The circuit was designed to create a spare and reserve power source with the use of batteries during the absence of power from the mains. BD139 – NPN power transistor used for driver stages in hi-fi ...

Is the battery empty, or is there something wrong with the device? That’s always a difficult question when your walkman or some other battery-powered device appears to be dead when you switch it on.

Testing a Li-ion battery charger using its natural load (i.e., a battery) is time consuming because the charging process can take an hour or more. The test time varies widely, depending on whether you ...