Circuit and method of operation for an electrical power supply

Inventors: Dusan Veselic, Martin G. A. Guthrie
Original Assignee: Research In Motion Limited

Patent number: 7999514
Filing date: Feb 16, 2011
Issue date: Aug 16, 2011
Application number: 13/028,361

A battery charging circuit comprising: a semiconductor switch having an output connected to a rechargeable battery; a battery charge controller for receiving power from an external source, and supplying output power to a portable device and the input of the semiconductor switch, the current output of the battery charge controller being controllable; and a voltage sensing circuit for: measuring the voltage drop across the battery charge controller; and responding to the voltage drop across the battery charge controller by modulating the semiconductor switch to reduce the quantity of current supplied to the rechargeable battery when the voltage drop is too great; whereby the total power dissipated by the battery charge controller is controlled, the portable device receiving the power it needs to operate and the rechargeable battery receiving any additional available power.

Claims

What is claimed is:

1. A battery charging circuit comprising:

a switch having an output connected to a rechargeable battery and configurable to isolate the rechargeable battery from a portable device;

a battery charge controller configured to receive power from an external power source and supply output power to the portable device; and

a voltage sensing circuit configured to:

respond to a voltage drop across the battery charge controller by modulating the switch to control a quantity of current supplied to the rechargeable battery such that the portable device receives a predetermined amount of power to operate and the rechargeable battery receives a reminder of the power available from the battery charge controller.

2. The battery charging circuit of claim 1, wherein the battery charge controller further comprises an external driving semiconductor for carrying supply current to the portable device and the switch, whereby load current passes through the external driving semiconductor instead of the battery charge controller.

3. The battery charging circuit of claim 2, wherein the voltage sensing circuit comprises an operational amplifier.

4. The battery charging circuit of claim 3 where the voltage sensing circuit comprises: an operational amplifier for receiving a voltage signal from the output of the battery charge controller and a reference voltage signal, and responds to the voltage signal being less than the reference voltage by reducing current flow through the switch.

5. The battery charging circuit of claim 4 wherein the voltage sensing circuit further comprises a voltage divider for scaling down the voltage signal from the battery charge controller and the reference voltage signal is scaled down proportionally.

6. The battery charging circuit of claim 5 where the external power source comprises a computer data bus having a power node.

7. The battery charging circuit of claim 6 wherein the computer data bus is a Universal Serial Bus (USB).

8. The battery charging circuit of claim 3, wherein the voltage sensing circuit comprises an operational amplifier for comparing the voltage on the output of the battery charge controller to a reference voltage.

9. The battery charging circuit of claim 3 wherein the voltage sensing circuit further comprises a capacitor coupling the output of the operational amplifier to ground, thereby smoothing out variances in the output of the operational amplifier.

10. The battery charging circuit of claim 2 where low-power, critical components of the portable device are fed from the battery charge controller, and high-power, non-critical components of the portable device are fed from the rechargeable battery.

11. The battery charging circuit of claim 10 where the low-power, critical components include at least one of: a memory and a microprocessor.

12. The battery charging circuit of claim 10 where the high-power, non-critical components include at least one of: a back lighting system and a vibrator.

13. The battery charging circuit of claim 2, wherein the external driving semiconductor comprises a transistor.

14. The battery charging circuit of claim 2, wherein a maximum current the battery charge controller provides is limited by an external resistance to ground.

15. The battery charging circuit of claim 14, wherein the maximum current the battery charge controller provides is limited by multiple sets of external resistors and switches, allowing the battery charge controller to be controlled to provide varying levels of current.

16. The battery charging circuit of claim 15, wherein the switch comprises a MOSFET (metal oxide silicon field effect transistor).

17. The battery charging circuit of claim 1 wherein:

the battery charge controller is configured to limit the output power such that the portable device and the rechargeable battery may not draw more than a maximum current available from the external source.

18. A method of charging a battery of a portable device via an external power supply, the method comprising:

connecting an input of a battery charge controller to the external power supply;

connecting an output of the battery charge controller, in parallel, to the portable device and an input of a switch;

connecting an output of the switch to the battery;

controlling current output of the battery charge controller; and

responding to a voltage drop across the battery charge controller by modulating the switch to control a quantity of current supplied to the battery such that the portable device receives a predetermined amount of power to operate and the battery receives a reminder of power available from the battery charge controller.

19. The method of claim 18, further comprising:

comparing a voltage signal from the battery charge controller with a reference voltage signal.

20. A power supply circuit comprising:

means for measuring a voltage drop across a battery charge controller providing power to a portable device and an input of a switch in parallel; and

means for responding to the voltage drop across the battery charge controller by modulating the switch to control a quantity of current supplied to a rechargeable battery such that the portable device receives a predetermined amount of power to operate and the rechargeable battery receives a remainder of power available from the battery charge controller.

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