Lithium-ion battery charger input pre-regulator

• US 20030057920A1
• Filed: 09/26/2001
• Published: 03/27/2003
• Est. Priority Date: 09/26/2001
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Dotzler, Kevin
• Granted Patent: US 6,859,016 B2
• Time in Patent Office: Days
• US Class Current: 320/162
• CPC Class Codes: H02J 7/007182 in response to battery voltage

Abstract

A battery charger for charging a battery from a power source is provided. The battery charger includes a current sense circuit in series with the power source and the battery. A linear preregulator includes a first controlled switch coupled to the power source to generate a regulated output. The first controlled switch is responsive to a preregulator control signal, varying the first controlled switch impedance so that the regulated output is generated. A control circuit is powered by the preregulator regulated output. The control circuit generates the preregulator control signal and a charger control signal. A second controlled switch is coupled between the regulated output and the battery. The impedance of the second controlled switch is varied in response to the charger control signal so that a regulated flow of charge is supplied to the battery.

Claims

1. A battery charger for charging a battery from a power source, comprising:

a current sense circuit in series with the power source and the battery;

a voltage reference circuit to generate a first control signal in response to a preregulator control signal;

a preregulator switch having an impedance, coupled to the power source to generate a regulated output, the preregulator switch being responsive to the first control signal, to vary the preregulator switch impedance such that the regulated output is generated;

a control circuit coupled to the regulated output, the control circuit to generate the preregulator control signal and a charger control signal; and

a charger regulator switch having an impedance, responsive to the charger control signal, to vary the controlled switch impedance so that a regulated flow of charge is supplied to the battery.

2. The battery charger of claim 1 wherein the current sense circuit is a resistor.

3. The battery charger of claim 1 wherein the preregulator switch is selected from the group of PNP transistors and N-channel MOSFETs.

4. The battery charger of claim 1 wherein the charger regulator switch is selected from the group of PNP transistors and N-channel MOSFETs.

5. The battery charger of claim 1 further comprising a unidirectional switch coupled in parallel with the charger regulator switch such that the battery supplies power to the control circuit.

6. The battery charger of claim 1 wherein the control circuit includes:

an A/D to digitize current sense and voltage sense signals;

a CPU to generate digital control signals computed from the digitized current sense and voltage sense signals; and

a D/A to convert the digital control signals to the preregulator control signal and charge control signal.

7. The battery charger of claim 6 included within a wireless device.

8. The battery charger of claim 7 wherein the wireless device is a cellular phone.

9. A method of charging a battery from a power source, comprising:

providing a first controlled impedance in series with the power source;

linearly controlling the first controlled impedance so that a regulated output having a first voltage level is generated;

supplying power from the regulated output to a control circuit;

the control circuit generating a preregulator control signal operable to adjust the regulated output to a second voltage level;

providing a second controlled impedance coupled between the regulated output and the battery;

controlling the second controlled impedance so that a charging current is supplied to the battery.

10. The method of claim 9 wherein the second voltage level is a function of dissipation in the first controlled impedance.

11. The method of claim 9 wherein the second voltage level is a function of dissipation in the second controlled impedance.

12. The method of claim 9 wherein the second voltage level is a function of dissipation in the second controlled impedance and dissipation in the first controlled impedance.

13. The method of claim 12 further comprising limiting the second voltage level to less than a maximum voltage.

14. The method of claim 12 further comprising controlling the charging current as a function of the dissipation in the second controlled impedance.

15. The method of claim 12 further comprising adjusting the second voltage level such that the dissipation in the second controlled impedance is approximately equal to the dissipation in the first controlled impedance.

16. The method of claim 15 further comprising limiting the second voltage level to less than a maximum voltage.

17. A battery charger for charging a battery from a power source, comprising:

a preregulator switch having an impedance, coupled to the power source to generate a regulated output;

a current sense circuit coupled in series with the battery to generate a current sense signal representative of battery current;

a controllable voltage reference coupled to the preregulator switch to control a voltage level of the regulated output, the controllable voltage reference having a first state and a second state;

during the first state, the controllable voltage reference setting the regulated output to an initial voltage level; and

during the second state, the controllable voltage reference, responsive to a preregulator control signal, sets the regulated output to a second voltage level;

a charger regulator circuit having a series impedance coupled between the regulated output and the battery, the charger regulator circuit, responsive to a charger control signal, to vary the series impedance so that a charging current is supplied to the battery;

a control circuit powered by the regulated output, the control circuit to generate the preregulator control signal and the charger control signal;

the preregulator control signal generated as a function of dissipation in the second controlled impedance and dissipation in the first controlled impedance; and

the charger control signal generated as a function of the battery current and the dissipation in the charger regulator circuit.

18. The battery charger of claim 17 further comprising a local voltage regulator coupled between the regulated output and the control circuit to limit the voltage level of the regulated output supplied to the control circuit.