A desk-top centrifuge is provided which includes a switching element disposed between a dc power supply and a motor and a controlling circuit. The controlling circuit receives a voltage of power regenerated by the motor to provide a pulse width-controlled on-off signal to the drive switching element to control speed of the motor. The controlling circuit increases an on-duration in which the on-off signal is at an on-level at a given rate to turns the motor slowly. The centrifuge has a safety guard system made up of a door switch and a door lock switch which are installed in series between the dc power supply and the motor and work to establish electric communication between the dc power supply and the motor when the door is closed and locked.
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