A medical infusion system with pulse width modulation and a safety circuit and a method thereof are disclosed. Embodiments of the system include a switching device and a pump motor, wherein the pump motor and the switching device are connected in series and constitute a power supply circuit to be connected to a power supply. Embodiments of the system further includes a control signal generator configured to generate a control signal e.g. PWM, and which is connected to input of the safety circuit. Output of the safety circuit is connected to a control input of the switching device such that the pump motor will not operate if there is no control signal applied to the input of the safety circuit.