Circuit and method of operation for an electrical power supply
View Patent ↗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.
1. A method for charging a rechargeable battery for a portable device having at least one function unrelated to the battery charge controller, using power supplied by a universal serial bus (USB) port, comprising:
receiving power from the USB port;
supplying the received power to the rechargeable battery and to the portable device, wherein the supplied power is limited such that the rechargeable battery and portable device may not draw more than a pre-determined maximum amount of current available from the USB port; and
controlling an amount of current supplied to the rechargeable battery such that the portable device receives a pre-determined amount of the received power needed to operate and the rechargeable battery receives a remainder of the received power.
2. The method of claim 1 , further comprising:
measuring a voltage drop across a circuit used to supply the received power to the rechargeable battery and the portable device; and
controlling the amount of current supplied to the rechargeable battery as a function of the measured voltage drop.