Abstract: A battery pack for an electrical device contains rechargeable batteries for supplying power to the electrical device and a transformerless pulse charging circuit. The pulse charging circuit generates a pulse charging current from received AC current, and charges the rechargeable batteries with the generated pulse charging current. A semiconductor switch (12) generates the pulse charging current from the received AC current and supplies the pulse charging current to the batteries. A ramp generator circuit (14) generates a linearly rising waveform beginning at each zero crossing of the rectified AC current. A current sense amplifier circuit (15) measures the average value of current pulses through the battery and generates a signal proportional to an average charging current. A triggering circuit (18) generates the gate firing pulses for the semiconductor switch (12) according to the linearly rising waveform and the average charging current amplifier waveform.

Abstract: A battery pack (20) holds one or more batteries (118) and connects to a mobile telephone (115). The battery pack includes a case (22) for holding the batteries, a recharging circuit (122) disposed in the case, a plug (86) rotatably connected to the case and electrically connected to the recharging circuit, and electrical terminals 46 mounted to the case. The plug includes a pair of generally parallel, spaced prongs (88). The plug rotates from a first position, having the prongs projecting from the case, to a second position having the prongs retracted into the case. Electrical leads (47) extend from each of the electrical terminals to battery terminals. A pair of contacts (110) and (112) spaced from another, interrupts each of the electrical leads. When the prongs retract, each electrical contact of a contact pair electrically connects to one another through a prong. When the prongs extend, the electrical contacts are disconnected from one another.