Temperature compensation monitoring circuit for a battery pack charging apparatus
First Claim
1. A monitoring circuit for a battery pack charging apparatus comprising:
- a) a sensor resistor coupled between charging circuitry of the battery pack charging apparatus and a battery pack being charged by the charging circuitry, a voltage drop across the sensor resistor being proportional to a charging current through the battery pack;
b) a voltage divider circuit coupled to the charging circuitry, the voltage divider circuit including a first resistor and a first thermistor coupled in series, a set point voltage being taken off a node of the voltage divider circuit between the first resistor and the first thermistor, the voltage divider circuit set point voltage varying as a function of battery pack temperature such that when a voltage across the battery pack exceeds the voltage divider circuit set point voltage, the battery pack has been charged to a charge condition of between 90 and 95 percent of a fully charged condition;
c) a comparator, wherein the voltage across the battery pack is coupled to a first input of the comparator and the voltage divider circuit set point voltage is coupled to a second input of the comparator and an output state of the comparator changes when the voltage across the battery pack exceeds the voltage divider circuit set point voltage; and
d) a second thermistor coupled in series between the first thermistor and ground and a diode coupled between an output of the comparator and a node between the first and second thermistors, an anode end of the diode being coupled to the node between the first and second thermistors and a cathode end of the diode being coupled to the output of the comparator.
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Accused Products
Abstract
A monitoring circuit for a Li-Ion battery pack charging apparatus is disclosed. The monitoring circuit modifies charging time for a Li-Ion battery pack inserted in the charging apparatus to compensate for temperature effects on the charging current input to the battery pack. In one embodiment of the monitoring circuit, a comparator is utilized to compare a voltage across the battery pack, Vcharge, to a set point voltage value, Vsp. The set point voltage value, Vsp, is taken off a temperature sensor circuit comprising a voltage divider circuit. The voltage divider circuit includes at least one thermistor in a ground connected leg of the divider. In a second embodiment of the monitoring circuit of the present invention, a differential amplifier is coupled to opposite ends of a low resistance sensor resistor. The sensor resistor is coupled between charging circuitry and the Li-Ion battery pack to be charged. The voltage differential across the resistor, Vsensor, is amplified by a gain of the differential amplifier. A gain adjusted differential voltage, Vgsensor, is compared by a microprocessor to a set point voltage value, Vsp. The set point voltage value, Vsp, is generated by a temperature sensor circuit. The temperature sensor circuit includes a voltage divider circuit and the set point voltage value, Vsp, is taken off the voltage divider which includes at least one thermistor in a ground connected leg of the divider.
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Citations
14 Claims
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1. A monitoring circuit for a battery pack charging apparatus comprising:
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a) a sensor resistor coupled between charging circuitry of the battery pack charging apparatus and a battery pack being charged by the charging circuitry, a voltage drop across the sensor resistor being proportional to a charging current through the battery pack; b) a voltage divider circuit coupled to the charging circuitry, the voltage divider circuit including a first resistor and a first thermistor coupled in series, a set point voltage being taken off a node of the voltage divider circuit between the first resistor and the first thermistor, the voltage divider circuit set point voltage varying as a function of battery pack temperature such that when a voltage across the battery pack exceeds the voltage divider circuit set point voltage, the battery pack has been charged to a charge condition of between 90 and 95 percent of a fully charged condition; c) a comparator, wherein the voltage across the battery pack is coupled to a first input of the comparator and the voltage divider circuit set point voltage is coupled to a second input of the comparator and an output state of the comparator changes when the voltage across the battery pack exceeds the voltage divider circuit set point voltage; and d) a second thermistor coupled in series between the first thermistor and ground and a diode coupled between an output of the comparator and a node between the first and second thermistors, an anode end of the diode being coupled to the node between the first and second thermistors and a cathode end of the diode being coupled to the output of the comparator. - View Dependent Claims (3)
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2. A monitoring circuit for a battery pack charging apparatus comprising:
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a) a sensor resistor coupled between charging circuitry of the battery pack charging apparatus and a battery pack being charged by the charging circuitry, a voltage drop across the sensor resistor being proportional to a charging current through the battery pack; b) a voltage divider circuit coupled to the charging circuitry, the voltage divider circuit including a first resistor and a first thermistor coupled in series, a set point voltage being taken off a node of the voltage divider circuit between the first resistor and the first thermistor, the voltage divider circuit set point voltage varying as a function of battery pack temperature such that when a voltage across the battery pack exceeds the voltage divider circuit set point voltage, the battery pack has been charged to a charge condition of between 90 and 95 percent of a fully charged condition; and c) a timer coupled to the charging circuitry and wherein the timer is set when the voltage across the battery pack exceeds the voltage divider circuit set point voltage causing the charging circuitry to continue charging the battery pack for a predetermined time such that the battery pack is charged to a charge condition of substantially 100 percent of the fully charged condition.
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4. A monitoring circuit for a battery pack charging apparatus comprising:
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a) a sensor resistor coupled between charging circuitry of the battery pack charging apparatus and a battery pack being charged by the charging circuitry, a voltage drop across the sensor resistor being proportional to a charging current through the battery pack; b) a differential amplifier having two inputs coupled to opposite ends of the sensor resistor, the differential amplifier outputting an amplified voltage whose magnitude is proportional to the voltage drop across the sensor resistor; and c) a temperature sensor circuit generating a set point voltage, the set point voltage varying as a function of battery pack temperature such that when the set point voltage exceeds the magnitude of the amplified voltage output by the differential amplifier, the battery pack has been charged to a charge condition of between 90 and 95 percent of a fully charged condition. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A battery recharging apparatus comprising:
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a) charging circuitry coupled to an external power supply and outputting a regulated source of power to charge a battery pack inserted into the apparatus for charging; and b) a monitoring circuit coupled to the charging circuit and the battery pack, the monitoring circuit including; i) a sensor resistor coupled between charging circuitry of the battery pack charging apparatus and a battery pack being charged by the charging circuitry, a voltage drop across the sensor resistor being proportional to a charging current through the battery pack; ii) a differential amplifier having two inputs coupled to opposite ends of the sensor resistor, the differential amplifier outputting an amplified voltage whose magnitude is proportional to the voltage drop across the sensor resistor; and iii) a voltage divider circuit having a voltage potential applied to the circuit and including a first resistor and a first thermistor coupled in series, a set point voltage being taken off a node of the voltage divider circuit between the first resistor and the first thermistor, the voltage divider circuit set point voltage varying as a function of battery pack temperature such that when the set point voltage exceeds the magnitude of the amplified voltage output by the differential amplifier, the battery pack has been charged to a charge condition of between 90 and 95 percent of a fully charged condition.
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Specification