Abstract: A switch control circuit includes a N-channel MOSFET, a first bleeder unit, a P-channel MOSFET and a second bleeder unit. The N-channel MOSFET has a first input terminal, a first output terminal and a first control terminal. The first output terminal is connected to ground. The first bleeder unit has a voltage-dividing function to the voltage from an input and output interface of a computer. The first bleeder unit is connected with the first control terminal and the first output terminal of the N-channel MOSFET. The P-channel MOSFET has a second input terminal, a second output terminal and a second control terminal. The second output terminal is connected to the working voltage terminal of the external hard disk. The second bleeder unit is connected between the external power supply and the first input terminal of the N-channel MOSFET. The P-channel MOSFET is connected with the first bleeder unit.

Abstract: A mobile hard disk, having a shield, a disk body having a front surface, an electric circuit board electrically connected to the disk body. The electric circuit board is parallel to and contacts with the front surface of the shield, wherein the electric circuit board and the disk body are both received in the shield. As the electric circuit board is parallel to and contacts with the front surface of the disk body, so the electric circuit board takes a little space of the shield, and the volume of the mobile hard disk is smaller than the traditional one.