Battery Charger Circuit and Control Schemes

• US 20110279079A1
• Filed: 05/10/2011
• Published: 11/17/2011
• Est. Priority Date: 05/13/2010
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Do Valle, Bruno Guimaraes, Wentz, Christian T., Sarpeshkar, Rahul
• Granted Patent: US 9,083,199 B2
• Time in Patent Office: Days
• US Class Current: 320/107
• CPC Class Codes: H02J 7/0071 with a programmable schedule
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage

Abstract

Described is a battery charger circuit for charging a battery. The battery charger circuit comprises a control element having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output, said control element having an output current response characteristic which varies with respect to the battery input such that said control element implements a saturating function that causes the charging current of the battery to automatically transition between a constant current operating mode and a constant voltage operating mode or a constant voltage operating mode to a constant current operating mode.

Claims

1. A battery charger circuit for charging a battery, the battery charger circuit comprising:

a control element having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output, said control element having an output current response characteristic which varies with respect to the battery input such that said control element implements a saturating function that causes the charging current of the battery to automatically transition between one of;

a constant current operating mode and a constant voltage operating mode;

or a constant voltage operating mode to a constant current operating mode.

2. The battery charger circuit of claim 1 wherein the output current response characteristic of said control element has a shape corresponding to the shape of a hyperbolic tangent function.

3. The battery charger circuit of claim 1 wherein said control element is implemented as a sub-threshold operational transconductance amplifier (OTA) having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output coupled to an output of the battery charger circuit.

4. The battery charger circuit of claim 1 wherein said control element is implemented as an above-threshold operational transconductance amplifier (OTA) having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output coupled to an output of the battery charger circuit.

5. The battery charger circuit of claim 1 further comprising a gain stage having a first input coupled to the output of said control element and having an output configured to couple to the battery and at which a battery charging current is provided.

6. The battery charger circuit of claim 5 further comprising an end-of-charge circuit having a first input coupled to the output of said control element and having an output coupled to a second input coupled of said gain stage.

7. The battery charger circuit of claim 6 further comprising a trickle charge circuit.

8. The battery charger circuit of claim 1 wherein said control element comprises a processor configured to apply a saturation function to signals provided thereto such that the battery charger circuit automatically transitions between one of:

a constant current operating mode and a constant voltage operating mode;

or a constant voltage operating mode to a constant current operating mode in response to voltage levels of the battery.

9. The battery charger circuit of claim 1 wherein said control element comprises:

an analog-to-digital converter (ADC) circuit having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output, said ADC circuit configured to receive analog signals provided thereto and to provide a digital signal at the output thereof;

a digital controller having an input coupled to the output of said ADC circuit and having an output, said digital controller configured to receive digital signals provided thereto from said ADC circuit and apply a saturation function to the digital signals such that the battery charger circuit automatically transitions between one of;

a constant current operating mode and a constant voltage operating mode;

or a constant voltage operating mode to a constant current operating mode in response to the digital signals provided to said digital controller; and

a digital-to analog converter (DAC) circuit having a first input configured to receive an input from said digital controller and an output coupled to said gain circuit, said ADC circuit configured to receive digital signals provided thereto from said digital controller and to provide an analog signal at the output thereof.

10. The battery charger circuit of claim 1 wherein said digital controller comprises a digital signal processor (DSP).

11. The battery charger circuit of claim 1 further comprising a low-power detector circuit having a plurality of input terminals at which battery voltage signals are provided and an output terminal at which a low-power detector circuit output signal is provided, wherein in response to detecting that a predetermined threshold level is reached, the low-power detector circuit cuts off power to a load.

12. The battery charger circuit of claim 3 further comprising:

an end-of-charge circuit having a first input coupled to the output of the OTA; and

a current gain circuit having a first input coupled to the output of the OTA, a second input coupled to an output of the end-of-charge circuit and having an output configured to couple to the battery.

13. The battery charger circuit of claim 12 wherein the end-of-charge circuit detects end-of-charge by comparing the output of said OTA to a reference current.

14. The battery charger circuit of claim 13 wherein the reference current is proportional to the reference current used to bias the OTA.

