Abstract: A charger device includes a switch, a voltage converter, a constant current circuit, and an automatic disconnecting circuit. The switch is connected to an alternating current (AC) power supply which triggers the charger device to work. The automatic disconnecting circuit is connected to the battery, the voltage converter and the constant current circuit automatically disconnect the voltage converter from the AC power supply when the battery is fully charged. The automatic disconnecting circuit comprises a first resistor, a voltage follower, a second resistor, a first zener diode, a variable resistor, a comparator, a third resistor, a first switch element, a diode and a relay. The relay comprises a coil and a normally-open switch connected between the AC power supply and voltage converter. The normally-open switch turns on or turns off to control a connection between the charger device and the AC power supply.

Abstract: A charger device includes a switch, a voltage converter, a constant current circuit, and an automatic disconnecting circuit. The switch is connected to an alternating current (AC) power supply which triggers the charger device to work. The automatic disconnecting circuit is connected to the battery, the voltage converter and the constant current circuit automatically disconnect the voltage converter from the AC power supply when the battery is fully charged. The automatic disconnecting circuit comprises a first resistor, a voltage follower, a second resistor, a first zener diode, a variable resistor, a comparator, a third resistor, a first switch element, a diode and a relay. The relay comprises a coil and a normally-open switch connected between the AC power supply and voltage converter. The normally-open switch turns on or turns off to control a connection between the charger device and the AC power supply.