The utility model discloses a control circuit for automatic change -over, this automatic change -over are used for switching between first via power and second way power, and this control circuit includes: select electric unit, it is connected between first via power and second way power and power transfer unit for according to the situation of first via power and second way power and select the voltage of one of first via power and second way power to carry supply power translation unit, and the power transfer unit, it is connected to and selects electric unit for the voltage conversion that will select electric unit to select becomes the DC voltage in order to offer the motor. According to this disclosed embodiment, can realize automatic change -over's miniaturization and low cost.