We can charge Ni-Cd or Ni-MH simply by placing a series resistor to limit current from the power source to make efficient loading. But not so with lithium ion cell (Li-Ion) which has a capacity greater than ever and don’t need to be completely discharged to charge them, but require a strictly controlled charging.
In this type of battery charging uncontrolled drip (common in alarm systems, for example) or the load resistor in series with the power lead, without exception, It will destroy itself
But there are a number of active components, semiconductors, capable of carrying the load, control and maintenance of these cells with almost no additional external components.
In the diagram we see the circuit typical Li-Ion battery charger, where it finds that it is easier to make a performance similar to discrete electronics. This chip is responsible for measuring the state of the battery (through its terminal FeedBack) and sent by the control voltage output terminal (Out). The capacitor allow to Serve as parasites RF filter and potentiometer 50 to adjust the system according to the operating voltage of the cell.
This Lithium Ion charger circuit can be powered by a DC voltage between 6 and 10V with a current equal to 1.5 times the capacity of cells to be charged.
Once the power is turned on or put the battery in the circuit, check the charging status of it and, if necessary, to the load. After a the circuit the load entering the standby mode, periodically check the status of the cells with whether it should continue to charging.
The Li-Ion Battery charger circuit is designed for the battery with a Li-Ion cell. Importantly, this battery can not charge either in series or in parallel, so the system must be assembled for each cell you want to charge simultaneously.