A power supply down-conversion, regulation, and low battery detection system has application in an implantible defirillator but is also directly applicable to any battery powered implantible device. Battery voltage is down-converted by a high efficiency switched capacitor voltage divider to a suitable intermediate voltage. This voltage is then linearly regulated down to the desired output voltage. A second regulator, which takes current directly from the battery, supports the output voltage in the event that the load current cannot be supplied by the voltage downconverter. A low battery detect circuit shuts down high current circuitry in the system in the event that battery voltage drops to a level such that the regulated output voltage is endangered.

A Portable Power System configured to supply an appropriate voltage to an electrical device. The system includes a battery pack having at least one cell supplying a first direct current voltage, and an adapter. The adapter, which is electrically connected to the battery pack by an electrical cord, is configured to be mechanically connected to the device. The adapter also includes a DC to DC voltage converter supplying a second direct current voltage to the device, the second voltage being smaller than the first voltage but sufficient to permit the intended operation of the device.

A switched capacitive voltage converter for converting an input voltage (U.sub.i) between an input terminal (I) and reference terminal (RF) to an output voltage (U.sub.o) between an output terminal (O) and the reference terminal (RF). The voltage converter comprises only two capacitors (C.sub.1, C.sub.2) and five switches (S.sub.1 -S.sub.5). The first (S.sub.1) and the second switch (S.sub.1) are coupled in series between the input terminal (I) and the output terminal (O). The third (S.sub.3) and the fifth (S.sub.5) switch are also coupled between the input terminal (I) and the output terminal (O). The first capacitor (C.sub.1) is coupled in series between a node common to the first (S.sub.1) and the second (S.sub.2) switches and a node common to the third (S.sub.3) and the fifth (S.sub.5) switch. The fourth switch (S.sub.4) is coupled between the node common to the third (S.sub.3) and the fifth (S.sub.5) switch and the reference terminal (RF). The second capacitor (C.sub.2) is coupled between the output terminal (O) and the reference terminal (RF). The voltage converter disclosed herein can operate as an up converter, a down converter as well as a buffer.

A portable power system for a hand tool employs a high-voltage transmission of power from a battery pack over a cord to a DC to DC converter, which steps the transmission voltage down to rated tool voltage. The system uses a switching transistor to transmit power according to a duty cycle which varies automatically according to tool current draw and voltage. The DC to DC converter employs synchronous rectification with an inductor-capacitor network to transform a duty cycle square wave into DC power. The startup voltage sense feature permits powering up the converter circuitry only when needed. The converter will shut down if no current has been drawn by the tool for a predetermined period of time or if the converter unit is in danger of overheating, as determined by a stored algorithm. The portable power system has safeguards to prevent fouling or shorting in wet environments, is adaptable to left or right handed users, and is physically configurable into a variety of carrying modes.