The revolution per minutes (rpm) of the DC motor is measured by using the digital stroboscope tachometer every time there are changes in output voltage. Fig. 5 shows the speed of DC motor changed with the output voltage of the driver. The results show that the driver manged to control the motor speed in a linear manner. Fig 6 shows the changes of the driver output power corresponding to various speed of the motor. As the speed of motor increase, the output power will remain closed to 5W. Which means that the driver output power has the ability to remain constant throughout the speed range. This characteristic enables the motor to turn slowly without lossing power, which is very important in promoting higher efficiency of solar tracking.