15. The battery charger circuit of claim 14 wherein said OTA is provided having a hyperbolic tangent (tanh) shaped output current profile which allows the battery charger circuit to automatically transition between constant current (CC) and constant voltage (CV) charging regions in response to a voltage level of the battery.

16. The battery charger circuit of claim 3 wherein the battery charger circuit corresponds to a lithium-ion battery charger circuit for biomedical applications.

19. The power management IC of claim 14 wherein said control element comprises:

an analog-to-digital converter (ADC) circuit having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output, said ADC circuit configured to receive analog signals provided thereto and to provide a digital signal at the output thereof;

a digital controller having an input coupled to the output of said ADC circuit and having an output, said digital controller configured to receive digital signals provided thereto from said ADC circuit and apply a saturation function to the digital signals such that the battery charger circuit automatically transitions from a constant current operating mode to a constant voltage operating mode in response to the digital signals provided to said digital controller; and

a digital-to analog converter (DAC) circuit having a first input configured to receive an input from said digital controller and an output coupled to said gain circuit, said ADC circuit configured to receive digital signals provided thereto from said digital controller and to provide an analog signal at the output thereof.

20. The power management IC of claim 19 wherein said digital controller comprises a digital signal processor (DSP).

23. The power management IC of claim 19 further comprising a low-power detector circuit having a plurality of input terminals at which voltage signals are provided and an output terminal at which a low-power detector circuit output signal is provided, wherein in response to detecting that a predetermined threshold level is reached, the low-power detector circuit cuts off power from the one or more cells to a load.

24. The power management IC of claim 23 wherein the one or more cells comprise a lithium-ion battery for biomedical applications.

17. A power management integrated circuit (IC) for use with one or more rechargeable cells, the power management IC comprising:

a control element having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output, said control element having an output current response characteristic which varies with respect to input voltage such that said control element provides a continuous charging current and automatically transitions from one of;

a constant current operating mode to a constant voltage operating mode;

or a constant voltage operating mode to a constant current operating mode;

an end-of-charge circuit having a first input coupled to the output of said control element and having an output;

a current gain circuit having a first input coupled to the output of said control element, a second input coupled to the output of said end-of-charge circuit and having an output configured to couple to the one or more rechargeable cells.

18. The power management IC of claim 17 wherein said control element comprises a processor configured to apply a saturation function to signals provided thereto such that the power management IC automatically transitions from a constant current operating mode to a constant voltage operating mode in response to voltage levels of the one or more rechargeable cells.

21. The power management IC of claim 17 wherein:

said control element is provided as an operational transconductance amplifier (OTA) having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output;

said end-of-charge circuit has a first input coupled to the output of the OTA; and

said gain circuit is provided as a current gain circuit having a first input coupled to the output of the OTA, a second input coupled to the output of the end-of-charge circuit and having an output configured to couple to the battery.

22. The power management IC of claim 21 further comprising:

a reference source coupled to a first one of the first and second inputs of said OTA; and

one or more cells coupled to a second one of the first and second inputs of said OTA.

25. A method for charging a battery, the method comprising:

comparing a voltage of a battery and a voltage of a reference source to determine a charging current; and

in response to the comparing, providing a continuous charging current and automatically transitioning between one of;

a constant current operating mode and a constant voltage operating mode;

or a constant voltage operating mode and a constant current operating mode.

26. A battery charger circuit for charging a battery, the battery charger circuit comprising:

a control element having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output, said control element having an output current response characteristic which varies with respect to the battery input such that said control element continuously provides a charging current that transitions the charging of the battery from one of;

a constant current operating mode to a constant voltage operating mode;

or a constant voltage operating mode to a constant current operating mode.

27. A battery charger circuit for charging a battery, the battery charger circuit comprising:

a control element having a first input configured to receive an input from a reference source, a second input configured to receive an input from the battery and an output, said control element having an output current response characteristic corresponding to a saturating function that causes the charging current of the battery to automatically transition between a constant current operating mode and a constant voltage operating mode or a constant voltage operating mode to a constant current operating mode which varies with respect to the battery input such that said control element implements.