OK, sorry, i will start over... I am trying to drive a Hard Disk actuator arm. I soldered two wires to the Arm's coil which placed between the magnets. While i'm connecting one of the wires to +5v and the other to 0 in external PowerSupply, it takes the arm to one side due to electro magnetic field which created by the current in the coil, but if i want the arm to go to other side, i need to switch the wires or to decrease the voltage to be negative (current will flow to another side). I need quite precise control of the arm, so i want to use the PWM with a high frequency to control the situation of the arm by changing the Duty Cycle on period of 500Hz.