| Simple Lithium Ion Battery Charger |
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The simple charger is designed around a very low dropout linear regulator. Input is from a 17 volt DC, 30 watt mains adapter which has a universal input voltage specification for world wide use. The charger is housed in an off-the-shelf heatsink box and charges a 5 ampere-hour, four cell lithium ion battery in approximately four hours. Charging is initiated by switching on the mains adapter or by pushing the reset button. The charger is limited to 1.75 amps in constant current mode and 16.4 volts in constant voltage mode. A yellow LED is on during charging. End of charge current is set to a low 0.015C for maximum capacity. The charger switches off at this point and a LED is latched on to indicate the charged condition. The charger is protected against reverse input and output voltage as it may be used with different mains adapters and the battery could be connected the wrong way round. The reverse output protection circuit also protects the battery. As this is a linear regulated charger, it also has output short circuit and over-temperature protection.
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