and the second state of the control signal when the output signal of the temperature sensing means exceeds said selected one of the first and second thresholds, whereby the battery is protected from damage due to charging current and temperature.

Automatic battery charging apparatus for charging a battery from a supply voltage generated by a voltage source, said battery including temperature sensing means for generating an output signal having a magnitude related to the temperature of the battery, said apparatus comprising:

• means for coupling to the battery a first charging current produced by first source means;
• means for coupling to and decoupling from the battery a second charging current produced by second source means in response to first and second states of a control signal, respectively, said second charging current having a magnitude greater than the first charging current;
• means for generating a reference voltage;
• means for selecting in response to the supply voltage one of first and second thresholds, said selecting means further including first means coupled to said reference voltage for producing the first threshold and second means coupled to said reference voltage and the supply voltage for producing the second threshold;
• means for generating the first state of the control signal initially and the second state of the control signal when the output signal of the temperature sensing means exceeds said selected one of the first and second thresholds, whereby the battery is protected from damage due to charging current and temperature.