Patent ID: 7735398

Claim:
A rechargeable motor-driven ratchet wrench having power-off protection comprising: a body made up by two half cases covering together; a motor hold by the two half cases, wherein a shaft is configured at one end of the motor and a gear is configured on the shaft of the motor; a rechargeable battery held by the two half cases and electrically connected to the motor; an electrical socket configured between the motor and the rechargeable battery having two pings for coupling with two electrodes of the rechargeable battery; a switch for electrically connecting between the electrical socket and the motor; a planetary gear assembly driven by the motor and comprising a rotation base, a plurality of planetary gears, a toothed ring, a transmission gear and a connector, wherein the planetary gears are configured at one side of the rotation base and facing the motor and the transmission gear is formed at the other side of the rotation base opposite to the motor, wherein the planetary gears respectively engage with the gear of the shaft of the motor, and the rotation base and the planetary gears are configured inside the toothed ring, wherein an inner toothed part is formed on an inner side of the toothed ring that engages with the planetary gears, wherein the toothed ring is spirally coupled to the connector; a locating ring configured inside the two half cases and also spirally coupled to the toothed ring; a ratchet part configured at one end of the body, wherein a ratchet configuration is configured inside the ratchet part and configured with a drive shaft, wherein the drive shaft is stretching out of the ratchet part and also coupled to the transmission gear of the rotation base; and a power-off protection device coupled between the switch and the electrical socket; wherein the power-off protection device comprises: a power transistor coupled between the motor and the rechargeable battery; a current detection circuit detecting loaded current, which is passing through the motor, via the power transistor to be coupled to the motor; a driver coupled to the rechargeable battery and a gate of the power transistor; and a comparator having: a first input terminal set to a default value; a second input terminal coupled to an output terminal of the current detection circuit to determine whether the loaded current passing through the motor is larger than the default value; and an output terminal coupled to a control terminal of the driver.