Patent ID: 6859016

Claim:
A battery charger for charging a battery from a power source, comprising: a current sense circuit connected in series with 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 said impedance thereof such that the regulated output is generated; a control circuit coupled to the preregulator switch, the control circuit to generate the preregulator control signal and a charge control signal; and a charge regulation circuit 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, wherein the control circuit includes at least two operating modes; during a first mode of the at least two operating modes, the control circuit controls the preregulator switch, through the voltage reference circuit, such that the regulated output increases as a voltage across the battery increases; and during a second mode of the at least two operating modes, the control circuit limits the regulated output in a constant level.