US Patent 7248019 Cordless power tool

A cordless power tool such as a power staple gun 1 includes a power supply circuit of an electric double layer capacitor 8 and a lithium-ion battery 11. In a standby state, the lithium-ion battery charges the electric double layer capacitor, and at a switch on time, the electric double layer capacitor supplies large current to the motor 5. By combining the lithium-ion battery with high energy density and the electric double layer capacitor capable of discharging large current, it is possible to greatly reduce the size and weight as compared with a case where a nickel-cadmium battery or a nickel-hydrogen battery is used. Besides, since the electric double layer capacitor has a very long lifetime, the running cost can also be reduced.