The over current protection has been widely used in many systems such as battery charging systems so as to prevent damages to electronic components in the systems. A typical over-current protection method is to sense the charging/discharging current and to compare the sensed current with a threshold. When the charging/discharging current or the sensed current exceeds a predetermined level, a timer will be initiated for blanking the current for a predetermined period so as to reduce or limit the current. If the charging/discharging current still exceeds the predetermined level after the predetermined period, the charging/discharging circuit will be shut down. If the charging/discharging current decreases below the predetermined level within the predetermined period, a controller can resume the charging/discharging process.
However, the current level might not be effectively ensured to be within a safe level by the above mentioned conventional method, which may be an issue in power tools with a heavy duty load, e.g., a circular saw. When a heavy duty job is performed and a relatively large load current is drawn, a transient over current condition might occur. If the blanking period is not chosen adequately, the power tools may be stopped abruptly and get stuck into objects. Even if the blanking period can be chosen appropriately for one specific application, the system protection might be only suitable for this specific application since different power tools may have different load duties. Consequently, the compatibility of the system protection in various applications may not be adequate.