The batteries used in remote diagnostic medical equipment, principally for aircraft use, need to be fast charged during routine maintenance periods. This custom designed charger is fully SMBus compliant. Housed in a purpose built plastic enclosure, it fully charges a 5 ampere-hour, four cell lithium ion battery in approximately three hours. The PCB layout was done in-house to minimise the area of the high speed switching traces. This attention to detail, together with input and output filtering meant that the unit passed its radiated and conducted interference specification in the unshielded enclosure. With an efficiency of 90% at full load, losses are kept to a minimum and the unit stays cool.

The battery has a SMBus gas gauge circuit which sends control signals to define maximum current and voltage limits. It also terminates the charge cycle when the battery reaches the specified taper current. Front panel LEDs on the charger provide power on, charging and charged indication. A production tester has been made to fully characterise these chargers.

Input is from a 55 watt mains adapter which has a universal input voltage specification for world-wide use.