Abstract: To control the speed of an alternating-current drive capacitor motor of a centrifuge, the motor is connected to the bridge arm of a single-phase inverter. The bridge arm is connected at each of its ends to the midpoints of a series circuit of two capacitors and two field-effect transistors, these series circuits being connected in parallel with one another and connected to the output of a rectifier operated by the a.c. voltage supply. During operation, the capacitors are discharged by means of triggering the field-effect transistors alternately via the capacitor motor, the triggering being performed via a microprocessor serving as a pulse generator.