1. Field of the Invention
The invention relates to a charger and, in particular, to a two-step charger that can adjust the level of its charging command voltage depending upon the charging status of the battery.
2. Description of Related Art
In view of environmental protection, many objects that cannot be decomposed by nature or cause pollution after they are decomposed are phasing out. For example, non-rechargeable batteries contain materials harmful to the environment. Therefore, rechargeable batteries become more popular nowadays. With an appropriate charger, the rechargeable batteries can be repeatedly used.
Most of the chargers on the market have the function of two-step charging. That is, they allow the user to decide whether to charge the batteries at a normal speed or a faster speed. The so-called quick charging refers to the charging with a larger current. Although this method can finish charging in a shorter time, people normally do not immediately remove the batteries from the charger once it is done. Therefore, the larger current usually produces a high temperature on the batteries. If the batteries are exposed to the high temperature for a long time, their lifetime may be greatly shortened.
Charging at a normal speed refers to the charging with a smaller current. As a result, the charging time is longer. It may take several hours to charge a battery in this scheme. Therefore, it is inconvenient.
From the above description, it is seen that current chargers are unable to charge batteries at a quicker speed without sacrificing their lifetime.