Patent ID: 7579807

Claim:
A battery charger comprising: an Alternating Current (AC) power supply; a first rectifier smoothing circuit for rectifying and smoothing the AC voltage; a switching circuit connected across output terminals of the first rectifier smoothing circuit to provide pulse signals; a second rectifier smoothing circuit for rectifying and smoothing the pulse signals, an output voltage of the second rectifier smoothing circuit being applied to a battery to be charged; a charging current control unit that detects a charging current flowing through the battery and controls the charging current in accordance with a charging current set value; trigger means connected across the battery to be charged for generating a first trigger voltage based on a residual voltage of the battery when the battery is connected to the charger; constant voltage generating means connected to the trigger means to receive the first trigger voltage and adapted to generate a constant voltage which is applied to the charging current control unit as an operating voltage thereof; and a microcomputer that detects if the battery is connected to the charger and applies a control signal to the constant voltage generating means to stop supplying the operation voltage to the charging current control unit when the battery is detached from the battery charge.