Battery charging unit

• US 5,889,387 A
• Filed: 12/13/1996
• Issued: 03/30/1999
• Est. Priority Date: 12/13/1996
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Massie, Harold L.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): SHIN, KYUNG E
• Application Number:
  US08/764,930
• Time in Patent Office: 837 Days
• Field of Search: 320/162, 320/163, 320/141, 320/145, 320/146
• US Class Current: 320/145
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A battery charging circuit, particularly useful in a laptop computer system, includes a voltage input terminal coupled to a dc voltage. A first switch couples the voltage input terminal to an output coupled to the battery through a current sense resistor. A first current sink which is on when the charger circuit is on draws current from the input side of the current sense resistor through a first resistor to develop a first voltage. This voltage and a voltage coupled through a second resistor from the battery side of the sense resistor are inputs to a comparator, the output of which controls the first switch. A second current sink, when on, draws current through the second resistor causing the first switch to be held off, turning the charging circuit off. An ON/OFF terminal, to which a variable duty cycle square wave is supplied, controls the turning on and off of the first and second current sinks, with the length of the duty cycle controlling the average current supplied to the battery.

Claims

1. A battery charger circuit comprising:

a. a voltage input terminal;

b. a voltage output terninal;

c. a first switch having an input, coupled to said voltage input terminal, an output, and a first switch control input;

d. a current sense resistor having one end coupled to said first switch output and another end coupled to said voltage output terminal;

e. a first current sink having a first current input and a first control input;

f. a second current sink having a second current input and a second control input;

g. a first resistor coupling said one end of said current sense resistor junction to said first current input;

h. a second resistor coupling said other end of said current sense resistor to said second current input;

i. a comparator having a first input coupled to said first current input and a second input coupled to said second current input and an output coupled to said first switch control input; and

j. an ON/OFF input terminal coupled to said first and second current sink first and second control inputs.

2. A battery charger circuit according to claim 1 and further including an inductor having one end coupled to said switch output and another end coupled to said one end of said current sense resistor.

3. A battery charger according to claim 2 and further including a first switch driver coupling said comparator output to said first switch control input.

4. A battery charger according to claim 3 and further including a circuit coupling said one end of said inductor to ground.

5. A battery charger according to claim 4 wherein said circuit coupling said one end of said inductor to ground comprises a catch diode.

6. A battery charger according to claim 4 wherein said circuit coupling said one end of said inductor to ground comprises a second switch having an input coupled to said inductor, an output coupled to ground and a second switch control input coupled to said comparator output.

7. A battery charger according to claim 6 and further including a second switch driver circuit coupled between said comparator output and said second switch control input.

8. A battery charger according to claim 7 wherein said first and second switches comprise FET switches.

9. A battery charger according to claim 3 wherein said first switch comprises a first FET.

10. A battery charger according to claim 9 wherein said first FET comprises a P-channel FET.

11. A battery charger according to claim 9 wherein said first FET comprises an N-channel FET.

12. A battery charger according to claim 3 wherein said first switch comprises a bipolar transistor.

13. A battery charger according to claim 3 and further including a first hystersis circuit coupled between said output of said comparator and one of its first and second inputs.

14. A battery charger according to claim 8 wherein said first hystersis circuit comprises a resistor and capacitor in parallel.

15. A battery charger according to claim 3 and further including a second hystersis circuit coupled between the output of said comparator and said first current sink first control input.

16. A battery charger according to claim 15 wherein said second hystersis circuit comprises a FET having a source, drain and gate, the gate of said FET coupled to said comparator output and one of its source and drain coupled to ground, the other of the source and drain coupled to said output terminal of said transistor switch in said first current sink.

17. A battery charger according to claim 1 wherein said first current sink comprises a first semiconductor switch having and an input terminal and an output terminal and a control input, and a voltage reference circuit having an output coupled to said semiconductor switch control input, the input of said switch forming said first control input and coupled to said first resistor and the output of said switch coupled to said ON/OFF terminal.

18. A battery charger according to claim 17 wherein said second current sink comprises a second semiconductor switch having an input coupled to said second current input, an output coupled to ground and a control input forming said second control input and coupled to said ON/OFF terminal.

19. A laptop computer system comprising:

a. a square wave generator circuit having a battery charger ON/OFF signal as an output;

b. a microprocessor coupled to control said circuit

c. a battery;

d. a battery charging circuit comprising;

i. a voltage input terminal;

ii. a voltage output terminal;

iii. a first switch having in input, coupled to said voltage input terminal, an output, and a switch control input;

iv. a current sense resistor having one end coupled to said switch output and another end coupled to said voltage output terminal;

v. a first current sink having a first current input and a first control input;

vi. a second current sink having a second current input and a second control input;

vii. a first resistor coupling said one end of said current sense resistor junction to said first current input;

viii. a second resistor coupling said other end of said current sense resistor to said second current input;

ix. a comparator having a first input coupled to said first current input and a second input coupled to said second current input and an output coupled to said switch control input; and

x. said ON/OFF signal coupled to said first and second current sink control first and second control inputs.

20. A laptop computer system according to claim 19 and further including a voltage converter having a dc output coupled to said voltage input terminal.

21. A laptop computer system according to claim 19 switch and further including a first switch driver between said comparator and said first switch.

22. A laptop computer system according to claim 21 and further including an inductor having one end coupled to said switch output and another end coupled to said one end of said current sense resistor.

23. A laptop computer system according to claim 22 and further including a circuit coupling said one end of said inductor to ground.

24. A laptop computer system according to claim 23 wherein said circuit coupling said one end of said inductor to ground comprises a catch diode.

25. A laptop computer system according to claim 23 wherein said circuit coupling said one end of said inductor to ground comprises a second switch having an input coupled to said inductor, an output coupled to ground and a second switch control input coupled to the output of said comparator.

26. A laptop computer system according to claim 20 and further including a first hystersis circuit coupled between said output of said comparator and one of its first and second inputs.

27. A laptop computer system according to claim 20 and further including a second hystersis circuit coupled between the output of said comparator and said first current sink first control input.

28. A method of charging a battery in a computer comprising:

a. switching a supply voltage to the battery on and off at a first predetermined frequency; and

b. controlling the average current supplied to said battery by controlling a duty cycle of said switching.

29. The method of charging a battery according to claim 28 wherein said step of switching a supply voltage comprises:

a. switching a supply voltage on to cause a current to flow to the battery;

b. sensing the current flowing to the battery;

c. switching said supply voltage off when a first predetermined value of current is sensed;

d. switching said supply voltage on again when said current drops below a second predetermined value;

e. continuing to repeat steps b-d to result in switching on and off at paid first predetermined frequency.

30. The method according to claim 29 wherein said step of sensing current flow comprises sensing the voltage drop across a current sense resistor having one end coupled to said supply voltage and the other end to the battery by steps comprising:

a. sinking current through a first resistor coupled to an input side of said resistor to establish an offset voltage;

b. comparing said offset voltage to the battery voltage at the other side of said resistor;

c. switching said supply voltage off when the battery voltage at the other side of said current sense resistor drops below said offset voltage; and

d. establishing a hystersis.

31. The method according to claim 30 wherein:

a. said step of controlling is accomplished by sinking current from said other side of said current sense resistor through a second resistor and stopping sinking of current through said first resistor to disable said switching on and off at said first frequency; and

b. said step of comparing comprises comparing the voltage developed across said first resistor with the voltage developed across said second resistor.