Sub-miniature high efficiency battery charger system and method

• US 6,091,229 A
• Filed: 03/30/1999
• Issued: 07/18/2000
• Est. Priority Date: 03/30/1999
• Status: Expired due to Term

• Current Assignee: Amperex Technology Limited (TDK Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Geren, Michael D., Oglesbee, John Wendell
• Primary Examiner(s): Berhane, Adolf Deneke
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/282,705
• Time in Patent Office: 476 Days
• Field of Search: 320/137, 320/140, 320/152, 320/157, 320/160, 320/163, 320/164
• US Class Current: 320/137
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Abstract

A battery charger system (10) consisting of a power supply unit (20) and a battery charger unit (70). The power supply unit (20) features a current profile generator (26) that defines a current profile of the output current of the power supply unit (20). The battery charger system (10) provides a unique way of communicating charging current demand between the battery charger unit (70) and the power supply unit (20). The power supply unit (20) is capable of determining the charging current demand by detecting specific logical operating states of the battery charger unit (70), and comparing the current to a set threshold. The battery charger unit (70) communicates charging current demand to the power supply unit (20), and the power supply unit (20) responds by adjusting its output current to meet the required demand.

Claims

1. A battery charger system comprising:

a power supply unit comprising;

a power converter for converting power from a power source to generate an output current;

an output current regulator for controlling the power converter;

a current profile generator coupled across the output terminals and controlling the output current regulator so as to cause the output current of the power converter to cycle between a first mode during which the output current increases and second mode during which the output current decreases;

a battery charger unit comprising;

input terminals for receiving the output current of the power converter;

output terminals for connection to a battery to be charged;

a switch coupled between the input terminals;

a current sense resistor connected between the transistor switch and an input terminal;

a controller connected to the switch and to the current sense resistor for sensing current therethrough and controlling a state of the switch, the controller responsive to output current from the power supply unit detected through the current sense resistor to close the switch when the output current from the power supply unit is increasing, and opening the switch and thereby coupling charging current to the battery when the output current from the power supply unit is decreasing.

2. The system of claim 1, wherein the controller of the battery charger unit monitors the voltage across the current sense resistor and opens the switch when the voltage across the current sense resistor exceeds an upper threshold, and closes the switch when the voltage across the current sense resistor reaches a lower threshold.

3. The system of claim 2, wherein the current profile generator comprises:

a comparator coupled to the output terminals of the power supply unit to compare the output voltage of the power supply unit with at least one threshold to generate an output signal, and

a controller coupled to the comparator and responsive to the output signal of the comparator to generate a current control signal which is coupled to the output current generator, wherein the controller is responsive to detecting that the output voltage of the power supply unit is below a minimum threshold to generate a current control signal that causes the power converter to increase the output current at a first rate, and is responsive to detecting that the output voltage of the power supply unit is above a maximum threshold to generate a current control signal that causes the power converter to decrease the output current a second rate.

4. The system of claim 3, herein the controller of the current profile generator stores programmable values for the first rate and the second rate, wherein the first rate is substantially greater than the second rate.

5. The system of claim 1, wherein the battery charger unit further comprises a super capacitor coupled in parallel with the output terminals.

6. A battery charging method comprising steps of:

converting power from a power source to generate a power supply output current that cycles between a first mode during which it increases and a second mode during which it decreases;

connecting the power supply output current to a terminal of the switch;

sensing current through the switch and maintaining the switch closed while the power supply output current increases until current through the switch exceeds an upper threshold;

opening the switch when current through it exceeds the upper threshold, thereby diverting the power supply output current to the battery to charge the battery, and causing the power supply output current to begin decreasing;

sensing current through the battery and maintaining the switch open until current through it reaches a lower threshold; and

closing the switch when the current through the battery reaches the lower threshold, thereby causing the power supply output current to begin increasing.

7. The method of claim 6, wherein the step of generating the power supply output current comprises causing the power supply output current to increase at a first rate and to decrease at a second rate, wherein the first rate is substantially greater than the second rate.

8. A battery charger system comprising:

a power supply unit comprising;

a power converter for converting power from a power source to generate an output current;

an output current regulator coupled to the power converter to regulator the output current generated by the power converter;

a current profile generator comprising a controller that monitors an output voltage of the power supply unit and defines a current profile of the output current of the power converter such that the output current cycles between a ramp up mode whereby the output current increases at a first rate, and a ramp down mode whereby the output current decreases at a second rate;

a battery charger unit comprising;

input terminals for receiving the output current of the power supply unit;

output terminals for connection to a battery to be charged;

a switch connected between the input terminals;

a current sense resistor connected between the transistor switch and an input terminal;

a controller connected to the switch and to the current sense resistor for sensing current therethrough and controlling the switch to maintain the switch closed during the ramp up mode of the output current from the power supply unit, open the switch when current through the current sense resistor reaches an upper threshold, maintain the switch open during the ramp down mode of the output current from the power supply unit to thereby divert the output current from the power supply unit to the battery, and close the switch when current through the current sense resistor reaches a lower threshold thereby short circuiting current through the switch and away from the battery.

9. The system of claim 8, wherein the controller of the current profile generator is responsive to the output voltage of the power supply unit so as to switch from the ramp up mode to the ramp down mode when the output voltage of the power supply unit is greater than a maximum threshold, and to switch from the ramp down mode to the ramp up mode when the output voltage of the power supply unit is less than a minimum threshold.

10. The system of claim 8, wherein the controller of the current profile generator stores programmable values for the first rate and the second rate, wherein the first rate is substantially greater than the second rate.

11. The system of claim 8, wherein the battery charger unit further comprises a low forward voltage diode connected in series between an input terminal and an output terminal of the battery charger unit.

12. The system of claim 8, wherein the battery charger unit further comprises a super capacitor coupled in parallel with the output terminals.